Hello again young science buffs! This week’s column is coming at you from Otago Uni’s very own Physics Department, where PhD candidate Ken Hughes has been doing some scintillating research on Antarctic sea ice. Specifically, Ken has been constructing a computer simulation of how sea ice is formed in the Ross Sea – the part of Antarctica which is under the supervision and protection of New Zealand (yes, we have our own slice of Antarctica).
To begin with, what you have to appreciate is that the sea ice is not the same as the ice shelf. The ice shelf is mainly fresh water (given that seawater tends to reject a lot of its salt when it freezes) and is most likely what you picture when you think of Antarctica. Sea ice is frozen seawater too, but has higher salt levels, so it also has a lower freezing point. The Ross Ice Shelf is like a novelty-sized ice-cube in the seawater: It keeps the surrounding water very cold, but because this water has a lower freezing point, it doesn’t freeze and forms what is known as super-cooled water.
At the bottom of the ice-shelf, there is a slightly melted layer called Ice Shelf Water (ISW). ISW adds freshwater to the mix, which lowers the density of the seawater. As a result it rises up along the inclined Ice Shelf, gathers momentum and “shoots off” into the open ocean, forming ice crystals and often more sea ice. In essence, this is how the Ice Shelf affects sea ice formation.
In November and December of 2011, Ken trekked down to Antarctica and spent a good month hauling around this sea ice, drilling holes and taking measurements of water temperature, salinity, and ice thickness. Astonishingly, Ken found that the ice shelf was able to produce supercooled water as far as 20km away from its edge. That’s one BIG ice-cube!
Now that Ken is back from the Antarctic and warmed up, he is in the process of combining his measurements with a previous model of ice-shelf ocean interaction, a model which uses some fancy math to replicate the physical ocean environment.
Although the model is not entirely complete, by the end of the year Ken should have enough info to reliably model sea ice formation, which is a step further in understanding the dynamic systems of the awesome Antarctic.
– Robbie Masters
Geekology | Issue 3
