High-resolution observations of aggregate flux during a sub-polar North Atlantic spring bloom

An aggregate flux event was observed by ship and by four underwater gliders during the 2008 subpolar North Atlantic spring bloom experiment (NAB08). At the height of the diatom bloom, aggregates were observed as spikes in measurements of both particulate backscattering coefficient (b(bp)) and chlorophyll a fluorescence. Optical sensors on the ship and gliders were cross-calibrated through a series of simultaneous profiles, and b(bp) was converted to particulate organic carbon. The aggregates sank as a discrete pulse, with an average sinking rate of similar to 75 m d(-1); 65% of aggregate backscattering and 90% of chlorophyll fluorescence content was lost between 100 m and 900 m. Mean aggregate organic carbon flux at 100 m in mid-May was estimated at 514 mg C m(-2) d(-1), consistent with independent flux estimates. The use of optical spikes observed from gliders provides unprecedented coupled vertical and temporal resolution measurements of an aggregate flux event. (C) 2011 Elsevier Ltd. All rights reserved.