Relationship between the trajectory of mid-latitude cyclones in the eastern Pacific Ocean and the isotopic composition of snowfall in the Sierra Nevada, California

Abstract:

Climate change has caused a change in the Sierra Nevada snowpack and the timing of its snowmelt, threatening a valuable water resource that provides for 25 million people and 5 million hectares of irrigated land. Understanding past and future variations in the snowpack is crucial in order to plan future water management. Of particular importance would be an archive of the variability of past snowfall, which can be recorded through the isotopic records found in local paleoproxies (e.g., diatoms). We propose to quantify the relationship between sources of atmospheric moisture in the Sierra Nevada and the isotopic composition of its snowpack to uncover whether isotopic variations recorded in paloearchives are a result of the isotopic composition of the precipitation, thereby showing whether these archives could serve as a reliable source of atmospheric moisture. Preliminary analysis conducted from December 2012 to March 2013 at Sequoia National Park resulted in statistically significant correlations between the isotopic composition of the winter snowfall and storm track trajectories. It was observed that storms originating from more northern latitudes had predominantly lighter isotopes (more negative δ ²H and δ¹⁸O) and sub-tropical/tropical Pacific storms showed more positive δ ²H and δ¹⁸O. This pattern reflects the isotopic gradient of the Pacific Ocean and can prove useful when interpreting the climatic significance of the δ²H and δ¹⁸O values in analyzed proxies.

While our initial investigation was promising, the winter of 2012 -2013 was abnormally dry compared to long-term averages. Before directing our investigation to known paleoproxies, we aim to determine if the correlation between storm tracks and isotopic composition of precipitation holds in years with average and above average precipitation through analysis of archived samples from calendar years 2007 – 2011 from Giant Forest in Sequoia National Park (southern sierra) and Manzanita Lake in Lassen Volcanic National Park (northern sierra).