Sources, transport, and fates of particulate trace metals in the Gulf of Maine-Scotian Shelf and Labrador Sea

This dissertation research describes three studies examining of the role of particulate metals in the northwest Atlantic Ocean. Manuscript 1 provides a discussion of the distribution of a suite of size-fractionated particulate trace metals (Al, Fe, Sr, Ba, Mn, Pb, Cu, V, and Co) in the Gulf of Maine, Scotian Shelf and Labrador Sea. An important facet of this study is the demonstration that the Challenger Oceanic Systems and Services large-volume in-situ pump is a valuable tool for the collection of size-fractionated particulate metals in the marine environment. In Manuscript 2, an empirical approach to quantify the downward flux of particulate trace metals is evaluated using simultaneous measurements of the 234Th-238U disequilibrium and particulate metal/234Th ratios. In shelf waters, sinking fluxes of particulate Al, Fe, and Pb, calculated at 50 m, are greater than the respective fluxes calculated at 50 m in slope waters and the Labrador Sea. Vertical particulate fluxes of Al, Ba (Labrador Sea only), and Pb in slope waters and the Labrador Sea increase between 50 and 100 m, whereas the particulate flux of Fe remains relatively invariant. The primary uncertainty in the 234Th-derived flux is variability in the particulate metal/234Th ratio with depth and particle size. The 234Th-derived flux of trace metals is within the range or approximately two to four times greater than published sediment trap results compiled for the world ocean. Manuscript 3 describes the use of stable Pb isotope ratios to trace the geographic source of anthropogenic Pb input to the marine environment and investigate size-dependent particle-particle interactions. Stable Pb isotope ratio measurements indicate that contaminant Pb in the Gulf of Maine-Scotian Shelf region is largely a mixture of inputs from U.S. and Canadian sources. In the Labrador Sea, Pb associated with water column particulate matter is a binary mixture of Pb from two ores; Broken Hill, Australia and SE Missouri, US. Size-fractionated particles from the Labrador Sea exhibit a lack of particulate Pb isotopic equilibrium in the upper 250 m. The apparent disequilibrium is likely due to the different residence times of suspended and large sinking particles