HR: 08:30h
AN: PP41F-03    [Abstracts]
TI: An 800 kyr Record of Weddell Sea Paleochemistry from Trace Metal Foraminiferal Proxies
AU: * Rickaby, R E
EM: rosr@earth.ox.ac.uk
AF: Oxford University, Department of Earth Sciences, Parks Road, Oxford, OX1 3PR, United Kingdom
AU: Elderfield, H
EM: he101@esc.cam.ac.uk
AF: Cambridge Univeristy, Department of Earth Sciences, Downing Street, Cambridge, CB2 3EQ, United Kingdom
AU: Roberts, N L
EM: natalie.l.roberts@googlemail.com
AF: Cambridge Univeristy, Department of Earth Sciences, Downing Street, Cambridge, CB2 3EQ, United Kingdom
AU: Hendry, K
EM: Katharine.Hendry@earth.ox.ac.uk
AF: Oxford University, Department of Earth Sciences, Parks Road, Oxford, OX1 3PR, United Kingdom
AU: Hillenbrand, C
EM: hilc@bas.ac.uk
AF: British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, United Kingdom
AU: Mackensen, A
EM: andreas.Mackensen@awi.de
AF: Alfred Wegener Institute, Columbusstrasse, Bremerhaven, D-27568, Germany
AB: The Southern Ocean has long been recognised as the major player in driving the climate oscillations of the Pleistocene glacial-interglacial cycles. The surface waters of the modern Southern Ocean act as a source of CO₂ to the atmosphere because of rapid mixing with nutrient, CO₂-rich deepwaters, and incomplete biological utilisation of major nutrients in the surface waters. Hypotheses to account for glacially reduced atmospheric carbon dioxide have focussed on increased stratification of the water column or enhanced nutrient utilisation in the surface waters of the Southern Ocean. A recent modelling study suggests that the critical parameter which determines the oceanic sink of atmospheric CO₂ is the preformed nutrient content of the major deepwater mass (AABW), sourced from surface waters south of the Polar front. The lower the preformed nutrients in AABW, the more efficient the biological pump and the oceanic carbon sequestration. Yet the lack of carbonate preservation in this area has largely prevented probing of the paleochemistry of the Southern Ocean with traditional foraminiferal proxies. Here we present an 800 kyr record of trace metal contents from both benthic and planktonic foraminifera from PS1506 (67.8^oS 5.8^oW, 2426m, Weddell Sea) to investigate the evolution of the water column chemistry and structure during Pleistocene glacial-interglacial cycles. Our preliminary results indicate that at these extreme low temperatures, the downcore variability in all trace metals in foraminifera is largely controlled by variations in the carbonate ion content of the ambient water. For instance, benthic B/Ca and Mg/Ca correlate closely and show a strong 100 kyr cyclicity but with higher values during the glacial periods. The glacial-interglacial amplitude of variation in carbonate ion derived from benthic B/Ca, for the last four glacial cycles is consistent with the 90 ppmv CO₂ oscillations, but intriguingly, does not parallel the diminished amplitude of the CO₂ oscillations of the previous two glacial cycles as documented in the EPICA ice core.
DE: 4924 Geochemical tracers
DE: 4926 Glacial
DE: 4930 Greenhouse gases
DE: 4954 Sea surface temperature
DE: 4964 Upwelling (4279)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting