Taylor Valley (77°00’S, 162°52’E) is one of the "ice-free" areas in the vicinity of Ross Island, Antarctica. It contains several unique, perennially ice-covered lakes in an arid environment. Although many aspects of the chemistry and nutrient cycling within the valley, and especially the lakes, have been thoroughly investigated since the International Geophysical Year (1959), no study has focussed on the carbon cycling in this area. The ice-cover that prevents gas exchange with the atmosphere all year long, and the nearly complete absence of vegetation outside the lakes cause the carbon cycle to differ significantly from well-studied carbon cycles in temperate climates.
In this dissertation, carbon isotopes are used to demonstrate how various processes, such as biologic uptake of carbon via photosynthesis, and different fluxes into these lakes affect their carbon composition. Lake Hoare water has a low solute content and is easily affected by changes in climate, while Lake Fryxell has a high solute component and is not as dependent on external recharge of carbon. The origins of these differences and how they will control the response of the lakes to climate changes are discussed. This dissertation also is the first to establish a carbon mass balance for three lakes in Taylor Valley. Although the lakes are located near one another, they show very different chemical compositions, including carbon contents. Two of the three lakes become highly undersaturated with respect to CO2 in the upper parts of their epilimnia during the growth season. The cyanobacterial carbon uptake via photosynthesis exceeds the recharge of carbon during the early part of the growth period. During the later part of the growth season, CO2 is abundant, leading to a carbon budget that is balanced on an annual frame. In the lower parts of the epilimnia, high diffusive flux of CO2 from supersaturated deep waters exceeds the carbon uptake. Fluxes and processes in the streams and lakes are compared over several years. Also, the results from carbonate mineral dissolution/precipitation experiments, sediment trap material analysis, carbon isotope measurements, and speciation modeling are used to draw a coherent qualitative and quantitative picture of the processes controlling the cycling of carbon and calcium in the streams and lakes of this ecosystem. Analysis of sediment trap material allows comparison, for the first time, of the stream input rates of calcium and bicarbonate into the lakes with lake sedimentation rates. It is shown that the importance of processes such as organic matter respiration and calcite dissolution to balance their calcium and carbon budgets varies from stream to stream and lakes to lake, and that these differences are reflected in the isotopic compositions of the streams and lakes. For one of the lakes (Hoare), this dissertation challenges the notion that convective mixing is absent under its protective ice cover. Finally, the establishment of an isotopic balance, rarely possible in lake ecosystems, has been attempted. Preliminary results are promising, but due to the scarcity of data a reliable budget will require further data collection and interpretation.