Stability of North Atlantic water masses in face of pronounced climate variability during the Pleistocene

Geochemical profiles from the North Atlantic Ocean suggest that the vertical δ 13 C structure of the water column at intermediate depths did not change significantly between glacial and interglacial time over much of the Pleistocene, despite large changes in ice volume and iceberg delivery from nearby landmasses. The most anomalous δ 13 C profiles are from the extreme interglaciations of the late Pleistocene. This compilation of data suggests that, unlike today (an extreme interglaciation), the two primary sources of northern deep water, Norwegian‐Greenland Sea and Labrador Sea/subpolar North Atlantic, had different characteristic δ 13 C values over most of the Pleistocene. We speculate that the current open sea ice conditions in the Norwegian‐Greenland Sea are a relatively rare occurrence and that the high‐δ 13 C deep water that forms in this region today is geologically unusual. If northern source deep waters can have highly variable δ 13 C, then this likelihood must be considered when inferring past circulation changes from benthic δ 13 C records.