Date of Award

8-2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Ecology and Evolutionary Biology

Major Professor

Jacqueline M. Grebmeier

Committee Members

Lee W. Cooper, James Drake, Carol Harden

Abstract

Drifting sediment traps were deployed in 2004 in the ChukchiSeato investigate the variability in the vertical flux of biogenic matter in the presence and absence of sea ice. Measurements of chlorophyll-a, particulate organic carbon (POC), particulate organic nitrogen, phytoplankton, zooplankton fecal pellets, and the stable carbon isotope composition of the sinking material were accomplished along two shelf-to-basin transects. POC fluxes obtained in ice-covered and ice-free conditions were of different composition but of similar magnitude, indicating that the export fluxes in the presence of ice cover contributed significantly to the annual export of biogenic matter in the Chukchi Sea. These results suggest that a reduction or disappearance of ice cover on the Chukchi continental shelf would not necessarily increase the annual export of POC.

Large-volume sampling of 234Th was conducted simultaneously with drifting sediment trap deployments in the Chukchi Sea. Measurements of 234Th and particulate organic carbon export fluxes obtained with in situ pumps and drifting sediments traps agreed to within a factor of 2 for 70% of the measurements. Despite the good agreement between methods, discrepancies in POC export fluxes measured using in situ pumps and sediment traps may be reasonably explained by differences in the estimated POC/234Th ratios that arise from differences between the techniques, such as time-scale of measurement and size and composition of the collected particles.

Large-volume sampling of 234Th was conducted to estimate POC export in conjunction with drifting sediment trap deployments in the northern Barents Sea in 2003 and 2005. Although 234Th fluxes measured with both methods agreed within a factor 2 at most stations and depths sampled, sediment trap POC fluxes were much lower than large-volume POC fluxes at almost every station. One possibility is that the offset between the two methods may be due to the prominent presence of the prymnesiophyte Phaeocystis pouchetii in the Barents Sea, which could potentially cause the large variation observed in POC/234Th ratios. If this is the case, the use of drifting sediment traps might be a more reliable method to measure the vertical export of biogenic matter in the Barents Sea, in particular during P. pouchetii blooms.

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