Show simple item record

dc.contributor.authorLerner, Paul  Concept link
dc.contributor.authorMarchal, Olivier  Concept link
dc.contributor.authorLam, Phoebe J.  Concept link
dc.contributor.authorBuesseler, Ken O.  Concept link
dc.contributor.authorCharette, Matthew A.  Concept link
dc.date.accessioned2017-08-02T15:16:18Z
dc.date.issued2017-05
dc.identifier.urihttps://hdl.handle.net/1912/9144
dc.description© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 125 (2017): 106-128, doi:10.1016/j.dsr.2017.05.003.en_US
dc.description.abstractThe high particle reactivity of thorium has resulted in its widespread use in tracing processes impacting marine particles and their chemical constituents. The use of thorium isotopes as tracers of particle dynamics, however, largely relies on our understanding of how the element scavenges onto particles. Here, we estimate apparent rate constants of Th adsorption (k1), Th desorption (k−1), bulk particle degradation (β-1), and bulk particle sinking speed (w) along the water column at 11 open-ocean stations occupied during the GEOTRACES North Atlantic Section (GA03). First, we provide evidence that the budgets of Th isotopes and particles at these stations appear to be generally dominated by radioactive production and decay sorption reactions, particle degradation, and particle sinking. Rate parameters are then estimated by fitting a Th and particle cycling model to data of dissolved and particulate 228,230,234Th, 228Ra, particle concentrations, and 234,238U estimates based on salinity, using a nonlinear programming technique. We find that the adsorption rate constant (k1) generally decreases with depth across the section: broadly, the time scale 1/k1 averages 1.0 yr in the upper 1000 m and (1.4–1.5) yr below. A positive relationship between k1 and particle concentration (P) is found, i.e., , k1 ∝ Pb where b ≥ 1, consistent with the notion that k1 increases with the number of surface sites available for adsorption. The rate constant ratio, K = k1/(k-1 + β-1), which measures the collective influence of rate parameters on Th scavenging, averages 0.2 for most stations and most depths. We clarify the conditions under which K/P is equivalent to the distribution coefficient, KD, test that the conditions are met at the stations, and find that decreases with P, in line with a particle concentration effect (dKD/dP < 0). In contrast to the influence of colloids as envisioned by the Brownian pumping hypothesis, we provide evidence that the particle concentration effect arises from the joint effect of P on the rate constants for thorium attachment to, and detachment from, particles.en_US
dc.description.sponsorshipWe acknowledge the U.S. National Science Foundation for providing funding for this study (grant OCE-1232578) and for U.S. GEOTRACES North Atlantic section ship time, sampling, and data analysis. The U.S. NSF also supported the generation of 230Th data (OCE-0927064 to LDEO, OCE-O092860 to WHOI, and OCE-0927754 to UMN) and 228,234Th data (OCE-0925158 to WHOI).en_US
dc.language.isoen_USen_US
dc.relation.urihttps://doi.org/10.1016/j.dsr.2017.05.003
dc.subjectGEOTRACESen_US
dc.subjectThoriumen_US
dc.subjectParticle Concentration Effecten_US
dc.subjectSingle-particle class modelen_US
dc.subjectInverse methoden_US
dc.titleKinetics of thorium and particle cycling along the U.S. GEOTRACES North Atlantic Transecten_US
dc.typePreprinten_US


Files in this item

Thumbnail

This item appears in the following Collection(s)

Show simple item record