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 (delta O-18(b)). Our approach is to estimate a non-linear transfer function between past sea level and delta O-18(b) over the last two glacial cycles, with additional information from the mid-Pliocene. Combining this transfer function with the relationship between temperature and delta O-18(b) permits a deconvolution Of a delta O-18(b) 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 degrees 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 similar to 100 kyr time scale during the late Pleistocene. Thus, according to this partition, there is more similar to 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. (C) 2009 Elsevier Ltd. All rights reserved.