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| Titel |
Mismatch between observed and modeled trends in dissolved upper-ocean oxygen over the last 50 yr |
| VerfasserIn |
L. Stramma, A. Oschlies, S. Schmidtko |
| 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 ; 9, no. 10 ; Nr. 9, no. 10 (2012-10-22), S.4045-4057 |
| Datensatznummer |
250007337
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| Publikation (Nr.) |
 copernicus.org/bg-9-4045-2012.pdf |
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| Zusammenfassung |
| Observations and model runs indicate trends in dissolved oxygen (DO)
associated with current and ongoing global warming. However, a large-scale
observation-to-model comparison has been missing and is presented here. This
study presents a first global compilation of DO measurements covering the
last 50 yr. It shows declining upper-ocean DO levels in many regions,
especially the tropical oceans, whereas areas with increasing trends are
found in the subtropics and in some subpolar regions. For the Atlantic Ocean
south of 20° N, the DO history could even be extended back to about
70 yr, showing decreasing DO in the subtropical South Atlantic. The global
mean DO trend between 50° S and 50° N at 300 dbar for the
period 1960 to 2010 is –0.066 μmol kg−1 yr−1. Results
of a numerical biogeochemical Earth system model reveal that the magnitude of
the observed change is consistent with CO2-induced climate change.
However, the pattern correlation between simulated and observed patterns of
past DO change is negative, indicating that the model does not correctly
reproduce the processes responsible for observed regional oxygen changes in
the past 50 yr. A negative pattern correlation is also obtained for model
configurations with particularly low and particularly high diapycnal mixing,
for a configuration that assumes a CO2-induced enhancement of the
C : N ratios of exported organic matter and irrespective of whether
climatological or realistic winds from reanalysis products are used to force
the model. Depending on the model configuration the 300 dbar DO trend
between 50° S and 50° N is −0.027 to
–0.047 μmol kg−1 yr−1 for climatological wind
forcing, with a much larger range of –0.083 to
+0.027 μmol kg−1 yr−1 for different initializations of
sensitivity runs with reanalysis wind forcing. Although numerical models
reproduce the overall sign and, to some extent, magnitude of observed ocean
deoxygenation, this degree of realism does not necessarily apply to simulated
regional patterns and the representation of processes involved in their
generation. Further analysis of the processes that can explain the
discrepancies between observed and modeled DO trends is required to better
understand the climate sensitivity of oceanic oxygen fields and predict
potential DO changes in the future. |
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