HR: 1340h
AN: OS43B-1241    [Abstracts]
TI: Enrichment of nitrous oxide in water column of Bering sea and Chukchi sea
AU: * Hirota, A
EM: akinari@mail.sci.hokudai.ac.jp
AF: Hokkaido Univ., N10-W8 Kita-ku, Sapporo, 060-0810, Japan
AU: Ijiri, A
EM: ijiri@jamstec.go.jp
AF: Hokkaido Univ., N10-W8 Kita-ku, Sapporo, 060-0810, Japan
AU: Komatsu, D D
EM: damboo@mail.sci.hokudai.ac.jp
AF: Hokkaido Univ., N10-W8 Kita-ku, Sapporo, 060-0810, Japan
AU: Ohkubo, S B
AF: Hokkaido Univ., N10-W8 Kita-ku, Sapporo, 060-0810, Japan
AU: Nakagawa, F
EM: fumiko-nakagawa@mail.sci.hokudai.ac.jp
AF: Hokkaido Univ., N10-W8 Kita-ku, Sapporo, 060-0810, Japan
AU: Tsunogai, U
EM: urumu@mail.sci.hokudai.ac.jp
AF: Hokkaido Univ., N10-W8 Kita-ku, Sapporo, 060-0810, Japan
AB: While dissolved N2O is close to equilibrium with the atmosphere at surface in wide area of open ocean, significant enrichment were found in the upwelling region having pronounced oxygen-depleted water at subsurface, such as Arabian sea and off northern Chile. Both Bering sea and Chukchi sea area, fully oxygenated in the water column, have been characterized by low DIN/DIP, probably caused by denitrification in the sediment (e.g. Rowe and Phoel, 1992). Because N2O is a intermediate product of denitrification, such DIN decomposition can produce N2O in the area. To test this hypothesis, samples of both sea water and pore water were collected from 23 sites in the area to determine both concentrations and stable isotopic compositions of N2O (δ15N and δ18O), during R/V Mirai (JAMSTEC) MR06-04 cruise. We found significant accumulation of dissolved N2O in both surface and subsurface water column shallower than 50m, with concentrations up to 25.1nM. The annual emission rates of N2O to the atmosphere can be estimated to be 0.06 - 0.36 Tg N yr-1 in the area. It turns out that the N2O enriched water mass can be characterized by low DIN/DIP ratios. Furthermore, the accumulated excess N2O can be characterized by both 15N-depletion and 18O-enrichment relative to atmospheric N2O. It is difficult to assume nitrification in the water column for the source of the excess N2O. We conclude that the excess N2O in both Bering sea and Chukchi sea had been produced through denitrification in the sediment.
DE: 4825 Geochemistry
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting