ANTARCTIC SEA ICE THICKNESS and MASS BALANCE

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ANTARCTIC SEA ICE THICKNESS and MASS
BALANCE Present State of Knowledge and Plans
for IPY and Beyond S.F.Ackley and A.P. Worby
ASPeCt and Antarctic Sea Ice in IPY

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CCSM3 sea ice trends, 1900-2100

• Historical forcing for 20th century
• Scenario A1B in 21st century (business as usual)
• Downward trend in Antarctic area and volume from
  1960
• Fastest retreat and thinning in Weddell Sea

Annual average ice area (km2)
Annual average ice volume (m3)
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GCM sea ice trends

• Average of 11 models used for AR4 (Arzel et al.
  2006)
• Table shows percentage change between 1981-2000
  and 2081-2100
• Summer losses exceed winter losses
• Thickness decreases faster than extent

Arctic extent Arctic volume Antarctic extent Antarctic volume
Winter -15.4 -47.8 -19.1 -27.4
Summer -61.7 -78.9 -49.0 -58.1
Annual average -27.7 -58.8 -24.0 -33.7
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Sea Ice Observation Program

• To devise a standard procedure and format for
  recording
• Antarctic sea ice data from vessels
  operating in the Antarctic pack ice.
• 2. To identify past voyages which recorded sea
  ice data that could be translated into a
  standard format.
• To compile an archive of Antarctic sea ice data,
  including
• - ice type, concentration and thickness
• - floe size and topography
• - snow cover type and thickness
• 4. To make the data readily available to the
  scientific community.

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Ship-based Observation Scheme
Hourly observations of - total ice
concentration - ice concentration of the three
main ice types present - ice type and
thickness of each category - topography and
floe size of each category - snow cover type
and thickness - open water classification Also
recorded are - position, date and time -
meteorological conditions - photographic record
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Tracks of 83 good voyages
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Progress to date

• A total of 100 voyages have been contributed to
  the archive, for the period 1980 2005
• Of these, 17 have not been used
• Too qualitative, inconsistent reporting
• Ship track clearly biased
• Inconsistencies between observers
• The remaining 83 voyages comprise approximately
  25,000 individual observations from Australia,
  US, Russia, Germany, and British ships

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Annual mean ice thickness including ridges
and open water 5 x 5º grid
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Seasonal mean ice thicknesses including ridges
and open water 5 x 5º grid
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Conclusions

• The ASPeCt archive is now populated with 83 fully
  quality controlled data sets, between 1980 and
  2005.
• Data products are now available
• mean ice and snow thicknesses for each
  observation
• ice thickness distribution information
• others on the way
• More data will always be welcome. Our plan is to
  maintain the ice observation program through IPY
  and beyond.
• Visit www.aspect.aq

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ASPeCt METHOD FOR AIRBORNE OBSERVATIONS
-Process used from helicopter flights during APIS
cruise, Dec 28 1999 to Feb 7 2000. -Result of
work was approximately 200, 60 min. videos that
were examined for 1 minute at 6 nm
intervals. -Dependable evaluation of the videos
is possible because of the consistent flight
altitude (100 m) and speed (85 knots).
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ULS measurement sites around Antarctica
AWI instruments on top of oceanographic
moorings, at depths of 120-180m
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3. AWI ULS Draft Data in NSIDC Archive

• At NSIDC, two data sets are available
• AWI moored ULS data Weddell Sea (1990-1998)
• AWI moored ULS-data Greenland Sea and Fram
  Strait (1991-2002)
• (see
• http//www.nsidc.com/data/sea_ice.htmlICE_DEPTH/
  THICKNESS)
• Since 2003, the AWI does not acquire ULS data in
  the North.
• Antarctic data since 1999 not yet submitted.

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3. AWI ULS Draft Data in NSIDC Archive

• At NSIDC, two data sets are available
• AWI moored ULS data Weddell Sea (1990-1998)
• AWI moored ULS-data Greenland Sea and Fram
  Strait (1991-2002)
• (see
• http//www.nsidc.com/data/sea_ice.htmlICE_DEPTH/
  THICKNESS)
• Since 2003, the AWI does not acquire ULS data in
  the North.
• Antarctic data since 1999 not yet submitted.

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Interannual ice thickness variability at Maud Rise

• Results
• As yet, no parameter trends indicating formation
  of a
• new Weddell Polynya
• Interannual variability in ice draft
• Hypothesized smallest ice draft at position
  closest to crest of
• Maud Rise (AWI 230) could not be confirmed
• Ice concentration in winter months at 3
  positions similar
• and very high (gt0.95)
• No confirmation of low-ice halo

By courtesy of Mario Hoppema
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7. Plans (1)

• Ice draft variations
• Along the Greenwhich meridian, ULS instruments
  have provided data since 1996, and data are still
  collected.
• The idea is to observe longer-term (interannual,
  decadel, and climatic) variabilities of ice
  thickness.
• Are the expected variations in ice draft over the
  years large enough to be assessed as significant,
  considering the measurement error of ULS-data?
• How important is the knowledge of ice thickness
  variations along the Greenwich meridian and of
  the mass flux crossing it compared to other
  gates ?

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What is the Autosub Autonomous Underwater vehicle

• Specifications
• Autosub built and operated by National
  Oceanography Centre, UK.
• 7 m long,
• 3.6 tonne
• powered by 500 kg of primary manganese alkaline
  batteries,
• range of 300 km at a speed of 1.8 m s-1.
• depth limit 1600 m.
• The navigation system relied on a Doppler sonar
  system, able to track the seabed at ranges of up
  to 500 m, and an Ixeas-Oceano PHINS, a fibre
  optic gyro -based inertia navigation system,
  positional accuracies of 0.1 of distance
  travelled.

