Quantifying the effects of changes in ocean circulation and endmember composition on variability in Late Pleistocene carbon isotope records

Benthic δ13C has a long history as a proxy for ocean circulation change. However, several recent studies (e.g., Rutberg and Peacock, 2006; Raymo et al., 2004) have suggested that variations in endmember δ13C values could confound reconstructions of glacial watermasses or even dominate variability in benthic δ13C. We analyze 29 benthic δ13C records to quantify what percent of variance in the data is associated with changes in endmember composition versus watermass distribution. We present a typical sequence of change in δ13C for a Late Pleistocene glacial cycle and a simple reconstruction of Atlantic watermass changes consistent with δ13C observations. Although watermass geometry cannot directly address the question of overturning rates, the spatial extent of δ13C gradients across boundaries can provide constraints on rates of production relative to mixing. We also combine information about watermass depths and benthic δ18O gradients to discuss the relative physical characteristics of Atlantic watermasses.