The PICCOLO cruise recently stopped by the Larsen Ice Shelf, an area visited only twice for oceanographic research since March 2002. Twenty-years ago, Keith Nicholls, from the British Antarctic Survey (BAS), was on that scientific cruise and witnessed the Larsen B Ice Shelf disintegrating, generating thousands of icebergs heading out to sea.
Keith Nicholls (BAS)
I remember looking out from the bridge of RRS James Clark Ross over to where Larsen B Ice Shelf should have been, and seeing a lot of icebergs swarming towards us. Clearly the captain could see them too, as he spent a lot of time looking over his shoulder to make sure his escape route was clear.
We managed to visit the northern end of the Larsen C ice front, and were able to measure the properties of the water flowing out from the ocean cavity beneath the ice shelf. Little did I know in 2002 that, 22 years later, I would be revisiting the same area on RRS James Clark Ross’ successor, RRS Sir David Attenborough during the PICCOLO cruise.
This time, though, we can do so much more. We have a ship full of eager biologists and geochemists with their attendant instruments, so we’ve been able to measure not only the temperature and salinity of the water flowing from beneath the ice front but also its detailed chemical composition and impact on the local ecosystem.
Sometimes it feels like you’re living in a painting.
Prof Karen Heywood (UEA)
Prof Karen Heywood
It’s been amazing and a privilege to be here. Since Keith Nicholls visited in 2002, only two groups of scientists have been here, on the German research vessel Polarstern. It’s usually completely inaccessible because there’s thick sea ice all year round. We were lucky this year that there was a gap in the ice so we could get there. I’ve tried to come here before, in 2012, but we had to work further north on the Antarctic Peninsula because it was inaccessible. Amazing to have made it!
Ice shelves are particularly interesting, both for the physical oceanographers like me, and for the biogeochemists. Snow falls on Antarctica, and forms a thick layer of ice. This ice flows slowly towards the sea in lots of huge glaciers. When these glaciers reach the sea, they float on the sea – that’s what we call an ice shelf. Ice is less dense than water, which is why ice cubes float in your drinks. That ice in the ice shelf is now old, maybe hundreds of years at the base of the ice shelf. The fronts of ice shelves break off every now and then, forming icebergs. This is a normal part of the cycle of water going from snow to ice to icebergs to the sea.
Ice shelves are also melting from their undersides where they come into contact with seawater that is warmer than the ice, and from their surface where they come into contact with winds that are warmer than the ice. The Larsen C Ice Shelf is believed to be melting both ways. As a physical oceanographer, I’m interested in how much meltwater is being produced, and where it is going.
The biogeochemists are interested in that meltwater too. Glaciers tend to include tiny particles of rocks from where they grind slowly over the continent. When they melt, these nutrients and minerals are released, and help the plankton to grow – like putting fertiliser on your lawn. Our PICCOLO project made the first measurements of how much the plankton are growing around the Larsen ice shelf, how healthy they were, and what’s feeding on them – the whole ecosystem.
The icebergs have been amazing too – they’re all different shades of blue, white or grey. Sometimes it feels like you’re living in a painting.
Keith Nicholls (BAS):
Steaming past Jason Peninsula brought back fond memories, and the Larsen C ice front, a 35 metre high ice cliff stretching away hundreds of miles to the south, is a spine tingling sight. The northern end of Larsen C Ice Shelf has been visited amazingly infrequently by ships in general, and especially for oceanographic research. The interaction between the ocean and ice shelves, the floating periphery of the Antarctic Ice Sheet, has fascinated me my whole career. I feel very privileged to have been present on two of the very few occasions that the ocean conditions have been explored in any sort of detail.
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