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Stable isotopic biogeochemistry of carbon and nitrogen in a perennially ice-covered Antarctic lakeLake Hoare (77 degrees 38' S, 162 degrees 53' E) is an amictic, oligotrophic, 34-m-deep, closed-basin lake in Taylor Valley, Antarctica. Its perennial ice cover minimizes wind-generated currents and reduces light penetration, as well as restricts sediment deposition into the lake and the exchange of atmospheric gases between the water column and the atmosphere. The biological community of Lake Hoare consists solely of microorganisms -- both planktonic populations and benthic microbial mats. Lake Hoare is one of several perennially ice-covered lakes in the McMurdo Dry Valleys that represent the end-member conditions of cold desert and saline lakes. The dry valley lakes provide a unique opportunity to examine lacustrine processes that operate at all latitudes, but under an extreme set of environmental conditions. The dry valley lakes may also offer a valuable record of catchment and global changes in the past and present. Furthermore, these lakes are modern-day equivalents of periglacial lakes that are likely to have been common during periods of glacial maxima at temperate latitudes. We have analyzed the dissolved inorganic carbon (DIC) of Lake Hoare for delta 13C and the organic matter of the sediments and sediment-trap material for delta 13C and delta 15N. The delta 13C of the DIC indicates that 12C is differentially removed in the shallow, oxic portions of the lake via photosynthesis. In the anoxic portions of the lake (27-34 m) a net addition of 12C to the DIC pool occurs via organic matter decomposition. The dissolution of CaCO3 at depth also contributes to the DIC pool. Except near the Canada Glacier where a substantial amount of allochthonous organic matter enters the lake, the organic carbon being deposited on the lake bottom at different sites is isotopically similar, suggesting an autochthonous source for the organic carbon. Preliminary inorganic carbon flux calculations suggest that a high percentage of the organic carbon fixed in the water column is remineralized as it falls through the water column. At nearby Lake Fryxell, the substantial (relative to Lake Hoare) glacial meltstream input overprints Fryxell's shallow-water biological delta 13C signal with delta 13C-depleted DIC. In contrast, Lake Hoare is not significantly affected by surface-water input and mixing, and therefore the delta 13C patterns observed arise primarily from biological dynamics within the lake. Organic matter in Lake Hoare is depleted in 15N, which we suggest is partially the result of the addition of relatively light inorganic nitrogen into the lake system from terrestrial sources.
Document ID
20040089756
Acquisition Source
Headquarters
Document Type
Reprint (Version printed in journal)
Authors
Wharton, R. A. Jr
(Desert Research Institute, University of Nevada System Reno 89506, United States)
Lyons, W. B.
Des Marais, D. J.
Wharton RA, J. r.
Date Acquired
August 21, 2013
Publication Date
January 1, 1993
Publication Information
Publication: Chemical geology
Volume: 107
ISSN: 0009-2541
Subject Category
Exobiology
Funding Number(s)
CONTRACT_GRANT: NAGW-1947
CONTRACT_GRANT: OPP8-41630
CONTRACT_GRANT: OPP9-21173
Distribution Limits
Public
Copyright
Other
Keywords
NASA Program Exobiology
Non-NASA Center
NASA Discipline Number 52-80
NASA Discipline Exobiology
NASA Center ARC

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