Primary production, water column changes, and the demise of a Phaeocystis bloom at the Marine Light‐Mixed Layers site (59°N, 21°W) in the northeast Atlantic Ocean

Abstract

Primary production in incubations is compared with daily changes in water column oxygen inventories and particulate organic carbon (POC, and estimated from the beam attenuation coefficient) at a station in the northeast Atlantic (the Marine Light‐Mixed Layers (MLML) site) in the spring of 1991. Drifters were followed over three periods. The first is characterized by a bloom of Phaeocystis pouchetii. Prior to the second and third deployments, there were storms that mixed the water column to >150 m over a period of 3 days, and consequently, the Phaeocystis bloom dissipated. After deployment of the third drifter, the water column restratified, followed by high rates of primary production. All incubation experiments for carbon assimilation were greater than that calculated from changes in oxygen or POC. The 14 C estimates agreed with the prediction of a bio‐optical model for primary production. During the early days of the cruise, 14 C estimates were high, while water column changes indicated negative net community production. In addition to the usual overestimate of net primary production by the 14 C estimates, the differences are ascribed to mixing losses for the first part of the cruise, and to grazing losses after restratification.