Gathering scientific data from one of the world's harshest environments
Could the Arctic Ocean become largely ice-free in future summers?
Scientists know the average surface area of Arctic sea ice is decreasing. Thirty years of satellite measurements have shown a continual decline in the extent, or surface area, of the ice.
The thickness of this ice is also changing. From 1981 to 2000, multi-year ice (ice which survives for one or more summer melt seasons and increases in thickness year on year) made up on average 30% of winter sea ice cover. By March 2009, only 10% of Arctic sea ice was more than two years old.
Catlin Arctic Survey 2009 set out to measure the thickness of sea ice in the northernmost Beaufort Sea area, near the North Pole. Three explorers trekked across terrain largely inaccessible for on-site research during spring. En route, they gathered valuable data on ice thickness and snow depth, density and temperature.
The findings from this Survey, taken together with decades of existing measurements by submarines, satellites and buoys, led scientists from the University of Cambridge to suggest there is a significant probability that from 2020 only 20% of the Arctic Ocean basin will have sea ice cover in the late summer.
Three explorers trekked across the floating sea ice of the Arctic Ocean for 73 days, beginning 1 March 2009.
The team covered a distance of 270 miles (435 km) heading in a northwards direction from 81˚83′N 129˚97′W, finishing on 7 May 2009 at 85˚45′N 124˚84′ W.
- Ice thickness measurements
- Ice freeboard measurements
- Snow thickness and density measurements
- Snow temperature
- Atmospheric conditions
Modal Ice Thickness Measurements
Each evening up to 10 holes were drilled through ice pans near each night’s camp that best reflected the characteristics of the terrain the team had encountered that day. Subjectivity was reduced by the limited variability in terrain covered daily, and given the expedition leader’s experience.
This methodology gives a measure of ice thickness, which is the modal average ice thickness of the total ice covering and can be used to determine ice age. It is not a measure of mean average ice thickness.
The modal results were converted to an inferred mean average thickness using the three methods of:
- Mode to mean coefficient calculations
- Ridge observation data
- Mean thickness measurements
The methodologies were developed in discussion with two world leaders in field techniques for gather sea ice data:
- Professor Peter Wadhams, Professor of Ocean Physics and Head of the Polar Ocean Physics Group, Department of Applied Mathematics and Theoretical Physics, University of Cambridge.
- Professor Christian Haas, University of Alberta.
Ice Freeboard Measurements
Sea ice density is determined by measuring the ice freeboard. An ice freeboard is the height between the top of the ice and the water level. When a hole is drilled through the ice, water rushes in to fill the space. The level the water rises to indicates how heavy, or dense, that particular ice pan is.
Because the measurement was taken from sample holes away from the edges of the ice pan, it was less impacted by ice movement and offered a better reflection of ice flotation, giving scientists an indication how quickly a sea ice pan thaws during the summer melt season.
Snow Thickness and Density Measurements
- The average (mean) thickness of the ice-floes or underformed ice along the route was found to be 1.8 metres.
- The average (mean) thickness of the total ice cover when the substantial volume of the ice contained in compressed ridges and rougher rubble fields increased to 4.8 metres.
The Survey’s findings, taken in the context of decades of existing measurements by submarines, satellites and buoys, led scientists from the Polar Ocean Physics Group at the University of the Cambridge to suggest that:
- By around 2020 only 20% of the Arctic Ocean basin will have sea ice cover in the late summer. In other words, 80% of the ocean will be ice-free.
- By 2030-40 there is a significant probability that the North Pole region’s sea ice cover will be transformed into an ice-free, open ocean in summer times, thereby making it a purely season feature.
Within the scientific community a range of conclusions have been drawn regarding the timeframe for ice-free summers. Nevertheless, there is a broad consensus that such ice-free summers are a distinct possibility.
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