Rapid δ18O and δ13C isotopic shifts in late Pleistocene marine varves on the California margin

Upper Pleistocene sediments on the continental slope off Northern California contain alternations of varves and bioturbation produced by fluctuations in intensity of the coastal upwelling system. Stable isotopic analyses of benthic Foraminifera across a particularly well developed varve/bioturbation sequence deposited ~26,000 years ago reveal rapid shifts of ~0.25‰ in δ18O and ~0.4‰ in δ13C. The δ18O shift occurs within a varved section. Based on varve counts, the isotopic change occurred in less than 100 years. Timing and magnitude of the shift coincide with similar shifts observed in almost all other high-resolution δ18O records that have been interpreted as primarily representing global in-volume fluctuations.