Historical variability of sea ice extent in the Nordic Seas

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Historical variability of sea ice extent in the
Nordic Seas

• D. Divine1 and C. Dick2
• 1 Norwegian Polar Institute, Polar Environmental
  Centre, Tromsø, Norway
• 2 International ACSYS/CliC Project Office, Polar
  Environmental Centre, Tromsø, Norway

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Why the study of sea ice extent variability is of
particular interest?

• Sea ice forms an insulating layer between the
  warm ocean and the cold atmosphere
• It forms a barrier to moisture transport
• Ice extent affects the mean albedo of the
  surface, thus influencing the overall energy
  balance of the Earth
• It may serve as an indicator of climate
  variability and change

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Data

• ACSYS historical ice chart archive (1850-1966).
• Modern NPI ice charts for the period 1967-1979.
  We used the boundary between open drift ice
  (4/10-7/10) and very open drift ice (1/10-4/10)
  as an ice edge.
• The satellite-derived passive microwave data for
  the period 1979-2003. The ice edge is defined as
  the outer boundary of ice having concentration of
  at least 30.

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April and August ice extents for 1850-1899
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The number of ice maps during 1851-2002 used in
the work
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Method(Shapiro and Colony, 2003)
fie - parametric function in a rectangular
coordinate system ?(s)-perpendicular distance
from observed ice edge to the mean one, a
function of arc length distance s along the mean
ice edge
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Mean ice extent in April during the periods
1850-1899, 1900-1950, 1951-2002
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Mean ice extent in August during the periods
1850-1899, 1900-1950, 1951-2002
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Standard deviation of the ice edge anomaly
smoothed with a 5-point running average(a)
April (b) August.
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The areas with a maximum ice edge position
variability Odden, Barents Sea between 20E and
45E. April
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August
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Time-series of the ice edge anomalies in the two
points of the mean ice edge for 1951-2002.
The linear fits for 1850-2002 are statistically
significant at the 95 confidence level.
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Is the observed ice retreat statistically
significant? If yes, where?
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(No Transcript)
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Conclusions

• The ice edge retreat revealed in the Nordic Seas
  over the last 153 years lies, in the main part of
  the study area, within the natural variability of
  the ice edge position
• The areas with statistically significant retreat
  of ice are found on the pathways of the warm
  Atlantic water inflow into the Barents Sea with a
  North Cape current and a West Spitzbergen current
  into the Arctic Ocean

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Future plans

• Assessing the ice edge variability within a month
  -to know how representative the single
  observation a month (typical for historical data)
  is for the monthly mean ice edge
• More comprehensive uncertainty analysis
• Consideration of all other months
• Extending the analysis to earlier times (AHICA
  goes back to 1553)
• Analysis of the relationships between variations
  in the Arctic atmosphere, sea ice and
  oceanographic conditions provided, e.g., by the
  ACSYS BarKode data set