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| Titel |
Role of photoacclimation on phytoplankton's seasonal cycle in the Mediterranean Sea through satellite ocean color data |
| VerfasserIn |
Marco Bellacicco, Gianluca Volpe, Simone Colella, Rosalia Santoleri |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250097717
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| Publikation (Nr.) |
 EGU/EGU2014-13326.pdf |
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| Zusammenfassung |
| Photoacclimation changes the intracellular chlorophyll-a concentration (Chl), a process that
is not currently taken into account by standard ocean colour algorithms. The cellular Chl
production is an energy-demanding process, so that it occurs when nutrients are
available and under light limiting conditions. Historically, Chl has been used as
a proxy for marine algal biomass. This work aims at comparing Chl-based with
Carbon-based estimates calculated from the particulate backscattering coefficient, bbp (λ)
(Behrenfeld et al., 2005). The equation for the phytoplankton carbon biomass is
C = (bbp(443) - bbpNAP(443))SF , where bbpNAP(443) represents the contribution of
non algal particles to bbp(443) and is a constant value, and SF a scalar factor (13,000
mg C m-2) to match the carbon biomass units. Here we allow bbpNAP to vary
monthly over the Mediterranean SeaWiFS time series, and use the 555 nm channel for
coherence with the method used to derive SF (Loisel et al., 2001). The comparison
between the two methods yields the Mediterranean Sea to be 2 to 7 times lower, and
closer to the real system variability as measured by in situ observations. In both
methods, the Chl:C ratio is the footprint showing that phytoplankton cells enhance
the major photosynthetic pigment production to optimize photosynthesis under
low light regime and high nutrients (e.g., winter). Minimum Chl:C ratio values
are observed during summer when photoinhibition is the dominant intracellular
process. We suggest that a new proxy for phytoplankton biomass is strongly needed,
particularly for the Mediterranean Sea, where Chl:C ratio varies of 1 order of magnitude,
clearly highlighting dominance of photoacclimation at seasonal and basin scales. |
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