10. Juni 2010

50 Studien pro MWP (2009-2010)

Ich führe in der Folge 50 weitere Studien an, die ich in verschiedensten Fachzeitschriften gefunden habe, und welche die Annahme der Existenz einer MWP im Text voraussetzen, darauf verweisen oder direkt bzw. indirekte Evidenz dafür liefern.
 
 
Clim. Past, 5, 171-181, 2009

Two millennia of climate variability in the Central Mediterranean
C. Taricco, M. Ghil, S. Alessio and G. Vivaldo

Abstract
This experimental work adresses the need for high-resolution, long and  homogeneous climatic time series that facilitate the study of climate variability over time scales of decades to millennia. We present a high-resolution record of foraminiferal Delt18O from a Central-Mediterranean sediment core that covers the last two millennia. The record was analyzed using advanced spectral methods and shows highly significant oscillatory components with periods of roughly 600, 350, 200, 125 and 11 years. Over the last millennium, our data show several features related to known climatic periods, such as the Medieval Optimum, the Little Ice Age and a recent steep variation since the beginning of the Industrial Era. During the preceding millennium, the Delta18O series also reveals a surprising maximum at about 0 AD, suggesting low temperatures at that time. This feature contradicts widely held ideas about the Roman Classical Period; it is, therefore discussed at some length, by reviewing the somewhat contradictory evidence about this period.

We compare Delta18O record with an alkenone-derived sea surface temperature time series, obtained from cores extracted in the same dCentral-Mediterranean area (Gallipoli Terrace, Ionian Sea), as well as with Italian and other European temperature reconstructions over the last centuries. Based on this comparison, we show that the long-term trend and the 200-y oscillation in the records are temperature driven and have a dominant role in describing temperature variatons over the last two millennia.

Geochimica et Cosmochimica Acta 
Volume 73, Issue 16, 15 August 2009, Pages 4635-4647

Impact of climate and CO2 on a millennium-long tree-ring carbon isotope record

Kerstin S. Treydte, David C. Frank, Matthias Saurer, Gerhard Helle, Gerhard H. Schleser and Jan Esper
Abstract
We present one millennium-long (1171-year), and thre 100 year long annually resolved Delta18C tree-ring chronologies from ecologically varying Juniperus stands in the Karakorum Mountains (northern Pakistan), and evaluate their response to climatic and atmospheric CO2 changes. All Delta13C records show a gradual decrease since the beginning of the 19th century, which is commonly associated with a depletion of atmospheric Delta13C due to fossil fuel burning. Climate calibration of high-frequency Delta13C variations indicates a pronounced summer temperature signal for all sites. The low-frequency component of the same records, however, deviates from long-term temperature trends, even after correction for changes in anthropogenic CO2. We hypothesize that these high-elevation trees show a response to both climate and elevated atmospheric CO2 concentration and the latter might explain the offset with target temperature data. We applied several corrections to tree-ring Delta13C records, considering a range of potential CO2 discrimination changes over the past 150 years and calculated the goodness of fit with the target via calibration/verification tests (R2, residual trend, and Durbin-Watson statistics). These tests revealed that at our sites, carbon isotope fixation on longer timescales is affected by increasing atmospheric CO2 concentrations at a discrimination rat eof about 0.012%°/ppmv. Although this statistically derived value may be site related, our findings have implications for the interpretation of any long-term trends in climate reconstructions using tree-ring Delta13C, as we demonstrate with our millennium-long Delta13C Karakorum record. While we find indications for warmth during the Medieval Warm Period (higher than today's mean summer temperature), we also show that the low-frequency temperature pattern critically depends on the correction applied. Patterns of long-term climate variation, including the Medieval Warm Period, the Little Ice Age, and 20th century warmth are most similar to existing evidence when a strong influence of increased atmospheric CO2 on plant physiology is assumed.

Making hay while the sun shines? Socio-economic change, cereal production and climatic deterioration in Early Medieval Ireland
Journal of Archaeological Science, Volume 36, Issue 12, December 2009, Pages 2868-2874
Thomas R. Kerr, Graeme T. Swindles, Gill Plunkett

Abstract
The Early Medieval period in Ireland (c. A.D. 400–1150) has been the subject of much archaeological and historical study. The recent application of various forms of archaeological sciences, as well as palaeoenvironmental studies, to the archaeological record have, however, added fresh impetus to this study area. It seems increasingly evident that significant changes to economy and society occurred during this period and were not recorded in detail in the contemporary documentary sources. This paper will attempt to outline those changes and to assess whether, or to what extent, they were influenced by climate change.

A quantitative high-resolution summer temperature reconstruction based on sedimentary pigments from Laguna Aculeo, central Chile, back to AD 850 
Lucien von Gunten, Martin Grosjean, Bert Rein, Roberto Urrutia Peter Appleby


We present a pigmetn-based quantitative high-resolution (five years) austral summer DJF (December to February) temperature reconstruction for Central Chile back to AD 850. We used non-destructive in situ multichannel reflection spectrometry data from a short sediment core of Laguna Aculeo (33°50'S/70°54'W, 355 m a.s.l., central Chile). Calibration-in-time (period AD 1901-2000, cross-validated with split periods) revealed robust correlations between local DJF temperatures and total sedimentary chlorin (relative absorption band depth (RABD) centred in 660-670 nm RABD 660;670: r=0.79, P<0.01; five-years triangular filtered) and the degree of pigment diagenesis (R660nm/670nm: r=0.82, P<0.01; five-years triangular filter). Root Mean Squared Error values are small (between 0.24 and 0.34°C) suggesting that most of the reconstructed decadal-scale climate variability is significant. Our data provide quantitative evidence for the presence of a Medieval Climate Anomaly (in this case, warm summers between AD 1150 and 1350; T = +0.28 to +0.37°C with respect to (wrt) twentieth century) and a very cool period synchronous to the 'Little Ice Age' starting with a sharp drop between AD 1350 and AD 1400 (-0.3°C/10 yr, decadal trend) followed by constantly cool (T = -0.70 to -0.90°C wrt twentieth century) summers until AD 1750. The structure of variability is consistent in great detail with annually resolved tree-ring based warm-season temperature and river discharge reconststructions from northern Patagonia (42°S) for the past 400 years, with qualitative climate reconstructions from Andean glacier fluctuations, and twith hydrological changes in Patagonian lake sediment records. 


The Holocene, Vol. 19, No. 6, 873-881 (2009)
DOI: 10.1177/0959683609336573

Long-term development of Holocene and Pleistocene gullies in the Protva River basin, Central Russia
Geomorphology, Volume 108, Issues 1-2, 1 July 2009, Pages 71-91
Andrey V. Panin, Julia N. Fuzeina, Vladimir R. Belyaev

Abstract
The specific geomorphic structure (a combination of flat or gentle watersheds with short steep valley sides) and the high resistance of surface material in the case study area in the centre of the Russian Plain are responsible for the specific pattern of Holocene erosion: no or minor sheet erosion, the occasional appearance of new gullies on the valley sides (four out of 19 studied), and a concentration of erosion activity in old gullies that had existed since pre-Holocene times (15 out of 19 studied). The erosion activity is studied using radiocarbon dating of gully sediments. Summed probability density distribution (SPDD) of 65 radiocarbon dates is applied to detect changes of erosion rates over the last five millennia. Three millennium-scale phases of erosion activity are distinguished: Phase 1 — 1200 years BP to the present (intensive erosion), Phase 2 — 2800 to 1200 years BP (weak erosion), and Phase 3 — > 4800 to 2800 years BP (intensive erosion). Short episodes, or single events of relatively strong erosion, have been found at around 4700, 3800, 3000, 2200, 1800, and 900 years BP. Erosion during Phase 3 coincided with the Holocene lowest population density in the whole region, and the start of Phase 1 coincided with a population gap at the case study area, which suggests other than anthropogenic causes for changing erosion regimes. These may be climatic factors because changes between millennium-scale phases of erosion activity coincide with pronounced climatic changes: the Subboreal–Subatlantic transition, and the start of the Medieval Warm period. However, a direct correlation between erosion activity and climatic parameters (warmer/cooler, wetter/drier) has not been found, presumably because the available palaeoclimatic reconstructions do not contain enough information on changing frequencies and magnitudes of hydrological extremes. According to population dynamics, charcoal frequency in erosion-derived sediments and pollen data, a human impact on erosion is suggested to have occurred from the 11th century AD, and more confidently from the 14th–16th centuries. This contributed to erosion acceleration that began some two centuries earlier, apparently for climatic reasons.

Colluvial and alluvial response to land use change in Midland England: An integrated geoarchaeological approach 
Geomorphology, Volume 108, Issues 1-2, 1 July 2009, Pages 92-106
Antony G. Brown

Abstract
This paper presents geomorphic, soils and palaeoecological data from a small sub-catchment in the English Midlands in an attempt to provide an integrated picture of Holocene landscape change. The area used has also been the focus of a multi-disciplinary and long-term archaeological survey (Raunds Area Project) and so has a wealth of archaeological and historical data which can be related to the environmental record. The paper combines these data, much of which are only published in the archaeological literature with new interpretations based upon unpublished data and new data particularly from the hillslopes and new radiocarbon dating from the valley floor. It is inferred that despite a long history of pastoral and arable agriculture (since the Neolithic/Bronze Age), colluviation on lower slopes, significant soil redistribution and overbank alluviation only began to a measurable extent in the Late Saxon–Medieval period (9th Century AD onwards). It is suggested that this is due to a combination of land-use factors, principally the laying out of an intensive open field system and the establishment of villages combined with a period of extremes in climate well known throughout Europe. Indeed the critical element appears to have been the social changes in this period that created this regionally distinctive landscape which happened to have a high spatial connectivity and facilitated intensive arable production with high tillage rates. Intense rainfall events during this period could therefore detach and mobilize high volumes of soil and the open field system facilitated transport to slope bases and valley floors. The need for detailed and spatially precise land-use data in order to interpret accelerated landscape change is stressed.

