Could krill schools significantly bias 234Th-based carbon flux models?

Rodriguez y Baena, Alessia M., Scott W. Fowler, Michel Warnau

Limnol. Oceanogr., 53(3), 2008, 1186-1191 | DOI: 10.4319/lo.2008.53.3.1186

ABSTRACT: To test the recent hypothesis that krill schools and their molting can hinder the accuracy of 234Th-based particle flux models under specific conditions, radiotracer experiments were conducted with northern krill, Meganyctiphanes norvegica, to examine how 234Th uptake and release kinetics may affect residual 234Th concentrations in seawater. Krill rapidly took up 234Th from seawater, reaching a steady-state concentration factor of ~180 in less than 1 week, and strongly retained the accumulated radionuclide until molting occurred. The nine molting events observed during the 18-d experimental period indicated that ~50% of krill whole-body 234Th activity was associated with the cast exoskeleton, and that a corresponding amount was rapidly adsorbed postecdysis on the newly formed cuticle. In regions characterized by the occurrence of high planktonic crustacean biomass, failure to link the presence of organisms with their effects on 234Th dynamics in the water column may induce significant biases (in some circumstances, up to one order of magnitude) in 234Th-derived particulate organic carbon flux estimations or sediment trap efficiency calculations based on this method. However, because of the patchy distribution of dense aggregations of krill, the overall likelihood of such dramatic modeling artifacts is estimated to be relatively low (<5% per sampling time).

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