Analysis of surface-sediment samples from 5 transects across the western North Atlantic Ocean shows the existence of 2 distinct populations of benthonic Foraminifera. The distribution of these populations correlates well with the distribution of the cold North Atlantic deep water (Epistominella exigua assemblage) and the very cold Arctic/Antarctic bottom-water masses (Epistominella umbonifera assemblage). Slight, but detectable, faunal differentiation is associated with the Arctic and Antarctic deep-water masses respectively. Abyssal, benthonic Foraminifera thus can be utilized to trace the thermohaline circulation of the deep ocean.

Analyses of core samples, dating from the last full-glacial period, indicate a shifting of faunal boundaries. First information points to an areal diminution of the fauna associated with the very cold bottom water, indicating a general warming of the bottom water during the last ice age, that possibly was due to the pack-ice cover over ocean areas that now provides the very cold bottom waters.

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