6. Januar 2011

1200 Jahre alte, marine Sedimentdaten aus Brasilien

In der neuen Studie Marine sediments from southeastern Brazilian continental shelf: A 1200 year record of upwelling productivity liefern uns Dezidério Souto et al. Sedimentdaten aus dem "Cabo Frio coastal shelf" (-23.19 S, -41.8 W; 117 m depth). 

Was wurde gemacht?
In this study, we examined foraminifera and organic markers in sediment cores to determine changes in ocean productivity over the last 1200 years. A box-core sediment sample collected from the continental shelf was analyzed (Fig. 1) for multiple proxy data, including: grain size, total organic carbon (TOC), carbon to nitrogen atomic ratio (C/N), organic palynomorphs and planktonic foraminifera. Data were then compared to paleoclimate and paleoceanographic records that have documented global climate extremes during the MCA and LIA, which were collected from the Peru upwelling region (Gutiérrez et al., 2009)[1], the Cariaco basin (Haug et al., 2001)[2], the Andes glaciers area (Rabatel et al., 2008)[3] and sea surface temperatures (SST) in the Sargasso Sea (van de Plassche et al., 1998)[4] (Fig. 1).

Die Ergebnisse zusammenfassend aus dem Abstract:
Foraminiferal and organic geochemical analyses indicate the occurrence of three distinct periods of productivitiy. From 850 AD until 1070 AD, foraminifera fluxes consisting primarily of Turborotalita quinqueloba indicate stronger South Atlantic Central Water (SACW) transport onto the shelf, which induced high biological productivity that was also recorded by high TOC and marine palynomorphs content and low C/N atomic ratio. This period coincided with a northward displacement of the atmospheric Intertropical Convergence Zone (ITCZ) and South Atlantic High (SAH) systems driven by positive temperature anomalies in the North Atlantic Ocean during the Medieval Climate Anomaly (MCA).

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[1] D. Gutiérrez, A. Sifeddine, D.B. Field, L. Ortlieb, G. Vargas, F.P. Chávez, F. Velazco, V. Ferreira, P. Tapia, R. Salvatteci, H. Boucher, M.C. Morales, J. Valdés, J.L. Reyss, A. Campusano, M. Boussafir, M. Mandeng-Yogo, M. García and T. Baumgartner, Rapid reorganization in ocean biogeochemistry off Peru towards the end of the Little Ice Age, Biogeosciences 6 (2009), pp. 835–848.
[2] G.H. Haug, K.A. Hughen, D.M. Sigman, L.C. Peterson and U. Röhl, Southward migration of the Intertropical Convergence Zone through the Holocene, Science 293 (2001), pp. 1304–1308.
[3] A. Rabatel, B. Francou, V. Jomelli, P. Naveau and D. Grancher, A chronology of the Little Ice Age in the tropical Andes of Bolivia (16°S) and its implications for climate reconstruction, Quaternary Research 70 (2008), pp. 198–212.
[4] O. van de Plassche, K. van der Borg and A.F.M. de Jong, Sea level–climate correlation during the past 1400 yr, Geology 26 (1998), pp. 319–322.