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| Titel |
Natural ocean carbon cycle sensitivity to parameterizations of the recycling in a climate model |
| VerfasserIn |
A. Romanou, J. Romanski, W. W. Gregg |
| 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 ; 11, no. 4 ; Nr. 11, no. 4 (2014-02-26), S.1137-1154 |
| Datensatznummer |
250117247
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| Publikation (Nr.) |
 copernicus.org/bg-11-1137-2014.pdf |
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| Zusammenfassung |
| Sensitivities of the oceanic biological pump within the GISS (Goddard Institute for Space Studies ) climate modeling
system are explored here. Results are presented from twin control simulations
of the air–sea CO2 gas exchange using two different ocean models coupled
to the same atmosphere. The two ocean models (Russell ocean model and Hybrid
Coordinate Ocean Model, HYCOM) use different vertical coordinate systems, and
therefore different representations of column physics. Both variants of the
GISS climate model are coupled to the same ocean biogeochemistry module (the
NASA Ocean Biogeochemistry Model, NOBM), which computes prognostic
distributions for biotic and abiotic fields that influence the air–sea flux
of CO2 and the deep ocean carbon transport and storage. In particular, the
model differences due to remineralization rate changes are compared to
differences attributed to physical processes modeled differently in the two
ocean models such as ventilation, mixing, eddy stirring and vertical
advection. GISSEH(GISSER) is found to underestimate mixed layer depth
compared to observations by about 55% (10%) in the Southern Ocean
and overestimate it by about 17% (underestimate by 2%) in the
northern high latitudes. Everywhere else in the global ocean, the two models
underestimate the surface mixing by about 12–34%, which prevents deep
nutrients from reaching the surface and promoting primary production there.
Consequently, carbon export is reduced because of reduced production at the
surface. Furthermore, carbon export is particularly sensitive to
remineralization rate changes in the frontal regions of the subtropical gyres
and at the Equator and this sensitivity in the model is much higher than the
sensitivity to physical processes such as vertical mixing, vertical advection
and mesoscale eddy transport. At depth, GISSER, which has a significant warm
bias, remineralizes nutrients and carbon faster thereby producing more nutrients and
carbon at depth, which eventually resurfaces with the global thermohaline
circulation especially in the Southern Ocean. Because of the reduced primary
production and carbon export in GISSEH compared to GISSER, the biological
pump efficiency, i.e., the ratio of primary production and carbon export at
75 m, is half in the GISSEH of that in GISSER, The Southern Ocean emerges as
a key region where the CO2 flux is as sensitive to biological
parameterizations as it is to physical parameterizations. The fidelity of
ocean mixing in the Southern Ocean compared to observations is shown to be a
good indicator of the magnitude of the biological pump efficiency regardless
of physical model choice. |
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