River-shelf interactions during Spring floods in the coastal Beaufort Sea

Spring floods carry 40 to more than 80% of the annual amounts of river water, suspended sediment and dissolved solids from Alaska to the coastal Beaufort Sea.

In this study, river water and suspended sediment were collected from the Sagavanirktok and Kuparuk rivers during the spring Floods of 2001, 2002, 2004 and 2006. Concentrations of dissolved Cu, Fe, Pb and some other trace metals, along with DOC, generally increased by 3-to-25-fold within 3 to 7 days of onset of the melt water event due to thawing of ponds and upper soil layers.

These peak concentrations then decreased over the next several days. Only minor shifts in concentrations of major ions were observed during the two to three week flood period. Interannual variations in flow patterns and peak concentrations of dissolved trace elements and suspended sediments were influenced by total flow and cooling and refreezing of flood water during any given year The transfer and fate of riverine inputs in the ocean was influenced by river volume and the presence of 2m thick ice in the coastal Beaufort Sea during spring. River flow was traced up to 15km offshore in 0.5 to 2m thick layers under the ice.

Water from the two rivers and from sea ice has geochemical characteristics that are different from ambient seawater as well as from each other that facilitated tracking of under-ice mixing. Conservative and some non-conservative mixing were observed for selected constituents across the freshwater-seawater interface; however, shifting concentrations of some dissolved substances in river water during the flood period complicated the tracking process.

Observed variations in river composition, flow and mixing with coastal seawater during this multi-year study provide insights to possible future responses to environmental change in the arctic.