Abstract:
Successful application of the alkenone palaeothermometer, the Uk37' 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 Uk37' 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 Uk37' record. The relative abundances of the C37 and C38 alkenones also
closely resembled those found in modern populations, and suggest a similar
temperature sensitivity of Uk37' during the early and mid-Pleistocene to that
found at present. These results support the application of the Uk37' index to
reconstruct sea-surface temperatures (SSTs) throughout the Quaternary.
The Uk37' 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
del18O 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. 
