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| Titel |
Spatial and temporal variability of the dimethylsulfide to chlorophyll ratio in the surface ocean: an assessment based on phytoplankton group dominance determined from space |
| VerfasserIn |
I. Masotti, S. Belviso, S. Alvain, J. E. Johnson, T. S. Bates, P. D. Tortell, N. Kasamatsu, M. Mongin, C. A. Marandino, E. S. Saltzman, C. Moulin |
| 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 ; 7, no. 10 ; Nr. 7, no. 10 (2010-10-20), S.3215-3237 |
| Datensatznummer |
250005020
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| Publikation (Nr.) |
 copernicus.org/bg-7-3215-2010.pdf |
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| Zusammenfassung |
| Dimethylsulfoniopropionate (DMSP) is produced in surface seawater by
phytoplankton. Phytoplankton culture experiments have shown that
nanoeucaryotes (NANO) display much higher mean DMSP-to-Carbon or
DMSP-to-Chlorophyll (Chl) ratios than Prochlorococcus (PRO), Synechococcus (SYN) or diatoms (DIAT).
Moreover, the DMSP-lyase activity of algae which cleaves DMSP into
dimethylsulfide (DMS) is even more group specific than DMSP itself.
Ship-based observations have shown at limited spatial scales, that sea
surface DMS-to-Chl ratios (DMS:Chl) are dependent on the composition of
phytoplankton groups. Here we use satellite remote sensing of Chl (from
SeaWiFS) and of Phytoplankton Group Dominance (PGD from PHYSAT) with
ship-based sea surface DMS concentrations (8 cruises in total) to assess
this dependence on an unprecedented spatial scale. PHYSAT provides PGD
(either NANO, PRO, SYN, DIAT, Phaeocystis (PHAEO) or coccolithophores (COC)) in each
satellite pixel (1/4° horizontal resolution). While there are
identification errors in the PHYSAT method, it is important to note that
these errors are lowest for NANO PGD which we typify by high DMSP:Chl. In
summer, in the Indian sector of the Southern Ocean, we find that mean
DMS:Chl associated with NANO + PHAEO and PRO + SYN + DIAT are 13.6±8.4 mmol g−1
(n=34) and 7.3±4.8 mmol g−1 (n=24), respectively. That
is a statistically significant difference (P<0.001) that is consistent
with NANO and PHAEO being relatively high DMSP producers. However, in the
western North Atlantic between 40° N and 60° N, we find no significant
difference between the same PGD. This is most likely because
coccolithophores account for the non-dominant part of the summer
phytoplankton assemblages. Meridional distributions at 22° W in the
Atlantic, and 95° W and 110° W in the Pacific, both show a marked drop
in DMS:Chl near the equator, down to few mmol g−1, yet the basins
exhibit different PGD (NANO in the Atlantic, PRO and SYN in the Pacific). In
tropical and subtropical Atlantic and Pacific waters away from the
equatorial and coastal upwelling, mean DMS:Chl associated with high and low
DMSP producers are statistically significantly different, but the difference
is opposite of that expected from culture experiments. Hence, in a majority
of cases PGD is not of primary importance in controlling DMS:Chl variations.
We therefore conclude that water-leaving radiance spectra obtained
simultaneously from ocean color sensor measurements of Chl concentrations
and dominant phytoplankton groups can not be used to predict global fields
of DMS. |
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