Palaeoenvironmental changes during the last 1600 years inferred from the sediment record of a cirque lake in southern Patagonia (Laguna Las Vizcachas, Argentina)
Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 281, Issues 3-4, 15 October 2009, Pages 363-375
Michael Fey, Christian Korr, Nora I. Maidana, María L. Carrevedo, Hugo Corbella, Sara Dietrich, Torsten Haberzettl, Gerhard Kuhn, Andreas Lücke, Christoph Mayr, Christian Ohlendorf, Marta M. Paez, Flavia A. Quintana, Frank Schäbitz, Bernd Zolitschka

Abstract
Laguna Las Vizcachas is a cirque lake located at the margin of an extra-Andean volcanic plateau in southern Patagonia, Argentina, within the area of steppe and semi-desert east of the Andes. The number of paleoenvironmental records is still limited in this region. Sediments of this lake were studied in order to obtain multi-proxy information about the paleoenvironmental history of this site for the ‘Medieval Climate Anomaly’ and the ‘Little Ice Age’ chronozones. In combination with results from other sites across southern Patagonia, our data enhance the understanding of spatial patterns of past hydrological changes and contribute to distinguishing between the signals of temperature and precipitation. As Laguna Las Vizcachas is situated at 1100 m a.s.l. in a cool ‘mountain climate’, the lake system is more sensitive to changes of temperature and winter ice cover than other sites from lower elevations in this region. Our interpretation of the multi-proxy dataset is based on signals of clastic sediment input, lake productivity, organic matter sources and preservation, dilution effects and early diagenetic overprint. The record reveals a period of enhanced fluvial runoff resulting from higher precipitation from the 12th until the end of the 14th century as inferred from high concentrations of Ti, Ca, and from magnetic susceptibility. This may coincide with higher wind intensities as suggested by higher proportions of epiphytic diatoms which point to an enhanced lateral transport from their littoral habitat towards the coring position at the center of the lake. In comparison with other records from southern Patagonia, the results from Laguna Las Vizcachas suggest opposite precipitation regimes between the western and eastern parts of Patagonia during that time which corresponds partly to the ‘Medieval Climate Anomaly’ chronozone. However, this proposal is compromised by the chronological uncertainties of the different records under consideration. The diatom record of Laguna Las Vizcachas indicates temperature changes: highest proportions of benthic diatoms point to coldest conditions from the mid-15th until the mid-17th century, followed by relatively warm conditions until the mid-18th century as suggested by a decrease of benthic taxa and a conspicuous rise of the planktonic/non-planktonic diatom ratio that can be used as an indicator for the length or presence/absence of winter ice cover.

Reviewing human–environment interactions in arid regions of southern South America during the past 3000 years
Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 281, Issues 3-4, 15 October 2009, Pages 283-295
M. Morales, R. Barberena, J.B. Belardi, L. Borrero, V. Cortegoso, V. Durán, A. Guerci, R. Goñi, A. Gil, G. Neme, H. Yacobaccio, M. Zárate

Abstract
Interactions between human societies and the environment that they inhabit have been a controversial topic in archaeology for at least the past fifty years. Currently, modern theoretical approaches take this subject as a key issue in their research agenda. This paper presents a review of the main outcomes of several archaeological and multidisciplinary South American projects related to this theme. The case-studies discussed here are all located within arid settings, and can be grouped into three broad geographic areas: Puna (or Altiplano) of northwestern Argentina, Cuyo (west-central Argentina), and southern Patagonia. These regions cover a wide latitudinal range extending from 22° to 52° S. They were selected for comparison due to environmental similarities, and a common record of past climate impacts mainly related to the Medieval Climatic Anomaly (MCA) and the Little Ice Age (LIA). Although the impacts of these climatic changes were locally heterogeneous in their intensity and the quality of the available information is regionally variable, they provide a base-line for comparison and supra-regional integration.
The integration of archaeological and palaeoenvironmental data on this broad supra-regional spatial scale allows us to identify interesting historical trajectories associated with particular time periods. As an example, there are some spatial rearrangements of large populations during the MCA, in the three areas. Additionally, there are variable patterns in the changes associated with the different social contexts that impose specific demographic and economic constraints. Finally, this study sets the basis for new questions and provides a guide to the methodological and theoretical issues that we need to address in order to answer them.

Evidence for a warmer period during the 12th and 13th centuries AD from chironomid assemblages in Southampton Island, Nunavut, Canada
Quaternary Research, Volume 72, Issue 1, July 2009, Pages 27-37
Nicolas Rolland, Isabelle Larocque, Pierre Francus, Reinhard Pienitz, Laurence Laperrière

Abstract
This study presents the Late-Holocene evolution of a northern Southampton Island (Nunavut, Canada) lake, using fossil chironomids supported by sedimentological evidences (XRF, grain size and CNS). All proxies revealed a relatively stable environment during the last millennium with short-lived events driving changes in the entire lake ecosystem. The chironomid-based paleotemperatures revealed variations of significant amplitude coincident with changes in the sediment density and chemical composition of the core. Higher temperature intervals were generally correlated to lower sediment density with higher chironomid concentration and diversity. Higher temperatures were recorded from cal yr AD 1160 to AD 1360, which may correspond to the Medieval Warm Period. Between cal yr AD 1360 and AD 1700, lower temperatures were probably related to a Little Ice Age event. This study presents new information on the timing of known climatic events which will refine our knowledge of the paleoclimate and climatic models of the Foxe Basin region. It also provides a new framework for the evolution of such freshwater ecosystems under the “Anthropocene” and underlines the importance of including sedimentological proxies when interpreting chironomid remains as this combined approach provides an extended overview of the past hydrological and geochemical changes and their impacts on lake biota.

Relict nebkhas (pimple mounds) record prolonged late Holocene drought in the forested region of south-central United States
Quaternary Research, Volume 71, Issue 3, May 2009, Pages 329-339
Christopher L. Seifert, Randel Tom Cox, Steven L. Forman, Tom L. Foti, Thad A. Wasklewicz, Andrew T. McColgan

Abstract
The origin and significance of pimple mounds (low, elliptical to circular dune-like features found across much of the south-central United States) have been debated for nearly two centuries. We cored pimple mounds at four sites spanning the Ozark Plateau, Arkansas River Valley, and Gulf of Mexico Coastal Plain and found that these mounds have a regionally consistent textural asymmetry such that there is a significant excess of coarse-grained sediment within their northwest flanks. We interpret this asymmetry as evidence of an eolian depositional origin of these mounds and conclude they are relict nebkhas (coppice dunes) deposited during protracted middle to late Holocene droughts. These four mounds yield optically stimulated luminescence ages between 2400 and 700 yr that correlate with well-documented periods of eolian activity and droughts on the southern Great Plains, including the Medieval Climate Anomaly. We conclude vegetation loss during extended droughts led to local eolian deflation and pimple mound deposition. These mounds reflect landscape response to multi-decadal droughts for the south-central U.S. The spatial extent of pimple mounds across this region further underscores the severity and duration of late Holocene droughts, which were significantly greater than historic droughts.

Late Holocene glacial and periglacial evolution in the upper Orco Valley, northwestern Italian Alps
Quaternary Research, Volume 71, Issue 1, January 2009, Pages 1-8
Carlo Giraudi

Abstract
The sediments present in some areas of the Orco Valley provide indications on climatic variations that occurred during the last 6000 years on the southern slopes of the Alps. In particular, distribution and ages of peat layers help define periods and extent of glacial fluctuation in the last 2200 years. Sampling of soils involved in periglacial processes provided a basis for development of a chronological framework of late Holocene environmental change. The data indicate a trend toward cooler climate in the second half of the Holocene. A strong relationship exists between phases of River Po flooding and expansion/retreat phases of the Swiss glaciers: major glacial advances were coeval with periods of intense flooding of the River Po, whereas the phases of glacial retreat coincided with periods of little flooding of the Po. Only in three cases do relationships between glacier activity and floods show weak correlations; two of the cases relate to the warmest periods in approximately the last 2200 years, while the third is the present period. Paleoclimatic evidence from the study region indicates the relatively warm Roman Period between about 2200 and 1900 cal yr BP appears to better represent modern conditions than does the Medieval Warm Period.

Climate changes over eastern China during the last millennium in simulations and reconstructions
Quaternary International
, Volume 208, Issues 1-2, 15 October 2009, Pages 11-18
Youbing Peng, Ying Xu, Liya Jin
Abstract
Climate change during the last millennium is simulated using fully coupled three-dimensional model CCSM 2.0.1. The model is driven by the natural and anthropogenic forcings. Simulated temperatures over the whole of China and over the Eastern part of China, from combined forcing correlate to some extend with the proxy data, while simulated precipitation in East China (East of 105°E, 25–40°N) and the middle and lower Yangtze River Valley (106–122°E, 26–34°N) shows some similarities with the reconstructions in some periods of time. Both simulated and reconstructed temperature anomalies indicate that the 20th century warming is anomalous in a long-term context. The model indicates that the wet and dry conditions appear alternately in the Medieval Warm Period over eastern China. Dry conditions dominate in the Little Ice Age, whereas wet conditions exist since 1890. The correlation of precipitation between simulated and reconstructed is better in the middle and lower Yangtze River Valley than in East China, especially before 1850. Regional differences are present in East China during the past thousand years and there are obviously no fixed modes of climate changes (warm–wet, cold–wet, warm–dry or cold–dry). The climate change over eastern China is affected by external factors and internal climate process. The changes of temperature and precipitation over eastern China are controlled mainly by the changes of effective solar radiation and volcanic activity during the last one thousand years, while the increase of the contents of greenhouse gases plays a big role on the fast warming over the past one hundred and fifty years.

Late Holocene monsoonal-climate change inferred from Lakes Ni-no-Megata and San-no-Megata, northeastern Japan
Quaternary International
, In Press, Corrected Proof, Available online 16 September 2009
Kazuyoshi Yamada, Masaki Kamite, Megumi Saito-Kato, Mitsuru Okuno, Yoshitsugu Shinozuka, Yoshinori Yasuda
Abstract
Micro-sedimentological, geochemical data from Lakes Ni-no-Megata and San-no-Megata in northeastern Japan are used to reconstruct environmental and climate changes over the last 2000 years. Comparing these records in two neighboring maar lakes allows reconstruction of centennial scale climate change concerned the East Asian monsoon activities without the influence of human activities. S content and coarse mineral grains records show that long-term climate changes, with one warm/humid interval from AD 1200 to 750, and two cold/dry intervals from AD 1 to 750, AD 1200 to the present. These climate changes have similar trends to Asian monsoon records in China, and could correspond to the Dark Age Cold Period (DACP), the Medieval Warm Period (MWP) and the Little Ice Age (LIA) climate changes in Europe. Moreover, short-term climatic deterioration events occurred in the 6th, 10th and 18th centuries. Particularly the event around the 10th century is well correlated with other paleoclimate proxies in China, Europe and Mesoamerica, suggesting tele-connection by atmospheric circulation through the Northern Hemisphere. However, the record is asynchronous with solar activity. This might suggest the solar forcing has indirectly influenced lake sedimentation associated with Asian monsoon activities in Japan.

Past and present interaction between the catchment and the valley floor: Upper Osoblaha basin, NE Sudetes slope and foreland
Quaternary International
, In Press, Corrected Proof, Available online 15 September 2009
Kazimierz Klimek

Abstract
The Osoblaha basin includes the north-eastern slope of the Zlatohorska Vrchovina ridge and the north-eastern foreland area of the undulating Głubczyce Plateau. Rainfall ranges from 1000 mm/year in the highlands to 650–700 mm/year on the Głubczyce Plateau.

The mountain part of the Osoblaha basin was already penetrated by humans in prehistoric times. Miners extracted gold from the alluvia and later from the slope covers. Their activities have left traces such as extant pits in sediments. Iron and other ores were mined and processed there from the early Middle Ages onwards. In the 12th or 13th century at the latest, settlements and towns were founded for mining (e.g. Janov, Zlate Hory) and by farmers who tilled the land at the foot of the valley slopes.

