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An assessment of particulate organic carbon to thorium-234 ratios in the ocean and their impact on the application of 234Th as a POC flux proxy


Buesseler, KO and Benitez-Nelson, CR and Moran, SB and Burd, A and Charette, M and Cochran, JK and Coppola, L and Fisher, NS and Fowler, SW and Gardner, WD and Guo, LD and Gustafsson, O and Lamborg, C and Masque, P and Miquel, JC and Passow, U and Santschi, PH and Savoye, N and Stewart, G and Trull, T, An assessment of particulate organic carbon to thorium-234 ratios in the ocean and their impact on the application of 234Th as a POC flux proxy, Marine Chemistry, 100, (3-4) pp. 213-233. ISSN 0304-4203 (2006) [Refereed Article]

DOI: doi:10.1016/j.marchem.2005.10.013


Thorium-234 is increasingly used as a tracer of ocean particle flux, primarily as a means to estimate particulate organic carbon export from the surface ocean. This requires determination of both the 234Th activity distribution (in order to calculate 234Th fluxes) and an estimate of the C / 234Th ratio on sinking particles, to empirically derive C fluxes. In reviewing C / 234Th variability, results obtained using a single sampling method show the most predictable behavior. For example, in most studies that employ in situ pumps to collect size fractionated particles, C / 234Th either increases or is relatively invariant with increasing particle size (size classes > 1 to 100s μm). Observations also suggest that C / 234Th decreases with depth and can vary significantly between regions (highest in blooms of large diatoms and highly productive coastal settings). Comparisons of C fluxes derived from 234Th show good agreement with independent estimates of C flux, including mass balances of C and nutrients over appropriate space and time scales (within factors of 2-3). We recommend sampling for C / 234Th from a standard depth of 100 m, or at least one depth below the mixed layer using either large volume size fractionated filtration to capture the rarer large particles, or a sediment trap or other device to collect sinking particles. We also recommend collection of multiple 234Th profiles and C / 234Th samples during the course of longer observation periods to better sample temporal variations in both 234Th flux and the characteristic of sinking particles. We are encouraged by new technologies which are optimized to more reliably sample truly settling particles, and expect the utility of this tracer to increase, not just for upper ocean C fluxes but for other elements and processes deeper in the water column. © 2006 Elsevier B.V. All rights reserved.

Item Details

Item Type:Refereed Article
Research Division:Earth Sciences
Research Group:Oceanography
Research Field:Chemical oceanography
Objective Division:Environmental Management
Objective Group:Marine systems and management
Objective Field:Measurement and assessment of marine water quality and condition
UTAS Author:Trull, T (Professor Thomas Trull)
ID Code:43325
Year Published:2006
Web of Science® Times Cited:200
Deposited By:IASOS
Deposited On:2006-08-01
Last Modified:2007-05-01

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