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| Titel |
Neural network-based estimates of Southern Ocean net community production from in situ O2 / Ar and satellite observation: a methodological study |
| VerfasserIn |
C.-H. Chang, N. C. Johnson, N. Cassar |
| 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. 12 ; Nr. 11, no. 12 (2014-06-20), S.3279-3297 |
| Datensatznummer |
250117473
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| Publikation (Nr.) |
 copernicus.org/bg-11-3279-2014.pdf |
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| Zusammenfassung |
Southern Ocean organic carbon export plays an important role in the global
carbon cycle, yet its basin-scale climatology and variability are uncertain
due to limited coverage of in situ observations. In this study, a neural network
approach based on the self-organizing map (SOM) is adopted to construct
weekly gridded (1° × 1°) maps of organic carbon export for
the Southern Ocean from 1998 to 2009. The SOM is trained with in situ measurements
of O2 / Ar-derived net community production (NCP) that are tightly linked
to the carbon export in the mixed layer on timescales of one to two weeks and
with six potential NCP predictors: photosynthetically available radiation (PAR),
particulate organic carbon (POC), chlorophyll (Chl), sea surface temperature
(SST), sea surface height (SSH), and mixed layer depth (MLD). This
nonparametric approach is based entirely on the observed statistical
relationships between NCP and the predictors and, therefore, is strongly
constrained by observations.
A thorough cross-validation yields three retained NCP predictors, Chl, PAR,
and MLD. Our constructed NCP is further validated by good agreement with
previously published, independent in situ derived NCP of weekly or longer
temporal resolution through real-time and climatological comparisons at
various sampling sites. The resulting November–March NCP climatology reveals
a pronounced zonal band of high NCP roughly following the Subtropical Front
in the Atlantic, Indian, and western Pacific sectors, and turns southeastward
shortly after the dateline. Other regions of elevated NCP include the
upwelling zones off Chile and Namibia, the Patagonian Shelf, the Antarctic coast, and
areas surrounding the Islands of Kerguelen, South Georgia, and Crozet. This
basin-scale NCP climatology closely resembles that of the satellite POC field
and observed air–sea CO2 flux. The long-term mean area-integrated NCP
south of 50° S from our dataset, 17.9 mmol C m−2 d−1,
falls within the range of 8.3 to 24 mmol C m−2 d−1 from other
model estimates. A broad agreement is found in the basin-wide NCP climatology
among various models but with significant spatial variations, particularly in
the Patagonian Shelf. Our approach provides a comprehensive view of the
Southern Ocean NCP climatology and a potential opportunity to further
investigate interannual and intraseasonal variability. |
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