CARBON DYNAMICS ALONG A DEPTH TRANSECT IN FOUR POLAR DESERT LAKES, TAYLOR VALLEY, EAST ANTARCTICA

Hydrologic properties of closed-basin lakes in Taylor Valley, East Antarctica, are controlled predominantly by their perennial 3-5 m thick ice cover. This ice cover limits wind-generated currents, gas exchange with the atmosphere, light penetration, and organic matter input. Most dry valley lakes are highly stratified and stable, creating strong vertical biological and chemical gradients. Typically, each lake is characterized by one central sampling site, where chemical, physical, and biological profiles are collected. Alternatively, we have investigated the three-dimensional variation by measuring water chemistry along lateral depth transects from the shore to the deepest part of each lake. Samples were collected from long-axis transects along Lake Fryxell, East Lake Bonney, and West Lake Bonney, encompassing minimum (moat) and maximum depths. We analyzed stable carbon isotopic compositions of microbial mat/sediment and the accompanying dissolved inorganic carbon (DIC) isotopic signature from the water column immediately above the mat, as well as major ion chemistry. The lake moats are an important component of carbon dynamics, as these are the areas that become ice-free on a seasonal basis and are most impacted by glacial meltwater runoff. Similar to previous studies, results of our analyses show a general increasing trend in [DIC] with depth in dry valley lakes. However, waters in the shallower zones and moat are isotopically more depleted. Moats are in isotopic equilibrium with the atmosphere. Also, although the bottom waters of all the lakes are saturated with respect to calcite, their isotopic composition is extremely variable. The largest variability is an 8‰ difference in bottom waters between the two lobes of Lake Bonney indicating vastly different carbon dynamics possibly related to the legacy left by their distinct draw-down and ice cover history.