The Effect of Past Saturation Changes on Noble Gas Reconstructions of Mean Ocean Temperature

The ocean's immense ability to store and release heat on centennial to millennial time scales modulates the impacts of climate perturbations. To gain a better understanding of past variations in mean ocean temperature (MOT), a noble gas-based proxy measured from ancient air in ice cores has been developed. Here we assess non-temperature effects that may influence the atmospheric noble gas ratios reconstructed from polar ice and how they impact the temperature signal with an intermediate complexity Earth system model. We find that changes in wind speed, sea-ice extent, and ocean circulation have partially compensating effects on mean-ocean noble gas saturation, leading to a slight reduction of noble gas undersaturation at the Last Glacial Maximum (LGM). Taking these effects and ice core measurements into account, our model suggests a revised MOT difference between the LGM and pre-industrial of -2.1 +/- 0.7 degrees C that is also in improved agreement with other independent temperature reconstructions.

Automated summary

A noble gas-based proxy is used to measure the mean ocean temperature (MOT) by analyzing ancient air in ice cores. The study finds that changes in wind speed, sea-ice extent, and ocean circulation have compensating effects on noble gas saturation, resulting in a slight reduction in noble gas undersaturation during the Last Glacial Maximum (LGM). Considering these effects and ice core measurements, the model suggests a revised MOT difference between the LGM and pre-industrial of -2.1 +/- 0.7 degrees Celsius, which is in better agreement with other temperature reconstructions.