New insights into the use of stable water isotopes at the northern Antarctic Peninsula as a tool for regional climate studies

The Antarctic Peninsula is one of the most challenging regions of Antarctica from a climatological perspective, owing to the recent atmospheric and oceanic warming. The steep topography and a lack of long–term and in situ meteorological observations complicate extrapolation of existing climate models to the sub-regional scale. Here, we present new evidence from the northern Antarctic Peninsula to demonstrate how stable water isotopes of firn cores and recent precipitation samples can reveal climatic processes related to nearby oceanic and atmospheric conditions. A noticeable effect of the sea ice cover on local temperatures and atmospheric modes, in particular the Southern Annular Mode (SAM), is demonstrated. In years with large sea ice extension in winter (negative SAM anomaly), an inversion layer in the lower troposphere develops at the coastal zone. Therefore, an isotope–temperature relationship valid for all seasons cannot be concluded. The d–T. relationship rather depends on seasonal variability of oceanic conditions. Transitional seasons (autumn and spring) are both stable seasons with an isotope–temperature gradient of +0.69‰ °C-1. The firn stable isotope composition reveals that the near–surface temperature at the most northern portion of the Antarctic Peninsula shows a decreasing trend (-0.33°C y-1) between 2008 and 2014. Moreover, the deuterium excess (dexcess) has been demonstrated to be a reliable indicator of seasonal oceanic conditions, and therefore suitable to improve a firn age model based on seasonal dexcess variability. The annual accumulation rate in this region is highly variable, ranging between 1060 kg m-2 y-1 and 2470 kg m-2 y-1 from 2008 to 2014. The combination of isotopic and meteorological data is a key for reconstructing climatic conditions with a high temporal resolution in polar regions where no direct observations exist