1. Shelf-basin exchange in the Western Arctic Ocean
(R. Pickart and M. Spall)
Objective: To observe and understand the processes that
contribute to the exchange of water (heat, salt,
carbon, etc) between the shelf and basin interior.
General approach: Combine in-situ observations, idealized and
more realistic models, remotely sensed data products,
simple theory
For today: Oceanic response to upwelling wind events
Wrangel Island
(Photo by D. Torres)

2. Shelf-break jet response to storms
mooring array
Chukchi Sea
Beaufort Sea
0.8 Sv
Beaufort Slope Mooring Array horizontal spacing of O(5km) (resolves the internal deformation radius)

3. High spatial and temporal resolution identifies several water masses
Present focus is on upwelled Atlantic water
First year time series at center of boundary current
Winter-transformed
Pacific water
Alaskan Coastal water
Upwelled Atlantic water
potential temperature (oC)

4. Western Arctic Boundary Current
Spring average - shelfbreak
jet of Pacific water

5. Western Arctic Boundary Current
Summer average – surface
intensified warm outflow

6. Western Arctic Boundary Current
Note deep velocity
core of Atlantic Water
Winter average – focus today

7. Storms impacting the Beaufort Sea
Pacific-born storm (upwelling)
Arctic-born storm (downwelling) L L
Focus is on upwelling storms (predominant, 28 in 2002)

8. WRF model simulation of storm (3 km resolution)
Composite wind speed during a storm event in Nov. 2002
Maximum winds in the
Chukchi Sea, over open
water
Located to the west
of the SBI array

9. Observations from SBI array
Eastward flowing modified Pacific water at shelfbreak
(deep core is renmant from previous storm)

10. Observations from SBI array
Offshore Ekman transport, Atlantic Water pulled onto,
shelf, strong westward flow at surface

11. Observations from SBI array
Wind ceases, isopycnals remain steep but current reverses,
driving deep eastward flow of Atlantic Water

12. Idealized primitive equation model
Initial Condition
Salinity
MITgcm : 30 levels
grid spacing 2-10 km
Initialize at rest, blow wind
for 4 days, turn off
No Wind
Wind
No Wind
2725 km Y
Shelf and slope X
3400 km

13. Model fields (east of wind forcing)
Salinity
Alongstream velocity (cm/s)
1 day after winds are
turned off
Ekman transport lifts
isopycnals, depresses SSH
near the coast, and drives a
westward flow

14. Model fields (east of wind forcing)
Salinity
Alongstream velocity (cm/s)
1 day after winds are
turned off
Salinity is slow to adjust to
change in wind but velocity
adjusts rapidly – due to fast
propagation of SSH
Results in deep eastward flow
similar to observations
3 days after winds are
turned off

15. Storm drives anticyclonic circulation over northern Chukchi
Results from a more realistic model
forced by NCEP winds – 3 phases
Broad scale response
prior during after
SSH
Storm drives anticyclonic circulation over northern Chukchi
Sea, eastward flow along shelf break, slow to decay

16. Similar reversal in Barrow Canyon, enhancement of
Observed currents at various
sites – 3 phases of storm
prior during after
Similar reversal in Barrow Canyon, enhancement of
eastward flow along Chukchi shelfbreak

17. Summary:
upwelling storms are common along north slope
of Alaska in winter
Ekman transport upwells Atlantic Water,
drives westward flow
Rapid propagation of barotropic waves results in
deep eastward flow of Atlantic Water
Wind stress curl (due primarily to ice) drives
basin-scale anticyclonic circulation over the
Chukchi Sea which is slow to decay, loss of
upwelled Atlantic Water
Next: momentum and tracer budgets