HR: 0800h
AN: PP41B-0652    [Abstracts]
TI: Comparative Reconstruction of North Atlantic Deep Water Variability During MIS 12-10
AU: * Hall, I R
EM: Hall@cardiff.ac.uk
AF: Cardiff University, School of Earth, Ocean and Planetary Sciences, Main Building, Park Place, Cardiff, CF10 3YE United Kingdom
AU: Bianchi, G G
EM: Giancarlo@ocean.cf.ac.uk
AF: Cardiff University, School of Earth, Ocean and Planetary Sciences, Main Building, Park Place, Cardiff, CF10 3YE United Kingdom
AU: Parry, T
EM: ParryT@cardiff.ac.uk
AF: Cardiff University, School of Earth, Ocean and Planetary Sciences, Main Building, Park Place, Cardiff, CF10 3YE United Kingdom
AB: Sediment from ODP Leg 172, Site 1061 (4 km water depth) on the Blake Outer Ridge (BOR) in the western North Atlantic has been used in conjunction with previously published benthic δ ¹⁸O and δ ¹³C data from ODP Leg 172, Site 1063 (after Poli et al., 2000) on the Bermuda Rise to investigate palaeoceanographic changes during Marine Isotope Stages (MIS) 12-10 (450-340 ka B.P.). These data have been compared to the MIS 2-1 transition (20 ka B.P. to recent). Mean sortable silt grain-size (SS) proxy measurements suggest the flow axis of the Deep Western Boundary Current (DWBC) lies deeper than Site 1061 during the peak interglacials of both MIS 11 and 1 whereas it occupies a shallower position during the glacial maxima of MIS 12 and 2. The position of the flow axis was close to or at Site 1061 during the initial period of net ice accumulation at the end of MIS 11 (410-360 ka B.P.), indicating an intermediate rate of North Atlantic Deep Water production. This longer-term trend is also characterised by higher frequency shifts in the DWBC flow axis between the interglacial (deep) and glacial (shallow) modes which occur in synchrony with changes in NADW production as inferred from the benthic δ ¹³C record of Poli et al. (2000). Rapid shoaling of the flow axis is associated with both the Younger Dryas and a similar deglacial step observed during Termination V. In both instances this is followed by a rapid return of the flow axis to its position preceding the event. The data appear to agree with the glacial threshold hypothesis of McManus et al. (1999) as the changes in SS are highest in amplitude when δ ¹⁸O values exceed 3.5 parts per mille, but appear to be somewhat dampened when the value exceeds 4.3 parts per mille. Least flow speed variation is observed for the peak interglacial of MIS 11. We find that regional SST variations appear to mimic, both structurally and temporally, deep ocean fluctuations or shifts in the DWBC flow vigour and depth. This suggests a direct linkage between surface processes in (or passing through) the sub-tropical NW Atlantic and deep circulation changes originating from, most probably, the northern overflow components of the Meridional Overturning Circulation. These results underscore the need to understand the forcing of ocean circulation changes in the absence of large ice sheets.
DE: 1600 GLOBAL CHANGE
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1635 Oceans (1616, 3305, 4215, 4513)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005