Least-squares estimates of thorium, particle, and nutrient cycling rate constants from the JGOFS North Atlantic Bloom Experiment

Abstract

Least-squares estimates of rate constants for the cycling of thorium, total particulate material, PON, and POC are presented at three different 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 sediment trap data at 150 m and 300 m. Rate constants are based on a particle cycling model with suspended small particles and rapidly sinking large particles. Conservation equations for POC, PON, total particle mass, 228Th, and 234Th in the large particle phase and conservation equations for POC and PON in the small particle phase are used as constraints in the least-squares problem. Rate constants are predicted for 100 and 33% trap efficiency scenarios. The 33% trapping efficiency scenario produces results that are consistent with the water column 234Th budget. The lower trapping efficiency increases aggregation and remineralization rate constants. Rate constants increase during the course 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 year −1 for remineralization. Over the course of the bloom, increases in predicted aggregation, disaggregation, and remineralization fluxes are also resolved.