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| Titel |
Methods to evaluate CaCO3 cycle modules in coupled global biogeochemical ocean models |
| VerfasserIn |
W. Koeve, O. Duteil, A. Oschlies, P. Kähler, J. Segschneider |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 7, no. 5 ; Nr. 7, no. 5 (2014-10-16), S.2393-2408 |
| Datensatznummer |
250115739
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| Publikation (Nr.) |
 copernicus.org/gmd-7-2393-2014.pdf |
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| Zusammenfassung |
| The marine CaCO3 cycle is an important component of the
oceanic carbon system and directly affects the cycling of natural and
the uptake of anthropogenic carbon. In numerical models of the marine
carbon cycle, the CaCO3 cycle component is often evaluated
against the observed distribution of alkalinity. Alkalinity varies in
response to the formation and remineralization of CaCO3 and
organic matter. However, it also has a large conservative component,
which may strongly be affected by a deficient representation of ocean
physics (circulation, evaporation, and precipitation) in models. Here
we apply a global ocean biogeochemical model run into preindustrial
steady state featuring a number of idealized tracers, explicitly
capturing the model's CaCO3 dissolution, organic matter
remineralization, and various preformed properties (alkalinity,
oxygen, phosphate). We compare the suitability of a variety of
measures related to the CaCO3 cycle, including alkalinity
(TA), potential alkalinity and TA*, the latter being
a measure of the time-integrated imprint of CaCO3 dissolution
in the ocean. TA* can be diagnosed from any data set of TA,
temperature, salinity, oxygen and phosphate. We demonstrate the
sensitivity of total and potential alkalinity to the differences in
model and ocean physics, which disqualifies them as accurate measures
of biogeochemical processes. We show that an explicit treatment of
preformed alkalinity (TA0) is necessary and possible. In our model
simulations we implement explicit model tracers of TA0 and
TA*. We find that the difference between modelled true
TA* and diagnosed TA* was below 10%
(25%) in 73% (81%) of the ocean's volume. In the
Pacific (and Indian) Oceans the RMSE of A* is below
3 (4) mmol TA m−3, even when using a global rather than
regional algorithms to estimate preformed alkalinity. Errors in the
Atlantic Ocean are significantly larger and potential improvements of
TA0 estimation are discussed. Applying the TA* approach
to the output of three state-of-the-art ocean carbon cycle models, we
demonstrate the advantage of explicitly taking preformed alkalinity
into account for separating the effects of biogeochemical processes
and circulation on the distribution of alkalinity. In particular, we
suggest to use the TA* approach for CaCO3 cycle
model evaluation. |
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