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| Titel |
Seasonal shifts in the contributions of the Changjiang River and the Kuroshio Current to nitrate dynamics in the continental shelf of the northern East China Sea based on a nitrate dual isotopic composition approach |
| VerfasserIn |
Y. Umezawa, A. Yamaguchi, J. Ishizaka, T. Hasegawa, C. Yoshimizu, I. Tayasu, H. Yoshimura, Y. Morii, T. Aoshima, N. Yamawaki |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 4 ; Nr. 11, no. 4 (2014-02-27), S.1297-1317 |
| Datensatznummer |
250117254
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| Publikation (Nr.) |
 copernicus.org/bg-11-1297-2014.pdf |
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| Zusammenfassung |
| The northern East China Sea (ECS) serves as a spawning and nursery ground
for many species of fish and squid. To clarify the basis of the food web in
the northern ECS, we examined the nitrate (NO3) dynamics along four
latitudinal transects based on stable nitrogen and oxygen isotopes of
NO3 (δ15NNO3 and δ18ONO3) and
temperature–salinity dynamics in both winter (February 2009) and summer
(July 2009 and July 2011). The δ15NNO3 and δ18ONO3, which were distinctly different among the potential
NO3 sources, were useful for clarifying NO3 sources and its actual
usage by phytoplankton. In winter, Kuroshio Subsurface Water (KSSW) and the
Yellow Sea Mixed Water (YSMW) predominantly contributed to NO3
distributed in the shelf water. In the surface water of the Okinawa Trough,
NO3 from the KSSW, along with a temperature increase caused by an
intrusion of Kuroshio Surface Water (KSW), seemed to stimulate phytoplankton
growth. In summer, Changjiang Diluted Water (CDW), Yellow Sea Cold Water
Mass (YSCWM), and KSSW affected the distribution and abundance of NO3
in the northern ECS, depending on precipitation in the Changjiang drainage
basin and the development of the YSCWM in the shelf bottom water. Although
isotopic fractionation during NO3 uptake by phytoplankton seemed to
drastically increase δ15NNO3 and δ18ONO3
in summer, relatively light nitrate with δ15NNO3 lower
than expected from this fractionation effect might be explained by
contribution of atmospheric nitrogen and/or nitrification to NO3
dynamics in the surface and subsurface layers. If the latter were a dominant
process, this would imply a tightly coupled nitrogen cycle in the shelf
water of the northern ECS. |
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