The year-to-year variability in the timing, duration, and spatial extent of the surface phytoplankton bloom over the winter-spring period is examined in the southern Adriatic Sea using SeaWiFS-derived chlorophyll images for three years (1998, 1999, 2000). Each years image time series shows that blooms were intermittent and differed in onset, duration, and intensity with relatively low values observed in 2000. The relation between atmospheric forcing and inter-annual variability of the bloom timing and intensity is investigated using a coupled physical-biological model. The simulations focus on the effect of cumulative buoyancy loss on convective depths and its implications on surface nutrient availability, chlorophyll concentrations, and other ecosystem components during the study period. We test the hypothesis that the South Adriatic bloom is essentially controlled by the local winter climatic conditions (i.e., maximum convective depth), as suggested by recent findings, rather than the available nutrient pool at the intermediate depths (200-800m), which also varies from year to year. For all three years, the simulations produced convective depths that were in good agreement with in situ observations. However, the fluctuations in SeaWiFS phytoplankton biomass could be reproduced only if the particular years nutrient pool was also taken into account. Thus, the most probable explanation for the low SeaWiFS phytoplankton biomass observed in 2000 is the reduced nutrient pool due to the return from the Transient phase to the pre-Transient regime of the Mediterranean Sea. Our results indicate that the South Adriatic bloom is a complex phenomenon, and cannot simply be explained by interannual changes in convective depth.
Year-to-year variability of the phytoplankton bloom in southern Adriatic Sea (1998-2000): SeaWiFS observations and modelling study
Santoleri R;
2003
Abstract
The year-to-year variability in the timing, duration, and spatial extent of the surface phytoplankton bloom over the winter-spring period is examined in the southern Adriatic Sea using SeaWiFS-derived chlorophyll images for three years (1998, 1999, 2000). Each years image time series shows that blooms were intermittent and differed in onset, duration, and intensity with relatively low values observed in 2000. The relation between atmospheric forcing and inter-annual variability of the bloom timing and intensity is investigated using a coupled physical-biological model. The simulations focus on the effect of cumulative buoyancy loss on convective depths and its implications on surface nutrient availability, chlorophyll concentrations, and other ecosystem components during the study period. We test the hypothesis that the South Adriatic bloom is essentially controlled by the local winter climatic conditions (i.e., maximum convective depth), as suggested by recent findings, rather than the available nutrient pool at the intermediate depths (200-800m), which also varies from year to year. For all three years, the simulations produced convective depths that were in good agreement with in situ observations. However, the fluctuations in SeaWiFS phytoplankton biomass could be reproduced only if the particular years nutrient pool was also taken into account. Thus, the most probable explanation for the low SeaWiFS phytoplankton biomass observed in 2000 is the reduced nutrient pool due to the return from the Transient phase to the pre-Transient regime of the Mediterranean Sea. Our results indicate that the South Adriatic bloom is a complex phenomenon, and cannot simply be explained by interannual changes in convective depth.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
