Oceanographic Observations from the

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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
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Outline Regional
Oceanographic Setting Ice Fresh
Water Wind Review of Previous Results New
Observations and Analyses Summary
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600 km
80 km
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June 4
January 16
Ice Cover 2005 Snapshots
Landfast ice and non-uniform melt affects wind
stress distribution over the shelf.
Lateral Melting Landfast Ice Intact Adjacent
Shelf Influence
100 Ice Cover Landfast Ice Immobile Lid From
November to June
August 14
July 25
Nearshore Melting All Ice in Free Drift
Offshore Melting Much Open Water
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River Discharge Annual Cycle
2005 Kuparuk River Streamflow
(USGS)
90 of annual runoff occurs in about 2 weeks
and beneath the landfast ice.
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Mean Monthly Along-shelf Wind Stress Annual
Cycle (Barrow 1945 2005)
5x
(K. Taylor)
Min Max
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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!
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Mesoscale Variability
Winds
Currents
Wind Speed
Ice
Fresh Water plumes?
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Mooring Configuration
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Previous Results

• 1999-2002 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?

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2004/2005 East-West Currents
Large currents large current variability in
summer Stronger westward component in Smith Bay
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2004/2005 Landfast Ice Period
Landfast Ice Breakout
Smith Bay
SAR Image Jan. 4, 2005 (A. Mahoney)
Alongshore variability apparent not clear why
Ice? - Implies cross-shelf transport Landfast
Ice Breakout event in Smith Bay
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Landfast Ice Season
Coherence Squared

• Camden Bay velocities are uncorrelated with
  those at Smith Bay and Prudhoe Bay
• In summer, velocities ARE coherent along the
  length of the shelf.

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Landfast Ice Season Alongshore Pressure gradient
currents They ARE coherent!
Coherence Squared
Allows us to estimate an under-ice friction
coefficient Needed for oceanographic analyses
and for incorporation into numerical
circulation models.
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Oil Spill Response Planning
Open Water Period Landfast Ice Period
Mean Displacement Frequency of Occurrence
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Under-ice topography is rough and poorly known
(Mahoney and Eicken, pers. comm.)
Exerts friction on water motion - May block or
channel under-ice flows - Changes through winter
and spatially
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• 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?