This exploitation of the mountainous part of the basin caused significant clearance of beech forests as the wood was used to manufacture charcoal. The deforestation of the valley slopes or the introduction of spruce forests in lieu of the beech forests changed the circulation of rain and thaw water. Exposed slope covers were prone to erosion or liquefaction and transfer towards the mountain valleys. Flood episodes caused the sedimentation of clayey overbank deposits, which cover the valley floor. The considerable cohesion of these sediments was conducive to the formation of meandering or anastomosing channels which were a typical feature of the Osoblaha valley floor in the area around the confluence of the Zlaty Potok–Prudnik in the second half of the 18th century and in the 19th century.
The Głubczyce Plateau is a 30–40 km wide area consisting of undulating plateaux ranging from 320 to 240 m a.s.l. These are dissected by dry valleys and descend gently towards the north. Fertile soils, the abundance of local streams and a climate conducive to farming led to this area being settled by farming and herding communities as early as the Neolithic period, around 7000 BP. This initiated the deforestation process and increased soil erosion, shown by the colluvia accumulated in the valley heads of dry valleys and by alluvial fan sediments close to their mouths where they entered the main valleys. The last stage of farming colonisation of this part of the Osoblaha basin, initiated by Slavs, had already led to the development of a dense network of settlements and considerable deforestation in the Mediaeval Period.

Human activity and the environment during the Late Iron Age and Middle Ages at the Impiltis archaeological site, NW Lithuania
Quaternary International
, Volume 203, Issues 1-2, 1 July 2009, Pages 74-90
Miglė Stančikaitė, Petras Šinkūnas, Jan Risberg, Vaida Šeirienė, Nerijus Blažauskas, Romas Jarockis, Sven Karlsson, Urve Miller

Abstract
Research carried out at the Impiltis hill fort and settlement area in NW Lithuania indicates the occurrence of environmental changes caused by climatic alterations and human impact during the Late Iron Age and the Middle Ages. Both the archaeological and palaeoenvironmental data confirm that intensive human activity began in the area shortly before 900 AD, generally coinciding with the onset of the “Medieval Warm Period”. The first appearance of rye (Secale cereale) and flax (Linum usitatissimum) pollen grains is the earliest in the region, which indicates the development of permanent agriculture using some field rotation system. Increasing pressure on the environment is seen in the reconstruction of the hill fort, the development of an agricultural system, and the introduction of new cultivated plants. According to the palaeoenvironmental data, farming persisted as the main activity of the Impiltis population during the period of prosperity dated back to about 1050–1260 AD. Afterwards, Impiltis existed as a typical agrarian settlement which may have been positively influenced by the mild climatic conditions of the “Medieval Warm Period”. A clearly marked regression of human activity coincides with the destruction of the Impiltis castle and settlement during the German Order conquest in 1263 AD. The subsequent resurgence of human activity in the area was influenced by the ensuing climatic deterioration known as the “Little Ice Age”.

Late Holocene climatic and environmental changes in arid central Asia
Quaternary International, Volume 194, Issues 1-2, 1 February 2009, Pages 68-78
Bao Yang, Jinsong Wang, Achim Bräuning, Zhibao Dong, Jan Esper
 
Abstract
Late Holocene climate and environmental changes in arid central Asia were analyzed using various paleoclimate archives such as ice cores, tree rings, lake sediments, historical documents, glacial fluctuations and archeological data. Over the last 2000 years, arid central Asia witnessed three humid periods from AD 0–410, 650–890 and 1500–1820s. Dry periods occurred in 420–660 and in 900–1510s. Concerning temperature, the most striking features are the existence of the Medieval Warm Period (MWP) and the Little Ice Age (LIA). The MWP was recorded in the 9–12th centuries and was accompanied by an anomalously dry climate, whereas the LIA extended from the 15–18th centuries and was accompanied by pluvial conditions. Temperature and precipitation show significantly negative correlations on annual, decadal and centennial timescales. Temperature was generally above average when dry climate conditions predominated on decadal to centennial timescales during the last 1000 years. The coldest decades of the last millennium, the period 1630–1650s, matched with an anomalously wet episode. The combination of paleoclimatic evidence clearly suggests that the combination of cold and wet climate condition during the LIA was responsible for the strong glacial advances in several mountain systems of central Asia.

Dust records from varved lacustrine sediments of two neighboring lakes in northeastern China over the last 1400 years
Quaternary International
, Volume 194, Issues 1-2, 1 February 2009, Pages 108-118
Guoqiang Chu, Qing Sun, Gu Zhaoyan, Patrick Rioual, Liu Qiang, Wang Kaijun, Jingtai Han, Jiaqi Liu
Abstract
Dust storms are natural phenomena, described in Chinese historical documents as early as 1150 BC. These documents provide a way to evaluate proxy data from different natural records. The minerogenic clastic content and grain size from two closed maar lakes located a short distance apart in northeastern China were analyzed. The area is located in the path of dust storms. The minerogenic clastics in the studied maar lakes originate mainly from dust deposition. General variations of the minerogenic clastic content in these two neighboring lakes show a good coincidence with dust concentration in a Tibet ice core and dust events as recorded in historical documents. The minerogenic clastic content in the lake sediments is linked with the climate conditions in the dust source regions and wind strength. Three periods of intensive dust events (AD 1050–1330, AD 1590–1690, and the last 200 years) have been identified during the past 1500 years. The recent increasing pattern of clastic content could be linked to human activity in the dust source regions. Significantly, most of the Medieval Warm Period (MWP) was marked by a high frequency of dust storms.

Late Holocene (0–2.4 ka BP) surface water temperature and salinity variability, Feni Drift, NE Atlantic Ocean
Quaternary Science Reviews, Volume 28, Issues 19-20, September 2009, Pages 1941-1955
T.O. Richter, F.J.C. Peeters, T.C.E. van Weering
Abstract
Planktonic foraminiferal Mg/Ca ratios and oxygen isotopic compositions of a spliced sediment record from Feni Drift, NE Atlantic Ocean (box core M200309 and piston core ENAM9606) trace late Holocene sea surface temperature (SST) and salinity changes over the past 2400 years. At this location, the variability of SST and oxygen isotopic composition of seawater (Delta18Ow) reflects variable northward advection of warm and saline surface waters, which appears linked to climate variability over the adjacent European continent. Our records reveal a general long-term cooling trend. Superimposed on this overall trend, partly higher temperatures and salinities from 180 to 560 AD and 750 to 1160 AD may be ascribed to the Roman and Medieval Warm Periods, respectively. Subsequently, our record displays highly variable surface water conditions; the main Little Ice Age SST minimum is restricted to the 15th and 16th centuries AD. Pervasive multidecadal- to centennial-scale variability throughout the sedimentary proxy records can be partly attributed to solar forcing and/or variable heat extraction from the surface ocean caused by shifts in the prevailing state of the North Atlantic Oscillation (NAO). High salinities in the 17th and 18th centuries are considered to reflect tropical anomalies linked to a southward shift of the Intertropical Convergence Zone, propagating across the North Atlantic Ocean.

Holocene and latest Pleistocene climate and glacier fluctuations in Iceland
Quaternary Science Reviews, Volume 28, Issues 21-22, October 2009, Pages 2107-2118
Áslaug Geirsdóttir, Gifford H. Miller, Yarrow Axford, Sædís Ólafsdóttir

Abstract
Multiproxy climate records from Iceland document complex changes in terrestrial climate and glacier fluctuations through the Holocene, revealing some coherent patterns of change as well as significant spatial variability. Most studies on the Last Glacial Maximum and subsequent deglaciation reveal a dynamic Iceland Ice Sheet (IIS) that responded abruptly to changes in ocean currents and sea level. The IIS broke up catastrophically around 15 ka as the Polar Front migrated northward and sea level rose. Indications of regional advance or halt of the glaciers are seen in late Alleröd/early Younger Dryas time and again in PreBoreal time. Due to the apparent rise of relative sea level in Iceland during this time, most sites contain evidence for fluctuating, tidewater glacier termini occupying paleo fjords and bays. The time between the end of the Younger Dryas and the Preboreal was characterized by repeated jökulhlaups that eroded glacial deposits. By 10.3 ka, the main ice sheet was in rapid retreat across the highlands of Iceland. The Holocene thermal maximum (HTM) was reached after 8 ka with land temperatures estimated to be 3 °C higher than the 1961–1990 reference, and net precipitation similar to modern. Such temperatures imply largely ice-free conditions across Iceland in the early to mid-Holocene. Several marine and lacustrine sediment climate proxies record substantial summer temperature depression between 8.5 and 8 ka, but no moraines have been detected from that time. Termination of the HTM and onset of Neoglacial cooling took place sometime after 6 ka with increased glacier activity between 4.5 and 4.0 ka, intensifying between 3.0 and 2.5 ka. Although a distinct warming during the Medieval Warm Period is not dramatically apparent in Icelandic records, the interval from ca AD 0 to 1200 is commonly characterized by relative stability with slow rates of change. The literature most commonly describes Little Ice Age moraines (ca AD 1250–1900) as representing the most extensive ice margins since early Holocene deglaciation, with temperature depressions of 1–2 °C compared to the AD 1961–1990 average. Steep north–south and west–east temperature gradients are reconstructed in the Holocene records of Iceland, suggesting a strong maritime influence on the terrestrial climate of Iceland

Evidence for millennial-scale climatic events in the sedimentary infilling of a macrotidal estuarine system, the Seine estuary (NW France)
Quaternary Science Reviews, Volume 28, Issues 5-6, March 2009, Pages 499-516
Philippe Sorrel, Bernadette Tessier, François Demory, Nicolas Delsinne, Dominique Mouazé
Abstract
High-resolution sedimentological and rock magnetic analyses from sediment cores collected in the Seine estuary record changes in coastal sedimentary dynamics linked to climatic variations during the late Holocene. Using AMS 14C and paleomagnetic data we present a first attempt in developing a reliable age model on macrotidal estuarine archives, with a decadal resolution. Correlations between sedimentary successions from the outer Seine estuary document the main sedimentary infilling phases of the system during the last 3000 years. Between 3000 and 1150 cal. BP sedimentary patterns reveal that sequence deposition and preservation are predominantly controlled by marine and tidal hydrodynamics while severe storm events are recorded at ca. 2700 and 1250 cal. BP in the outermost estuary. Conversely, the Medieval Warm Period (MWP; 900–1200 AD) is characterized by a drastic waning of the influence of marine hydrodynamics on sediment preservation. Pronounced episodes of Seine river floods indicate a much stronger impact of continental inputs on sedimentary patterns during this period. The onset of the Little Ice Age marks a diminishing influence of continental inputs while tidal and open marine hydrodynamics again exerted a primary control on the sedimentary evolution of the system during 1200–2003 AD. Coastal sedimentary dynamics as preserved within sedimentary successions appear to have been largely influenced by changes in storminess during the last 3000 years. We have matched the preservation of MWP Seine river floods, as revealed by sedimentological and rock magnetic proxy data, to a prolonged interval of weakened storminess in Normandy permitting the preservation of estuarine flood deposits within a context of reduced coastal erosion in northern Europe. The preservation of sedimentary successions in the Seine estuary is therefore maximal when climate conditions resembled those of the preferred low phase of the NAO on multidecadal timescales such as during 800–1200 AD (MWP). In contrast, increased removal and transport of estuarine sediments occur when winter storm activity greatly intensified over northwestern France. We report four prominent centennial-scale periods of stronger storminess, occurring with a pacing of 1500 years, which are likely to be related to the last four Bond's Holocene cold events. Our results documenting a close link between coastal sedimentary dynamics, millennial-scale variations in Holocene climate and North Atlantic atmospheric circulation are fairly consistent with other records from Scandinavia, central Greenland and southern Europe.

