Spatio-temporal variability of a chlorophyll-a based biomass index and influence of coastal sources of enrichment in the Algerian Basin

This study investigates the spatial distribution and temporal variability of chlorophyll-a (Chl-a) biomass in Algerian Basin (AB) along its meridional cross-shore dimensions, focusing on coastal enrichments. After correcting most atmospheric disturbances daily MODIS Level-2 data series between 2003 2018, a fortnightly climatology 1-km resolution Chl-a has been generated to account for specific features previously poorly evidenced from 4-km Level-3 data. The AB is characterised by two extreme seasons high low biomass, separated sharp transitions, that characterise offshore domain. area (<10 km) reveals an intense distinct dynamic associated with highly productive local hotspots rather than seasonal variability. A index proposed as horizontally integrated concentration coastline extension 0.5 mg m-3 isopleth. separately quantifies cumulative both domains large alongshore Low values (<5 g m-2) were observed during summer spring blooms (up 40 m-2), while maximum (>50 locally narrow alone represents 44% total where enrichment up 5 times higher offshore. Multivariate modelling potential factors favouring enrichments shows phytoplanktonic waters mainly wadis seasonally city sewage well presence bay. separate source undoubtedly aquaculture cages.