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| Titel |
Quantifying the biological impact of surface ocean light attenuation by colored detrital matter in an ESM using a new optical parameterization |
| VerfasserIn |
G. E. Kim, M.-A. Pradal, A. Gnanadesikan |
| 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 ; 12, no. 16 ; Nr. 12, no. 16 (2015-08-28), S.5119-5132 |
| Datensatznummer |
250118079
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| Publikation (Nr.) |
 copernicus.org/bg-12-5119-2015.pdf |
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| Zusammenfassung |
| Light attenuation by colored detrital material (CDM) was included in a fully
coupled Earth system model (ESM). This study presents a modified parameterization
for shortwave attenuation, which is an empirical relationship between 244
concurrent measurements of the diffuse attenuation coefficient for
downwelling irradiance, chlorophyll concentration and light absorption by
CDM. Two ESM model runs using this parameterization were conducted, with and
without light absorption by CDM. The light absorption coefficient for CDM was
prescribed as the average of annual composite MODIS Aqua satellite data from
2002 to 2013. Comparing results from the two model runs shows that changes in
light limitation associated with the inclusion of CDM decoupled trends
between surface biomass and nutrients. Increases in surface biomass were
expected to accompany greater nutrient uptake and therefore diminish surface
nutrients. Instead, surface chlorophyll, biomass and nutrients increased
together. These changes can be attributed to the different impact of light
limitation on surface productivity versus total productivity. Chlorophyll and
biomass increased near the surface but decreased at greater depths when CDM
was included. The net effect over the euphotic zone was less total biomass
leading to higher nutrient concentrations. Similar results were found in a
regional analysis of the oceans by biome, investigating the spatial
variability of response to changes in light limitation using a single
parameterization for the surface ocean. In coastal regions, surface
chlorophyll increased by 35 % while total integrated phytoplankton
biomass diminished by 18 %. The largest relative increases in modeled
surface chlorophyll and biomass in the open ocean were found in the
equatorial biomes, while the largest decreases in depth-integrated biomass and
chlorophyll were found in the subpolar and polar biomes. This mismatch of
surface and subsurface trends and their regional dependence was analyzed by
comparing the competing factors of diminished light availability and
increased nutrient availability on phytoplankton growth in the upper 200 m.
Understanding changes in biological productivity requires both surface and
depth-resolved information. Surface trends may be minimal or of the opposite
sign than depth-integrated amounts, depending on the vertical structure of
phytoplankton abundance. |
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