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Radionuclide fluxes in the Arabian Sea: the role of particle composition |
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| Authors: | JC Scholten J Fietzke A Mangini P Stoffers T Rixen B Gaye-Haake T Blanz V Ramaswamy F Sirocko H Schulz V Ittekkot |
| Institution: | aInstitute of Geosciences, University Kiel, Olshausenstr. 40, 24118 Kiel, Germany bHeidelberger Akademie der Wissenschaften, Im Neuenheimer Feld 299, 69120 Heidelberg, Germany cZentrum für Marine Tropenoekologie, University Bremen, 28334 Bremen, Germany dInstitut für Biogeochemie und Meereschemie, University Hamburg, 20146 Hamburg, Germany eInstitut fuer Ostseeforschung-Warnemuende, University Rostock, 18119 Rostock-Warnemuende, Germany fNational Institute of Oceanography, Dona Paula, Goa 403 004, India gInstitut für Geowissenschaften, Johannes Gutenberg-University Mainz, 55099 Mainz, Germany hInstitut für Geowissenschaften, University Tuebingen, 72076 Tuebingen, Germany |
| Abstract: | We investigated the influence of the composition of the vertical particle flux on the removal of particle reactive natural radionuclides (230Th and 231Pa) from the water column to the sediments. Radionuclide concentrations determined in sediment traps moored in the western, central and eastern Arabian Sea were related to the major components (carbonate, particulate organic matter (POC), opal, lithogenic material) of the particle flux. These data were combined with sediment trap data previously published from the Southern Ocean, Equatorial Pacific and North Atlantic Z. Chase, R.F. Anderson, M.Q. Fleisher, P.W. Kubik, The influence of particle composition and particle flux on scavenging of Th, Pa and Be in the ocean, Earth Planet. Sci. Lett. 204 (2002) 215–229; J.C. Scholten, F. Fietzke, S. Vogler, M. Rutgers van der Loeff, A. Mangini, W. Koeve, J. Waniek, P. Stoffers, A. Antia, J. Kuss, Trapping efficiencies of sediment traps from the deep eastern North Atlantic: The 230Th calibration, Deep Sea Research II 48 (2001) 2383–2408]. The correlations observed between the particle-dissolved distribution coefficients (Kd) of 230Th and 231Pa and the concentrations of the particle types depend on the sediment trap data set used. This result suggests that scavenging affinities of the nuclides differ between oceanic regions. Several factors (Kd values, reactive surface areas of particles, inter-correlations in closed data set) can, however, influence the observed relationships and thus hamper the interpretation of these correlation coefficients as a measure of relative scavenging affinities of the nuclides to the particle types investigated. The mean fractionation factor (F(Pa/Th)=Kd(Pa)/Kd(Th)) from the Equatorial Pacific (F=0.11±0.03) is similar to that from the North Atlantic (F(Pa/Th)=0.077±0.026), and both are lower than the factors from the Arabian Sea (F(Pa/Th)=0.35±0.12) and from the Southern Ocean (F(Pa/Th)=0.87±0.4). For opal concentrations exceeding  60%, an increase in the fractionation factors is observed causing a higher mean fractionation factor for the Southern Ocean trap data set. For the other areas investigated, differences in the mean fractionation factors cannot be related to the particles types considered. In the Arabian Sea, seasonally variable 231Paex/230Thex ratios observed in the sediment traps as well as differences of the ratios between recently deposited phytodetritus (fluff) and normal surface sediments indicate seasonal changes in scavenging processes which the generally accepted reversible scavenging models do not envisage. We assume that variable sinking rates of particles, and/or particles not considered in this study (e.g. colloids, manganese oxides, transparent exopolymer particles) may play an important but as yet unexplored role in deep-water scavenging processes. |
| Keywords: | radionuclides scavenging fractionation factor Arabian Sea sediment traps boundary scavenging |
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