Synoptic variability in the Ross Sea region, Antarctica, as seen from back-trajectory modeling and ice core analysis

Synoptic variability in the Ross Sea region, Antarctica over the last thirty years is investigated using back-trajectory modeling and cluster analysis. We identify two dominant air-mass trajectory clusters: oceanic/West Antarctic and continental/East Antarctic. Our analysis shows that the oceanic/West Antarctic trajectories have an annual cycle similar to the Semiannual Oscillation and on average peak in frequency during April, while continental/East Antarctic trajectories reach their annual maximum during December. We demonstrate a causal association between the El Nino Southern Oscillation (ENSO) and the frequency of oceanic/West Antarctic trajectories originating from the Ross Sea and Amundsen Sea regions. In contrast, we find that the Southern Annular Mode (SAM) has little influence on the trajectory cluster frequencies. We then develop proxy records for synoptic variability using a shallow firn core from Gawn Ice Piedmont in Southern Victoria Land. Continental/East Antarctic trajectory frequency correlates with concentrations of nitrate (NO3), which is sourced from stratospheric air-masses descending over the Antarctic interior. At seasonal to inter-annual scales, the frequency of oceanic/West Antarctic trajectory clusters strongly correlate with deuterium excess, which is sensitive to changes in relative humidity and sea surface temperature in the Ross and Amundsen Seas. Inter-annual variability in the frequency of oceanic/West Antarctic trajectories is discussed with respect to ENSO and changes in SST and sea ice extent.