HR: 16:00h
AN: PP54B-01    [Abstracts]
TI: North Atlantic Deep Water Variability During MIS 11-15: Evidence from the Portuguese Margin
AU: * Voelker, A H
EM: antje.voelker@ineti.pt; avoelker@softhome.net
AF: INETI; Departamento Geologia Marinha, Estrada da Portela; Zambujal, Alfragide, 2721-866 Portugal
AU: de Abreu, L
EM: luciaabreu@yahoo.com
AF: INETI; Departamento Geologia Marinha, Estrada da Portela; Zambujal, Alfragide, 2721-866 Portugal
AU: de Abreu, L
EM: luciaabreu@yahoo.com
AF: University of Cambridge - Godwin Laboratory, Pembroke Street - New Museums Site, Cambridge, CB2 3SA United Kingdom
AU: Lebreiro, S M
EM: susana.lebreiro@ineti.pt
AF: INETI; Departamento Geologia Marinha, Estrada da Portela; Zambujal, Alfragide, 2721-866 Portugal
AU: Abrantes, F G
EM: fatima.abrantes@ineti.pt
AF: INETI; Departamento Geologia Marinha, Estrada da Portela; Zambujal, Alfragide, 2721-866 Portugal
AB: Studies off the southwestern Portuguese margin revealed that the boundaries between the North Atlantic Deep Water (NADW) and the Antarctic Bottom Water as well as the the one of the NADW and the Mediterranean Outflow (MOW) shoaled on glacial - interglacial and millennial timescales. Centennial-scale changes in the deeper water chemistry and flow strength in the eastern North Atlantic are reconstructed from benthic isotope and grain size data for two sites from the western Portuguese margin. Calypso core MD03-2699, whose record extends approximately back to MIS 16, was retrieved from the base of the Estremadura promontory north of Lisbon from a water depth of 1895 m. For the overlapping interval from MIS 10 to 11, its data is compared to those of core MD01-2443 from the southwestern margin and a water depth of 2941 m. Between 420 and 405 kyr, the shallower site MD03-2699 shows heavier values that slowly decrease towards the northern hemisphere insolation maximum at 405 kyr, accompanied by a rise in water mass ventilation. Under peak interglacial conditions of MIS 11 (405 to 385 kyr), both sites have similar isotope values indicating that the same type of NADW filled the water column from 1800 to 3000 m. While the oxygen record of the deeper site follows the global stack after 385 kyr, values at the shallower site remain lighter and oscillate between 3.5 and 4.5 permil between 385 and 350 kyr. These rapid, short-termed oscillations are associated with carbon isotope changes that sometimes exceed 1 permil. Around 383 kyr and 355 kyr sandy layers indicate an increased current speed at 1895 m water depth, which could point to the presence of MOW at this site and consequently a deepening of the MOW/ NADW interface. The poor ventilation, on the other hand, could indicate a GNAIW-type water mass, so that this water depth might experience rapid changes in the prevailing water mass during the interglacial - glacial transition. Upcoming isotope and grain size data will reveal, if similar oscillations also occurred during the earlier interglacial-glacial transitions and under full glacial conditions, because all of them are associated with periods, during which strong currents formed foraminiferal sands at site MD03-2699.
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4962 Thermohaline
DE: 9604 Cenozoic
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005