 |
| Titel |
From the chlorophyll a in the surface layer to its vertical profile: a Greenland Sea relationship for satellite applications |
| VerfasserIn |
A. Cherkasheva, E.-M. Nöthig, E. Bauerfeind, C. Melsheimer, A. Bracher |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1812-0784
|
| Digitales Dokument |
URL |
| Erschienen |
In: Ocean Science ; 9, no. 2 ; Nr. 9, no. 2 (2013-04-09), S.431-445 |
| Datensatznummer |
250018046
|
| Publikation (Nr.) |
 copernicus.org/os-9-431-2013.pdf |
|
|
|
|
|
| Zusammenfassung |
| Current estimates of global marine primary production range over a factor of
two. Improving these estimates requires an accurate knowledge of the
chlorophyll vertical profiles, since they are the basis for most primary
production models. At high latitudes, the uncertainty in primary production
estimates is larger than globally, because here phytoplankton absorption shows
specific characteristics due to the low-light adaptation, and in situ data
and ocean colour observations are scarce. To date, studies describing the
typical chlorophyll profile based on the chlorophyll in the surface layer
have not included the Arctic region, or, if it was included, the dependence of
the profile shape on surface concentration was neglected. The goal of our
study was to derive and describe the typical Greenland Sea chlorophyll
profiles, categorized according to the chlorophyll concentration in the
surface layer and further monthly resolved profiles. The Greenland Sea was chosen
because it is known to be one of the most productive regions of the Arctic
and is among the regions in the Arctic where most chlorophyll field data are
available. Our database contained 1199 chlorophyll profiles from R/Vs
Polarstern and Maria S. Merian cruises combined with data
from the ARCSS-PP database (Arctic primary production in situ database) for
the years 1957–2010. The profiles were categorized according to their mean
concentration in the surface layer, and then monthly median profiles within
each category were calculated. The category with the surface layer
chlorophyll (CHL) exceeding 0.7 mg C m−3 showed values gradually
decreasing from April to August. A similar seasonal pattern was observed when
monthly profiles were averaged over all the surface CHL concentrations. The
maxima of all chlorophyll profiles moved from the greater depths to the
surface from spring to late summer respectively. The profiles with the
smallest surface values always showed a subsurface chlorophyll maximum with
its median magnitude reaching up to three times the surface concentration.
While the variability of the Greenland Sea season in April, May and June
followed the global non-monthly resolved relationship of the chlorophyll
profile to surface chlorophyll concentrations described by the model of Morel
and Berthon (1989), it deviated significantly from the model in the other
months (July–September), when the maxima of the chlorophyll are at quite
different depths. The Greenland Sea dimensionless monthly median profiles
intersected roughly at one common depth within each category. By applying a
Gaussian fit with 0.1 mg C m−3 surface chlorophyll steps to the median
monthly resolved chlorophyll profiles of the defined categories, mathematical
approximations were determined. They generally reproduce the magnitude and
position of the CHL maximum, resulting in an average 4% underestimation in
Ctot (and 2% in rough primary production estimates) when
compared to in situ estimates. These mathematical approximations can be used
as the input to the satellite-based primary production models that estimate
primary production in the Arctic regions. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|