Antarctic report – hurry up and wait

By Guest Author 23/01/2012 1

by Dr Craig Stevens, Physical Oceanographer at the National Institute of Water and Atmospheric Research (NIWA)

The flight up to Mario Zuchelli Station in Terra Nova Bay was brought forward by two days so we had to pack early. Now it’s been dropped back a day due to aircraft commitments for weather balloon experiment recovery.

This is all OK and normal. It doesn’t pay to get too precious about timing. It is a good time to tuck away somewhere in the nooks and crannies of Scott Base and get some work done on previous data sets. I’m looking at data from the preceding experiment in this series conducted 14 months previously. It’s interesting to reflect that if we’d be doing that experiment this season it wouldn’t have gone ahead in anything nearly like the form it did. The same week as the February 2011 Christchurch earthquake the largest sea ice breakout in McMurdo Sound for 12 years occurred exposing the ocean as far south as Scott Base. The subsequent sea ice evolution resulted in serious cracks around our 2010 field site at the tip of the Erebus Glacier Tongue.

Map sketch showing experiment location to the north and relevant features along with coastal current presumed path.
Map sketch showing experiment location to the north and relevant features along with coastal current presumed path.

Part of this breakout opened up water in Haskell Strait — the stretch of water between Cape Spencer-Smith on White Island and Cape Armitage near Scott Base. In otherwords the view out the window from Scott Base. This massive oceanic valve is normally hidden beneath ice shelf and sea ice. We were immensely proud to have been able to name this after Tim Haskell, a long time mentor and collaborator who essentially has made sea ice research in the region possible.

Tim’s science career epitomises a successful approach to science in New Zealand where one has to be flexible to changing initiatives and funding models while at the same time keeping an eye on what makes for demonstrably good science. To have played a role in officially naming a piece of water the size and magnitude of the Straits of Gibraltar or Cook Strait after him is pretty satisfying.

The Strait acts as a valve between the literally supercool (we’ll come to this later) water beneath the vast Ross Ice Shelf and the waters of the western Ross Sea. The flow rate through the valve influences the sea ice growth in the region. Sea ice being the largest annual geophysical change on the planet — millions of square km of the globe literally changes reflectivity every six months.

This dramatically affects how heat and gases exchange between atmosphere and ocean, provides a vast habitat for growth of algae — the basis of the ocean food chain, and drives the thousand year global oceanic thermohaline conveyor belt. Natalie Robinson in our group neatly describes this annual fluctuation as the global heartbeat.

Anyway, the preceding experiment involved collaborative work with some pioneers of sea ice research from the US — Miles McPhee and Tim Stanton (actually a Kiwi but long-since based in California). We setup one of Tim Haskell’s field camps around 50 m away from the Erebus Glacier Tongue in October 2010 looking at the effect of the glacier on local flow.

This is driving us to look at how the glacier melting might relate to the flow itself as well as the influence of the glacier on the local ocean and sea ice growth. One interesting feature is the supercool nature of the ocean in the area mean that ice crystals were forming on the underside of the ice driven by the coldness of the ocean rather than the atmosphere.

These crystals change the roughness of the ice and so change the heat exchange. This is the underpinning motivation for the present experiment — does this effect persist further to the north?

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