EXTREME SUPERSATURATION OF NITROUS-OXIDE IN A POORLY VENTILATED ANTARCTIC LAKE

Lake Bonney, a permanently ice-covered Antarctic lake, has a middepth maximum N2O concentration of 41.6 mu M N (>580,000% saturation with re spect to the global average mixing ratio of N2O) in its east lobe, rep resenting the highest level vet reported for a natural aquatic system. Atmospheric N2O over the lake was 45% above the global average, indic ating that this lake is an atmospheric source of N2O. Apparent N2O pro duction (ANP) was correlated with apparent oxygen utilization (AOU), a nd denitrification was not detectable, implying that nitrification is the primary source for this gas. The slope of a regression of ANP on A OU revealed that potential N2O production per unit of potential O-2 co nsumed in the east lobe of Lake Bonney is at least two orders of magni tude greater than reported for the ocean. The maximum yield ratio for N2O [ANP/(NO2- + NO3-)] in Lake Bonney is 26% (i.e. 1 atom of N appear s in N2O for every 3.9 atoms appearing in oxidized N), which exceeds p revious reports for pelagic systems, being similar to values from redu ced sediments. Areal N2O flux from the lake to the atmosphere is >200 times the areal flux reported for oceanic systems; most of this gas ap parently enters the atmosphere through a small moat that occupies simi lar to 3% of the surface of the lake and exists for similar to 10 week s in summer.