Kinetics of thorium and particle cycling along the U.S. GEOTRACES North Atlantic Transect
Lam, Phoebe J.
Buesseler, Ken O.
Charette, Matthew A.
MetadataShow full item record
KeywordGEOTRACES; Thorium; Particle Concentration Effect; Single-particle class model; Inverse method
The 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.
© 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.
Suggested CitationPreprint: Lerner, Paul, Marchal, Olivier, Lam, Phoebe J., Buesseler, Ken O., Charette, Matthew A., "Kinetics of thorium and particle cycling along the U.S. GEOTRACES North Atlantic Transect", 2017-05, https://doi.org/10.1016/j.dsr.2017.05.003, https://hdl.handle.net/1912/9144
Showing items related by title, author, creator and subject.
Testing models of thorium and particle cycling in the ocean using data from station GT11-22 of the U.S. GEOTRACES North Atlantic section Lerner, Paul; Marchal, Olivier; Lam, Phoebe J.; Anderson, Robert F.; Buesseler, Ken O.; Charette, Matthew A.; Edwards, R. Lawrence; Hayes, Christopher T.; Huang, Kuo-Fang; Lu, Yanbin; Robinson, Laura F.; Solow, Andrew R. (2016-03-31)Thorium is a highly particle-reactive element that possesses different measurable radio-isotopes in seawater, with well-constrained production rates and very distinct half-lives. As a result, Th has emerged as a key tracer ...
Improvements to 232-thorium, 230-thorium, and 231- protactinium analysis in seawater arising from GEOTRACES intercalibration Auro, Maureen E.; Robinson, Laura F.; Burke, Andrea; Bradtmiller, Louisa I.; Fleisher, Martin Q.; Anderson, Robert F. (Association for the Sciences of Limnology and Oceanography, 2012-07)The GEOTRACES program requires the analysis of large numbers of seawater samples for 232Th, 230Th, and 231Pa. During the GEOTRACES international intercalibration exercise, we encountered unexpected difficulties with recovery ...
Maiti, Kanchan; Buesseler, Ken O.; Pike, Steven M.; Benitez-Nelson, Claudia R.; Cai, Pinghe; Chen, Weifang; Cochran, Kirk; Dai, Minhan; Dehairs, Frank; Gasser, Beat; Kelly, Roger P.; Masqué, Pere; Miller, Lisa A.; Miquel, Juan Carlos; Moran, S. Bradley; Morris, Paul J.; Peine, Florian; Planchon, Frederic; Renfro, Alisha A.; Rutgers van der Loeff, Michiel M.; Santschi, Peter H.; Turnewitsch, Robert; Waples, James T.; Xu, Chen (Association for the Sciences of Limnology and Oceanography, 2012-09)Intercomparision of 234Th measurements in both water and particulate samples was carried out between 15 laboratories worldwide, as a part of GEOTRACES inter-calibration program. Particulate samples from four different ...