Estimates of particle‐ and thorium‐cycling rates in the northwest Atlantic Ocean

Abstract

We provide least squares estimates of particle‐cycling rate constants and their errors at 13 depths in the Northwest Atlantic Ocean using a compilation of published results and conservation equations for thorium and particle cycling. The predicted rates of particle aggregation and disaggregation vary through the water column. The means and standard deviations, based on lognormal probability distributions, for the lowest and highest rates of aggregation (β2) and disaggregation (β−2) in the water column are 8±27 y−1 < β2 < 18±90 y−1, and 580±2000 y−1 < β−2 < 3×103±104y−1. Median values for these rates are 2.1 y−1 < β2 < 3.2y−1, and 149 y−1 < β−2 < 156 y−1. Predicted rate constants for thorium adsorption (k1 = 5.0 ± 1.0 × 104 m3 kg−1 y−1) and desorption (k−1 = 3.1±1.5 y−1) are consistent with previous estimates. Least squares estimates of the sum of the time dependence and transport terms from the particle and thorium conservation equations are on the same order as other terms in the conservation equations. Forcing this sum to equal zero would change the predicted rates. Better estimates of the time dependence of thorium activities and particle concentrations and of the concentration and flux of paniculate organic matter would help to constrain estimates of β2 and β−2.