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: Ice Fresh Water Wind Review of Previous Results New Observations and Analyses Summary

80 km 600 km

Ice Cover 2005 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 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 Wind Speed Mesoscale Variability Currents

Mooring Configuration

Previous Results : 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 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