Abstract
Desert dust deposition is thought to act as fertilizer for phytoplankton growth, since it is rich in the required nutrients. The Mediterranean Sea is a nutrient poor marine environment—with its eastern part being the most oligotrophic—which is subject to dust transport. The Hellenic Seas are part of this low-nutrient, low-chlorophyll environment and they are also affected by dust deposition events. Thus, the dust fertilizing effect can be particularly important, especially during the stratification period, when the nutrients needed for phytoplankton growth are not imported from deeper layers. Some individual dust events are examined here in respect of their possible influence on phytoplankton, through the observed variations of satellite derived chlorophyll concentrations. Two strong dust events that were also extreme weather events and three events in the June–September stratification period are examined for the Hellenic Seas as well as a strong dust event in the Central Mediterranean Sea. The results, only when based on absolute chlorophyll differences above 50%, show that dust events seem to favour phytoplankton abundance mainly during the low productive period; however, these differences are area-limited. The difficulty of reaching safe results through specific dust events and discriminating between other meteorological factors favouring phytoplankton growth are also discussed.
Highlights
Phytoplankton is the basis of the marine food chain, with its photosynthesis being comparable with that of the terrestrial plants [1]
Desert dust deposition is thought to act as fertilizer for phytoplankton growth, since it is rich in the required nutrients
Two strong dust events that were extreme weather events and three events in the June–September stratification period are examined for the Hellenic Seas as well as a strong dust event in the Central Mediterranean Sea
Summary
Phytoplankton is the basis of the marine food chain, with its photosynthesis being comparable with that of the terrestrial plants [1]. In contrary: chlorophyll increases were observed shortly after dust deposition events [55]; weekly chlorophyll concentration data and model dust deposition data were found correlated in quite large areas especially of the Eastern Mediterranean and the Central part of the Sea was characterized as “the most responsive to dust deposition” [56]; small positive statistically significant correlations were found between chlorophyll and dust deposition, mainly in spring and for the Central and Eastern basins, with the seasonally detrended chlorophyll data resulting in lower and more limited correlations [57]; significant chlorophyll peaks in respect to the week before were found after very large dust events along with a possible pattern of an eastward decrease in the Sea’s responsiveness to high deposition dust events [33]. Chlorophyll differences before and after the events were calculated for the dust-affected areas and separately for the subareas of wet dust deposition The results show both increases and decreases in chlorophyll concentrations after the events; when based on the area-limited absolute chlorophyll differences above 50%, they indicate a possible favourable effect of dust on phytoplankton, mainly during the low productive period. The present paper contributes to the relevant research through the study of specific events that is quite rare especially for the Hellenic Seas; the difficulties in drawing a safe conclusion are highlighted as well
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