Successful application of the alkenone palaeothermometer, the U37K′ 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 U37K′ data from ODP Site 1087 in the south-east Atlantic between 1500 and 500 ka, and show that evolutionary events and changes in species dominance within the coccolithophore populations had little impact on the U37K′ record. The relative abundances of the C37 and C 38 alkenones also closely resembled those found in modern populations, and suggest a similar temperature sensitivity of U37K′ during the early and mid-Pleistocene to that found at present. These results support the application of the U37K′ index to reconstruct sea-surface temperatures (SSTs) throughout the Quaternary. The U37K′ 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 δ18O some 250-kyr earlier, at ca 1150-1000 ka. This results in a permanent fall in average SSTs of around 1.5°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.