Meltwater Forcing of Surface and Deep Ocean Change During the Cold Climate Event 8,200 Years ago

HR: 12:05h
AN: PP12A-08 [Abstracts]
TI: Meltwater Forcing of Surface and Deep Ocean Change During the Cold Climate Event 8,200 Years ago
AU: * Chapman, M R
EM: m.chapman@uea.ac.uk
AF: School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ United Kingdom
AU: Ellison, C R
EM: c.ellison@uea.ac.uk
AF: School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ United Kingdom
AU: Hall, I R
EM: hall@cardiff.ac.uk
AF: School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3YE United Kingdom
AB: Evaluating the role of ocean circulation during the largest climate perturbation in our present interglacial, `the 8.2 kyr event', is crucial for assessing the sensitivity of the Meridional Overturning Circulation to freshwater perturbations. We present data from core MD99-2251 retrieved from the southern limb of the Gardar Drift in the subpolar North Atlantic (57°26'N, 27°54'W). Calibrated ^1⁴C dates indicate a mean sediment accumulation rate of ~120 cm/kyr^-¹ through the interval 9.5-7.5 kyr BP. We have generated multi-proxy reconstructions of planktonic δ^1⁸O, sea surface temperature and salinity and deep flow speed that reveal changes in North Atlantic palaeoceanography in unprecedented detail and provide unambiguous information concerning the sequence of events and the phasing of early Holocene surface and deep ocean changes. The polar foraminifer Neogloboquadrina pachyderma (sinistral) is largely absent through the Holocene with the exception of a single interval, when temperatures were 2°C colder than at present. We identify two cold events, one at 8.49 kyr BP and a more prominent cooling at 8.29 kyr BP. The initial cooling, shown in the N. pachyderma sin. and SST data, was coincident with a ~0.6 ‰ depletion in planktonic δ^1⁸O values. This shift implies a surface ocean freshening, which we estimate to represent a 1-1.3 salinity reduction. The 8.49 kyr event coincides with the first signs of a reduction in the flow-speed of Iceland Scotland Overflow Water (ISOW), as deduced from sortable silt data. At 8.29 kyr BP, a second smaller freshwater event coincides with a major sea surface cooling and drawdown in ISOW flow speeds within a few decades. This cooling episode is similar in structure and duration to the 8.2 kyr event observed in the Greenland ice cores. Surface salinity reductions strongly suggest that these changes are forced by pulsed meltwater outbursts from the proglacial lakes Agassiz and Ojibway. A two step drawdown model, where the meltwaters discharge in separate pulses, appears to be consistent with the sequence of events found in our palaeoceanographic records.
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4936 Interglacial
DE: 4944 Micropaleontology (0459, 3030)
DE: 4962 Thermohaline
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005