1. Chukchi and Beaufort Seas Open Water Circulation Tom Weingartner Institute of Marine Science, University of Alaska Workshop on Effects of Dispersed Oil with Emphasis on the Beaufort and Chukchi Seas Anchorage, AK March 26, 2006 Minerals Management Service National Science Foundation Office of Naval Research Japan Marine Science and Technology Center Alaska Department of Environmental Conservation

2. The Chukchi Sea 1.Mean flow Field (moorings, model) 2.Wind-forced variability 3.Stratification The Beaufort Sea 4.The “open water” season 5.Wind-forced variability 6.Mesoscale Variability The continental slope Important considerations/unknowns

3. Bathymetry is the key Shoals Channels “flat” regions Steeply sloping shelfbreak Convention Line

4. Composite Mean Flow Field From Moorings (1990 – 1995) Mean (and Varying Flow) parallels isobaths and is “northward” Mean currents oppose winds!!!! ( Wind)

5. (Courtesy M. Spall, WHOI) Model Mean Streamlines Mean flow is “northward” and bathymetrically “steered”. Shoals are isolated “trapping” Circulation around Hanna shoal (western and central shelf connects to eastern shelf/Barrow Canyon) Shelfbreak flow intensified north of Hanna Shoal

6. The Mean Flow reflects global processes that transports water From the Pacific to the Atlantic via the Arctic Ocean.

7. The Mean Flow is reflected in the ice- edge meltback pattern “Post-office Point” Hanna Herald HV CC BC

8. The “Russian Connection”: East- or Northeastward Flow over the North Central Shelf Russian EEZ connected to Northeastern Shelf. But the connection is poorly understood. Contaminants from Russian EEZ may enter the NE Chukchi Sea.

9. Current strength varies in proportion to bottom slope: ~2 kt Barrow Canyon ~0.5 kt Central Channel ~.25 kt elsewhere Wind-forced variability: Accounts for ~50% of current variance Coherence scales ~300km Rapid response ~1 day Current fluctuations are along-isobath and have a distinct seasonal cycle: Winter: Max Variance Summer: Min Variance

10. West-East Hydrographic Section The shelf is stratified for at least part of the year (Spring through fall). MAY NOT Surface flow MAY NOT BE the same as that measured at depth. Stratification can exasperate these differences. Moored current meters do not measure the upper 1 m. HV HERALD CC HANNA BC

11. The Beaufort Sea

12. SEASONAL VARIATIONS: Ice Thickness, Set-up & Alongshore Currents TIDAL; Along-shore P-Grads

13. Beginning and end of the open water season varies spatially: (Central Alaskan Beaufort melts last)

14. Winds-currents coherent; Wind-forced reversals are frequent and can occur rapidly October 2006 Mean winds: 20 kts westward Mean Along-shelf Flow: 20 cm/s 500 km displacement in 30 days! eastward westward

15. Probabilistic 12-day particle displacements during the open water season Red: 20% open water season average = 15 km/day Yellow: 40% “ “ “ maximum = 60 km/day Green: 60% Cyan: 80% Blue: 100%

16. “Turbid Fresh” plumes Runoff and Ice melt fronts + stratification induce: Mesoscale Variations (  x = 5 – 30 km; T= 2 – 5 days; U=0.5kt) Results in cross-shelf transport and mixing Ice

18. Chukchi and Beaufort unknowns 1.) Flow at air-water and ice-water boundary (presumed downwind and in direction of ice or wind). Technology exists to make these measurements (CS). 2.) Hanna Shoal region is a potential trapping and recirculation zone (CS) 3.) Flow connections to the western Chukchi Sea (e.g., Russian EEZ) 4.) Mesoscale variations: ice edges (BS and CS) Freshwater runoff (BS): seasonality, vigor, frequency? 5.) Confluence of Chukchi (Barrow Canyon) and Beaufort shelf flows in western Beaufort: eddies, meanders, etc.