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| Titel |
The Mediterranean subsurface chlorophyll dynamic and its impact on the Mediterranean bioregions. |
| VerfasserIn |
Julien Palmiéri, Jean-Claude Dutay, Fabrizio Dortenzio, Camille Richon, Loïc Houpert, Laurent Bopp |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250152865
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| Publikation (Nr.) |
 EGU/EGU2017-17764.pdf |
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| Zusammenfassung |
| Ocean bioregions are generally defined using remotely-sensed sea surface chlorophyll fields,
based on the assumption that surface chlorophyll is representative of euphotic layer
phytoplankton biomass. Here we investigate the impact of subsurface phytoplankton
dynamics on the characterisation of ocean bioregions. The Mediterranean Sea is known for its
contrasting bioregimes despite its limited area, and represents an appropriate case for this
study. We modelled this area using a high resolution regional dynamical model,
NEMO-MED12, coupled to a biogeochemical model, PISCES, and focused our analysis on
the bioregions derived from lower trophic levels. Validated by Bio-Argo observations, our
model shows that chlorophyll phenology can be significantly different when estimated
from surface concentrations or integrated over the euphotic layer. This was found
in both low chlorophyll, oligotrophic bioregions as well as in high chlorophyll,
bloom bioregions. The underlying reason for this difference is the importance of
subsurface phytoplankton dynamics, in particular those associated with the Deep
Chlorophyll Maximum (DCM) at the base of the upper mixed layer. Subsurface
phytoplankton are found to significantly impact the bloom bioregions, while in
oligotrophic regions are of similar productivity to the surface layer. Consequently, our
results show that surface chlorophyll is not representative of total phytoplankton
biomass. Analysis of the DCM finds that it is extremely homogeneous throughout the
Mediterranean Sea, and that it follows the annual cycle of solar radiation. In the
most oligotrophic bioregion, the total phytoplankton biomass is almost constant
along the year, implying that the summertime DCM biomass increase is not due to
DCM photoacclimation, nor an increase of DCM production, but instead of the
"migration" − with photoacclimation − of surface phytoplankton into the DCM. |
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