Oceanographic Observations from the

Inner Beaufort Sea Shelf

Seth Danielson

Tom Weingartner

Jeremy Kasper

David Leech

Kevin Taylor

Institute of Marine Science

University of Alaska Fairbanks

Funding: MMS, ADEC

Outline

Regional Oceanographic Setting:IceFresh WaterWind

Review of Previous Results

New Observations and Analyses

Summary

80 km

600 km

Ice Cover2005 Snapshots

100% Ice Cover

Landfast Ice: Immobile Lid

From November to June

Lateral Melting

Landfast Ice Intact

Adjacent Shelf Influence

Offshore Melting

Much Open Water

Nearshore Melting

All Ice in Free Drift

January 16

August 14

July 25

June 4

Landfast ice and non-uniform melt

affects wind stress distribution over

the shelf.

River Discharge

Annual Cycle

~ 90% of annual runoff occurs in about 2 weeks and beneath the landfast ice.

2005 Kuparuk River Streamflow

(USGS)

Min Max

(K. Taylor)

5x

Mean Monthly Along-shelf Wind Stress

Annual Cycle(Barrow 1945 – 2005)

Ocean Stratification

The annual cycles of Ice, Fresh Water and Winds set the stage for and drive the stratification and the shelf circulation.

Stratified oceans (driven by runoff and melting) and unstratified oceans (driven by wind mixing and freezing) respond differently to winds.

Stratification is not well known over the Beaufort Shelf!

Fresh Water plumes?

Ice

Winds

Win

d S

pee

d

Mesoscale Variability

Currents

Mooring Configuration

Previous Results1999-2002: The first year-round oceanographic measurements

from beneath landfast ice on an arctic shelf

• Currents are primarily directed alongshore• Strong seasonality in current magnitude

– Vigorous currents during open water season– Currents under landfast ice are generally weak but are not zero

• Velocity coherence length scales are at least 30km in winter• Under-ice currents NOT coherent with the wind• Summer currents ARE coherent with the wind• Baseline data for oil spill response planning• New questions: led to the 2004-2007 field program

– What drives the currents underneath the landfast ice?– What are the decorrelation length scale upper bounds? Do they

vary with season?– How much frictional influence does ice present to the water?– What is the coupling between currents offshore and those under

the landfast ice?

Large currents & large current variability in summer

Stronger westward component in Smith Bay

2004/2005 East-West Currents

2004/2005 Landfast Ice Period

Alongshore variability apparent – not clear why: Ice?

- Implies cross-shelf transport

Landfast Ice Breakout event in Smith Bay

Landfast Ice Breakout

Smith Bay SAR Image: Jan. 4, 2005 (A. Mahoney)

Landfast Ice Season

• Camden Bay velocities are uncorrelated with those at Smith Bay and Prudhoe Bay

• In summer, velocities ARE coherent along the length of the shelf.

Coherence

Squared

Landfast Ice Season Alongshore Pressure gradient & currents:

They ARE coherent!

Allows us to estimate an under-ice friction coefficient:

Needed for oceanographic analyses and for incorporation into numerical circulation models.

Coherence

Squared

Oil Spill Response Planning

Mean Displacement

Frequency of Occurrence

Open Water Period Landfast Ice Period

(Mahoney and Eicken, pers. comm.)

Under-ice topography is rough and poorly known

– Exerts friction on water motion

- May block or channel under-ice flows

- Changes through winter and spatially

Wrap-up:There is much left unknown about the Beaufort shelf system.

• The year-round stratification field is (still) undescribed.

• What are the sources of motion beneath the landfast ice?Pressure gradient is not the whole answer.

• What does the 2-dimensional under-ice topography look like?

• How do mesoscale flows vary with stratification & ice cover?

• How does the shelf flow field vary offshore? Relation between flow under landfast ice & pack ice Some indications that it varies along the shelf Seasonal changes in stratification, ice concentration & type

• How far offshore do under-ice river plumes spread? Influence of stratification on shelf waters