The McMurdo Dry Valleys of Antarctica are a polar desert region with watersheds dominated by glacial melt. Recent ground exploration reveals unusual surface-flow-seep features not directly supplied by glacial melt. Much of this seep water is potentially derived from permafrost, snow patches, refrozen precipitation accumulated in the subsurface, buried glacier ice, or even groundwater from the deep subsurface. Flow features that lack obvious glacier melt sources were identified in archived aerial photographs of Taylor Valley. This valley was surveyed for extant and extinct seeps, and the locations of geomorphic features in five active seeps were documented. Water samples from seeps were analyzed for major ions and stable isotopes of hydrogen and oxygen. Solute chemistry and isotopic signatures of seeps are distinct from those of nearby streams and glaciers, with the seeps having elevated solute concentrations.

All but one seep had water isotopically heavier than water from nearby glaciers and streams, suggesting that seep waters have been substantially modified if they had been derived originally from the same meteoric sources that supply local glaciers and streams. The seeps are important because they compose a previously overlooked component of the desert hydrological cycle. Seep features in the dry valleys are potential terrestrial analogs for the geologically young gullies observed on Mars, which are thought to be evidence of groundwater seepage and surface runoff.

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