Millennial scale resolution Mean Ocean Temperature over the MIS 9 glacial inception

The two major heat reservoirs on the Earth’s surface are oceans and the latent heat required to melt glaciers and ice sheets. Of these, the ocean is the largest and the fluctuations in Ocean Heat Content (OHC) therefore yield insights into Earth’s energy balance through time. We reconstruct OHC fluctuations through Mean Ocean Temperature (MOT) change, in turn reconstructed through the measurement of noble gas ratios in ice cores. Noble gases are inert; on the Earth’s surface they mainly partition between the atmosphere and the oceans depending on the latter’s temperature. From ice core measurements, past atmospheric noble gas ratios can be determined and from these a global, integrated, mean ocean temperature record is obtained. Until recently, MOT reconstructions were mostly focused on glacial Terminations, leaving the sections separating them sparsely covered.

Here, we present a millennial scale resolution MOT reconstruction for the MIS 9 glacial inception. The MIS 9e overshoot (centred around 336 kyrs) sees an intermittent 2°C MOT rise before returning to interglacial values. During the glacial inception itself (~325 – 307 kyrs), the oceans cooled by approximately 2°C, roughly two thirds of the glacial period’s total. This initial MOT drop coincides with a decline in both Southern Ocean and Antarctic plateau temperatures. However, we note a decoupling between decreasing temperatures and CO2 concentration; the latter plateaus for around five millennia after the start of ocean temperature decline. Further MOT measurements are planned on the Beyond EPICA ice core covering the most recent glacial inception (104-126 kyrs). These could lead to additional insights into glacial inceptions.