Foraminiferal evidence of a modern warming of the North Atlantic Ocean

Abstract

A comprehensive numerical comparison of living and fossil assemblages of planktonic Foraminifera on an ocean-wide scale suggests that the present ocean is 1·5-2·0°C warmer than a mixed late Recent average. More than 300 core top samples distributed beneath the major North Atlantic water masses as far north as 60°N were compared with the mean annual species compositions at five open-ocean plankton stations in the Western North Atlantic located in an arc from Bermuda to the Labrador Sea. A total of 437 plankton samples collected during 1959–1963 were combined to compute these mean annual assemblages. The core-top assemblages that most closely resemble each of the composite modern plankton averages are consistently displaced to the south and east towards regions of warmer surface waters. The simplest explanation of this geographic shift is that of a recent warming of the ocean. Since most of the surface sediment samples contain mixed species assemblages spanning the last 1000–4000 years, the modern ocean appears to be 1·5-2·0°C warmer than this broad post-hypsithermal average. This is a large deviation for an interval that is generally considered part of the stable climatic regime of a postglacial phase.