Deep Western Boundary Current variability in the subtropical northwest Atlantic Ocean during marine isotope stages 12-10

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Hall, Ian Robert ; Becker, Julia (2007)

High-resolution (125–500 year temporal resolution) sortable silt mean grain size data of subtropical northwest Atlantic Ocean Drilling Program (ODP) Leg 172, Site 1061, monitor fluctuations of the Deep Western Boundary Current (DWBC) throughout marine oxygen isotope stages (MIS) 12–10 (330–460 kyr) in great detail. Comparison with foraminiferal stable isotope data from the same site and ODP Site 1063 (Bermuda Rise, data of Poli et al. (2000)) shows that the DWBC shoals during glacial times in relation to a reduced North Atlantic Deep Water production and increased advection of southern ocean waters. Superimposed fluctuations in the flow speed/position of the DWBC at a semiprecession scale are persistent throughout MIS 10–12 and independent of the glacial state. Additional millennial-scale variations in DWBC flow speed parallel surface water cooling events and ice-rafted debris episodes especially at the transition of MIS 11/10, indicating the sensitivity of deep current flow variations to changes in the surface water conditions. These millennial-scale variations are amplified when benthic foraminiferal δ 18O values exceed ∼3.8‰ and may be related to the transition of an ice volume threshold where climate variability is possibly amplified by feedback mechanisms associated with ice sheet growth.
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