a fiveyear thematic programme

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? a five-year thematic programme
? a five-year thematic programme ? total
budget 5.86 million
About the programme
to explore the marine environment beneath
floating ice shelves using an Autonomous
Underwater Vehicle and investigate the role of
sub-ice shelf processes in the climate system
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Autosub was deployed from the James Clark Ross
during the programme at Bellingshausen-Amundsen
Sea, West Antarctica --March 2003 NE
Greenland Sea Ice and Kangerdlussaq Fjord,
Greenland--Aug-Sept 2004 Fimbul Ice Shelf --
Feb 2005 (Eastern Weddell Sea)
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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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The Technical Challenge
Currents?
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Navigational Accuracy

• Pre AUI Accuracy 1 of distance travelled
• Up to 200m above bottom
• 1000m error after 100km track
• After installation of Fibre Optic Gyro, 150kHz
  downward and 300kHz upward ADCPs - Accuracy 0.1
  of distance travelled
• Up to 500m above bottom
• Up to 200m below ice
• 100m error after 100km track

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• Well-rounded first-year floes (draft 1.2 m)
  glued together by very young ice (thickness 0.25
  m), with a young (probably first-year) ridge in
  the centre of the image and an old worn-down
  hummock in the front. Between the two is a
  multi-year floe of thickness 1.85-2.25 m
  containing the hummock. The contrast between the
  sharpness of topography in the two ridges is
  dramatic, showing the effect of a number of years
  of ageing and partial melt in rounding off the
  blocky topography of the older ridge.

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• Thick multi-year ridged floe of draft 3-5 m, with
  linear edges suggesting production from fracture
  of larger ice sheet, embedded in undeformed fast
  ice of draft 1.8 m. Fast ice shows pattern of
  depressions due to mirroring of surface melt
  pools. Thicker ice contains pressure ridge of
  maximum draft 11 m which has partly disintegrated
  into individual ice blocks of diameter 5-20 m.
  Evidence is that thicker floe came from MIZ.

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Krill under sea ice
First evidence of extensive krill swarms under ice
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M365 Oceanic properties at 40 m

• Two opposing currents Southward and a northward
  flowing current
• Southward current
• Over Belgica Bank
• heavily deformed ice
• warmer and fresher
• Northward current
• Over Norske Trough
• Level Ice
• Colder and saltier

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Unit offset
2
3
1
4
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Corrected for unit offset
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PDFs
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Weddell Sea
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Distance (km)
0
5
10
15
20
25
Ice shelf
Depth (metres)
Bedrock
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-50
19.0
0
Across track (m)
Distance along track (km)
19.5
50
20.0
100
20.5
21.0
160
Ice draft (m)
180
200
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During Autosub missions, the ship is very busy!
JR106S August -September 2004 Kangerdlugssuaq
fjord, East Greenland
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Installation of Aqualab water sampler in nose of
Autosub
Aqualab collects up to forty-nine water samples
in sealed plastic bags. A 200 ml sample takes 11
minutes to collect.
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Water samples were collected from the bottles on
the CTD rosette package and from the Autosub
Aqualab for subsequent ?18O analysis. Autosub
also continuously measures temperature and
salinity of the water.
Autosub potential temperature
Autosub salinity
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?18O Oxygen isotope from CTD water samples
?18O from Autosub Aqualab water samples
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The results show that the water in the fjord is
primarily a mixture of salty ocean water, and
fresh water melting into the fjord from the
Greenland Ice Cap.
This means that we can calculate the amount of
ice sheet meltwater coming out of the fjord into
the Nordic Seas.
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