Alkenone and coccolith records of the mid-Pleistocene in the south-east Atlantic:: Implications for the UK37 index and South African climate

Successful application of the alkenone palaeothermometer, the U-37(K') index, relies upon the assumption that fossil alkenone synthesisers responded to growth-temperature changes in a similar manner to the modern producers, chiefly the coccolithophores Emiliania huxleyi and Gephyrocapsa oceanica. We compare coccolith and U-37(K') data from ODP Site 1087 in the south-east Atlantic between 1500 and 500ka, and show that evolutionary events and changes in species dominance within the coccolithophore populations had little impact on the U-37(K') record. The relative abundances of the C-37 and C-38 alkenones also closely resembled those found in modern populations, and suggest a similar temperature sensitivity of U-37(K') during the early and mid-Pleistocene to that found at present. These results support the application of the U-37(K') index to reconstruct sea-surface temperatures (SSTs) throughout the Quaternary. The U-37(K') record at ODP Site 1087 contains an SST signal that documents the emergence of the 100-kyr cycles that characterise the late Quaternary ice volume records. This is preceded by significant cooling at ODP Site 1087, marked by a negative shift in SSTs and a positive shift in the planktonic delta O-18 some 250-kyr earlier, at ca 1150-1000 ka. This results in a permanent fall in average SSTs of around 1.5 degrees C. The predicted increase in aridity onshore as a result of this cooling can be identified in a number of published records from southern Africa, and may have played a role in some important evolutionary events of the mid-Pleistocene. (c) 2005 Published by Elsevier Ltd.