A new Late Holocene sea-level record from the Mississippi Delta: evidence for a climate/sea level connection?
Quaternary Science Reviews, Volume 28, Issues 17-18, August 2009, Pages 1737-1749
Juan L. González, Torbjörn E. Törnqvist
Abstract
A detailed relative sea-level (RSL) record was constructed for the time interval 600–1600 AD, using basal peat to track sea level and containing 16 sea-level index points that capture 60 cm of RSL rise. The study area is in the Mississippi Delta where the spring tidal range is 0.47 m, the impact of ocean currents on sea-surface topography is limited, and crustal motions are well constrained. Age control was obtained by AMS 14C dating and most ages represent weighted means of two subsamples. Sample elevations were determined by combining differential GPS measurements with optical surveying. All index points were plotted as error boxes using 2σ confidence intervals for the ages, plus all vertical errors involved in sampling and surveying, as well as the indicative range of the samples. A striking clustering of sea-level index points between 1000 and 1200 AD suggests a possible acceleration in the rate of RSL rise. Removal of the long-term trend (0.60 mm yr−1) allows for the possibility of a sea-level oscillation with a maximum amplitude of 55 cm. However, given the size of the error boxes the possibility that oscillations did not occur cannot be entirely ruled out. Comparison of the new RSL record with various proxy climate records suggests that sea level in this area may have responded to hemispheric temperature changes, including the Medieval Warm Period and the Little Ice Age. However, given the error margins associated with this reconstruction, it is stressed that this causal mechanism is tentative and requires corroboration by high-resolution sea-level reconstructions elsewhere.

Sea ice variations in the central Canadian Arctic Archipelago during the Holocene
Quaternary Science Reviews, Volume 28, Issues 13-14, June 2009, Pages 1354-1366
Lindsay L. Vare, Guillaume Massé, Thomas R. Gregory, Christopher W. Smart, Simon T. Belt
Abstract
A sea ice record for Barrow Strait in the Canadian Arctic Archipelago (CAA) is presented for the interval 10.0–0.4 cal. kyr BP. This Holocene record is based primarily on the occurrence of a sea ice biomarker chemical, IP25, isolated from a marine sediment core obtained from Barrow Strait in 2005. A core chronology is based on 14C AMS dating of mollusc shells obtained from ten horizons within the core. The primary IP25 data are compared with complementary proxy data obtained from analysis of other organic biomarkers, stable isotope composition of bulk organic matter, benthic foraminifera, particle size distributions and ratios of inorganic elements. The combined proxy data show that the palaeo-sea ice record can be grouped according to four intervals, and these can be contextualised further with respect to the Holocene Thermal Maximum (HTM). Spring sea ice occurrence was lowest during the early–mid Holocene (10.0–6.0 cal. kyr BP) and this was followed by a second phase (6.0–4.0 cal. kyr BP) where spring sea ice occurrence showed a small increase. Between 4.0 and 3.0 cal. kyr BP, spring sea ice occurrence increased abruptly to above the median and we associate this interval with the termination of the HTM. Elevated spring sea ice occurrences continued from 3.0 to 0.4 cal. kyr BP, although they were more variable on shorter timescales. Within this fourth interval, we also provide evidence for slightly lower and subsequently higher spring sea ice occurrence during the Mediaeval Warm Period and the Little Ice Age respectively. Comparisons are made between our proxy data with those obtained from other palaeo-climate and sea ice studies for the CAA.

Preliminary paleoclimate reconstruction based on a 12,500 year old speleothem from Vancouver Island, Canada: stable isotopes and U–Th disequilibrium dating
Quaternary Science Reviews, Volume 28, Issues 23-24, November 2009, Pages 2507-2513
Daniel Marshall, Bassam Ghaleb, Robert Countess, Janet Gabities
Abstract
A combination of Delta18C and Delta18O analyses with U–Th disequilibrium dating on a stalagmite and groundwater from the deep and extensive Arch Cave network on northeastern Vancouver Island has produced a preliminary 12,200 y paleoclimatic profile. Speleothem depositional rates vary from 6 to 41 mm/ka and are consistent with the “Hendy” test for speleothem deposition under high-humidity equilibrium conditions. Relative to present day conditions, warmer periods are indicated at the end of the Younger Dryas, during the Holocene maximum, a possible Medieval Warming event, with the warmest period represented by a narrow peak at 8000 y BP. Relatively cooler periods are recorded at 3500, 8200, 9300 and 11,500 y BP with indications of minor cooling during the Little Ice Age and indications of relatively dry conditions during the earlier part of the Younger Dryas followed by warmer wetter conditions. The profile shows excellent agreement with other paleoclimatic indicators locally, most notably some partial speleothem records from Vancouver Island and Oregon, and some high-resolution global records such as the Greenland ice cores and speleothems from the Hulu Cave, China.

Glacial to Holocene climate changes in the SE Pacific. The Raraku Lake sedimentary record (Easter Island, 27°S)
Quaternary Science Reviews, Volume 28, Issues 25-26, December 2009, Pages 2743-2759
Alberto Sáez, Blas L. Valero-Garcés, Santiago Giralt, Ana Moreno, Roberto Bao, Juan J. Pueyo, Armand Hernández, David Casas
Abstract
Easter Island (SE Pacific, 27°S) provides a unique opportunity to reconstruct past climate changes in the South Pacific region based on terrestrial archives. Although the general climate evolution of the south Pacific since the Last Glacial Maximum (LGM) is coherent with terrestrial records in southern South America and Polynesia, the details of the dynamics of the shifting Westerlies, the South Pacific Convergence Zone and the South Pacific Anticyclone during the glacial–interglacial transition and the Holocene, and the large scale controls on precipitation in tropical and extratropical regions remain elusive. Here we present a high-resolution reconstruction of lake dynamics, watershed processes and paleohydrology for the last 34 000 cal yrs BP based on a sedimentological and geochemical multiproxy study of 8 cores from the Raraku Lake sediments constrained by 22 AMS radiocarbon dates. This multicore strategy has reconstructed the sedimentary architecture of the lake infilling and provided a stratigraphic framework to integrate and correlate previous core and vegetation studies conducted in the lake. High lake levels and clastic input dominated sedimentation in Raraku Lake between 34 and 28 cal kyr BP. Sedimentological and geochemical evidences support previously reported pollen data showing a relatively open forest and a cold and relatively humid climate during the Glacial period. Between 28 and 17.3 cal kyr BP, including the LGM period, colder conditions contributed to a reduction of the tree coverage in the island. The coherent climate patterns in subtropical and mid latitudes of Chile and Eastern Island for the LGM (more humid conditions) suggest stronger influence of the Antarctic circumpolar current and an enhancement of the Westerlies. The end of Glacial Period occurred at 17.3 cal kyr BP and was characterized by a sharp decrease in lake level conducive to the development of major flood events and erosion of littoral sediments. Deglaciation (Termination 1) between 17.3 and 12.5 cal kyr BP was characterized by an increase in lake productivity, a decrease in the terrigenous input and a rapid lake level recovery, inaugurating a period of intermediate lake levels, dominance of organic deposition and algal lamination. The timing and duration of deglaciation events in Easter Island broadly agree with other mid- and low-latitude circum South Pacific terrestrial records. The transition to the Holocene was characterized by lower lake levels. The lake level dropped during the early Holocene (ca 9.5 cal kyr BP) and swamp and shallow lake conditions dominated till mid Holocene, partially favored by the infilling of the lacustrine basin. During the mid- to late-Holocene drought phases led to periods of persistent low water table, subaerial exposure and erosion, generating a sedimentary hiatus in the Raraku sequence, from 4.2 to 0.8 cal kyr BP. The presence of this dry mid Holocene phase, also identified in low Andean latitudes and in Patagonian mid latitudes, suggests that the shift of storm tracks caused by changes in the austral summer insolation or forced by “El Niño-like” dominant conditions have occurred at a regional scale. The palm deforestation of the Easter Island, attributed to the human impact could have started earlier, during the 4.2–0.8 cal kyr BP sedimentary gap. Our paleoclimatic data provides insights about the climate scenarios that could favor the arrival of the Polynesian people to the island. If it occurred at ca AD 800 it coincided with the warmer conditions of the Medieval Climate Anomaly, whereas if it took place at ca AD 1300 it was favored by enhanced westerlies at the onset of the Little Ice Age. Changes in land uses (farming, intensive cattle) during the last century had a large impact in the hydrology and limnology (eutrophication) of the lake.

Lateglacial and Holocene palaeohydrology in the western Mediterranean region: The Lake Estanya record (NE Spain)
Quaternary Science Reviews, Volume 28, Issues 25-26, December 2009, Pages 2582-2599
Mario Morellón, Blas Valero-Garcés, Teresa Vegas-Vilarrúbia, Penélope González-Sampériz, Óscar Romero, Antonio Delgado-Huertas, Pilar Mata, Ana Moreno, Mayte Rico, Juan Pablo Corella
Abstract
The multi-proxy analysis of sediment cores recovered in karstic Lake Estanya (42°02′ N, 0°32′ E; 670 m a. s. l., NE Spain), located in the transitional area between the humid Pyrenees and the semi-arid Central Ebro Basin, provides the first high-resolution, continuous sedimentary record in the region, extending back the last 21 000 years. The integration of sedimentary facies, elemental and isotopical geochemistry and biogenic silica, together with a robust age model based on 17 AMS radiocarbon dates, enables precise reconstruction of the main hydrological and environmental changes in the region during the last deglaciation.
Arid conditions, represented by shallow lake levels, predominantly saline waters and reduced organic productivity occurred throughout the last glacial maximum (21–18 cal kyrs BP) and the lateglacial, reaching their maximum intensity during the period 18–14.5 cal kyrs BP (including Heinrich event 1) and the Younger Dryas (12.9–11.6 cal kyrs BP). Less saline conditions characterized the 14.5–12.6 cal kyrs BP period, suggesting higher effective moisture during the Bölling/Allerød. The onset of more humid conditions started at 9.4 cal kyrs, indicating a delayed hydrological response to the onset of the Holocene which is also documented in several sites of the Mediterranean Basin. Higher, although fluctuating, Holocene lake levels were punctuated by a mid Holocene arid period between 4.8 and 4.0 cal kyrs BP. A major lake-level rise occurred at 1.2 cal kyrs BP, conducive to the establishment of conditions similar to the present and interrupted by a last major water level drop, occurring around 800 cal yrs BP, which coincides with the Medieval Climate Anomaly.
The main hydrological stages in Lake Estanya are in phase with most Western Mediterranean and North Atlantic continental and marine records, but our results also show similarities with other Iberian and northern African reconstructions, emphasizing peculiarities of palaeohydrological evolution of the Iberian Peninsula during the last deglaciation.

