CS08 Biogeochemical Cycles
Date: Tuesday, June 11, 2002
Location: Poster Session - VCC
 
Tanaka Tomoyuki, FORSGC-IARC, Univ. Alaska Fairbanks, Fairbanks, USA, tomo@iarc.uaf.edu
Noriyuki, T, , FORSGC-IARC, Univ. Alaska Fairbanks, Fairbanks, USA, norit@ees.hokudai.ac.jp
KyungHoon, S, , FORSGC-IARC, Univ. Alaska Fairbanks, Fairbanks, USA, shinkh@iarc.uaf.edu
 
Nitrogen isotopic composition of nitrate in the Chukchi and Beaufort Seas
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In order to understand potential source of nitrate maximum on continental shelves and their slopes in the Chukchi and Beaufort Seas, nitrogen isotopic composition of the nitrate observed by R/V Mirai in October 2000 were used as a tracer. Substantial enrichment of delta 15N (~6 permil) were observed at 100 to 200m depth at all stations, while delta 15N values of nitrate in deeper water (>250m) were ~3.5 permil. The subsurface delta 15N maximum corresponds to a nitrate and an AOU maximum. Based on the relationship between the nitrate and the AOU in the subsurface water, preformed nitrate concentration is calculated to be ~10 uM. When we assumed nitrogen isotopic ratio in the new nitrate is 3.5 permil, the nitrogen isotopic ratio in the preformed nitrate of nitrate maximum could be estimated by an isotope-mass balance equation to be 7 permil. This result suggested that nitrogen isotope in the preformed nitrate is contributed from the Pacific water in winter season. The implication of these results on the nitrogen isotope will be discussed.