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| Titel |
How significant is submarine groundwater discharge and its associated dissolved inorganic carbon in a river-dominated shelf system? |
| VerfasserIn |
Q. Liu, M. Dai, W. Chen, C.-A. Huh, G. Wang, Q. Li, M. A. Charette |
| 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. 5 ; Nr. 9, no. 5 (2012-05-22), S.1777-1795 |
| Datensatznummer |
250007029
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| Publikation (Nr.) |
 copernicus.org/bg-9-1777-2012.pdf |
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| Zusammenfassung |
| In order to assess the role of submarine groundwater discharge (SGD) and its
impact on the carbonate system on the northern South China Sea (NSCS) shelf,
we measured seawater concentrations of four radium isotopes
223,224,226,228Ra along with carbonate system parameters in June–July,
2008. Complementary groundwater sampling was conducted in coastal areas in
December 2008 and October 2010 to constrain the groundwater end-members. The
distribution of Ra isotopes in the NSCS was largely controlled by the Pearl
River plume and coastal upwelling. Long-lived Ra isotopes (228Ra and
226Ra) were enriched in the river plume but low in the offshore surface
water and subsurface water/upwelling zone. In contrast, short-lived Ra
isotopes (224Ra and 223Ra) were elevated in the subsurface
water/upwelling zone as well as in the river plume but depleted in the
offshore surface water. In order to quantify SGD, we adopted two independent
mathematical approaches. Using a three end-member mixing model with total
alkalinity (TAlk) and Ra isotopes, we derived a SGD flux into the NSCS shelf
of 2.3–3.7 × 108 m3 day−1. Our second approach
involved a simple mass balance of 228Ra and 226Ra and resulted in
a first order but consistent SGD flux estimate of
2.2–3.7 × 108 m3 day−1. These fluxes were equivalent to 12–21 % of the Pearl
River discharge, but the source of the SGD was mostly recirculated seawater.
Despite the relatively small SGD volume flow compared to the river, the
associated material fluxes were substantial given their elevated
concentrations of dissolved inorganic solutes. In this case, dissolved
inorganic carbon (DIC) flux through SGD was
153–347 × 109 mol yr−1, or ~23–53 % of the riverine DIC export flux. Our
estimates of the groundwater-derived phosphate flux ranged 3–68 × 107 mol yr−1, which may be responsible for new production on the
shelf up to 0.3–6.3 mmol C m−2 d−1. This rate of new production
would at most consume 11 % of the DIC contribution delivered by SGD.
Hence, SGD may play an important role in the carbon balance over the NSCS
shelf. |
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