(8-14June) shows that the spatial heterogeneity is reproduced by the
model and agrees well with the observed concentration values (fig. 3).
Coastal meshes are more productive than offshore ones. In the offshore
water masses, nutrient depletion is strong at this period just following
the spring algae development. Thus, chlorophyll concentrations of these
water masses are very low. Nevertheless, in front of the Gironde estuary,
the simulation under-estimates the extension of the primarv production
towards the west. Herbland et al. (1998) have pointed out that phosphorus is the first limiting nutrient of the phytoplankton spring bloom in
the waters coming from the Gin onde estuan on the continental shelf. The
model can reproduce this limitation but lighdy over-estimates it in June.
Figure 3 - a- Spatial distribution of chiorophyll concentrations observed during Modycot 2 (8-14 June 1999).
b- Simulated near surface chlorophyll field on June 12, 1999 in mg/m
3 of chlorophyll a.
The ocean colour has been used to calibrate the modei, and to estimate
its capacity to reproduce the biological structure of the surface laver
(Druon et al., in press). Satellite images are a useful complementary tool
for in situ measurements. They are less precise but they provide an instantaneous synoptical view of the whole area.
This method has allowed us to test the capacity of the model to reproduce the seasonal variabilityy with a late winter case, a spring case and a
summer case.
The model reproduces the early phytoplankton development in March
(Morin et al., 1991; Herbland e.t al., 1998) in the haline structure of the
coastal waters. The phytoplankton development initiation results mainly
from the establishment of the haline stratification and from the adequation between the shallow mixed surface layer rich in nutrients and the decrease of suspended matter concentrations. It reproduces also the high
primary production levels that follow the spring big rising of the Ixiire
and Gironde waters of the year 1998, with the highest values found in
front of the Loire estuary. In summer, only the coastal waters present
weak chlorophyll concentrations. This weak production is due to the
110
model and agrees well with the observed concentration values (fig. 3).
Coastal meshes are more productive than offshore ones. In the offshore
water masses, nutrient depletion is strong at this period just following
the spring algae development. Thus, chlorophyll concentrations of these
water masses are very low. Nevertheless, in front of the Gironde estuary,
the simulation under-estimates the extension of the primarv production
towards the west. Herbland et al. (1998) have pointed out that phosphorus is the first limiting nutrient of the phytoplankton spring bloom in
the waters coming from the Gin onde estuan on the continental shelf. The
model can reproduce this limitation but lighdy over-estimates it in June.
Figure 3 - a- Spatial distribution of chiorophyll concentrations observed during Modycot 2 (8-14 June 1999).
b- Simulated near surface chlorophyll field on June 12, 1999 in mg/m
3 of chlorophyll a.
The ocean colour has been used to calibrate the modei, and to estimate
its capacity to reproduce the biological structure of the surface laver
(Druon et al., in press). Satellite images are a useful complementary tool
for in situ measurements. They are less precise but they provide an instantaneous synoptical view of the whole area.
This method has allowed us to test the capacity of the model to reproduce the seasonal variabilityy with a late winter case, a spring case and a
summer case.
The model reproduces the early phytoplankton development in March
(Morin et al., 1991; Herbland e.t al., 1998) in the haline structure of the
coastal waters. The phytoplankton development initiation results mainly
from the establishment of the haline stratification and from the adequation between the shallow mixed surface layer rich in nutrients and the decrease of suspended matter concentrations. It reproduces also the high
primary production levels that follow the spring big rising of the Ixiire
and Gironde waters of the year 1998, with the highest values found in
front of the Loire estuary. In summer, only the coastal waters present
weak chlorophyll concentrations. This weak production is due to the
110