Ocean circulation at the Last Glacial Maximum: A combined modeling and magnetic proxy‐based study

Abstract

Formation of North Atlantic Deep Water (NADW) is an important component of the ocean thermohaline circulation, but debate exists over the ocean circulation state during glacial stages. Some geological and modeling studies suggest decreased NADW and increased formation of Southern Ocean deep water during the Last Glacial Maximum (LGM); others indicate similar, or higher, rates of NADW advection. Here we test three different potential LGM ocean states by comparing the modeled iceberg trajectories each produces with magnetically mapped patterns and sources of LGM ice‐rafted debris (IRD). The three LGM states are characterized by vigorous NADW formation; deepwater production in the Southern Ocean; and a third, “intermediate” state, with Southern Ocean deepwater formation but also some North Atlantic intermediate water formation. Cluster analysis of sediment magnetic properties was used to characterize North Atlantic IRD patterns and sources, which match most closely iceberg trajectories arising from some combination of the “southern sinking” and “intermediate” ocean circulation states. The magnetic data indicate two major IRD sources, Fennoscandia and Greenland/Iceland, and one minor source, the St. Lawrence region. The model and magnetic data suggest that the LGM North Atlantic circulation was dominated by a cyclonic central North Atlantic gyre, separated from the North Atlantic Current, which was displaced south of ∼42°N.