Utilizing Ice Core and Climate Model Data to Understand Seasonal West Antarctic Variability

Reconstructions of past West Antarctic Ice Sheet (WAIS) climate rely on the isotopologues of water recorded in ice cores that extend the local surface temperature record back tens of thousands of years. Here, we utilize continuous flow sampling and novel back-diffusion techniques with the WAIS Divide ice core (WDCobs) to construct a seasonal record of the δ18O value of the precipitation (δ18Op) at the time of deposition from 1980 to 2000. We then use a water isotope enabled global climate model, iCESM1, to establish seasonal drivers of WAIS climate and of δ18Op variability at the WAIS Divide location to compare with the WDCobs and MERRA-2 data. Our results show that the WAIS seasonal climate variability is driven by the position and strength of the Amundsen Sea low (ASL) caused by variations in the southern annual mode and the two Pacific–South American patterns (PSA1 and PSA2). The largest year-to-year seasonal δ18Op anomalies at the WAIS Divide location occur with respect to PSA2 during austral winter (JJA) as a result of an eastward displacement of the ASL that shifts the associated onshore winds toward the Weddell Sea, reducing temperatures and precipitation near the WAIS Divide location. Additionally, the iCESM1 experiment suggests that changes to the moisture path from the source to the WAIS Divide location are an important driver of seasonal WDCobs δ18Op variability. This work highlights the potential of using a single ice core to reconstruct past WAIS climate at seasonal time scales.