SOLUTE AND ISOTOPE GEOCHEMISTRY OF NEAR-SURFACE ICE MELT SEEPS IN TAYLOR VALLEY, ANTARCTICA

The McMurdo Dry Valleys of Antarctica are a polar desert region with a glacial-melt dominated watershed. However, recent ground exploration has revealed unique surface flow seep features that are not directly supplied by glacial melt. Instead, seep water is potentially derived from permafrost, snow patches, re-frozen precipitation that has accumulated in the subsurface, buried glacier ice (e.g. ice-cored moraine), or even groundwater from the deep subsurface. Prior to fieldwork, flow features lacking obvious glacier melt sources were identified in archived aerial photographs of Taylor Valley, located in the middle of the McMurdo Dry Valleys. During the 2005 Antarctic summer field season, the length of Taylor Valley was surveyed for extant and extinct seeps. The precise GPS location and geomorphic features of five active seeps were documented. Water samples from seeps were collected for major ion analysis via ion chromatography and isotopic analysis of δD and δ¹⁸O. Geochemical data favors a subsurface origin for the seep water. The solute chemistry and isotopic signatures of the seeps are distinct from those of nearby streams and glaciers. Seep water analysis showed elevated solute concentrations compared to glacial streams in the vincinity. With the exception of one seep, all of the seep water δ¹⁸O values were isotopically heavier than water samples from nearby glaciers and streams. This suggests that seep waters have been substantially modified if they are originally derived from the same meteoric sources supplying local glaciers and streams. This study reveals that melting near-surface ice is a unique source of liquid water in the polar desert of the McMurdo Dry Valleys, and that seeps are an important and previously overlooked component of the polar desert hydrological cycle. Seep features in the Dry Valleys are also potential terrestrial analogs for the geologically young gullies observed on Mars, thought to be evidence of groundwater seepage and surface runoff.