Persistent multidecadal power of the Indian Summer Monsoon
Earth and Planetary Science Letters, Volume 290, Issues 1-2, 15 February 2010, Pages 166-172
Max Berkelhammer, Ashish Sinha, Manfred Mudelsee, Hai Cheng, R. Lawrence Edwards, Kevin Cannariato
Abstract
The instrumental record of Indian Summer Monsoon (ISM) precipitation displays two complete manifestations of an inferred multidecadal cycle. Hitherto, no precipitation-sensitive proxy record from the Indian subcontinent has had the necessary resolution and length to adequately assess whether this observed feature is an inherent aspect of the ISM system on longer timescales. Here we present compelling evidence for persistence of this cycle using a millennial length (AD 600–1550) and sub-annually resolved speleothem oxygen isotope record (Delta18O) from Dandak Cave in east-central India. The record displays a high degree of correlation with a speleothem-based Asian monsoon reconstruction from Wanxiang Cave in north-central China on annual to decadal timescales showing the regional significance of these findings. The observed period in our monsoon reconstruction is similar to that associated with the Gleissberg solar cycle and multidecadal sea surface temperature variability in the north Atlantic (AMO), both of which are often cited as the prominent pacemakers of ISM variability on multidecadal timescales. We document transient coherence between ISM precipitation amount and solar variability that persists exclusively in the century prior to and during the Medieval Climate Anomaly (nominally, AD 950–1300). The non-stationary nature of the SFV–monsoon relationship presented here may be evidence of the time-varying influence of tropical ocean–atmosphere dynamics on the solar–monsoon link; however, it is not possible to show with significance that this period of coherence is anything more than an artifact of two timeseries with similar spectra. We therefore, are inclined to interpret our record as evidence of a minimal role of solar variability in driving persistent multidecadal variability of the ISM. Multidecadal SST variability in the North Atlantic remains as the likely alternative driver for persistence of this cycle. Regardless of the causative mechanism(s), the amplitude and regional signature of the observed cycle in ISM precipitation highlight its societal importance with respect to forecasting ISM precipitation on multidecadal timescales.

Reconstructing 2000 years of hydrological variation derived from laminated proglacial sediments of Lago del Desierto at the eastern margin of the South Patagonian Ice Field, Argentina
Global and Planetary Change, In Press, Accepted Manuscript, Available online 25 April 2010
Stephanie Kastner, Dirk Enters, Christian Ohlendorf, Torsten Haberzettl, Gerhard Kuhn, Andreas Lücke, Christoph Mayr, Jean-Louis Reyss, Stefan Wastegård, Bernd Zolitschka
Abstract
Lago del Desierto (49°02'S, 72°51'W) is situated in the climatically sensitive area of Southern Patagonia close to the Hielo Patagonico Sur (HPS or South Patagonian Ice Field, Argentina). Next to marine records and Antarctic ice cores, this continental area is important to reveal hemispheric and global climate trends. As instrumental climate records from this region are generally short and scarce, environmental archives are the only source of long-term records of climate variations. In this study, the potential of laminated proglacial sediments from Lago del Desierto as a palaeoclimate archive is evaluated. Two parallel gravity cores (max. length 283 cm) were analysed using a multi-proxy approach. Radiometric dating (14C, 210Pb and 137Cs) and tephrochronology document that the sediment cover the last 2000 years. Especially in the middle part of the record, numerous turbidites make climate variations difficult to decipher. However, after exclusion of event layers changes in sedimentological, mineralogical, and geochemical parameters reveal a long-term trend of runoff variations and sediment accessibility controlled by changes in temperature and precipitation. An abrupt transition in sediment composition occurred around AD 850 and is interpreted as a change in sediment availability related to the initial exposure of formerly glaciated areas in the catchment. This striking change mirrors the onset of warmer climate conditions during the Medieval Climate Anomaly. Moreover, the Little Ice Age cooling and the subsequent 20th century warming can be traced in the sediment record corresponding to an overall trend observed for southern South America. The proglacial lacustrine sediment record of Lago del Desierto thus constitutes a link between glacier studies of the HPS and other terrestrial climate archives in a region were long, and continuous climate records are still rare.

PALEOCEANOGRAPHY, VOL. 25, PA1102, 7 PP., 2010
doi:10.1029/2009PA001871
Coordinated hydrological regimes in the Indo-Pacific region during the past two millennia
Coordinated hydrological regimes in the Indo-Pacific region during the past two millennia
Jessica E. Tierney, Delia W. Oppo, Yair Rosenthal, James M. Russell, Braddock K. Linsley

Instrumental data suggest that major shifts in tropical Pacific atmospheric dynamics and hydrology have occurred within the past century, potentially in response to anthropogenic warming. To better understand these trends, we use the hydrogen isotopic ratios of terrestrial higher plant leaf waxes (δDwax) in marine sediments from southwest Sulawesi, Indonesia, to compile a detailed reconstruction of central Indo-Pacific Warm Pool (IPWP) hydrologic variability spanning most of the last two millennia. Our paleodata are highly correlated with a monsoon reconstruction from Southeast Asia, indicating that intervals of strong East Asian summer monsoon (EASM) activity are associated with a weaker Indonesian monsoon (IM). Furthermore, the centennial-scale oscillations in our data follow known changes in Northern Hemisphere climate (e.g., the Little Ice Age and Medieval Warm Period) implying a dynamic link between Northern Hemisphere temperatures and IPWP hydrology. The inverse relationship between the EASM and IM suggests that migrations of the Intertropical Convergence Zone and associated changes in monsoon strength caused synoptic hydrologic shifts in the IPWP throughout most of the past two millennia.

Citation: Tierney, J. E., D. W. Oppo, Y. Rosenthal, J. M. Russell, and B. K. Linsley (2010), Coordinated hydrological regimes in the Indo-Pacific region during the past two millennia, Paleoceanography, 25, PA1102, doi:10.1029/2009PA001871

Holocene vegetation and climate history of central Quintana Roo, Yucatán Península, Mexico
Review of Palaeobotany and Palynology, Volume 160, Issues 3-4, May 2010, Pages 189-196
Alicia Carrillo-Bastos, Gerald A. Islebe, Nuria Torrescano-Valle, Norma Emilia González
Abstract
Pollen analysis and oxygen isotope measurements on a sediment core recovered from Lake Tzib, revealed the vegetation and climate history of central Quintana Roo, southeast Mexico for the last  7900 cal yr. During the early Holocene (7900–7000 cal yr BP), vegetation changed from medium- and low-stature forest with nearby mangroves, to medium-stature forest. Between 6500 and 4700 cal yr BP, climate proxies indicate a transition from relatively moist to drier environmental conditions. Around 3500 cal yr BP, even drier conditions prevailed. These dry conditions correspond to the onset of dry phases identified elsewhere in Mexico and Central America. An inferred dry event at 1200 cal yr BP is correlated temporally with dry conditions inferred from a marine core taken in the Cariaco Basin, north of Venezuela. The dry episode falls within the ancient Maya Terminal Classic archaeological period. We found evidence for strong forest disturbance during that period. Around 700 cal yr BP (1200 AD), sediment variables indicate moister environmental conditions that fall within the period of the medieval climate optimum.

Diatom-based reconstruction of palaeoceanographic changes on the North Icelandic shelf during the last millennium
Palaeogeography, Palaeoclimatology, Palaeoecology, In Press, Corrected Proof, Available online 14 February 2010
Lihua Ran, Hui Jiang, Karen Luise Knudsen, Jón Eiríksson

Abstract
Pronounced palaeoceanographic changes during the last millennium are revealed by high-resolution diatom records from site MD99-2275 on the North Icelandic shelf. There is a high degree of consistency between the reconstructed summer sea surface temperature (SST) record based on diatoms and the instrumental and documentary data during the last 100 years. This confirms the reliability of this proxy for the study of palaeoceanographic and palaeoclimatic changes on the North Icelandic shelf. The present diatom-based summer SST reconstruction shows that the last millennium was characterized by a general cooling trend, but with some fluctuations. Warm and stable conditions with relatively strong influence of the Irminger Current on the North Icelandic shelf are indicated during the interval AD 940–1300, corresponding in time to the Medieval Warm Period (MWP). A considerable cooling at  AD 1300 indicates the transition to the Little Ice Age (LIA) with increased influence of Polar and Arctic water masses deriving from the East Greenland and East Icelandic currents. An extended cooling period between AD 1300 and 1910 is characterized by approximately century-scale oscillations, with marked cold intervals at AD 1325–1375, AD 1460–1500, AD 1610–1670 and AD 1810–1910, separated by relatively mild spells. A two-step warming during the last 100 years is interrupted by three cool events around AD 1920, in the AD 1960s and in the late AD 1990s. In general, the diatom-based indication of palaeoceanographic changes on the North Icelandic shelf during the last millennium corresponds to other proxy-based palaeoclimatic and palaeoceanographic records in the North Atlantic region.

A radiocarbon dated bat guano deposit from N.W. Romania: Implications for the timing of the Little Ice Age and Medieval Climate Anomaly
Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 291, Issues 3-4, 15 May 2010, Pages 217-227
Vanessa E. Johnston, Frank McDermott, Tudor Tămaş
Abstract
There is considerable interest in the potential of bat guano as an alternative record of palaeoclimate in regions that are devoid of more commonly utilised archives. In this study, designed originally to evaluate the potential of cave hosted bat guano to preserve temporal variations in the flux of cosmogenic 36Cl, it was found that the guano depositional history is strongly linked to climatic conditions. Radiocarbon measurements on a 2.7 metre long core of bat guano from Măgurici Cave, N.W. Romania indicate a maximum depositional age of 1195 AD for the base of the core. Deposition of the lowermost portion of the accumulation occurred during the Medieval Climate Anomaly. The cave roost was subsequently devoid of bats during a regional cold phase linked to the Little Ice Age, with bats returning when local temperatures increased. The rate of guano accumulation then appears to increase in tandem with anthropogenic warming. This indicates that bat occupation at this roost site in Măgurici Cave is strongly linked to regional climate variability, with habitation during warm periods, possibly associated with the abundance of insects upon which the bats feed.
Comparison of large peaks in anthropogenic 14C and 36Cl production associated with nuclear weapons testing indicates downward migration of 36Cl, probably reflecting post-depositional migration within the guano deposit. Elevated 36Cl/Cl at the top of the core in comparison with modern atmospheric values may indicate recycling of bomb 36Cl in vegetation. Therefore, we show that while bat guano contains abundant atmospherically-derived chloride it has severe limitations as a potential archive of atmospherically-derived 36Cl (a solar proxy), because of post-depositional mobility. However, separation of organically bound chloride, or the use of an alternative cosmogenic isotope 10Be, in bat guano, may offer an unexploited solar proxy that contains contemporaneous environmental signals, such as stable isotopes (e.g. Delta13C) and pollen, in association with radiocarbon dating.

