Stable carbon and nitrogen isotopic composition of benthic and pelagic organic matter in lakes of the McMurdo Dry Valleys, Antarctica. Aquatic Geochemistry 10

• Main Authors: Jennifer Lawson, Peter T. Doran, Fabien Kenig, David J. Des Marais, John C. Priscu
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2004
• Subjects: Bonney; Fryxell; Hoare; Lake Bonney; Lake Fryxell; Lake Hoare; McMurdo Dry Valleys; Taylor Valley; Antarc*; Antarctica
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.525.3723; http://tigger.uic.edu/~fkenig/Lawson et al 2004-Aquatic Chemistry.pdf

Abstract. The perennially ice-covered lakes in the McMurdo Dry Valleys, Antarctica, are part of the coldest and driest ecosystem on earth. To understand lacustrine carbon and nitrogen cycling in this end-member ecosystem, and to define paleolimnological proxies for ice-covered lakes, we measured the stable carbon and nitrogen isotopic composition of particulate organic matter (POM) and benthic organic matter (BOM) within the lakes of Taylor Valley. The d13C com-positions of seasonally ice-free edges of the lakes (moats) are enriched relative to under-ice organic matter. Thus, the organic carbon isotopic composition of buried sediments may be a proxy for sample position within the lake. In the moats, d13C values are governed by limited CO2 diffusion across benthic cyanobacterial cell membranes. During a high glacial melt (2001–2002) season, both d13CPOM and d 13CBOM in the moats were more depleted than during previous low melt years. We propose that this occurred in response to higher [CO2](aq) and/or reduced growth rates resulting from turbidity-induced light limitation. Though moats and under-ice environ-ments are usually poorly connected, during the 2001–2002 season, the enrichment of the d13CPOM values at 6 m depth in the stream-proximal sites relative to deep-profile sites implies enhanced connectivity between these environments. The d13C compositions of BOM and POM profiles in Lake Hoare and Lake Fryxell indicate that these lakes are dominated by benthic productivity. In contrast, in Lake Bonney, the similarity of the d13C values of BOM and POM indicates the pelagic component dominance in the carbon cycle. Key words: carbon stable isotope, nitrogen stable isotope, organic matter, limnology, Antarctica, dry valleys, Taylor Valley 1.