Time series analysis of aerosol optical thickness and chlorophyll concentration in the North Atlantic Ocean and Caribbean Sea using satellite data

Atmospheric transport of aerosols from the Sahara and Sahel regions of Africa supply large amounts of limiting nutrients, such as iron, to oligotrophic regions of the North Atlantic Ocean and the Caribbean Sea. As phytoplanktonic organisms in the ocean's surface use the bio-available iron, their rate of photosynthesis increases resulting in enhanced chlorophyll concentrations. This work aims at investigating the possible iron fertilization of oligotrophic North Atlantic Tropical and Caribbean waters using data from SeaWiFS, MODIS Terra and MODIS Aqua satellite sensors. Level 3 weekly averaged images from September 1997 through December 2007 were used to evaluate long term records of aerosol optical thickness (AOT) and chlorophyll (chl_a) pigment concentration for three areas in the North Atlantic Ocean and the Caribbean Sea. The stations were located at the Caribbean Time Series Station, CaTS (17.5„a N, 67.0„a W), the Atlantic, north of Puerto Rico (20„a N, 67„a W) and the Western Atlantic Ocean (19„a N, 57„a W). Results from a time series analysis exhibited a seasonal cycle with a summer maximum for mean AOT concentration. The strongest correlation between both parameters was observed for the Western Atlantic station with a time-lag between AOT and chl_a concentration of approximately 1 month. This station is located far from coastal influences and is situated directly in the path of the seasonal African dust storms. The other two stations present higher variability which might be the consequence of external factors due to their proximity to terrigenous nutrient sources.