WA6 Alaska North-Slope Environmental Monitoring
Room 18A/B, Level 4
8:00 AM - 12:00 PM, Wednesday, 12 November 2003
Chair: Boehm, Paul ,
(372) Sources, concentrations, composition and dispersion pathways for suspended sediment in the coastal Beaufort Sea.
Trefry, J1, Rember, R1, Trocine, R1, Savoie, M2, 1 Florida Institute of Technology, Melbourne, FL, USA2 Kinnetics Laboratories Inc, Anchorage, AK, USA
ABSTRACT- More than half the annual load of suspended sediment carried to the coastal Beaufort Sea by the Sagavanirktok, Kuparuk and Colville rivers is transported in two to three weeks. During June 2001, concentrations of total suspended solids (TSS) in the Sagavanirktok River increased from 40 mg/L to 600 mg/L in 10 days, and then decreased to 30 mg/L six days later on June 18. During July and August 2001, concentrations of TSS averaged 2 mg/L. Total sediment transport by the Sagavanirktok River during 2001 was about 0.3 million metric tons, with 87% of total sediment transport occurring during 12 days in June. Particles transported >90% of the river load of Cu, Fe, Pb and Zn, but <40% of the organic carbon, during peak flow in the Sagavirktok River during 2001. Suspended sediment carried by rivers during spring floods flows out over and under the 2-m thick ice that covers the Beaufort Sea during June. Near the mouth of the Sagavanirktok River, concentrations of TSS in 2001 and 2002 averaged about 40 mg/L in a 1- to 2-m thick lens of freshwater that extended 20 km offshore, directly under the ice. This suspended sediment was rich in fine-grained aluminosilicates (clays) as demonstrated through electron-microscopy and by levels of Al, K and other metals. During the brief open-water season, turbidity in the coastal Beaufort Sea is directly related to the speed and duration of the wind. For example, TSS levels >100 mg/L were observed following a 6-day, >25-knot storm in 1999 relative to TSS levels that were <1 mg/L in calm waters, sheltered by floating ice. Transects made by towing a turbidimeter-CTD package near an oil development island during August 2001 showed uniform, background levels of TSS at 2 mg/L just above the pycnocline at a water depth of 1.5 m. Levels of TSS below the pycnocline were <1 mg/L. No significant deviations in TSS values were observed during 2000 and 2001 along various transects adjacent to the island at distances as close as 100-500 m. Sedimentation rates throughout the study area, determined using Cs-137 and excess Pb-210 techniques, range from 0.1 cm/yr to no discernible recent deposition. These results support previous conclusions that the study area is a net erosional environment with a sizeable fraction of the incoming sediment most likely being carried off the shelf into deeper water.
Key words: trace metals, suspended sediments, Alaska, Beaufort Sea