Inferring Surface Water Equilibrium Calcite δ18O during the Last Deglacial Period from Benthic Foraminiferal δ18O Records: Implications for Ocean Circulation

Monday, 15 December 2014
Daniel E Amrhein1,2, Geoffrey Gebbie2, Olivier Marchal2 and Carl I Wunsch3, (1)Massachusetts Institute of Technology, Cambridge, MA, United States, (2)Woods Hole Oceanographic Inst., Woods Hole, MA, United States, (3)Harvard University, Cambridge, MA, United States
The ocean mass transport communicates tracers from the ocean mixed layer (ML) to the deep ocean on many time scales. When they are sufficiently well-resolved in time, paleoceanographic tracer proxy time series at multiple locations sample the propagation of tracer signals through the global ocean and can be used to constrain the ocean circulation, including during times of climate transience. Using a Green function approach, we derive a time-dependent solution for ML equilibrium calcite δ18O (δ18Oc) during the last deglaciation from a least-squares fit of eight benthic foraminiferal δ18O records to an estimate of the modern ocean circulation. Within uncertainty, inferred deglacial histories of ML δ18Oc in the Northern North Atlantic and in the Southern Ocean mixed layers are indistinguishable. A comparison of the derived solution to planktonic foraminiferal δ18O records is unable to disprove the null hypothesis that the modern ocean circulation persisted during the last deglaciation. In order to disprove the null hypothesis, it is necessary to reduce uncertainties in inferred ML δ18Oc histories, perhaps by including additional records. The utility of benthic records to reduce uncertainties is quantified, with implications for future paleoceanographic sampling strategies.