Sensitivity of south-east Atlantic planktonic foraminifera to mid-Pleistocene climate change
The last one million years are important in terms of climate development during the so-called Mid-Pleistocene Transition when amplification of the glacial–interglacial cycles occurred. This study describes abundance changes in fossil planktonic foraminifera in sediments from Core T89-40, retrieved from the Walvis Ridge in the south-east Atlantic, across this time period. Cycles between upwelling and subtropical planktonic foraminiferal assemblages are shown to mirror changes between glacial and interglacial periods, respectively. During interglacial marine isotopic stages (MIS) 9, 11 and 31, however, anomalously high abundances of the polar left-coiled Neogloboquadrina pachyderma occur, presumably linked to unusual seasonal upwelling waters. The planktonic foraminiferal abundance record shows 41-ky cyclic variations in the regional oceanography linked to cycles in insolation influenced by changes in the Earth’s axial tilt (obliquity). These orbitally induced oscillations in oceanographic change occurred throughout the entire record. The most conspicuous feature of the planktonic foraminiferal record is the near absence of left-coiled Globorotalia truncatulinoides between 960 and 610 ka (MIS 26-15). The abrupt disappearance of this species is synchronous with the onset of the Mid-Pleistocene Transition in MIS 26.