In situ measurements of photosynthesis in the benthic microbial mats at high depths under the perennial ice cover of Lake Hoare, Taylor Valley

In situ measurements of photosynthesis in the benthic microbial mats, that grow under the perennial ice cover, of Lake Hoare were measured to determine if photosynthesis is positive at considerable depth (compared with rates measured under laboratory conditions) in the lake itself. In the first season of study, one dive site, at depths of 8 and 16m, was used to measure the fine scale distribution of dissolved oxygen on the lake floor. The information was combined with ancillary data on the distribution of actively photosynthetic organism of spectrally resolved underwater light attenuation and limited laboratory high-resolution. The penetration of photosynthetically active radiation through the lake ice and lake water and the attenuation of light by the microbial mat itself was measured. Results indicate that the total amount of radiation reaching the microbial mats at 8 and 16m was at wavelengths suitable for plant absorption. To determine whether net photosynthesis production of oxygen was occurring, measurements of fine scale distribution of oxygen associated with the mats was conducted. In addition, a Imaging PAM fluorometer was used to determine the distribution and activity of pigments within the microbial mat. The photosynthetic structure of the microbial mats was determined using a suite of measurements. The measurements were repeated in a second season of study during the course of a day to show the 3-5 fold diurnal variations in photosynthetically active radiation were paralleled by variations in the net oxygen production, with little change in photosynthetic yield.