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Abstract: The distribution of dissolved (soluble and total) and particulate (leachable and total) aluminum was examined in the Columbia River and estuary, in near-field and far-field river plumes, and in adjacent coastal waters of Washington and Oregon during the River Influence on Shelf Ecosystems (RISE) cruise of May/June 2006. Dissolved and particulate aluminum (Al) concentrations were significantly greater in the river than in the coastal waters that mixed to form the plume. Dissolved Al concentrations in the Columbia River (∼80nM) were low relative to other major rivers. Leachable and total particulate Al concentrations within the river reached concentrations greater than 1000nM and 18,000nM, respectively. Dissolved Al within the Columbia River estuary showed a significant removal (∼60%) at salinities between 0 and 10 with salt-induced flocculation of colloidal Al complexes and enhanced particle scavenging being probable explanations for aluminum removal. Dissolved and particulate Al concentrations were significantly greater in near-field plumes relative to surrounding coastal waters. As the plume advected from near-field to far-field away from the river mouth, dilution of the plume with lower dissolved Al surface waters as well as particle scavenging along the flow path appeared to be controlling dissolved Al distributions. Particle settling as well as dilution with lower particle-load waters led to observed decreases in particulate Al as the plume moved from near-field to far-field. However, the percent-leachable particulate aluminum in both near-field and far-field plumes was remarkably constant at ∼7%. Dissolved and particulate Al in a far-field plume over 100km southwest of the Columbia River mouth were over an order-of-magnitude greater than surrounding waters, illustrating the importance of the Columbia River plume as a mechanism for transporting Al offshore. Aluminum could be used to trace the input of biologically-required elements such as iron into waters off the shelf. [Copyright &y& Elsevier]

Abstract: The coastal northern Gulf of Alaska receives significant fluvial inputs from the numerous glaciers and rivers that border the region. The distribution of dissolved (soluble and total) and particulate aluminum (leachable and total) was examined in coastal surface water transects and vertical profile samples from shelf stations in the northern Gulf of Alaska in August and September 2007. Both dissolved and particulate aluminum concentrations were dramatically increased in low-salinity plumes, indicative of the significant riverine/glacial input to coastal waters in the region. The percent-leachable particulate Al fraction in these low-salinity plumes was quite low (∼7%), indicative of the large refractory nature of the lithogenic material being delivered to the coastal waters. A consistency in Si:Al ratios from different time periods in the freshwater endmembers that mix to form the low-salinity plumes is discussed in terms of the weathering of biotite in this region. The dissolved Al in these coastal waters appears entirely in the soluble (<0.03µm) fraction, likely a consequence of the freshwater sources to the region being very low in dissolved organic carbon and organic colloidal complexes. An extreme decreasing gradient of dissolved Al in surface waters was observed moving offshelf and into the waters of the Alaskan subarctic gyre where some of the lowest dissolved Al concentrations reported in the world ocean were observed. A high-degree of particle scavenging of dissolved Al in the coastal waters is discussed with a residence time of dissolved Al in coastal shelf waters estimated to be ∼10days. [ABSTRACT FROM AUTHOR]