Changes in deep Pacific temperature during the mid-Pleistocene transition and Quaternary

An attempt is made to unravel the dual influences of seawater temperature and isotopic composition upon the oxygen-isotope records of benthic foraminifers from the deep Pacific (δ18Ob). Our approach is to estimate a non-linear transfer function between past sea level and δ18Ob over the last two glacial cycles, with additional information from the mid-Pliocene. Combining this transfer function with the relationship between temperature and δ18Ob permits a deconvolution of a δ18Ob record from the deep Pacific into its temperature and sea-level constituents over the course of the Plio-Pleistocene. This deconvolution indicates that deep Pacific temperature is stable through much of the last glacial (MISs 4 through 2) and then increases by approximately 2 °C during the last deglaciation. This pattern of variability appears to generally be replicated every glacial cycle back to the mid-Pliocene, suggesting a pulse of warming in the deep Pacific on a ∼100 kyr time scale during the late Pleistocene. Thus, according to this partition, there is more ∼100 kyr variability in temperature than in ice variability. Spectral analysis reveals that this variability is likely the product of multiple obliquity cycles rather than a simple 100-kyr signal. The non-linear behaviour of deep ocean temperature, dominated by pulses at 100 kyr time scales, may identify it as a key player in governing the glacial cycles.