HR: 11:20h
AN: PP12A-05    [Abstracts]
TI: Holocene Southern-Ocean Surface Radiocarbon Ages: Implications for Ocean Circulation and Ice-shelf Flow Rates
AU: * Henderson, G M
EM: gideonh@earth.ox.ac.uk
AF: University of Oxford, Department of Earth Sciences, Oxford, OX1 3PR, United Kingdom
AU: Hall, B L
EM: BrendaH@maine.edu
AF: University of Maine, Department of Earth Sciences and the Climate Change Institute, Orono, ME 04469, United States
AU: Baroni, C
AF: Universita  di Pisa, Dipartimento di Scienze della Terra, Pisa, 000, Italy
AU: Kellogg, T B
AF: University of Maine, Department of Earth Sciences and the Climate Change Institute, Orono, ME 04469, United States
AB: The Southern Ocean features high surface-water ¹⁴C reservoir ages, reflecting substantial upwelling of old deep water and poor air-sea exchange. These high values complicate ¹⁴C dating in the circum-Antarctic region, and encode information about past ocean circulation (particularly the rate of deep-water ventilation in the Atlantic). Here we present new results from the Ross Sea that provide a history of Holocene Southern Ocean ¹⁴C. Freezing at the base of the McMurdo ice shelf traps sediment (including solitary corals) which is then transported to the ice surface by ice ablation. Forty-five solitary corals from the McMurdo Ice Shelf and from Hells Gate have been dated precisely using U/Th and ¹⁴C techniques to provide a detailed reconstruction of surface-water reservoir ages for the past 6,000 years. With the exception of two young samples that show the impact of bomb radiocarbon, other samples indicate a constant ¹⁴C reservoir age during this period of 1300±200 years. The constancy of this value is reassuring for studies conducting chronology in the Southern Ocean, or relying on knowledge of deep-water source regions for ¹⁴C ventilation ages. It also allows constraints to be placed on changes in the flow of NADW with time, since slower flow leads to older upwelling water in the Southern Ocean. The systematic increase in age of samples with distance from Black Island also allows reconstruction of the flow rate of the McMurdo Ice Shelf. This indicates a constant flow of about 4 m/yr for the last 5000 years, with flow about three times faster before this period. These flow rates compare with short term estimates of flow in the region of about 16 m/yr suggesting that flow may have increased in recent times.
DE: 0728 Ice shelves
DE: 1105 Quaternary geochronology
DE: 4924 Geochemical tracers
DE: 4962 Thermohaline
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting