Distributions of chlorophyll and primary productivity in relation to water column structure in the eastern North Atlantic Ocean

Latitudinal variations in the megascale (10 3 km) distribution of biological properties are described in relation to water column structure between 60° and 7°N in the eastern North Atlantic Ocean. Stations were occupied along a meridional transect of stations at 20°W in August‐September, 1988, during the third leg of the National Oceanic and Atmospheric Administration Global Change Expedition. An additional transect to the south (38°N to 7°N) was occupied to extend the total range of latitudinal observations. Chlorophyll a concentrations were highest in the northern latitudes (<2.51 mg m −3 ) , decreasing to >0.2 mg m −3 in the vicintiy of the subtropical gyre, south of 40°N. The nitracline was associated with a shoaling of the pycnocline in the northern latitudes. At 7°N, high chlorophyll concentrations (approximately 0.5 mg m −3 ), and enhanced primary productivity (375.5 mg C m −2 d −1 ) were associated with a lens of fresh Amazon River Water. Primary productivity rates were variable throughout the transect, ranging from 646.10 mg C m −2 d −1 to 138.26 mg C m −2 d −1 . Productivity maxima were located south of Iceland, at 46°N (646.10 mg C m −2 d −1 ) and in the vicinity of the Azores Front at 35°N (259.85 mg C m −2 d −1 ). Latitudinal distributions of primary productivity corresponded closely to a model of productivity along a transect at 40°N by Yentsch (1990).