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| Titel |
A strong CO2 sink enhanced by eutrophication in a tropical coastal embayment (Guanabara Bay, Rio de Janeiro, Brazil) |
| VerfasserIn |
L. C. Jr. Cotovicz, B. A. Knoppers, N. Brandini, S. J. Costa Santos, G. Abril |
| 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 ; 12, no. 20 ; Nr. 12, no. 20 (2015-10-27), S.6125-6146 |
| Datensatznummer |
250118141
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| Publikation (Nr.) |
 copernicus.org/bg-12-6125-2015.pdf |
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| Zusammenfassung |
| In contrast to its small surface area,
the coastal zone plays a disproportionate role in the global carbon cycle.
Carbon production, transformation, emission and burial rates at the
land–ocean interface are significant at the global scale but still poorly
known, especially in tropical regions. Surface water pCO2 and
ancillary parameters were monitored during nine field campaigns between
April 2013 and April 2014 in Guanabara Bay, a tropical eutrophic to
hypertrophic semi-enclosed estuarine embayment surrounded by the city of Rio
de Janeiro, southeast Brazil. Water pCO2 varied between 22 and 3715 ppmv in
the bay, showing spatial, diurnal and seasonal trends that mirrored those of
dissolved oxygen (DO) and chlorophyll a (Chl a). Marked pCO2
undersaturation was prevalent in the shallow, confined and thermally
stratified waters of the upper bay, whereas pCO2 oversaturation was
restricted to sites close to the small river mouths and small sewage
channels, which covered only 10 % of the bay's area. Substantial daily
variations in pCO2 (up to 395 ppmv between dawn and dusk) were also
registered and could be integrated temporally and spatially for the
establishment of net diurnal, seasonal and annual CO2 fluxes. In
contrast to other estuaries worldwide, Guanabara Bay behaved as a net sink of
atmospheric CO2, a property enhanced by the concomitant effects of
strong radiation intensity, thermal stratification, and high availability of
nutrients, which promotes phytoplankton development and net autotrophy. The
calculated CO2 fluxes for Guanabara Bay ranged between −9.6 and
−18.3 mol C m−2 yr−1, of the same order of magnitude as the
organic carbon burial and organic carbon inputs from the watershed. The
positive and high net community production (52.1 mol C m−2 yr−1)
confirms the high carbon production in the bay. This autotrophic metabolism is apparently
enhanced by eutrophication. Our results show that global CO2
budgetary assertions still lack information on tropical, marine-dominated
estuarine systems, which are affected by thermal stratification and
eutrophication and behave specifically with respect to atmospheric CO2. |
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