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Particulate organic carbon : natural radionuclide ratios in zooplankton and their freshly produced fecal pellets from the NW Mediterranean (MedFlux 2005)
Author(s) -
Rodriguez y Baena Alessia M.,
Fowler Scott W.,
Miquel Juan Carlos
Publication year - 2007
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.2007.52.3.0966
Subject(s) - zooplankton , pellets , bioaccumulation , environmental chemistry , chemistry , zoology , environmental science , oceanography , biology , ecology , geology
To discern controls on particulate organic carbon (POC) : natural radionuclide (RN) ratio variability in order to enhance the accuracy of water column radionuclide‐based carbon flux estimates, 234 Th, 210 Po, and POC were analyzed in seven size classes of mixed micro‐ and mesoplankton (1‐1,500‐µm size range), in larger zooplankton from different taxa (salps, euphausiids, copepods, pteropods), and in freshly produced feces from zooplankton collected during spring in the NW Mediterranean. POC:RN ratios in zooplankton ranged between 120 and 11,600 and between 89 and 9,200 µmol dpm −1 for 234 Th and 210 Po, respectively. In fecal pellets, POC:RN ratios were one to three orders of magnitude lower for 234 Th and 3‐fold to 30‐fold lower for 210 Po; the only exception was euthecosome pteropods, which had a higher POC: 210 Po ratio in their pellets than in their whole bodies. Significant increases in POC:RN ratios with organism size were best described by a power relationship for POC: 234 Th (p < 0.0006) and a saturation exponential equation for POC: 210 Po (with a constant POC: 210 Po ratio above 70 µm; p < 0.004), suggesting that the observed trend most likely results from surface adsorption processes for 234 Th and food chain bioaccumulation for 210 Po. This inference is further supported by the observation that, for the >33‐µm size classes, 210 Po specific activity correlates negatively with the surface : volume ratio, while 234 Th correlates positively with it (p < 0.004 and p < 0.001, respectively). POC:RN ratios vary greatly among species and to a lesser extent among fecal pellet types, most probably due to differences in zooplankton feeding strategies. Partial removal of most zooplankton “wimmers” from trap samples would not likely confound assessment of 234 Th flux; however, it could considerably bias similar measurements of 210 Po flux as well as those of POC:RN ratios.