HR: 16:45h
AN: PP44B-04 INVITED    [Abstracts]
TI: Millennial-scale climate variability in the North Atlantic beyond the last glacial cycle inferred from IODP Site U1308 (re-occupation of DSDP Site 609)
AU: * Hodell, D
EM: hodell@ufl.edu
AF: Department of Geological Sciences, University of Florida, PO Box 112120, Gainesville, FL 32611, United States
AU: Channell, J
EM: jetc@ufl.edu
AF: Department of Geological Sciences, University of Florida, PO Box 112120, Gainesville, FL 32611, United States
AU: Curtis, J
EM: curtisj@ufl.edu
AF: Department of Geological Sciences, University of Florida, PO Box 112120, Gainesville, FL 32611, United States
AU: Romero, O
EM: oromero@ugr.es
AF: Center for Marine Environmental Sciences (MARUM), Bremen University, MARUM/0220 Leobener Strasse, Bremen, 28359, Germany
AU: Romero, O
EM: oromero@ugr.es
AF: Instituto Andaluz de Ciencias de la Tierra (IACT-CSIC) Facultad de Ciencias, Universidad de Granada, Campus Fuentenueva, Granada, 18002, Spain
AU: Roehl, U
EM: uroehl@rcom-bremen.de
AF: Center for Marine Environmental Sciences (MARUM), Bremen University, MARUM/0220 Leobener Strasse, Bremen, 28359, Germany
AB: DSDP Site 609 has featured prominently in studies of millennial-scale climate variability of the last glacial cycle, including the recognition of Heinrich events and their correlation to Greenland Ice cores. During IODP Exp 303, Site 609 was re-occupied and a complete composite section was obtained to 247 mcd at Site U1308 (corresponding to ~3.1 Ma). Core logging and scanning XRF data at Site U1308 were compared with existing high-resolution petrologic counts of ice-rafted detritus (IRD) at DSDP Site 609 (measured by Gerard Bond for the last glacial period) to develop rapid, non-destructive proxies for tracking various components of IRD. We found that magnetic susceptibility is a good proxy for total lithic grains per gram in the >150 um sediment fraction (i.e., IRD) and Ca/Sr is a sensitive indicator of detrital carbonate. A time scale was constructed for the last ~1.4 Ma at Site U1308 by correlating the benthic oxygen isotope signal in the upper 100 mcd to the stacked record of Lisiecki and Raymo (2005). IRD events rich in detrital carbonate (i.e., Heinrich-like events) first appeared in the sedimentary record of Site U1308 at ~650 ka during Marine Isotope Stage (MIS) 16. Wavelet analysis of the isotopic and elemental data reveals an abrupt increase in the amplitude of the 100-ka cycle at this time, suggesting that detrital-carbonate-rich IRD events were limited to glacial periods of the "100-k world" when continental ice volume was large. At site U1308, detrital-carbonate-rich IRD events tend to occur towards the latter part of glacial stages and almost always occur at glacial terminations. MIS 6 and 14 are exceptional in that they are the only two glacial stages where detrital carbonate events are absent at Site U1308. IRD events also occurred in glacial periods prior to 650 kyrs but the lithic fraction did not contain large amounts of detrital carbonate as during Heinrich events. We observe that most of the major peaks in IRD (magnetic susceptibility) at Site U1308 coincide with a minimum values of benthic d13C, supporting a link between iceberg discharge and weakening of meridional circulation. The long Pleistocene record from Site U1308 generally supports the hypothesis that as Northern Hemisphere ice sheets grew larger in the late Pleistocene (especially after 650 kyrs), they became more prone to instability. The meltwater produced from the production of abundant ice bergs decreased sea surface salinity, enhanced stratification and stability of surface waters, and diminsihed rates of meridional overturning circulation. As a result, the climate system of the North Atlantic became more prone to abrupt change and variability in the suborbital band increased.
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4940 Isotopic stage
DE: 4962 Thermohaline
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting