Last glacial benthic foraminiferal d18O anomalies in the polar North Atlantic: A modern analogue evaluation

Modern processes are evaluated to understand the possible mechanisms behind last glacial benthic foraminiferal δ18O anomalies that occurred concurrent with meltwater events in the polar North Atlantic; such anomalies in the Nordic seas were recently interpreted to be caused by brine formation. Despite intensive sea-ice production on circumarctic shelves, modern data show that brines ejected from sea-ice formation containing low δ18O water do not significantly contribute to deep waters in the Arctic Ocean today. Assuming that this process was, nevertheless, responsible for δ18O anomalies in Nordic seas deep water during the last glaciation, a broad, shallow shelf area adjacent to the Nordic seas, such as the Barents Sea, had to be seasonally free of sea-ice in order to serve as an area for brine formation. Another process which may explain δ18O-depleted water at depth is found in the Weddell Sea today, where a low δ18O signal in deep waters originates from ice shelf interactions. If temperature were considered the main mechanism for the low benthic δ18O values, an increase of 4°C must have occurred in the deep water. An analogous situation with a reversed water temperature pattern due to a subsurface inflow of warm Atlantic water is found today in the eastern Arctic Ocean, and deep water warming is observed in the Greenland Gyre in the absence of deep convection. Because paleoproxy data also indicate an Atlantic water inflow into the Nordic seas during such benthic δ18O anomalies, temperature as a principal mechanism of changing δ18O cannot be excluded