Science

K063: Antarctic Sea Ice Mapping at McMurdo Sound

K063: Antarctic Sea Ice Mapping at McMurdo Sound


Pat Langhorne
University of Otago

Simultaneous and co-incident surveys of sea ice from the air, on the ground and from the ocean, near parallel to satellite overflights.

Objectives: 1 - Helicopter survey of sea ice thickness and surface properties; 2 - On-ice survey of snow, ice thickness & oceanography on subset of helicopter grid; 3 - AUV at ice-water interface coincident with helicopter or EM31; 4 - Surveying of tidal movement.

The important issue is why has Antarctic sea ice extent in the Ross Sea becomes greater in the past decade when global climate models say that it should be decreasing?

We believe (along with others) that part of the discrepancy is that land ice that is floating on the ocean (called an ice shelf) contributes and the effect of ice shelves on the ocean is not a part of global models. In natural circumstances there is melting at the deep part of ice shelves and then refreezing at shallower depths and under sea ice. In fact under sea ice near an ice shelf, there may be many meters of loose ice crystals that have originated from beneath the ice shelf. Over the past decade our own observations and models have shown that this source can make a 20% increase in sea ice thickness.

But here there is another problem. While sea ice area can be measured from satellite, there is no direct means to obtain sea ice thickness from satellite. Instead a satellite altimeter measures how far sea ice floats above sea level. Then you need to guess snow thickness and density and sea ice density and worry about whether or not there are ice crystals underneath the sea ice. So there is a big international effort to make sea ice thickness observations beneath the satellite altimeters that overfly Antarctic sea ice. Our project is a part of this effort.

The only technique that makes direct, airborne sea ice thickness measurements is electromagnetic induction. Our Canadian colleague is the guru of these measurements and will be joining us for the third time at Scott Base with his latest helicopter electromagnetic induction device - the HEM bird. The really great thing about this device is that it not only selects sea ice thickness but can also detect the loose crystals, the refrozen ice shelf melt, beneath the sea ice.

So in Nov 2013 we will fly the HEM bird over the sea ice of McMurdo Sound to measure sea ice thickness. In addition we will be on the sea ice to measure snow and ice thickness, density and the thickness of the layer of loose crystals. The key task is to follow the lines of the satellite so all measurements can be tied together. The project is also coordinated with the new technology in the form of a snow radar from the University of Kansas that will be flown from light aircraft. This will give us snow thickness over a large area. The Kiwi team we will deploy radar reflectors on the sea ice so that the Kansas team can test their technology. Most exciting too is that we will have some coordination with NASA who will overfly satellite tracks also.