Comparative role of salps and other zooplankton in the cycling and transport of selected elements and natural radionuclides in Mediterranean waters

Abstract

Salps, salp fecal pellets and other zooplankton species were analyzed for a suite of elements and natural radionuclides to assess their role in the biogeochemical cycling of nuclides in oceanic waters. The nuclide/Al ratios in organisms normalized to the same ratio in crustal rock indicated that Ca, Sr, Zn, Cu, U, ²¹⁰Po, and ²¹⁰Pb are enriched in the organisms. The concentrations of Fe, Al, Th isotopes and ²¹⁰Pb in salps and fecal pellets were about an order of magnitude higher than those in salps, whereas Ca, Cu, Zn, Mn and Po were higher by factors of about 2-5. Fluxes via salp defecation were higher than those which have been measured in crustacean zooplankton species, a result primarily due to the high defecation rates characteristic of salps. High nuclide levels in salp fecal pellets coupled with high defecation rates and presumed high salp biomass in many areas underscore the importance of these indiscriminate filter feeders in packaging and transporting to depth particulate-associated nuclides in surface waters.