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| Titel |
Insignificant enhancement of export flux in the highly productive subtropical front, east of New Zealand: a high resolution study of particle export fluxes based on 234Th: 238U disequilibria |
| VerfasserIn |
K. Zhou, S. D. Nodder, M. Dai, J. A. Hall |
| 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 ; 9, no. 3 ; Nr. 9, no. 3 (2012-03-12), S.973-992 |
| Datensatznummer |
250006838
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| Publikation (Nr.) |
 copernicus.org/bg-9-973-2012.pdf |
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| Zusammenfassung |
| We evaluated the export fluxes of Particulate Organic Carbon (POC) in the
Subtropical Frontal zone (STF) of the SW Pacific sector of the Southern
Ocean. The site is characterized by enhanced primary productivity, which has
been suggested to be stimulated through so-called natural iron fertilization
processes where iron-depleted subantarctic water (SAW) mixes with
mesotrophic, iron-replete subtropical water (STW). We adopted the
small-volume 234Th method to achieve the highest possible spatial
sampling resolution in austral late autumn-early winter, May–June, 2008.
Inventories of chlorophyll-a, particulate 234Th and POC observed in the
upper 100 m were all elevated in the mid-salinity water type
(34.5 < S < 34.8), compared with low salinity waters (S < 34.5) which were
of SAW origin with high macronutrients and high (S > 34.8) salinity waters
which were of STW origin with low macronutrients. However, Steady-State
234Th fluxes were similar across the salinity gradient being, 25 ± 0.78
((1.5 ± 0.047) × 103) in the mid-salinity, and 29 ± 0.53
((1.8 ± 0.032) × 103) and 22 ± 1.1 Bq m−2 d−1
((1.3 ± 0.066) × 103 dpm m−2 d–1) in the
high and low salinity waters respectively. Bottle POC/Th ratios at the depth
of 100 m were used to convert 234Th fluxes into POC export fluxes. The derived
POC flux did not appear to be enhanced in mid-salinity waters where the
primary productivity was inferred to be the highest at the time of sampling,
with a flux of 11 ± 0.45 mmol C m−2 d−1, compared to
14 ± 0.39 mmol C m−2 d−1 in high salinity waters and
8.5 ± 0.66 mmol C m−2 d−1 in low salinity waters. This study thus implied
that natural iron fertilization does not necessarily lead to an enhancement
of POC export in STF regions. |
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