Sensitivity of planktonic foraminifera to Mid-Pleistocene climate change in the SE Atlantic

In this paper we describe a record of planktonic foraminiferal relative abundance changes in Core T89-40 retrieved from the Walvis Ridge, SE Atlantic. The planktonic foraminiferal relative abundance changes reflect past (sub)surface water hydrography during the Mid-Pleistocene Transition. Statistical analysis shows that most variability in the planktonic foraminiferal relative abundance record was caused by cycles in eutrophic (nutrient-rich) versus oligotrophic (nutrient-poor) (sub)surface water conditions, driven by shifts in subtropical SEAtlantic gyre and/or tropical northern Angolan waters versus Benguelan upwelling waters over the site. Oligotrophic waters occurred during peaks of boreal insolation within, or just preceding, the interglacials, and eutrophic conditions prevailed during glacials. Large oligotrophic-eutrophic cycles began around 600 ky at the end of the Mid-Pleistocene Transition, in line with the late Pleistocene amplification of the large amplitudinal glacial-interglacial cycles. The abundance patterns of leftand right-coiled Globorotalia truncatulinoides and leftcoiled Neogloboquadrina pachyderma are of special interest. The left-coiled G. truncatulinoides exited from the record at around 960 ky at the onset of the Mid-Pleistocene Transition, when (sub)surface waters cooled as evidenced in stable oxygen isotopes, and this species remained absent during the course of the Mid-Pleistocene Transition until about 600 ky. The left-coiled N. pachyderma shows anomalously high abundances during Marine Isotopic Stage (MIS) 9, 11 and 31, reflecting strong upwelling during these interglacials, whilst the presence of the tropical species Globorotalia menardii during the same MIS 9, 11 and 31 reflects on flow of Indian Ocean waters into the S. Atlantic at the same time.