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| Titel |
Assimilating water column and satellite data for marine export production estimation |
| VerfasserIn |
X. Yao, R. Schlitzer |
| 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 ; 6, no. 5 ; Nr. 6, no. 5 (2013-09-16), S.1575-1590 |
| Datensatznummer |
250084993
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| Publikation (Nr.) |
 copernicus.org/gmd-6-1575-2013.pdf |
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| Zusammenfassung |
| Recent advances in satellite retrieval methodology now allow for estimation of
particular organic carbon (POC) concentration in ocean surface waters
directly from satellite-based optical data. Because of the good coverage,
these data reveal small-scale spatial and temporal concentration gradients
and document the evolution of surface water POC as well as the underlying
driving biogeochemical processes throughout the seasons. Water column
nutrient data also reveal biogeochemical activity. However, because of the
scarcity of data, the deduction of temporal changes of particle production
and export is not possible in most parts of the ocean. Here we present
first results from a new study combining both data streams, thereby
exploiting the high spatio-temporal resolution of surface POC concentrations
from satellite optical sensors with water column nutrient data having
sparser coverage but providing information throughout the entire water
column. We use a medium-resolution global model with steady-state 3-D
circulation that has been optimized by fitting to a large number of
hydrographic parameters and tracers, including CFCs and natural radiocarbon.
Production and export of POC is allowed to vary monthly, and the magnitudes
of the monthly export fluxes are determined by fitting the model to
satellite POC data as well as water column nutrient data using the adjoint
method. Two cases have been investigated: (1) the production rate of POC is
set to be proportional to export production (EP) and the seasonal changes are
assumed sinusoidal (meridionally varying amplitude and phase), and (2) the
POC production rate is linked to primary production rates (literature). Both
cases were run with the same initial state and model settings, and show
total cost function decreases of 12 and 95%, respectively. The POC misfit
term alone decreased by 75 and 99.8%. The integrated annual global POC
exports of the two cases are 9.9 and 12.3 Gt C yr−1, respectively.
Overall, the remaining POC and phosphate misfits of both solutions are
considered too large, and the difference fields still exhibit significant
systematic geographical patterns. This indicates that the present model runs
are too simplistic and do not fully explain the data. Further, more refined
model setups are needed. |
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