Innovative water tracers and water isotopes enhance Antarctic research with climate models

Abstract

Antarctic research is important for our understanding of sea level changes, polar amplification, and palaeoclimate dynamics. While instrumental records are often too short to distinguish anthropogenic impacts from natural variability, Antarctic ice cores preserve valuable information about past climate evolution. As the interpretation of ice core records is confounded by many influencing factors, climate models are instrumental in elucidating relevant processes. Here I aim to leverage climate models for Antarctic studies. Firstly, I developed innovative water tracing diagnostics in an isotope-enabled atmospheric general circulation model ECHAM6-wiso. These water tracers provide new detailed information on moisture sources of atmospheric humidity and precipitation. While previous studies suggested that poleward moisture transport tends to follow constant equivalent potential temperature, notable deviations are found in the lower troposphere due to radiative cooling. Differences in moisture sources of Antarctic precipitation are quantified between heavy and light precipitation, and between positive and negative phases of the Southern Annular Mode. These results help elucidate dynamic and thermodynamic drivers of Antarctic precipitation. Secondly, I applied the moisture source information to examine the interpretation of deuterium excess in Antarctic ice cores. I focused on modelled relationships between deuterium excess and moisture source properties. The logarithmic definition of deuterium excess dln is found to be superior to the linear definition dxs in Antarctic studies. The modelling results demonstrate the potential to use dln in Antarctic precipitation as a proxy for moisture source temperature, but large model bias calls for further research and palaeoclimate modelling is required to test the stationarity of the modelled relationship. Thirdly, I investigated palaeoclimate modelling on the early last interglacial (127 thousand years ago, ka). While marine sediment and ice core records suggest warmer Southern Ocean and Antarctica at 127 ka than preindustrial, state-of-the-art climate models do not reproduce the magnitude of warming when only forced by orbital parameters and greenhouse gas concentrations during that period. Much of the warming can be reproduced by a climate model HadCM3 with a 3000-year freshwater forcing over the North Atlantic. These results highlight the importance of transient features of the early last interglacial climate. This thesis advances our understanding of the drivers on Antarctic precipitation, moisture source controls on deuterium excess in Antarctic precipitation, and southern mid-to-high latitude warming at the early last interglacial. Future research is required to develop the potential of the water tracing diagnostics.