Sedimentary record of the mid-Pleistocene climate transition in the southeastern South Atlantic (ODP Site 1090)

One important goal of Leg 177 of the Ocean Drilling Program (ODP) was to explore the nature of the mid-Pleistocene climate transition (MPT) on the southern hemisphere. A suitable MPT record was encountered at Site 1090 in the southeastern South Atlantic, where a 44-m-thick sequence of Quaternary diatom-bearing foraminiferal muds and oozes was recovered on the Agulhas Ridge. Environmental responses to the MPT comprised changes in terrestrial climate, biological productivity, and regional ocean circulation, as inferred from compositional sediment data and clay mineralogy. A shift towards more arid conditions occurred between 900 and 800 ka in southern Africa. Changes in palaeoceanography already started earlier. Since 1150 ka, northward displacements of the Polar Front appeared during glacial periods and shifted the area of dominant diatom deposition towards Site 1090. Likewise, glacial–interglacial contrasts in regional conveyor circulation strengthened after 1200 ka and became most severe after 650 ka. However, while changes in regional conveyor circulation likely responded in tune with global ice-volume changes and show the onset of 100-kyr cycles after 1200 ka, an unusual 130-kyr pattern characterises the pattern of frontal movements between 1200 ka and 650 ka, probably in response to imperfect adaptation of regional climate to the global 100-kyr climate cycles.