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Results: In November 2012, light transmitted through the ice and water resulted in 1 µmol photons/m2s (the lower limit for net photosynthesis [1]) reaching 10.4 m depth in Lake Fryxell. However, the water column transitioned from oxygen supersaturated at 9.1 m to complete anoxia below~ 9.8 m. Net oxygen production in benthic mats at 9.8 m was demonstrated by a peak in oxygen at 1 mm depth in the mat. The spatial distribution of oxygen indicates a flux to the water column of 0.04 µmol O2/m2s and into the sediment of 0.013 µmol O2/m2s. A net export of 0.05 µmol O2/m2s is consistent with expected local net photosynthetic rates based on productivity analysis in nearby Lake Hoare [1].

8.9 m: 0.74% Incident Photosynthetically Active Radiation (PAR)

10.4 m: Minimum PAR for Net Cyanobacterial Photosynthesis (1 µmol photon/m2s daily average [1])

9.8 m: 0.27% Incident PAR (3 µmol photon/m2s daily average; 1.6 µmol/m2s November 2012 montly average)

1 cm