PLEISTOCENE EXTINCTIONS OF DEEP-SEA BENTHIC FORAMINIFERA: THE SOUTH ATLANTIC RECORD

Abstract:  Sixty-two species and 19 genera of elongate, cylindrical benthic foraminifera disappeared from the deep-sea in the south-east Atlantic (ODP Sites 1082 and 1083) and the Atlantic sector of the Southern Ocean (ODP Site 1088) during the Early and Middle Pleistocene as part of the global extinction of the families Pleurostomellidae, Stilostomellidae and portions of the Nodosariidae. During the mid-Pleistocene Climate Transition (1·2–0·6 Ma) in the Southern Ocean, these extinct taxa exhibited three pulses of glacial decline in abundance and diversity separated by partial interglacial recoveries. Beneath the high-productivity Benguela Current upwelling region (Sites 1082, 1083), glacial declines in the extinct taxa were suppressed by favourable high organic-carbon flux and consequent low-oxygen bottom conditions. Here two major pulses of diversity loss occurred at c.  1·3–1·2 Ma and 1·0–0·7 Ma. At all three locations, the most dramatic decline in abundance and diversity occurred c.  0·85–0·80 Ma (marine isotope stage 20), and the final disappearance of Extinction Group taxa was completed by 0·67 Ma beneath the Benguela Current and 0·60 Ma in the Southern Ocean. We speculate that this period of enhanced global extinctions was linked to a pulsed decline in glacial temperatures and/or increase in ventilation of deep and intermediate water masses, associated with polar ice cap growth since the late Pliocene.