Phytoplankton Chl a, primary production and nutrient distributions across a coastal frontal zone off Georgia, U.S.A.

Abstract

Using results obtained by ship and aircraft surveys of near-shore waters off Georgia, U.S.A. we describe the gradients in major plant nutrients, near-surface cholorphyll (Chl a) and near-surface primary production in relation to near-surface density gradients of a coastal frontal zone. The results show that a relatively narrow band (∼10 km wide) of high phytoplankton biomass (Chl a) is a ubiquitous feature of the shoreward side of the coastal frontal zone. Chl a decreases across the frontal zone as salinity increases and near surface Chl a concentrations are approximately 10-fold greater in the high Chl a band than on the seaward side of the frontal zone. Near-surface phosphate and silicate concentrations are distributed similarly to Chl a. In contrast to silicate and phosphate, we did not detect significant cross-shelf gradients of inorganic nitrogen (N) concentrations. The distributions imply high rates of primary production in the coastal band throughout the year, total consumption of available inorganic N brought in by rivers or other sources and high rates of N recycling.