Plutonium and americium concentrations in sea water and in sinking particles

DOI

Vertical fluxes of 239+240Pu and 241Am and temporal changes in their inventories in the northwestern Mediterranean Sea have been examined through high-resolution water column sampling coupled with direct measurements of the vertical flux of particle-bound transuranics using time-series sediment traps. Water column profiles of both radionuclides showed well-defined sub-surface maxima (2391240Pu between 100-400 m; 241Am at 100-200 m and 800 m), the depths of which are a result of the different biogeochemical scavenging behavior of the two radionuclides. Comparison of deep water column (0-2,000 m) transuranic inventories with those derived from earlier measurements demonstrate that the total 2391240Pu inventory had not substantially changed between 1976-1990 whereas 241Am had decreased by approximately 24%. Enhanced scavenging of 241Am and a resultant, more rapid removal from the water column relative to 239+240Pu was also supported by the observation of elevated Am/Pu activity ratios in sinking particles collected in sediment traps at depth. Direct measurements of the downward flux of particulate 239+240Pu and 241Am compared with transuranic removal rates derived from observed total water column inventory differences over time, show that particles sinking out of deep waters (1,000-2,000 m) could account for 26-72% of the computed total annual 239+240Pu loss and virtually all of the 241Am removal from the water column. Upper water column (0-200 m) residence times based on direct flux measurements ranged from 20-30 yr for 239+240Pu and 5-10 yr for 241Am. The observation that 241Am/239+240Pu activity ratios in unfiltered Mediterranean seawater are six times lower than those in the north Pacific suggests the existence of a specific mechanism for enhanced scavenging and removal of 241Am from the generally oligotrophic waters of the open Mediterranean. It is proposed that atmospheric inputs of aluminosilicate particles transported by Saharan dust events which frequently occur in the Mediterranean region could enhance the geochemical scavenging and resultant removal of 241Am to the sediments.

Supplement to: Fowler, Scott W; Noshkin, V E; La Rosa, J; Gastaud, J (2000): Temporal variations in plutonium and americium inventories and their relation to vertical transport in the northwestern Mediterranean Sea. Limnology and Oceanography, 45(2), 446-458

Identifier
DOI https://doi.org/10.1594/PANGAEA.738655
Related Identifier https://doi.org/10.4319/lo.2000.45.2.0446
Metadata Access https://ws.pangaea.de/oai/provider?verb=GetRecord&metadataPrefix=datacite4&identifier=oai:pangaea.de:doi:10.1594/PANGAEA.738655
Provenance
Creator Fowler, Scott W; Noshkin, V E; La Rosa, J; Gastaud, J
Publisher PANGAEA
Publication Year 2002
Funding Reference European Commission https://doi.org/10.13039/501100000780 Crossref Funder ID ERBIC20-CT98-0103 Mediterranean Data Archaeology and Rescue; European Commission https://doi.org/10.13039/501100000780 Crossref Funder ID MAS3-CT98-0174 Mediterranean Data Archaeology and Rescue
Rights Creative Commons Attribution 3.0 Unported; https://creativecommons.org/licenses/by/3.0/
OpenAccess true
Representation
Language English
Resource Type Supplementary Publication Series of Datasets; Collection
Format application/zip
Size 4 datasets
Discipline Ancient Cultures; Archaeology; Humanities
Spatial Coverage (5.933W, 41.950S, 7.867E, 43.428N)
Temporal Coverage Begin 1988-06-05T00:00:00Z
Temporal Coverage End 1989-12-15T00:00:00Z