Buoyancy Barrier to Convection from Bailey, Rhines

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An Innovative Observational Network for Critical
Arctic Gateways Understanding Exchanges through
Davis (and Fram) Strait
Craig Lee, Jason Gobat, Beth Curry,
Applied Physics Laboratory, University of
WashingtonRichard Moritz, Kate Stafford Brian
Petrie Bedford Institution of
Oceanography Malene Simon Greenland
Nature Institute
Buoyancy Barrier to Convection (from Bailey,
Rhines Häkkinen)

• 0-500m difference between thermal and haline
  components of dynamic height (blue S, red T)
• Transport and fresh over-capping of the subpolar
  gyre and Nordic Seas modulates MOC

• Fluxes at major ocean gateways
• Understand partitioning between FW exchange west
  and east of Greenland, impacts on deep water
  formation and meridional overturning circulation.
• CAA/Davis Strait Fram Strait captures nearly
  all of the Arctic FW discharge and primary
  Atlantic inflow.
• Technology development for the Arctic Observing
  Network
• Ice-capable gliders
• New mooring technologies- ice-ocean interface,
  shallow shelves, light-weight through-ice
  (Switchyard).
• Acoustic navigation and communications.

from Dickson et al, 2005
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Project Status and Progress

• Mooring-based transport est. much smaller than
  previous.
• Autumn hydro- deep waters warmer, more saline
  than climatology.
• First successful under-ice excursion (glider and
  navigation system functioning properly).
• ICECAT technology mature, consistent success near
  ice-ocean interface over shelves.

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Coordination and Integration

• Collaboration with modeling efforts- BIO (Tang et
  al.), DAMOCLES (Karcher et al.) and Danish
  Meteorological Institute (Ribergaard Kliem).
  Model evaluation and intercomparison,
  interpretation of observations.
• Greenland Nature Institute- marine mammal studies
  (Simon), potential coordination of measurement
  programs and analysis efforts (Rysgaard).
  Training GINR personnel for glider operations.
• Analysis incorporating narwhal-based measurements
  in Baffin Bay (Laidre).
• CATS efforts (including Falkner, Melling,
  Munchow, Straneo, Prinsenberg) to provide
  comprehensive view of CAA exchange.
• DAMOCLES- Fram Strait collaboration- glider
  technology and science. Integration with Davis
  Strait analysis. Training AWI personnel.
• Norwegian Meteorological Institute (Mautitzen).
  Norwegian Coastal Current at Station M. Training
  Norwegian Meteorological Institute personnel.
• Transfer of mature ICECAT technology to Bering
  Strait investigations (Aagard, Woodgate).
• Coordination of international efforts toward
  acoustic navigation and communications (ANCHOR
  workshop). Aiming for interoperable standards.

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Future Directions and 2008 Planning

• Multi-year water mass property and flux (volume,
  heat and freshwater) estimates to assess change.
• Continue collaboration with modeling efforts
  (BIO, DMI, AWI, others?). Incorporate model
  results in our analysis.
• Refine array configuration. Improved horizontal
  resolution over Greenland slope, reduced over
  Baffin shelf. Enhanced vertical resolution.
• Improve public-access data distribution- CADIS
  and local site.http//iop.apl.washington.edu/seag
  lider
• Continue glider-based sampling with AWI (Fram
  Strait) and Norwegian Meteorological Institute
  (Station M). Outflows and inflows.
• Training other institutions for independent
  glider operations and working to prepare for
  next step Arctic glider deployments.
• Many improvements to glider technology- extended
  endurance, reliability, new CPU architecture,
  acoustics, sensors. Leveraged from other
  programs.
• Develop acoustic communications and data depot
  to reduce risk for extended under-ice missions,
  looking toward future Arctic applications.
• Extend ICECAT for light-weight, long-endurance
  through-ice moorings, near-surface reach for
  conventional subsurface moorings?

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• Challenges
• Small internal deformation scale- dynamically
  wide strait.
• Broad West Greenland shelf.
• Ice cover icebergs.
• Freshwater moves in thin (50 m) surface layer.
• Quantify liquid ice contributions at monthly to
  inter-annual time scales.

Moorings Ice draft/velocity, absolute
geostrophic velocity, low-mode u, T, S structure,
marine mammals (06-08) Shelf Moorings
Low-cost (10k) ICECAT for T-S near ice-ocean
interface, upward looking acoustic current
profilers and bottom-mounted T-S. Acoustically-nav
igated Gliders Repeated sections (5 km, resolves
deformation scale) at O(week) timescales between
500-m isobaths. Samples at ice-ocean interface.
Temperature, salinity, dissolved oxygen (other?).
Ship-based Hydrographic Sections Autumn.
Biogeochemical tracers (nutrients, trace metals,
TOC, TAlk, CFCs, oxygen isotopes. Spans broad
region from S. Baffin Bay to N. Labrador Sea.
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Seaglider and Sensors

• Hull length 1.8 m, Wing span 1.0 m
• Mass 52 kg
• Surface to 1000 m.
• Slow horizontal speed 0.1 - 0.45 m/s (22 km or
  12 nm per day _at_0.25 m/s)
• Vertical speed 0.06 m/s (minimum)
• Endurance depends on ambient stratification, dive
  depth and desired speed
• Longest range to date 3900 km
• Longest endurance to date 31 weeks
• Sensors SBE conductivity tempreature, SBE43 or
  Aanderaa optode dissolved oxygen. Fluorometers,
  backscatter, ADCP may be possible.

Operations beneath ice require acoustic
navigation (RAFOS), advanced autonomy. Acoustic
data upload desirable for insurance. First
section beneath ice-covered western Davis Strait
in Dec 2006 the system works, but there have
also been setbacks associated with platform
reliability. IPY/AON developments include
refining under-ice glider system, implementing
moored data depot for periodic data offload
while operating under ice.

• ICECAT for shallow shelves, moorings
• Samples in ice-threatened near-surface layer.
• Shallow element expendable, data logged below.
• Inexpensive (10k), deploy many.
• 2004(1), 2005(2), 2006(4)
• Contributing this technology to Bering Strait,
  other projects.

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• Autumn 2004 Autumn 2010
• One cruise (mooring/glider service, hydrographic
  surveys) each autumn.
• Data dissemination- Project web site.- As
  specified by AON and ARCSS data managers.-
  DAMOCLES WP6.
• Working on near real-time distribution for glider
  data not yet there.
• Science and engineering collaborations
  withCanadian IPY (Melling, Carmack
  projects)DAMOCLES (AWI, Fram Strait)Norwegian
  IPY (NMI, NPI, Station M line)Nares
  Strait/Baffin and Hudson Strait (proposed)
• Platform development for Switchyard.