(By Nick)
The purpose of our presence in the Arctic, during the seasonal extent minimum of September 2011, is two-fold:
1) The timing of the expedition coincides with the predicted lowest extent of sea ice since the record breaking minimum of 14 September 2007 (Comiso et al., 2008). Sea ice area and extent in 2007 were 37% and 38% lower than the climatological averages respectively (3.6 × 10^6 km^2 and 4.1 × 10^6 km^2), and predictions that the declining trends were going to continue accelerating in 2008, have been borne out by satellite measurement.
Causes of the declines in area and extent are postulated as arising from an increase in the heat flux of water to the Arctic from the North Atlantic Ocean (Spielhagen et al. 2011), and atmospheric forcing anomalies (Zhang et al. 2008), both of which are made worse by the already delicate ice cover that does not recover to its full extent after decades of thinning and retreat.
Furthermore, a predictor of annual sea ice extent, atmospheric circulation, no longer can be relied upon to determine the state of the basin-wide coverage of sea ice after a melt season. Sea ice extent in 2010 was the third lowest on record, despite Arctic Oscillation patterns that should have favored a buffering effect, allowing more multi-year ice to survive the spring melt season (Stroeve et al. 2011). Observations of shifting centers of the Arctic Oscillation which leads to local variations (from past decades) of sea ice areal flux across the Arctic basin are indicators of a changing Arctic climate.
Our goal in measuring Arctic sea ice properties will be to document, by in-situ observations, what will likely be a record low extent situation. Data collected on snow and ice thickness, salinity, and temperature, will provide validation to satellite measurements that must make assumptions about snow and ice parameters in their measurements of thickness and mass balance.
2) We are physicists, thus interested and knowledgeable in the dynamics and deformations of sea ice. The most dramatic deformation effect, in our opinion, that sea ice presents us with, is the much reverently feared pressure ridge.
If you are interested in geophysics, by way of the ice mass budget and volume of the total ice present, you must understand pressure ridge structure and how it changes with time, and their frequency of occurrence. Ships and offshore structures, namely oil drilling platforms, are concerned with pressure ridges because they present a large risk to the integrity of hull and frame.
Pressure ridges are formed when wind and underwater currents conspire to forcefully crack a sea ice floe into two parts (and sometimes more, in a further complex treatment). The open water between the two sections of the floes freezes quickly due to the sharp temperature difference between sea water and air. The ice that has grown between the floes is thinner and weaker than the ice comprising the surrounding floes and can be easily crushed when the same forces that drove the original floe apart in the first instance, drive the floes together again. The site of the original crack was a region of local weakness, and it is thus reasonable to expect that this process can repeat several times - closing and opening until seasonal and physical constraints due to internal stresses and buoyancy limit the motion. Each time the floes close upon themselves, newly broken ice from the middle of the floes (the open water region is called a 'lead') is piled under and above the water. The consolidated rubble of ice that remains is a pressure ridge. They are typically linear features that have been known to extend more than a kilometer.
The portion of the pressure ridge above the water is called the sail. It is upon the sail that we will construct a systematic grid to drill into the ridge to determine its total thickness. The part of the ridge under the water is called the keel. It generally is composed of a consolidated and unconsolidated layer, the properties and relative height of each is of great interest to the scientific and engineering communities, for reasons listed above.
We expect to measure the following properties of a pressure ridge:
- Level ice thickness (of the floe containing the ridge)
- Snow Thickness
- Sail thickness
- Max sail height
- Keel thickness
- Max keel depth
- Consolidated layer
- Porosity
- Salinity
If we can repeatedly visit a ridge, to see how it changes over the three weeks of the voyage, that would be a huge bonus to our research.
With a laser range finder, LIDAR, instrument, we will determine the external geometry of a ridge; this should tell us the relative age of the ridges we are examining, as we expect older ridges to be smoother than newly formed ridges. It's hard to discriminate between first-year or multi-year by this, but it may prove useful.
This will be no small task! But the pay-off may be, especially if we devise a method to determine ridge volume, enhanced values for ridge isostasy (a measure of how big a ridge can physically grow).
It looks like we're going to have a great crew supporting our research, including a helicopter to fly us to interesting deformation sites, and an armed polar bear lookout to escort us at all times. We are grateful to Greenpeace for providing us with the facilities necessary to conduct this research, and to Professor Peter Wadhams for supporting our education in this highly relevant area of global climate studies.
