Evolution of Small Particle Distribution During the North Atlantic Bloom
During the April/May leg of the North Atlantic Bloom Experiment, CTD/Transmissometer profiles were taken at 47°N, 20°W every morning and evening. Water samples were filtered to obtain particulate matter samples, to determine particle mass concentrations, and to calibrate the transmissometer. Particle concentrations in the surface mixed layer, calculated from beam attenuation coefficients, increased three-fold (from 0.17 mg/1 to 0.52 mg/1) over a two-week period, indicative of a phytoplankton bloom. The overall trend in the surface-layer beam attenuation during the second cruise (May/June) was flat, with the exception of a spike (concentrations > 1 mg/1), related to a storm and/or the edge of a mesoscale eddy. Superimposed on the April/May increase were diel variations (0.06 mg/1 to 0.12 mg/1), with evening highs and morning lows. Increases in particle mass easily account for the uptake of CO2 (LDGO CO2 group), suggesting that CO2 is rapidly converted to the particulate phase, after which it may be converted to DOC directly, or incorporated into large aggregates, which could release DOC as they settle and are remineralized. Decreases in particle concentration are, presumably, associated with biological consumption, large-particle production, and subsequent particle settling (fecal pellets, aggregates), or consumption and bioactive transport by organisms migrating to deeper depths.