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Supersaturated N2O in a perennially ice‐covered Antarctic lake: Molecular and stable isotopic evidence for a biogeochemical relict
Author(s) -
Priscu John C.,
Christner Brent C.,
Dore John E.,
Popp Brian N.,
Casciotti Karen L.,
Lyons W. Berry
Publication year - 2008
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2008.53.6.2439
Subject(s) - biogeochemical cycle , water column , nitrification , nitrogen , sink (geography) , nitrate , isotopes of nitrogen , oceanography , environmental chemistry , supersaturation , biogeochemistry , geology , chemistry , ecology , biology , geography , organic chemistry , cartography
The east lobe of Lake Bonney, a permanently ice‐covered lake in the McMurdo Dry Valleys, Antarctica, has a mid‐depth maximum N 2 O concentration of 43.3 [mol N L ‐1 (>700,000% saturation with respect to air), representing one of the highest concentrations reported for a natural aquatic system. δ 15 N and δ 18 O measurements indicate that this is the most isotopically depleted N 2 O yet observed in a natural environment (minimum δ 15 N‐N 2 O of ‐79.6‰ vs. air‐N 2 ; minimum δ 18 O‐N 2 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 N 2 O, imply that most of the N 2 O 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 N 2 O concentrations occur and contemporary biogeochemical reactions cannot explain the extreme excesses of N 2 O 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 N 2 O produced by past microbial activity could persist in the cold saline waters of Lake Bonney for >10 4 years.