• Scientific Payload
• Dual conductivity, temperature and depth (SBE-911
  CTD)
• Dissolved oxygen sensor (SBE-43)
• Upward (300kHz) and downward (150 kHz) looking RD
  Instruments Acoustic Doppler Current Profilers
• Simrad EM-2000 swath multibeam bathymetric
  mapping system was mounted looking upwards

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Strass et al.(1998)
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Under ice data
SEA ICE
Krill swarms
AUV travelling this way
Brierley, Fernandes, Brandon Science, 2002.
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Autosub draft PDF
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Project plan for 2003
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EM induction sea ice thickness sounding
Zi dEM dLaser (snow ice)
Surface elevation from Laser DGPS
dLaser
dEM
?Ice ltlt ?Sea water
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ISPOL Nov. 6, 2004 Jan 19, 2005
Ice edge
http//www.ispol.de
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250 km
Envisat SAR
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NIC Ice Charts
Sensor Wavelength Resolution
SAR Microwave 8-100 m
AVHRR Visible and IR 1 km
OLS Visible and IR 0.5-2.7 km
SSM/I Microwave 25-40 km

• Routinely produce weekly ice charts since the
  1970s
• Trained ice analysts discern sea ice
  concentration and during 1995-2000 stage of
  development using a host of available satellite
  data
• Show average ice conditions integrated over 3-5
  day period.
• Represent the only continental scale estimates of
  ice type

SAR Image
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Sample Ice Chart Digitized
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Data Processing

• NIC
• Digitize 1997
• Egg 1995-1997
• Spatially reference and project
• Merge hemispheres
• Validate typology
• Calculate thickness using classification
• Ship
• Calculate thickness for level, levelsnow,
  levelsnowridge
• Temporal join and spatially merge NIC with ship.

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Time comparisons using GIS are unusual but
essential for studies such as these.
Ship ridge estimates included
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• Illustrates 2 cm range precision of ICESat.
• 2 cm precision is important, because mean
  freeboard is about 30 cm.
• Footprint spacing is 170 m.

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Ron Kwok, JPL
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East Antarctic Sea Ice
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IceCam

• An automated system for
• Sea ice observing
• Environmental data logging
• Supplements (and maybe replaces) the traditional
  ice log
• Deployable on Ships-Of-Opportunity (SOO)
• Developed jointly by SAMS and NPI
• Richard Hall

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Concept
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Method ship-based observation -
Video-2
Video-1
EM and Laser
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The Current Challenge

• We need to integrate the various data sets and
  put them together in acceptable form for
  co-analysis, validation of remote sensing, and
  comparison with model output.
• Data sets include Surface drilling profiles,
  ULS data, Autosub profiles, Ship Observations,
  Ice Chart Analyses, Airborne Digital(and
  Analog)Photography, and Airborne EMI sounding.

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The Australian Antarctic Data Centre

• central facility for managing (Australian)
  Antarctic data
• metadata
• data repository, database applications
• analyses
• mapping GIS

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Sea Ice Thickness Database

• integrated collection of Antarctic sea ice
  thickness data
• single point of access for all thickness data
• documentation on each sub-collection
• web accessible, search and extract data

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PLANS for IPY-Field Work

• Continuation and Expansion of ASPeCt Observations
  using all research and logistic vessels (e.g. ice
  observors on CASO, SASSI, and ICED cruises)
• SIMBA-South, (Sea Ice Mass Balance), two winter
  cruises in Aug-Oct 2007, NB Palmer-Amundsen Sea,
  Aurora Australis-E Antarctic, deploying ice
  deformation arrays and mass balance buoys
• Concurrent Transects (NBP and AA) conducting ice
  observations, ship and airborne EMI, drilling
  profiles, IceCam
• Remote Sensing Intensive Observations during
  Cruise Periods (altimeter and SAR)
• Additionally to the AWI Weddell Sea ULS
  deployments, new deployments of ULS in Cape
  Darnley polynya (Japan) and Prydz Bay (China)

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PLANS FOR IPY-Other

• Organizing an Antarctic Sea Ice Modeling
  Intercomparison Project
• Analysis of Surface Data to Test and Validate
  Satellite Algorithms (passive microwave-concentrat
  ion altimeters-elevation to thickness SAR
  drift-buoy drift)
• Re-institute detailed analyses of ice charts for
  ice thickness (stage-of-development) by
  international collaboration with National Ice
  Center

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BEYOND IPY

• Ice Thickness Activities during IPY are only a
  good start our IPY goal is to establish a
  rudimentary baseline of Antarctic Sea Ice
  Thickness
• However, errors will be large because of the
  composite nature of the data set, with gaps, both
  seasonally and regionally, because of the
  limitations of ship, airborne and ULS array
  coverage.
• It is therefore problematic as to whether future
  change will be detectable outside the errors of
  the composite IPY thickness data set, so it will
  also be necessary to carefully quantify those
  errors.
• It is projected that continued monitoring will be
  necessary to determine Antarctic sea ice response
  to global change as a Responsibility to Society
• Design of an International Monitoring Programme
  for Antarctic Sea Ice for the LongTerm should
  therefore be undertaken based on IPY results and
  implemented soon after IPY
• Based on current knowledge, elements of the
  monitoring programme should include an expanded
  ULS array, automatic recording of ice conditions
  from ships(IceCam), seasonal AUV transects of the
  sea ice zone at selected meridians and satellite
  monitoring by altimeters, SAR, and passive
  microwave