Supersaturated N₂O in a Perennially Ice-Covered Antarctic Lake: Molecular and Stable Isotopic Evidence for a Biogeochemical Relict

• Published in: Limnology and oceanography 2008-11, Vol.53 (6), p.2439-2450
• Main Authors: Priscu, John C., Christner, Brent C., Dore, John E., Westley, Marian B., Popp, Brian N., Casciotti, Karen L., Lyons, W. Berry
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Antarctic regions; Bacteria; Biological and medical sciences; Chemical composition; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fresh water; Fresh water ecosystems; Fundamental and applied biological sciences. Psychology; Geochemistry; Hydrology; Hydrology. Hydrogeology; Ice; Lakes; Mineralogy; Nitrification; Nitrogen; Nitrous oxide; Oxygen; Silicates; Synecology; Water geochemistry
• ISSN: 0024-3590; 1939-5590
• DOI: 10.4319/lo.2008.53.6.2439

The east lobe of Lake Bonney, a permanently ice-covered lake in the McMurdo Dry Valleys, Antarctica, has a mid-depth maximum N₂O concentration of 43.3 micromol N L⁻¹ (>700,000% saturation with respect to air), representing one of the highest concentrations reported for a natural aquatic system.¹⁵N and Oδ¹⁸O measurements indicate that this is the most isotopically depleted N₂O yet observed in a natural environment (minimum δ¹⁵N-N₂O of -79.6‰ vs. air-N₂; minimum $\delta ^{18} {\rm{O - N}}_2 {\rm{O}}$ of -4.7‰ vs. Vienna standard mean ocean water), providing new end points for these parameters in natural systems. The extremely depleted nitrogen and oxygen isotopes, together with nitrogen isotopic isomer data for N₂O, imply that most of the N₂O was produced via incomplete nitrification and has undergone virtually no subsequent consumption. However, molecular evidence provides little support for metabolically active nitrifying populations at depths where the maximal N₂O concentrations occur and contemporary biogeochemical reactions cannot explain the extreme excesses of N₂O in Lake Bonney. The gas appears to be a legacy of past biogeochemical conditions within the lake, and in the absence of a significant sink and the presence of a highly stable water column, gradients in N₂O produced by past microbial activity could persist in the cold saline waters of Lake Bonney for >1⁴0 years.