The Effect Of Freshwater Input On δ18o Distribution At The Younger Dryas

Abstract

The Younger Dryas cooling event (~12.9-11.5 δ18O ka BP) is a recognized example of an abrupt decline of the Atlantic meridional overturning circulation and thus may serve as an analog for expected rapid future climate change. Prediction of the atmospheric and oceanic conditions at the onset of Younger Dryas presents various challenges and this study is aimed to contribute towards the better understanding of the changes in the oceanic tracer distribution. Here, output from a fully coupled coarse resolution model from the National Center of Atmospheric Research, the Community Climate System Model version 3 (CCSM3) have been utilized to predict diagnostically the oxygen isotope ratio relative to standard mean ocean water δw. By using an inverse paleotemperature equation, distribution of oxygen isotopes in carbonate shells δc can be predicted. While present-day CCSM3 simulation of δw generally agree with observations from the World Ocean Circulation Experiment, a significant bias occurs for the North Atlantic benthic isotope data δc plot with a mean error of 1.73 /. For the Younger Dryas the distribution of two scenarios have been analyzed. The first with present-day freshwater input and the second with Northern Hemisphere fresh forcing. Comparison of simulated δc with observed benthic stable oxygen isotope data suggest that changes in freshwater forcing need to be considered in order to explain the oxygen isotopic distribution of the Younger Dryas. The approximated prediction of δw and lack of data for the North Atlantic subsurface suggest significant uncertainties.