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| Titel |
Formation and maintenance of high-nitrate, low pH layers in the eastern Indian Ocean and the role of nitrogen fixation |
| VerfasserIn |
A. M. Waite, V. Rossi, M. Roughan, B. Tilbrook, P. A. Thompson, M. Feng, A. S. J. Wyatt, E. J. Raes |
| 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 ; 10, no. 8 ; Nr. 10, no. 8 (2013-08-28), S.5691-5702 |
| Datensatznummer |
250085313
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| Publikation (Nr.) |
 copernicus.org/bg-10-5691-2013.pdf |
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| Zusammenfassung |
| We investigated the biogeochemistry of low dissolved oxygen high-nitrate
(LDOHN) layers forming against the backdrop of several interleaving regional
water masses in the eastern Indian Ocean, off northwest Australia adjacent
to Ningaloo Reef. These water masses, including the forming Leeuwin Current,
have been shown directly to impact the ecological function of Ningaloo Reef
and other iconic coastal habitats downstream. Our results indicate that
LDOHN layers are formed from multiple subduction events of the Eastern Gyral
Current beneath the Leeuwin Current (LC); the LC originates from both the
Indonesian Throughflow and tropical Indian Ocean. Density differences of up
to 0.025 kg m−3 between the Eastern Gyral Current and the Leeuwin
Current produce sharp gradients that can trap high concentrations of
particles (measured as low transmission) along the density interfaces. The
oxidation of the trapped particulate matter results in local depletion of
dissolved oxygen and regeneration of dissolved nitrate (nitrification). We
document an associated increase in total dissolved carbon dioxide, which
lowers the seawater pH by 0.04 units. Based on isotopic measurements
(δ15N and δ18O) of dissolved nitrate, we determine
that ~ 40–100% of the nitrate found in LDOHN layers
is likely to originate from nitrogen fixation, and that, regionally, the
importance of N-fixation in contributing to LDOHN layers is likely to be
highest at the surface and offshore. |
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