Analysis of Various Post-Depositional Effects as Possible Causes of Inconsistencies Between Stable Isotopes Ice Core Records and Air Temperature During 1940s and the 2003 Heat Wave from the Ortles Glacier, Italian Alps

Abstract:

Studying how stable isotopes in glacial ice are modified by post-depositional effects such as water vapor exchange between snowpack and atmosphere has rapidly expanded as researchers use ice cores to make increasingly precise paleoclimate reconstructions. However, limited work has been done to apply this newfound knowledge to preexisting Alpine ice records. In 2011, our team collected a series of ice cores near the summit of Mt. Ortles at 3869 m in the Eastern Italian Alps. These cores contain the only ice collected from the Eastern Alps cold enough to preserve isotopic signals, making their data crucial for reconstructing paleoclimate at high elevation in Central Europe. But two isotopic events within these cores show an apparent inconsistency with instrumental climatic records. First, the isotopic record is positively correlated with extrapolated air temperature from nearby weather stations for the past 100 years except during the 1940s. The 1940s were a time of regional positive temperature anomalies, but the δ¹⁸O record is characterized by negative anomalies during that period which cannot be explained by temperature alone. Second, extreme ablation observations from Mt. Ortles during the 2003 European heatwave may suggest that all the snow that fell on Mt. Ortles in the 2002-2003 season melted that year. However, there are highly enriched δ¹⁸O values at the supposed 2003 layer, indicating processes in addition to meltwater percolation were operating at that time. By refining the ice core chronology to better correlate temperature with δ¹⁸O and adopting air temperature reconstructions and snow mass balance models, we aim to explore if these inconsistencies in the ice core record could be due to meltwater percolation, removal of entire annual layers, or perhaps post-depositional isotopic modification of snow. If we can better understand these isotopic signals, we could be able to correct for these effects and more accurately reconstruct paleoclimate in Central Europe.