HR: 0800h
AN: PP51F-1374    [Abstracts]
TI: Late Pleistocene-Holocene Paleoenvironmental Setting in the SE Pacific Inferred From Paleoproductivity Variations
AU: * Mohtadi, M
EM: mohtadi@uni-bremen.de
AU: Hebbeln, D
EM: dhebbeln@uni-bremen.de
AB: A multiparameter investigation of several sediment cores collected along the Chilean continental margin between $24\deg$S and $44\deg$S served to reconstruct the spatial and temporal variability in the (paleo)environmental setting through the last 40,000 years. The faunal and isotopic composition of planktic foraminifera suggest that marine productivity was relatively high between 40,000 and 32,000 cal yr BP, highest between 32,000 and 16,000 cal yr BP, lowest between 16,000 and $\sim$4000 cal yr BP, and relatively low from 4000 cal yr BP towards the present. The comparatively consistent pattern of planktic foraminifera along $20\deg$ of latitude points to changes in the oceanic circulation affecting the entire study area. Thus, periods of higher paleoproductivity appear during stronger advection and/or a northerly position of the Peru-Chile Current as the dominant oceanographic current off Chile, and vice versa. The relative variations in the paleoproductivity calculated from accumulation rates of organic carbon, opal, and calcium carbonate generally support these findings, although with some local differences mainly during the last deglaciation. We suppose that only a shift in the position of the zonal systems (the Antarctic Circumpolar Current, ACC, and the Southern Westerly Belt, SW) is capable of provoking such nearly synchronous large-scale changes in the marine productivity. The ACC is the main macronutrient source off Chile, and its position is strongly tied to the location of the SW, which contributes the supply of micronutrients to the coast by precipitation onshore and the successive continental runoff. Displacement of these circulation systems in the short run occurs during ENSO events, as observed presently and for the Late Holocene, when changes in the strength of the Hadley Cell and the South Pacific High parallel the movement of the ACC and SW. During the Last deglaciation, our data suggest that the reorganisation of the thermo-haline circulation led to the southward return of the ACC and the SW with the ensuing lowest marine productivity during the Early and Middle Holocene.
DE: 4870 Stable isotopes
DE: 4267 Paleoceanography
DE: 4516 Eastern boundary currents
DE: 3030 Micropaleontology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting