Remote continental forcing of phytoplankton biogeochemistry: Observations across the “Caribbean‐Atlantic front”

Abstract

A persistent front, in large part generated by the confluence of western tropical North Atlantic (WTNA) surface waters with the massive freshwater plumes of the Orinoco and Amazon Rivers, separates waters of the Caribbean Sea from those of the adjacent WTNA. We characterized physical and biogeochemical properties across this front in order to elucidate the processes leading to enhanced near surface phytoplankton biomass within the front. Although chlorophyll content of the water column to either side of the front is similar, phytoplankton in waters within this “Caribbean‐Atlantic front” resides for the most part above the pycnocline and sustains large production rates in comparison with the lower rates of deep, sub‐pycnocline WTNA phytoplankton. Nitrogen budgets indicate that a substantial fraction of the production within the front may arise from biological nutrient recycling while the deeper WTNA communities rely to a greater extent on nutrients from below the nutricline.