HR: 0800h
AN: PP31B-0418    [Abstracts]
TI: The Search for Eight Glacial Cycles of Deep-Water Temperatures and Global ice Volume From the Southern Hemisphere
AU: * Ferretti, P
EM: patrizia00@esc.cam.ac.uk
AF: The Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
AU: Elderfield, H
EM: harrye@esc.cam.ac.uk
AF: The Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
AU: Greaves, M
AF: The Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
AU: McCave, N
AF: The Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
AB: It has been recently suggested "a substantial portion of the marine 100-ky cycle that has been object of so much attention over the past quarter of a century is, in reality, a deep-water temperature signal and not an ice volume signal" (Shackleton, 2000). There are currently few records available of deep-water temperature variations during the Pleistocene and most of our understanding is inferred from the oxygen isotopic composition (δ¹⁸O) of benthic foraminifera from deep-sea sediments. However, variations in benthic δ¹⁸O reflect some combination of local to regional changes in water mass properties (largely deep- water temperature) as well as global changes in seawater δ¹⁸O (δ¹⁸O_sw) resulting from the growth and decay of continental ice. Recent studies suggest that benthic foraminiferal Mg/Ca may be useful in reconstructing deep-water temperature changes, but the application of this method to benthic species has been hampered by a number of unresolved issues, such as uncertainties related to the calibration for benthic Mg at the coldest temperatures. Here we present deep-sea Mg/Ca and δ¹⁸O records for the past eight glacial cycles in benthic foraminiferal ( Uvigerina spp.) calcite from a marine sediment core recovered in the mid Southern latitudes. Ocean Drilling Program Site 1123 was retrieved from Chatham Rise, east of New Zealand in the Southwest Pacific Ocean (3290 m water depth). This site lies under the Deep Western Boundary Current (DWBC) that flows into the Pacific Ocean, and is responsible for most of the deep water in that ocean; DWBC strength is directly related to processes occurring around Antarctica. Temperatures derived via pore fluid modeling of the last glacial maximum are available from Site 1123 and represent an important tool to constrain deep-water temperatures estimates using Mg/Ca. In selected time slices, we measured B/Ca ratios in Uvigerina in order to gain information on the deep-water carbonate saturation state and have data of Mg/Ca and B/Ca on planktonic species, which also provides evidence on carbonate saturation state. These results permit preliminary discussion of the magnitude of the deep-water temperature changes during glacial/interglacial transitions and the interglacials themselves. In particular, our deep-water temperature estimates confirm that interglacial stages before 430 ka were characterized by less pronounced warmth - at least in the deeper southern Pacific - than those of the past four climatic cycles, a pattern previously observed in the deuterium record from EPICA Dome C. We examine the relative contributions of deep-water temperature and ice volume to the benthic δ¹⁸O signal. The phase relationship between the two signals is tentatively assessed for the middle/late Pleistocene, when different patterns of climate variability have been inferred from marine and ice cores records.
DE: 4924 Geochemical tracers
DE: 4932 Ice cores (0724)
DE: 4936 Interglacial
DE: 4940 Isotopic stage
DE: 4944 Micropaleontology (0459, 3030)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting