ASSESSING THE INFLUENCE OF EXTREME PRECIPITATION EVENTS ON THE ISOTOPIC VALUES OF DRIP WATER FROM A SOUTHERN SIERRA NEVADA CAVE

Crystal Cave, in Sequoia National Park, CA (36.59⁰ N; 118.82⁰ W; 1386m) is ideally located to capture moisture transported over the Pacific Ocean and is the site of ongoing speleothem-based paleoclimate research. A recent study utilizing Crystal Cave stalagmite oxygen (δ¹⁸O) isotope variations found a strong positive correlation between the sea surface temperatures in the Kuroshio extension region of the northwest Pacific and the δ¹⁸O. This was interpreted as reflecting the moisture source delivering precipitation to this region, with the lowest isotopic values arriving from the North Pacific storm track and the highest from the tropical Pacific. Here, we will present results of a modern calibration study conducted to better understand the controls on the isotopic composition of precipitation in Southern California and, in particular, to investigate the influence of extreme precipitation events on speleothem isotopes. Stalagmate drip logger data from this site shows three anomalous drip rate increases on Dec. 20 and 30, 2010 and March 8, 2011 in response to three large storms known as 'atmospheric rivers'. Atmospheric rivers are extensive fluxes of water vapor transported from the subtropics that can deliver substantial precipitation and contribute to flooding when they encounter mountains. The west coast of the US is particularly vulnerable to atmospheric rivers, with 30-50% of annual precipitation in this region occurring from a few atmospheric river events, so the influence on cave dripwater isotopes may be large. Because of the subtropical origin of atmospheric rivers, they can carry unique isotopic properties. We will present the results of isotopic analyses on 221 weekly precipitation samples collected from near the cave site at Giant Forest, (36.57° N; 118.78° W; 1921m) from 2001 to 2011 and compare the results to Crystal Cave drip water isotopic values from 2007 to 2011. Furthermore, we will compare with reanalysis and isotope enabled climate model IsoGSM data.