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| Titel |
CO2 maximum in the oxygen minimum zone (OMZ) |
| VerfasserIn |
A. Paulmier, D. Ruiz-Pino, V. Garçon |
| 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 ; 8, no. 2 ; Nr. 8, no. 2 (2011-02-07), S.239-252 |
| Datensatznummer |
250005438
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| Publikation (Nr.) |
 copernicus.org/bg-8-239-2011.pdf |
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| Zusammenfassung |
Oxygen minimum zones (OMZs), known as suboxic layers which are mainly localized in the
Eastern Boundary Upwelling Systems, have been expanding since the 20th "high
CO2" century, probably due to global warming. OMZs are also known to
significantly contribute to the oceanic production of N2O, a greenhouse
gas (GHG) more efficient than CO2. However, the contribution of the
OMZs on the oceanic sources and sinks budget of CO2, the main GHG,
still remains to be established.
We present here the dissolved inorganic carbon (DIC) structure, associated
locally with the Chilean OMZ and globally with the main most intense OMZs
(O2<20 μmol kg−1) in the open ocean. To achieve this, we examine
simultaneous DIC and O2 data collected off Chile during 4 cruises
(2000–2002) and a monthly monitoring (2000–2001) in one of the shallowest
OMZs, along with international DIC and O2 databases and climatology for
other OMZs.
High DIC concentrations (>2225 μmol kg−1, up to 2350 μmol kg−1) have
been reported over the whole OMZ thickness, allowing the definition for all
studied OMZs a Carbon Maximum Zone (CMZ). Locally off Chile, the shallow
cores of the OMZ and CMZ are spatially and temporally collocated at 21° S, 30° S
and 36° S despite different cross-shore, long-shore and
seasonal configurations. Globally, the mean state of the main OMZs also
corresponds to the largest carbon reserves of the ocean in subsurface
waters. The CMZs-OMZs could then induce a positive feedback for the
atmosphere during upwelling activity, as potential direct local sources of
CO2. The CMZ paradoxically presents a slight "carbon deficit" in its
core (~10%), meaning a DIC increase from the oxygenated ocean to
the OMZ lower than the corresponding O2 decrease (assuming classical
C/O molar ratios). This "carbon deficit" would be related to regional
thermal mechanisms affecting faster O2 than DIC (due to the carbonate
buffer effect) and occurring upstream in warm waters (e.g., in the Equatorial
Divergence), where the CMZ-OMZ core originates. The "carbon deficit" in
the CMZ core would be mainly compensated locally at the oxycline, by a
"carbon excess" induced by a specific remineralization. Indeed, a possible
co-existence of bacterial heterotrophic and autotrophic processes usually
occurring at different depths could stimulate an intense aerobic-anaerobic
remineralization, inducing the deviation of C/O molar ratios from the canonical
Redfield ratios. Further studies to confirm these results for all OMZs are
required to understand the OMZ effects on both climatic feedback mechanisms
and marine ecosystem perturbations. |
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