Springtime distributions and variability of biogenic particulate matter in Gulf Stream warm-core ring 82B and surrounding N.W. Atlantic waters

Abstract

Distributions of particulate matter, chlorophyll and other physical/bio-optical properties were investigated during April–May 1982 in warm-core ring (WCR) 82B and surrounding Shelf, Slope, Gulf Stream and Sargasso Sea waters. Biogenic particles present in the core waters of WCR 82B were strongly influenced by the day-to-day variation in air-sea heat flux. Particles grew/accumulated in surface waters during periods of transient stratification/quiescence and were removed from the euphotic zone as deep as 400 m during periods of strong heat loss and deep convective mixing. This process enriched ring core waters below the euphotic zone compared to all other waters sampled. Outside of ring-core waters, stratification was already permanently established and surface concentrations of particles/chlorophyll increased radially outward to maximum values in entrainment zone waters at the ring periphery. Slightly lower concentrations were observed in the Slope Water and Shelf Water. Comparisons of chlorophyll and beam attenuation coefficient data suggested that the beam attenuation coefficient reflects bulk distributions of particulate mass and not pigment biomass, consistent with earlier studies. Profiles of SPM and chlorophyll at a Gulf Stream station showed subduction of high (650 μg kg −1) concentrations of biogenic particles produced at the surface near the Gulf Stream/Slope Water front. Such subduction events may have significant impact on the oxygen budget of the N. Atlantic thermocline.