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| Titel |
Air–sea exchange of CO2 at a Northern California coastal site along the California Current upwelling system |
| VerfasserIn |
H. Ikawa, I. Faloona, J. Kochendorfer, Paw U. K. T., W. C. Oechel |
| 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. 7 ; Nr. 10, no. 7 (2013-07-01), S.4419-4432 |
| Datensatznummer |
250018321
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| Publikation (Nr.) |
 copernicus.org/bg-10-4419-2013.pdf |
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| Zusammenfassung |
| It is not well understood whether coastal upwelling is a net CO2 source
to the atmosphere or a net CO2 sink to the ocean due to high temporal
variability of air–sea CO2 exchange (CO2 flux) in coastal upwelling
zones. Upwelling transports heterotrophic, CO2 enriched water to the
surface and releases CO2 to the atmosphere, whereas the presence of
nutrient-rich water at the surface supports high primary production and
atmospheric CO2 uptake. To quantify the effects of upwelling on CO2
flux, we measured CO2 flux at a coastal upwelling site off of Bodega
Bay, California, with the eddy covariance technique during the summer of 2007
and the fall of 2008, and the bulk method with partial pressure of CO2
of surface water (pCO2) data from November 2010 to July 2011.
Variations in sea surface temperatures (SST) and alongshore wind velocity
suggest that the measurement period in 2007 coincided with a typical early
summer upwelling period and the measurement period in 2008 was during a
typical fall relaxation period. A strong source of CO2
(~ 1.5 ± 7 SD (standard deviation) g C m−2 day−1)
from the ocean to the atmosphere during the upwelling period was concurrent
with high salinity, low SST, and low chlorophyll density. In contrast, a weak
source of CO2 flux (~ 0.2 ± 3 SD g C m−2 day−1)
was observed with low salinity, high SST and high chlorophyll density during
the relaxation period. Similarly, the sink and source balance of CO2
flux was highly related to salinity and SST during the pCO2
measurement periods; high salinity and low SST corresponded to high
pCO2, and vice versa. We estimated that the coastal area off Bodega
Bay was likely an overall source of CO2 to the atmosphere based on the
following conclusions: (1) the overall CO2 flux estimated from both eddy
covariance and pCO2 measurements showed a source of CO2; (2)
although the relaxation period during the 2008 measurements were favorable to
CO2 uptake, CO2 flux during this period was still a slight source;
(3) salinity and SST were found to be good predictors of the CO2 flux
for both eddy covariance and pCO2 measurements, and 99% of the
historical SST and salinity data available between 1988 and 2011 fell within
the range of our observations in May–June 2007, August–September 2008 and
November 2010–July~2011, which indicates that our data set was
representative of the annual variations in the sea state. Based on the
developed relationship between pCO2, SST and salinity, the study area
between 1988 and 2011 was estimated to be an annual source of CO2 of
~ 35 mol C m−2 yr−1. The peak monthly CO2 flux of
~ 7 mol C m−2 month−1 accounted for almost 30% of the
dissolved inorganic carbon in the surface mixed layer. |
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