LEAST-SQUARES ESTIMATES OF THORIUM, PARTICLE, AND NUTRIENT CYCLING RATE CONSTANTS FROM THE JGOFS NORTH-ATLANTIC BLOOM EXPERIMENT

Least-squaresestimates of rate constants for the cycling of thorium, t otal particulate material, PON, and POC are presented at three differe nt times during the North Atlantic Bloom Experiment. The estimates are based on previously published data collected between 24 April and 30 May 1989 and include water column profiles between 100 and 400 m and s ediment trap data at 150 m and 300 m. Rate constants are based on a pa rticle cycling model with suspended small particles and rapidly sinkin g large particles. Conservation equations for POC, PON, total particle mass, Th-228, and Th-234 in the large particle phase and conservation equations for POC and PON in the small particle phase are used as con straints in the least-squares problem. Rate constants are predicted fo r 100 and 33% trap efficiency scenarios. The 33% trapping efficiency s cenario produces results that are consistent with the water column Th- 234 budget. The lower trapping efficiency increases aggregation and re mineralization rate constants. Rate constants increase during the cour se of the bloom, from 2+/-0.2 to 76+/-9 year(-1) for aggregation, 156/-17 to 524+/-74 year(-1) for disaggregation, and 13+/-1 to 77+/-10 ye ar(-1) for remineralization. Over the course of the bloom, increases i n predicted aggregation, disaggregation, and remineralization fluxes a re also resolved. Copyright (C) 1996 Elsevier Science Ltd.