Biogeochemical and geocryological characteristics of wedge and thermokarst‐cave ice in the CRREL permafrost tunnel, Alaska

Partially eroded ice wedges and lenticularly shaped bodies of massive thermokarst‐cave ice in ice‐rich syngenetic permafrost (yedoma) are exposed in the CRREL tunnel near Fairbanks, Alaska. The ice wedges, which formed 25 000 − 40 000 years ago, were subsequently affected by localised thermal erosion, resulting in underground cavities that filled with surface water infiltrating through a network of conduits. This water froze inward from the walls of the cavity. We report the biogeochemical characteristics of one of these thermokarst‐cave ice features and four nearby ice wedges. The thermokarst‐cave ice has 30 times the dissolved organic carbon concentration, 20 times the total dissolved nitrogen concentration and five to 20 times the inorganic solute concentrations of the surrounding (original) ice wedge material. Based on these results we present a schematic model to describe how the thermokarst‐cave ice was formed and preserved and what processes led to its current biogeochemical characteristics. Current estimates of soluble solutes stored in permafrost may underestimate the total carbon and nutrient load where wedge material has been extensively replaced by surface water rich in organic carbon, nutrients or inorganic solutes. Published in 2011 by John Wiley & Sons, Ltd.