Diatom-inferred climatic and environmental changes over the last  9000 years from a low Arctic (Nunavut, Canada) tundra lake
Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 291, Issues 3-4, 15 May 2010, Pages 205-216
C.A. Paul, K.M. Rühland, J.P. Smol
Abstract
Diatom assemblage changes over the Holocene were examined from a 14C-dated sediment core retrieved from Lake TK-2, a small low Arctic lake located ca. 200 km north of the forest–tundra ecotone in mainland Nunavut, Canada. Notable changes in the diatom assemblages were recorded throughout the core, suggesting that the Holocene epoch in this region has been environmentally and climatically dynamic. The earliest diatom assemblages (ca. 9000 cal yr BP) were dominated by taxa that are atypical of post-glacial assemblages commonly recorded throughout the Arctic, and may suggest that early Holocene conditions at Lake TK-2 were relatively warmer. A shift to dominance by small, benthic, opportunistic Fragilaria taxa followed (after ca. 8550 cal. yr BP), more typical of Arctic assemblages during initial lake ontogeny, suggesting the onset of cooler, more alkaline conditions. An abrupt and short-lived marked decrease in diatoms between ca. 8550 and 8500 cal. yr BP, with corresponding changes in physical and chemical indicators (e.g., sedimentation rate, siliciclastic content, % organic matter content), provides potential evidence for the 8.2 k cooling anomaly, an event rarely recognized from other paleolimnological studies in the Canadian north. Following ca. 7000 cal. yr BP, a substantial shift occurred to a more complex and diverse diatom assemblage that now included more acidophilic taxa. This compositional change is likely indicative of a natural, long-term loss of alkalinity in the lake, and marks the onset of the Holocene Thermal Maximum, consistent with the timing of this warm period for this region. The relatively stable diatom assemblage composition during the Neoglacial period was punctuated by fluctuations in key species potentially correlative with the so-called Medieval Warm Period and Little Ice Age. In the most recent sediments, the post-industrial expansion of the small, planktonic Cyclotella stelligera complex, and a concurrent decline in the heavily-silicified Aulacoseira lirata complex, are similar to shifts that are increasingly being recognized as geographically widespread diatom responses to recent climate warming. The Lake TK-2 diatom record provides important insights into the Holocene environmental history of this understudied region of the Canadian Arctic. Furthermore, it is one of the few Arctic lakes in which the 8.2 k cold event is possibly expressed.

Interplay between detrital and diagenetic processes since the last glacial maximum on the northwest Iberian continental shelf
Quaternary Research, Volume 73, Issue 3, May 2010, Pages 507-520
Kais Jacob Mohamed, Daniel Rey, Belen Rubio, Federico Vilas, Thomas Frederichs
Abstract
Integrated analyses of magnetic, geochemical and textural data on six cores from the northwestern Iberian continental shelf allowed the reconstruction of the paleoenvironmental evolution of this area since the last glacial maximum (LGM). Four sedimentary units were identified, representing a succession from fluvial and subaerial settings to high and finally low-energy marine deposits subsequent to the post-LGM sea-level rise. The uppermost unit was deposited during the Holocene and its magnetic properties were controlled by the interplay between detrital input and early diagenetic reductive dissolution of magnetic minerals. Identification of a primary steady-state early diagenetic signal allowed the recognition of periods of increased detrital input, bounded by intervals of lower detrital input and intensified reductive diagenesis related to intensified upwelling in the area. These paleoenvironmental alternations are consistent with the climatic evolution of the late Holocene. During the Roman Warm Period and Medieval Warm Period, the combined effect of greater humidity and intense agricultural and mining activities led to a greater erosion and transport of detrital sediments to the shelf. In contrast, enhanced diagenetic reduction intervals, caused by upwelling intensification, were roughly coincident with the colder Dark Ages and the Little Ice Age.

Erosional effects on terrestrial resources over the last millennium in Reykjanes, southwest Icelan
Quaternary Research
, Volume 73, Issue 1, January 2010, Pages 20-32

Guðrún Gísladóttir, Egill Erlendsson, Rattan Lal, Jerry Bigham


Abstract

The study presents the effect of soil erosion on vegetation, soil accumulation (SA), SA rate (SAR), soil quality, soil mass, and the soil organic carbon (SOC) pool in Brown Andosols and Histosols in a 24-km2 area in southwest Iceland. Undisturbed prehistoric soils were distinguished from disturbed historic soils using tephrochronology. Soil erosion has been severe during historic time (last 1135 yr), resulting in the increase of the soil mass deposited in soils covered by vegetation by a factor of 7.3–9.2 and net loss of soil in unvegetated areas. The SAR correlated positively with SOC sequestration. SOC is easily transported and, given the extensive accumulation of soil, the net effect of burial and subsequent reduction in decomposition is to increase SOC storage. Nevertheless, the increased accumulation and soil depletion has decreased soil quality, including the SOC, and reduced soil resistance to erosion with the depleted SOC contributing to enrichment of atmospheric CO2. The initial terrestrial disturbance was triggered by anthropogenic land use during the Medieval Warm Period, followed by volcanic activity approximately three centuries later. The combination of harsh climate during the Little Ice Age and drastic anthropogenic perturbations has led to land degradation at a catastrophic scale.

A bimillennial-length tree-ring reconstruction of precipitation for the Tavaputs Plateau, Northeastern Utah
Quaternary Research, Volume 73, Issue 1, January 2010, Pages 107-117
Troy A. Knight, David M. Meko, Christopher H. Baisan
Abstract
Despite the extensive network of moisture-sensitive tree-ring chronologies in western North America, relatively few are long enough to document climatic variability before and during the Medieval Climate Anomaly (MCA) ca. AD 800-1300. We developed a 2300-yr tree-ring chronology extending to 323 BC utilizing live and remnant Douglas-fir (Pseudotsuga menziesii) from the Tavaputs Plateau in northeastern Utah. A resulting regression model accounts for 70% of the variance of precipitation for the AD 1918–2005 calibration period. Extreme wet and dry periods without modern analogues were identified in the reconstruction. The MCA is marked by several prolonged droughts, especially prominent in the mid AD 1100s and late 1200s, and a lack of wet or dry single-year extremes. The frequency of extended droughts is not markedly different, however, than before or after the MCA. A drought in the early AD 500s surpasses in magnitude any other drought during the last 1800 yr. A set of four long high-resolution records suggests this drought decreased in severity toward the south in the western United States. The spatial pattern is consistent with the western dipole of moisture anomaly driven by El Niño and is also similar to the spatial footprint of the AD 1930s “Dust Bowl” drought.

A multiproxy lake record from Inner Mongolia displays a late Holocene teleconnection between Central Asian and North Atlantic climates
Quaternary International, In Press, Corrected Proof, Available online 18 March 2010
Huei-Fen Chen, Sheng-Rong Song, Teh-Quei Lee, Ludvig Löwemark, Zhenqing Chi, Yong Wang, Eason Hong
Abstract
In order to study how the Holocene Central Asian climate is coupled to the global climate system, a 4.24 m long lake core from western Inner Mongolia in China was studied using a multiproxy approach. Sedimentology and geochemical parameters such as gypsum and dolomite content, presence of lakeshore sand changing to aeolian sand, and changes in paleomagnetic properties bear witness to a trend toward a generally drier climate over the late Holocene. Aridification is linked to the southward retreat of the northern boundary of the Asian summer monsoon, leaving central Asia under the influence of the westerly belt. The weakening of the Asian summer monsoon in turn was caused by an orbitally driven decrease in summer insolation. The weakening summer insolation also likely increased the intensity of the Siberian High pressure system, further promoting aridification of central Asia. On a shorter time scale, the multiproxy record shows the climate to have been relatively dry during the Medieval Warm Period (AD 800–1100) with the ensuing humid environment at the end of this period gradually turning to become extremely dry (AD 1100–1550) at the Little Ice Age Maximum. Switches in the North Atlantic Oscillation caused these changes through a teleconnection in the form of westerlies. These westerlies provided most of central Asia’s moisture after the retreat of the Asian summer monsoon. The central Asian climate therefore corresponds closely with late Holocene European climate changes.

Holocene landscape response to seasonality of storms in the Mojave Desert
Quaternary International, Volume 215, Issues 1-2, 15 March 2010, Pages 45-61
David M. Miller, Kevin M. Schmidt, Shannon A. Mahan, John P. McGeehin, Lewis A. Owen, John A. Barron, Frank Lehmkuhl, Rene Löhrer
Abstract
New optically stimulated and radiocarbon ages for alluvial fan and lake deposits in the Mojave Desert are presented, which greatly improves the temporal resolution of surface processes. The new Mojave Desert climate-landscape record is particularly detailed for the late Holocene. Evidence from ephemeral lake deposits and landforms indicates times of sustained stream flow during a wet interval of the latter part of the Medieval Warm Period at ca. AD 1290 and during the Little Ice Age at ca. AD 1650. The former lakes postdate megadroughts of the Medieval Warm Period, whereas the latter match the Maunder Minimum of the Little Ice Age. Periods of alluvial fan aggradation across the Mojave Desert are 14–9 cal ka and 6–3 cal ka. This timing largely correlates to times of increased sea-surface temperatures in the Gulf of California and enhanced warm-season monsoons. This correlation suggests that sustained alluvial fan aggradation may be driven by intense summer-season storms. These data suggest that the close proximity of the Mojave Desert to the Pacific Ocean and the Gulf of California promotes a partitioning of landscape-process responses to climate forcings that vary with seasonality of the dominant storms. Cool-season Pacific frontal storms cause river flow, ephemeral lakes, and fan incision, whereas periods of intense warm-season storms cause hillslope erosion and alluvial fan aggradation. The proposed landscape-process partitioning has important implications for hazard mitigation given that climate change may increase sea-surface temperatures in the Gulf of California, which indirectly could increase future alluvial fan aggradation.

Records of late-Holocene East Asian winter monsoon in the East China Sea: Key grain-size component of quartz versus bulk sediments
Quaternary International, In Press, Corrected Proof, Available online 6 February 2010
Shuqing Qiao, Zuosheng Yang, Jingpu Liu, Xiaoxia Sun, Rong Xiang, Xuefa Shi, Dejiang Fan, Yoshiki Saito
Abstract
Quartz isolated from bulk sediments taken from a core obtained from the distal mud area in the outer shelf of the East China Sea was used as a proxy in order to determine the strength of the East Asian Winter Monsoon (EAWM). This data was compared with the grain-size of bulk sediment from the same core. It was found that the content of the key quartz-based indicator fraction (15.2–65.6 μm) correlated well with the EAWM strength. With reference to current conditions, high content of quartz in the selected fraction reflected strong EAWM and vice-versa. The core record spanned 2100 years, and three periods of change in EAWM strength were identified. A period of increased EAWM strength prior to 1520 cal. BP was followed by a period of weakened EAWM strength from 1520 to 720 cal. BP, which is consistent with the Sui-Tang Warm Period and the Medieval Warm Period. This is followed by a period of slightly increased EAWM between 720 and 220 cal. BP, which corresponds to what is called the Little Ice Age. The history of EAWM revealed by the quartz-based proxy is in striking agreement with results from a previous study on bulk sediment-based proxy. However, the quartz-based proxy showed much higher sensitivity and resolution to the EAWM strength, and displayed much more distinct and sharper boundaries of transition across the three intervals of EAWM change compared to the bulk sediment records. Eleven short EAWM strengthening periods were found, compared with four by the bulk sediment-based proxy. Therefore, this suggests that the quartz grain-size proxy is a superior indicator of the winter monsoon strength in the study area.

