Climatological, annual, and seasonal variability in chlorophyll concentration in the Gulf of Mexico, western Caribbean, and Bahamas using NASA colour maps

Abstract

This study investigates climatological, seasonal, and interannual variability in chlorophyll concentration (Chl) throughout the Gulf of Mexico (GM), the western Caribbean Sea (WC), and the Bahamas (BI). For this purpose, Coastal Zone Color Scanner (CZCS) (1979–1986), Ocean Color and Temperature Scanner (OCTS) (1996–1997), and Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) (1997–2008) NASA climatology, yearly, and seasonal Level-3 Standard Mapped Image series were used. Inspection of the original Chl and the obtained fuzzy unsupervised classified maps show the existence of a transition zone between the already known coastal and open waters. The extension (total number of pixels) and form of polygons representing these water masses vary both annually and seasonally, showing their greatest differences during spring and autumn in the northeastern and northwestern GM, Campeche Sound, and the Honduras coast in the Caribbean. In contrast, the BI present polygons having an almost invariant extension and form. The seasonal averaged Chl values up to 0.8 mg m−3 present a cyclic variation, showing the highest Chl during winter months and the lowest Chl during summer months, independent of the basin or the sensor under consideration. The CZCS and OCTS products must be considered with care; however, they provide results that are compatible with findings from the SeaWiFS time series. Annual and winter/autumn trends – a decrease in Chl – were identified in the GM and BI. The Caribbean reports constant Chl values during the two periods under study. Possible interpretations of these trends will come from detailed interpretation of local data.