NOAA/WDS Paleoclimatology - Global Sea-level and Deep-sea Temperature Reconstructions over the past 40 Million Years

Sea level and deep-sea temperature variations are key indicators of global climate changes. For continuous records over millions of years, deep-sea carbonate microfossil–based d18O (dc) records are indispensable because they reflect changes in both deep-sea temperature and seawater d18O (dw); the latter are related to ice volume and, thus, to sea level changes. Deep-sea temperature is usually resolved using elemental ratios in the same benthic microfossil shells used for dc, with linear scaling of residual dw to sea level changes. Uncertainties are large and the linear-scaling assumption remains untested. Here, we present a new process-based approach to assess relationships between changes in sea level, mean ice sheet d18O, and both deep-sea dw and temperature and find distinct nonlinearity between sea level and dw changes. Application to dc records over the past 40 million years suggests that Earth’s climate system has complex dynamical behavior, with threshold-like adjustments (critical transitions) that separate quasi-stable deep-sea temperature and ice-volume states.