An Atlantic lead over Pacific deep-water change across Termination I: implications for the application of the marine isotope stage stratigraphy

Globally synchronous changes in glacioeustatic sea-level provide a particularly useful stratigraphic reference in the study of glacial-interglacial climate change, and form the basis for the marine isotope stage (MIS) system, which posits a dominant glacioeustatic signal in benthic foraminferal δ18O. However, benthic δ18O strictly does not represent a pure sea-level record, and it is shown here that, due to local changes in deep-water hydrography, the MIS 2/1 boundary (i.e. benthic δ18O change) occurred ∼4000 years later in the deep eastern equatorial Pacific than in the deep Northeast Atlantic. This discrepancy is too large to be attributed entirely to the Pacific lag that may be expected due to the mixing time of the ocean basins. Instead, multiple proxies (including benthic foraminiferal Mg/Ca) suggest that the large offset in benthic δ18O most probably resulted from a late rise in deep-water temperature at the Pacific site and a series of coupled deep-water temperature and δ18O changes at the Northeast Atlantic site. These findings have important implications for the application of the MIS stratigraphy and the interpretation of benthic δ18O records in general, as they show that benthic δ18O fluctuations and MIS boundaries from different hydrological settings may be significantly diachronous. These results call into question the leads and lags that we might infer from a 'naïve' interpretation of benthic δ18O as a sea-level proxy, with a direct bearing on the mechanisms that we may propose to explain glacial-interglacial climate transitions.