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| Titel |
Past and present of sediment and carbon biogeochemical cycling models |
| VerfasserIn |
F. T. Mackenzie, A. Lerman, A. J. Andersson |
| 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 ; 1, no. 1 ; Nr. 1, no. 1 (2004-08-20), S.11-32 |
| Datensatznummer |
250000069
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| Publikation (Nr.) |
 copernicus.org/bg-1-11-2004.pdf |
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| Zusammenfassung |
| The global carbon cycle is part of the much more extensive sedimentary cycle
that involves large masses of carbon in the Earth's inner and outer spheres.
Studies of the carbon cycle generally followed a progression in knowledge of
the natural biological, then chemical, and finally geological processes
involved, culminating in a more or less integrated picture of the
biogeochemical carbon cycle by the 1920s. However, knowledge of the ocean's
carbon cycle behavior has only within the last few decades progressed to a
stage where meaningful discussion of carbon processes on an annual to
millennial time scale can take place. In geologically older and
pre-industrial time, the ocean was generally a net source of CO2 emissions to the atmosphere owing to the mineralization of land-derived
organic matter in addition to that produced in situ and to the process of
CaCO3 precipitation. Due to rising atmospheric CO2 concentrations
because of fossil fuel combustion and land use changes, the direction of the
air-sea CO2 flux has reversed, leading to the ocean as a whole being a
net sink of anthropogenic CO2. The present thickness of the surface
ocean layer, where part of the anthropogenic CO2 emissions are stored,
is estimated as of the order of a few hundred meters. The oceanic coastal
zone net air-sea CO2 exchange flux has also probably changed during
industrial time. Model projections indicate that in pre-industrial times,
the coastal zone may have been net heterotrophic, releasing CO2 to the
atmosphere from the imbalance between gross photosynthesis and total
respiration. This, coupled with extensive CaCO3 precipitation in
coastal zone environments, led to a net flux of CO2 out of the system.
During industrial time the coastal zone ocean has tended to reverse its
trophic status toward a non-steady state situation of net autotrophy,
resulting in net uptake of anthropogenic CO2 and storage of carbon in
the coastal ocean, despite the significant calcification that still occurs
in this region. Furthermore, evidence from the inorganic carbon cycle
indicates that deposition and net storage of CaCO3 in sediments exceed
inflow of inorganic carbon from land and produce CO2 emissions to the
atmosphere. In the shallow-water coastal zone, increase in atmospheric
CO2 during the last 300 years of industrial time may have reduced the
rate of calcification, and continuation of this trend is an issue of serious
environmental concern in the global carbon balance. |
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