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| Titel |
A neural network-based estimate of the seasonal to inter-annual variability of the Atlantic Ocean carbon sink |
| VerfasserIn |
P. Landschützer, N. Gruber, D. C. E. Bakker, U. Schuster, S. Nakaoka, M. R. Payne, T. P. Sasse, J. Zeng |
| 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 ; 10, no. 11 ; Nr. 10, no. 11 (2013-11-29), S.7793-7815 |
| Datensatznummer |
250085449
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| Publikation (Nr.) |
 copernicus.org/bg-10-7793-2013.pdf |
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| Zusammenfassung |
| The Atlantic Ocean is one of the most important sinks for atmospheric carbon
dioxide (CO2), but this sink has been shown to vary substantially in
time. Here we use surface ocean CO2 observations to estimate this sink
and the temporal variability from 1998 through 2007 in the Atlantic Ocean. We
benefit from (i) a continuous improvement of the observations, i.e. the
Surface Ocean CO2 Atlas (SOCAT) v1.5 database and (ii) a newly developed
technique to interpolate the observations in space and time. In particular,
we use a two-step neural network approach to reconstruct basin-wide monthly
maps of the sea surface partial pressure of CO2 (pCO2) at a
resolution of 1° × 1°. From those, we compute the
air–sea CO2 flux maps using a standard gas exchange parameterization and
high-resolution wind speeds. The neural networks fit the observed pCO2
data with a root mean square error (RMSE) of about 10 μatm and with
almost no bias. A check against independent time-series data and new data
from SOCAT v2 reveals a larger RMSE of 22.8 μatm for the entire
Atlantic Ocean, which decreases to 16.3 μatm for data south of
40° N. We estimate a decadal mean uptake flux of
−0.45 ± 0.15 Pg C yr−1 for the Atlantic between
44° S and 79° N, representing the sum of a strong uptake
north of 18° N (−0.39 ± 0.10 Pg C yr−1), outgassing
in the tropics (18° S–18° N,
0.11 ± 0.07 Pg C yr−1), and uptake in the subtropical/temperate
South Atlantic south of 18° S
(−0.16 ± 0.06 Pg C yr−1), consistent with recent studies. The
strongest seasonal variability of the CO2 flux occurs in the
temperature-driven subtropical North Atlantic, with uptake in winter and
outgassing in summer. The seasonal cycle is antiphased in the subpolar
latitudes relative to the subtropics largely as a result of the biologically
driven winter-to-summer drawdown of CO2. Over the 10 yr analysis period
(1998 through 2007), sea surface pCO2 increased faster than that of
the atmosphere in large areas poleward of 40° N, while in other
regions of the North Atlantic the sea surface pCO2 increased at a
slower rate, resulting in a barely changing Atlantic carbon sink north of the
Equator (−0.01 ± 0.02 Pg C yr−1 decade−1). Surface
ocean pCO2 increased at a slower rate relative to atmospheric CO2
over most of the Atlantic south of the Equator, leading to a substantial
trend toward a stronger CO2 sink for the entire South Atlantic
(−0.14 ± 0.02 Pg C yr−1 decade−1). In contrast to the
10 yr trends, the Atlantic Ocean carbon sink varies relatively little on
inter-annual timescales (±0.04 Pg C yr−1; 1 σ). |
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