Po-210 and Pb-210 concentration factors for zooplankton and faecal pellets in the oligotrophic South-West Pacific

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dc.contributor.authorJeffree, RAen_AU
dc.contributor.authorSzymczak, Ren_AU
dc.contributor.authorPeck, GAen_AU
dc.date.accessioned2021-06-10T06:45:03Zen_AU
dc.date.available2021-06-10T06:45:03Zen_AU
dc.date.issued2004-10-24en_AU
dc.date.statistics2021-03-15en_AU
dc.description.abstractIn a previous study on zooplankton sampled from very low productivity waters of French Polynesia [1], their Po-210 concentrations were found to be unexpectedly elevated, compared to values measured in marine zooplankton from various other geographical regions of the world. For the French Polynesian samples their Po-210 concentrations also increased appreciably as their biomass declined. A simple conceptual and mathematical model, that incorporated the established role of zooplankton faecal pellets in the removal of Po-210 and particle-reactive radionuclides and stable metals from the water column, could capture the shape of this empirical relationship between Po-210 concentration and their biomass and also explained the biomass-related mechanism that increases Po-210 concentrations in zooplankton [2]. Similarly, a field investigation in the Timor Sea showed that a range of particle-reactive elements showed elevated water concentrations as particle removal rates, as inferred from Th-234: U-238 disequilibria, reduced in the euphotic zone [3]. However, in these previous studies simultaneous in situ measurements of a range of parameters valuable in assessment of the role of zooplankton in the biogeochemical cycling of particle-reactive elements like Po-210 and Pb-210 were not made. Here we report preliminary results of a field study, that was undertaken in the oligotrophic waters of the South-West Pacific between New Caledonia and Fiji, where we simultaneously measured a) zooplankton biomass and their faecal pellet production rates, b) Po-210 and its progenitor Pb-210 in water, zooplankton and their faecal pellets and c) particle flux rates using U-238:Th-234 disequilibria, to further assess the role of zooplankton in Po-210 and Pb-210 biogeochemistry in the euphotic zone of oligotrophic systems [4]. Zooplankton sampled from the oceanic region of the South-West Pacific between Fiji and New Caledonia had biomasses ranging from 0.1 to 7.1 mgDW/m3, with a median value of 3.6 and mean of 2.65 mgDW/m3. Their faecal pellet production rates were measured on board and varied between 1.82.10-4-3.78.10-3 g dry faecal pellet. g dry zooplankton-1. hour-1, median ). Their measured Po-210 and Pb-210 concentrations were 830-2655 Bq.KgDW-1 and 44-617Bq. KgDW-1, respectively. Po-210 and Pb-210 concentrations in zooplankton varied between 565-1736 Bq.Kg dry weight-1 and 47-551 Bq.Kg dry weight-1, respectively. Po-210 concentration factors that only varied between 1.3 –3.3. 105 were elevated compared to the IAEA recommended value of 3.104 based on previous values [5]. Similarly, Pb-210 concentration factors ranging from 0.9-9.1. 104, were considerably elevated compared to the IAEA recommended value of 1.103 [5], indicating the presence of a further concentrating mechanism. Our results for Po-210 and Pb-210 show a consistency with published values [5,6] in that the concentration factor for Po-210 is elevated relative to Pb-210, but contrast with previous reported values in both being elevated by about an order of magnitude. Their comparably elevated concentrations in faecal pellets suggest that enhanced concentrations in zooplankton are a reflection of the heightened concentrations in their dietary phytoplankton.en_AU
dc.identifier.booktitleBook of extended synopsesen_AU
dc.identifier.citationJeffree, R. A., Szymczak, R., Peck, G. A. (2004). Po-210 and Pb-210 concentration factors for zooplankton and faecal pellets in the oligotrophic South-West Pacific. Paper presented to International Conference on Isotopes in Environmental Studies – Aquatic Forum 2004 Monte-Carlo, Monaco 25–29 October 2004. In Book of extended synopses. Retrieved from https://inis.iaea.org/collection/NCLCollectionStore/_Public/36/003/36003223.pdf?r=1#page=5&zoom=auto,-15,800en_AU
dc.identifier.conferenceenddate29 October 2004en_AU
dc.identifier.conferencenameIsotopes in Environmental Studies Aquatic Forum 2004en_AU
dc.identifier.conferenceplaceMonacoen_AU
dc.identifier.conferencestartdate25 October 2004en_AU
dc.identifier.placeofpublicationVienna, Austriaen_AU
dc.identifier.urihttps://inis.iaea.org/collection/NCLCollectionStore/_Public/36/003/36003223.pdf?r=1#page=5&zoom=auto,-15,800en_AU
dc.identifier.urihttps://apo.ansto.gov.au/dspace/handle/10238/10865en_AU
dc.language.isoenen_AU
dc.publisherInternational Atomic Energy Agencyen_AU
dc.subjectPacific Oceanen_AU
dc.subjectPlanktonen_AU
dc.subjectAquatic ecosystemsen_AU
dc.subjectMathematical modelsen_AU
dc.subjectTimor Seaen_AU
dc.subjectNew Caledoniaen_AU
dc.subjectFijien_AU
dc.titlePo-210 and Pb-210 concentration factors for zooplankton and faecal pellets in the oligotrophic South-West Pacificen_AU
dc.typeConference Abstracten_AU
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