| Popis: |
From October 1986 through May 1988, seven cruises took place at approximately three-month intervals at the VERTEX time-series station (33°N, 139°W) in the North Pacific. Data on plutonium (239+240Pu) and, in some cases, 241Am in unfiltered sea water, suspended particulate matter, sediment trap material, and zooplankton and their fecal pellets were collected over a 2000 m water column in order to examine temporal variations in particulate-associated transuranic flux and its relationship to biological activity in the upper water layers. Some seasonality in 239+240Pu flux was noted with the highest fluxes corresponding to the lowest mass fluxes below 400 m in summer through early winter (possibly due to scavenging by fine particles), and the lowest 239+240Pu fluxes corresponding to the highest mass fluxes above 150 m at the same time of year (due apparently to minimal scavenging in the euphotic zone). Little apparent difference was noted in the relationship between 239+240Pu flux and mass flux during late winter and spring at all depths, suggesting minimal scavenging at depth and generally small mass fluxes out of the euphotic zone. Salps which feed on tiny particles have relatively high concentrations of 239+240Pu in their fecal pellets while copepods which feed more selectively on larger particles have lower transuranic concentrations in their pellets. |
