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Uncertainty versus variability in upper ocean carbon flux estimates
Author(s) -
BenitezNelson Claudia R.,
Charette Matthew A.
Publication year - 2004
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2004.49.4.1218
Subject(s) - south carolina , citation , library science , limnology , oceanography , archaeology , geology , geography , computer science , political science , public administration
The recent article written by Moran et al. (2003) (herein referred to as M2003) poses the question whether thorium234 (234Th) provides an accurate record of particulate organic carbon (POC) export from the upper ocean. Although there is little argument that 234Th : 238U disequilibrium can be attributed to particle flux, we agree that there are still many unknowns regarding the factors that control the ratio of POC to 234Th among various particle size classes. However, we argue that the M2003 article misapplies POC : 234Th ratios and confuses ‘‘natural range and variability’’ with ‘‘uncertainty’’ in the 234Th technique to support its hypothesis. Rather than clarifying how the 234Th technique should be applied, the M2003 article clouds the issue. We feel that its narrow focus and interpretation do not reflect the 234Th community’s current understanding and application of the 234Th method for deriving export. Thus, it is misleading to the rest of the oceanographic community. In seawater, highly particle reactive 234Th is produced from its conservative parent 238U. The basis for the 234Th technique is straightforward: disequilibrium between measured and expected concentrations of 234Th in seawater can be directly attributed to removal by scavenging onto sinking particles. 234Th fluxes are converted into other elemental fluxes by simply multiplying the 234Th flux by the ratio of a particular element (i.e., POC) to 234Th on sinking particles at the base of the depth range of interest. The M2003 article focuses on only a subset of issues associated with the 234Th technique: depth-integrated 234Th fluxes and POC : Th ratios collected by in situ pumps.