One of the unusual features of Lakes Fryxell and Hnare in Taylor Valley,
southern Victoria Land, Antarctica, is their perennial ice cover. This ice cover
limits gas exchange between the atmosphere and the lake water, and causesa very
stable stratification of the lakes. We analyzed a series of water samples from
profiles of these lakes and their tributaries for δ13C of the
dissolved inorganic carbon (DIC) in order to qualify the carbon flux from the
streams into the lakes, and to investigate the carbon cycling with in the lakes.
Isotopic values in the uppermost waters (δ13C = +l.3‰ to 5.3‰
in Lake Hoare, +0.4‰ to +3.0‰ in Lake Fryxell) are close to the carbon-isotope
values encountered in the streams feeding Lake Fryxell, but distinctively heavier
than in streams feeding Lake Hoare (δ13C= — 2.3%n to 1.4%).
These ratios are much heavier than ratios found in the moat that forms around the
lakes injanuary February (δC = -10.1%). in the oxic
photic zones of the lakes, photosynthesis clearly influences the isotopic
composition, with layers of high productivity having enriched carbon-isotope
signatures δ13C= +2.7‰ to +6.1‰). in both lakes, the isotopic
values become lighter with depth, reaching minima of 3.2‰ and 4.0% in Lakes
Fryxell and Hoare, respectively. These minima are caused by the microbial
remineralization of isotopically light organic carbon. We present DIC flux
calculations that help to interpret the isotopic distribution. For example, in
Lake Hoare the higher utilization of CO2aq, and a
substantially smaller inflow of CO2 from streams cause the
heavier observed isotopic ratios. Differences in the hydrology and stream
morphologies of the tributaries also greatly influence the carbon budgets of the
basins.
Inorganic carbon-isotope distribution and budget in the Lake Hoare and Lake
Fryxell basins, Taylor Valley, Antarctica
