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                                                                                                                       Monthly Climatologies - Chlorophyll
PIRANA
Potential Influences of Riverine and Aeolian inputs on Nitrogen fixation in the Atlantic

The western equatorial Atlantic Ocean (WEQAT) is a complex and understudied ecosystem that has significant impacts on marine resources in the region as well as in downstream areas such as the Caribbean Sea.  Our study centers on diazotrophic (nitrogen fixing) microorganisms as keystone species.  Geological, physical, biological, chemical and even social factors all have a major influence on population biology and activity of diazotrophs in the WEQAT. Diazotrophs in turn have a major impact on other phytoplankton and trophic levels through input of fixed nitrogen (N).

The Amazon River affects the region physically by changing salinity; thereby changing water column stratification.  The Amazon also affects the region geochemically by introducing iron and silicate which can then biologically stimulate the growth of diatoms that contain the N₂ fixing endosymbiont Richelia intracellularis. Futhermore, the area receives significant seasonal atmospheric inputs of iron in dust from the Sahel region of Africa, which can promote the growth of the important N₂ fixing cyanobacterium Trichodesmium.  This atmospheric iron source is directly deposited on the surface waters where biological activity is greatest.   For Trichodesmium, the physical environment (e.g. high wind speed) may inhibit activity and the formation of blooms.   Diazotrophs may be affected by land use practices in the Amazon Basin and the African Sahel, and N₂ fixed by marine plankton can affect humans by stimulating primary productivity and fishery yields.