Santa Barbara Basin diatom and silicoflagellate response to global climate anomalies during the past 2200 years
Quaternary International, Volume 215, Issues 1-2, 15 March 2010, Pages 34-44
John A. Barron, David Bukry, David Field
Abstract
Santa Barbara Basin (SBB) diatom and silicoflagellate assemblages are quantified from a box core record spanning AD 1940–2001 and an Ocean Drilling Program Hole 893A record from 220 BC to AD 1880. The combined relative abundance of the diatoms Fragilariopsis doliolus and Nitzschia interrupteseriata from continuous two-year sampling intervals in the box core varies with sea surface temperature (SST), suggesting its utility in SST reconstruction. The assemblage data from the ODP 893A record indicate a broad interval of generally cooler SSTs between AD 800 and 1350, which corresponds to the Medieval Climate Anomaly (MCA), a period of generally warmer temperatures across other regions of the northern hemisphere. The assemblages also indicate an interval of generally warmer SSTs between AD 1400 and 1800, a period of otherwise global cooling referred to as the Little Ice Age (LIA). The changes in assemblages of diatoms and silicoflagellates support the hypothesis that the widespread droughts of the Medieval Climate Anomaly in the Western US were associated with cooler eastern North Pacific SST. The box core assemblages have higher percentages of tropical and subtropical compared to temperate and subpolar species than the ODP samples, reflecting a response of phytoplankton communities to an unusual 20th century warming. Pseudonitzschia australis, a diatom linked with domoic acid production, begins to become more common (>3% of the diatom assemblage) in the box core only after AD 1985, suggesting a link to anthropogenic activity.

Thousand years of climate change reconstructed from chironomid subfossils preserved in varved lake Silvaplana, Engadine, Switzerland
Quaternary Science Reviews, In Press, Corrected Proof, Available online 20 May 2010
Isabelle Larocque-Tobler, Martin Grosjean, Oliver Heiri, Mathias Trachsel, Christian Kamenik
Abstract
Fossil chironomids (non-biting midges) from varved Lake Silvaplana, Switzerland, were used to reconstruct climate (mean July air temperatures) during the last millennium. At the beginning of the record, corresponding to the last part of the “Medieval Climate Anomaly” (MCA) (here the period between ca 1032 and 1262 AD), the chironomid-inferred mean July air temperatures were 1 °C warmer (p < 0.01) than the climate reference period (1961–1990). The “Little Ice Age” seems to have been separated into three phases: significantly colder (−1.1 °C in average, p < 0.001) temperatures were inferred between ca 1262 and 1481 AD, between ca 1514 and 1718 AD (−1.2 °C in average, p < 0.001) and between ca 1734 and 1782 AD (−0.6 °C in average, p < 0.1). Although the average temperature changes inferred by chironomids were within the error of prediction (1.5 °C) of the chironomid-temperature inference model used for reconstruction, the pattern of temperature changes corresponds well with records of the past millennium in Switzerland, in Europe and in the Northern Hemisphere. The average inferred July temperatures between ca 1900 and 2001 AD were significantly warmer (p < 0.05) than the climate reference period (1961–1990) by 1 °C which is in agreement with the instrumental data. The inferred July temperatures were in the same range as the inferred temperatures during the last part of the MCA suggesting that during the 20th century, at Lake Silvaplana, the chironomid-inferred temperatures do not exceed the natural climate variability of the past millennium.

Moisture changes over the last millennium in arid central Asia: a review, synthesis and comparison with monsoon region
Quaternary Science Reviews, Volume 29, Issues 7-8, April 2010, Pages 1055-1068
Fa-Hu Chen, Jian-Hui Chen, Jonathan Holmes, Ian Boomer, Patrick Austin, John B. Gates, Ning-Lian Wang, Stephen J. Brooks, Jia-Wu Zhang
Abstract
There is a strong chance that 20th century warming will cause differences in precipitation distribution, hydrological cycle and effective moisture changes over the globe. Arid central Asia (ACA), a unique dry-land area whose atmospheric circulation is dominated today by the westerlies, is one of the specific regions that are likely to be strongly impacted by global warming. An understanding of past variations in effective moisture in such regions is an important prerequisite for the prediction of future hydrological change. Here we evaluate spatial and temporal patterns of effective moisture variations documented by different proxies from 17 records in ACA, and synthesize a decadal-resolution moisture curve for ACA over the past millennium, using 5 of the 17 records selected on the basis of reliable chronologies and robust proxies. The high- and low-resolution data all show that, over the past millennium, ACA has been characterized by a relatively dry Medieval Warm Period (MWP; the period from 1000 to 1350 AD), a wet Little Ice Age (LIA; from 1500 to 1850 AD) and increasing moisture during recent decades. As a whole, the LIA in the ACA was not only relatively humid but also had high precipitation. Over the past millennium, the multi-centennial moisture changes in ACA show a generally inverse relationship with the temperature changes in the Northern Hemisphere, China, and western central Asia. The effective moisture history in ACA also shows an out-of-phase relationship with that in monsoon Asia (especially during the LIA). We propose that the humid LIA in ACA, possibly extending to Mediterranean Sea and Western Europe, may have resulted from increased precipitation due to more frequent mid-latitude cyclone activities as a result of the strengthening and equator-ward shift of the westerly jet stream, and the predominantly negative North Atlantic Oscillation conditions, coupled with a decrease in evapotranspiration caused by the cooling at that time.

Climatic signals in multiple highly resolved stable isotope records from Greenland
Quaternary Science Reviews, Volume 29, Issues 3-4, February 2010, Pages 522-538
B.M. Vinther, P.D. Jones, K.R. Briffa, H.B. Clausen, K.K. Andersen, D. Dahl-Jensen, S.J. Johnsen
Abstract
Twenty ice cores drilled in medium to high accumulation areas of the Greenland ice sheet have been used to extract seasonally resolved stable isotope records. Relationships between the seasonal stable isotope data and Greenland and Icelandic temperatures as well as atmospheric flow are investigated for the past 150–200 years. The winter season stable isotope data are found to be influenced by the North Atlantic Oscillation (NAO) and very closely related to SW Greenland temperatures. The linear correlation between the first principal component of the winter season stable isotope data and Greenland winter temperatures is 0.71 for seasonally resolved data and 0.83 for decadally filtered data. The summer season stable isotope data display higher correlations with Stykkisholmur summer temperatures and North Atlantic SST conditions than with SW Greenland temperatures. The linear correlation between Stykkisholmur summer temperatures and the first principal component of the summer season stable isotope data is 0.56, increasing to 0.66 for decadally filtered data.
Winter season stable isotope data from ice core records that reach more than 1400 years back in time suggest that the warm period that began in the 1920s raised southern Greenland temperatures to the same level as those that prevailed during the warmest intervals of the Medieval Warm Period some 900–1300 years ago. This observation is supported by a southern Greenland ice core borehole temperature inversion. As Greenland borehole temperature inversions are found to correspond better with winter stable isotope data than with summer or annual average stable isotope data it is suggested that a strong local Greenland temperature signal can be extracted from the winter stable isotope data even on centennial to millennial time scales.

Marine climate variability during the last millennium: The Loch Sunart record, Scotland, UK
Quaternary Science Reviews, In Press, Corrected Proof, Available online 3 April 2010
A.G. Cage, W.E.N. Austin
Abstract
The first decadal-scale reconstruction of British coastal temperature anomalies spanning the last millennium is presented from a sea loch (fjord) basin, Loch Sunart, NW Scotland. Based on modern observation and the results of previous numerical modeling of fjord circulation, benthic foraminiferal oxygen isotope records are interpreted as a record of summer temperature. A significant climate transition, apparently driven by large-scale reorganization of northern Hemisphere atmospheric circulation, occurs in the record around AD 1400. An abrupt, but relatively short-lived climate warming occurs between AD 1540–1610, when the bottom water temperature anomalies are 1.1 °C above the long-term average, which is warmer than most of the 20th century and the late Medieval Warm Period. A long-term cooling occurs throughout the Little Ice Age culminating in the coldest recorded temperature anomalies between the late 1920s and 1940s. The warmest reconstructed temperatures of the past millennium occurred in the last 5 years of the record, which ends in 2006. A replicated post-AD 1900 shift in benthic foraminiferal Delta13C of ca −0.6‰ provides evidence of the Oceanic Delta13C Suess Effect; this feature provides an independent test of the age model and demonstrates the value of benthic foraminifera as palaeo-proxies in the Loch Sunart record.

Modern and late Holocene wind regimes over the Great Plains (central U.S.A.)
Quaternary Science Reviews, Volume 29, Issues 3-4, February 2010, Pages 554-566
Rebecca L. Schmeisser, David B. Loope, Joseph A. Mason
Abstract
The Great Plains of the central United States contain numerous presently stabilized dune fields that were active during the late Holocene. The most recent period of reactivation occurred about 700–1000 years ago during the Medieval Climatic Anomaly, a period of frequent, severe drought recognized throughout the North American West. Dune orientations and internal bedding preserve information about paleowinds from this time period. We compared paleowind information with modern winds and potential sand transport analyzed from meteorological data. While both reconstructed paleowinds and modern winds include a strong northwesterly component over the northern to central portions of the Great Plains, a significant difference exists to the south. During the late Holocene, southwesterly winds had a strong influence on dune forms over the central and southern Great Plains, while modern potential sand transport is dominated by southerly to southeasterly winds that bring moisture to the region from the Gulf of Mexico. Hypothetical dune types forming under modern winds would be different and have different crestal orientations than those preserved from the late Holocene. In order for such a shift in southerly winds to take place it is likely that: 1) the typical position of the Bermuda High in summer was shifted either to the east or to the south resulting in weaker low-level winds from the south and southeast and greater extent of southwesterly winds on the Great Plains, and/or 2) drought, likely enhanced by evapotranspiration and soil moisture feedbacks, brought the normally higher-level southwesterly flow down to the land surface. Given our understanding of megadroughts over the Great Plains as well as recent climate predictions for increased warmth and drought over this area, future reactivation of the dunes seems likely.

Sedimentary archives of the French Atlantic coast (inner Bay of Vilaine, south Brittany): Depositional history and late Holocene climatic and environmental signals
Continental Shelf Research, Volume 30, Issues 10-11, 15 June 2010, Pages 1250-1266
Philippe Sorrel, Bernadette Tessier, François Demory, Agnès Baltzer, Firas Bouaouina, Jean-Noël Proust, David Menier, Camille Traini
Abstract
The late Holocene is of particular interest to our understanding of the evolution of coastal sedimentary systems because this period encompasses warmer and cooler periods, and rising sea level in northern Europe. Based on an approach combining AMS 14C, sedimentological and rock magnetic analyses on sediment cores complemented with seismic data collected in the macrotidal Bay of Vilaine (south Brittany), we document the depositional history of the inner bay coeval to the mid- to late-Holocene transgression in south Brittany. Correlation between sedimentary archives revealed the main sedimentary infilling phases during the last 6000 years. Four units (U1–U4) are recognized in the coastal sediment wedge of the system, corresponding to the stepwise marine invasion of the bay. We show that (1) marine inundation, due to the steep morphology of the bedrock, is diachronous between distal and proximal records. A time lag of 1000 years is inferred over a distance of less than 5 km; (2) in the outer areas, the sedimentation has been condensed since 3000 years; (3) proximal estuarine archives offer the best record of sedimentary processes covering the last 2000 years, including the Medieval Warm Period (MWP).
Correlations in proximal records in the Bay of Vilaine assess the connection between coastal sedimentary dynamics, climatic conditions and anthropogenic activities during the MWP. We match the preservation of clay deposits to increased river-borne suspended matter transported to the estuary probably as a result of accelerated land-use development (higher soil erosion) in the catchment area between ca. 880 and 1050 AD. Because the preservation of estuarine sedimentary successions is favoured when coastal wave sediment reworking is minimal, it is proposed that the prevailing climatic regime in south Brittany during the MWP likely resembled to that of the preferred negative phase of the North Atlantic Oscillation (NAO). Our data are fairly consistent with other late Holocene records from northern Europe including the Atlantic seaboard. However, they outline the difficulty in interpreting climatic and anthropogenic signatures in coastal sedimentary records where high-resolution chronologies required to unravel their respective influences are still missing.

Megadroughts and late Holocene dune activation at the eastern margin of the Great Plains, north-central Kansas, USA
Aeolian Research, Volume 1, Issues 3-4, January 2010, Pages 101-110
P.R. Hanson, A.F. Arbogast, W.C. Johnson, R.M. Joeckel, A.R. Young
Abstract
Optical and radiocarbon dating indicates that alluvium underlying dunes near Abilene was deposited at or before 45 ka, and that the overlying dunes were active at 1.1–0.5 ka. Geochemical data indicate that the Abilene dune sand is immature and was derived from the underlying Pleistocene alluvium, and not from Holocene age Smoky Hill River deposits. These findings suggest that dune activation was a response to increased aridity and local reduction in vegetation cover as opposed to changes in sediment availability from nearby rivers. The time interval of dune activation at Abilene overlaps Medieval Warm Period megadroughts, similar to the larger and more westerly dune fields on the Great Plains, including the Nebraska Sand Hills and the Great Bend Sand Prairie. The activation of smaller dune fields such as the Abilene dunes near the more humid eastern margin of the Great Plains shows the geographic extent and severity of paleodrought events. Unlike the Duncan dunes, another plains-marginal dune field, however, the Abilene dunes show no evidence for multiple drought events during the Holocene. This difference in dune activity, if it is not a result of sampling or preservation bias, indicates variations in the extent and severity of older drought events at the eastern margin of the Great Plains.

20th century acidification and warming as recorded in two alpine lakes in the Tatra Mountains (South Poland, Europe)
Science of The Total Environment, Volume 408, Issue 5, 1 February 2010, Pages 1091-1101
Michał Gąsiorowski, Elwira Sienkiewicz
Abstract
Sediment profiles of two alpine lakes located in the Tatra Mountains, the Toporowy Staw Niżni (TSN) and the Zielony Staw Gąsienicowy (ZSG), were studied for their chronology, lithology, diatom and cladoceran remains. The sediment sequences, 50 cm long from TSN and 30 cm long from ZSG, were deposited during the last 1000 and 300 years, respectively. Vertical changes in lithology, diatom and Cladocera allow the reconstruction of three periods in the lakes' evolution: mild climatic conditions during Medieval Warm Period (MWP, only in TSN), severe conditions between the end of 14th and 19th centuries, identified as the Little Ice Age (LIA), and 20th century warming. The LIA was recorded in the sediments of both lakes in the form of intensified erosion and lower lake ecosystem productivity, as indicated by organic matter lower content, changes in diatom species composition, and decline in Daphnia.
The 20th century was a time of acidification in both lakes. The scale of acidification was assessed based on the decline in diatom-inferred pH (DI-pH). DI-pH dropped by 1.2 pH units during the last century in TSN and by 0.4 pH unit in ZSG. The decline of DI-pH was noted in both lakes, but its intensity was clearly higher in TSN due to the lower acid neutralisation capacity (ANC) of this lake. The lower pH during the final decades of the 20th century was lethal to some water organisms while attracting others, such as Daphnia. The Daphnia population increased after the pH drop, probably due to the high food flexibility of this genus. A similar increase was not observed in ZSG, where planktonivorous fishes were introduced in the 1940s, which effectively limited the crustacean plankton density.

Paleoenvironment changes in the NW Okhotsk Sea for the last 18 kyr determined with micropaleontological, geochemical, and lithological data
Deep Sea Research Part I: Oceanographic Research Papers, Volume 57, Issue 6, June 2010, Pages 797-811
S.A. Gorbarenko, O.Yu. Psheneva, A.V. Artemova, A.G. Matul’, R. Tiedemann, D. Nürnberg
Abstract
Lithological, geochemical, and micropaleontological data indicate that the Late Glacial of the northwestern Okhotsk Sea (OS) is characterised by severe climatic and environmental conditions with mainly perennial sea ice coverage and low productivity accompanied by weak deep-water ventilation and a temperate formation of the upper Sea of Okhotsk Intermediate Water (SOIW). The age model of the studied core sediments was constructed by AMS 14C dating. The most severe environmental conditions occurred during the period 15.8–14.8 kyr, synchronous with cold Heinrich event 1. Insignificant regional environmental amelioration accompanied by an increase of productivity and ice weakening during summer occurred almost simultaneously with the Bølling–Allerøed (BA) warming. The obtained results distinguished both the Bølling and Allerøed warmings as having different environmental conditions. Oxygen content in the surface sediment was low, as seen from the production of the benthic foraminifera (BF) species. During 12.6–11.1 kyr, synchronous with the Younger Dryas (YD) cold event, the regional environment conditions were cold, but not as severe as the glacial ones. Some climatic warming since the Preboreal has stimulated sea ice melting and surface amelioration during the summer season, which in turn led to a productivity rise and changes in the water column and bottom environment. Some increase in the surface water stratification and the intensified oceanic diatom and surface radiolarian production is parallel with the development of a mesopelagic regime of productivity. The surface sediment condition favours BF abundance and domination by BF species tolerant to oxygen deficiencies. During the Boreal period more stable surface conditions were accompanied by continuously high productivity and an intensifying of its mesopelagic regime.Significant regional climate warming since the Atlantic (9 kyr ago) strongly intensified the summer sea ice melting in the OS, and this created considerable surface environment amelioration with the preferential transport of bacteria and phytodetritus into the SOIW. Further considerable warming of the regional climate from 6 kyr ago contributed to slight sea ice changes, surface water warming, and the enhancement of its stratification; all typical for most of the OS. Along with a high nutrient supply from the Amur River, the NW OS experienced a strong diatom production increase with the maximum amount occurring during the last 3.6 kyr. This changed the productivity type and organic matter export into the water column while increasing the feeding of the “productive” Plagoniidae spp. group and decreasing the microbial biomass supply into the upper SOIW. Some sea surface water cooling or saltier conditions at the beginning of the Subatlantic (2.4–1.8 kyr) was followed by its warming or freshening 1.5–1.0 kyr ago, which likely correlated with the Medieval Warm Period. In turn, that probably led to strong surface water stratification, productivity deterioration and considerable changes in the overall NW OS environment. The established sequence of the northwestern OS environmental changes during the Late Glacial–Holocene is related to the Northern Hemispheric climate changes and was likely forced by atmospheric teleconnection in line with the polar circulation index variability.

Biomarkers in a peat deposit in Northern Spain (Huelga de Bayas, Asturias) as proxy for climate variation
Journal of Chromatography A
, Volume 1217, Issue 21, 21 May 2010, Pages 3538-3546
V. López-Días, Á.G. Borrego, C.G. Blanco, M. Arboleya, J.A. López-Sáez, L. López-Merino
Abstract
Peatlands are peculiar ecosystems in which well-adapted communities grow and develop, recording the variation in climate and hydrological conditions inland. In addition necromass is well preserved and therefore peatlands can be used as palaeo-archives for environmental variation. In this work a peat core of depth 60 cm dated at the bottom of the peat deposit as ca. 250 cal AD from Huelga de Bayas (Asturias, Northern Spain) was studied to a resolution of 2–4 cm to investigate the evolution of the environmental conditions in the area. Samples were extracted with a dichloromethane/methanol ratio of 3:1 and studied by means of gas chromatography (GC) and mass spectrometry (GC–MS) in order to identify possible biomarkers of climatic variation during the period of peat formation. Lipid biomarker study allows the identification of periods in which Sphagnum or higher plants preferentially contributed to the peat profile. The absolute dating of the profile combined with the n-alkane record displayed five episodes of wetter conditions around ca. 250 cal AD (Roman Warm Period), 1080 and 1270 cal AD (Medieval Warm Period), 1460 cal AD (Little Ice Age) and 1920 cal AD (Recent warming), which are consistent with climate evolution in the region. Pentacyclic triterpenoids with hopane skeleton derived from microorganisms and with oleanane skeleton derived from higher plants were identified. The presence of their ketone and acetyl-derivatives, along with the presence of unstable hopane configurations indicates a low maturity of the peat profile. A tendency for the functionalised triterpenoids to decrease with depth was observed in the profile.

A 8000 year fire history from an Arizona/Sonora borderland ciénega
Journal of Arid Environments, Volume 74, Issue 4, April 2010, Pages 475-481
A. Brunelle, T.A. Minckley, S. Blissett, S.K. Cobabe, B.L. Guzman
Abstract
Sediment cores from the San Bernardino Ciénega near Douglas, Arizona and Agua Prieta, Sonora, Mexico were examined to reconstruct the fire history of this region and inform restoration efforts. A 8000 year vegetation and fire history record was reconstructed from these sediments using fossil pollen and charcoal. Results from the fire reconstruction show an increase in fire activity coincident with the onset of ENSO, and an increase in fire frequency during the Medieval Climate Anomaly. Preliminary pollen data show taxa that reflect winter-dominated precipitation (Ephedra and Artemisia) correspond to times of greater fire activity. These fire data shed light on the long-term history of fire in desert environments that may be helpful in understanding what fire regimes may be expected with global warming and also how to best incorporate fire into management plans.