It is a relief when we finally see the iceberg emerging, first as a line on the ship鈥檚 radar and then as a wall of ice emerging from a foggy horizon, stretching further than we can see.
This is the remains of iceberg A-68, the third largest iceberg ever recorded, which broke away from Antarctica鈥檚 Larsen C ice shelf in 2017. After drifting northwards, A-68 was on a collision course with the island of South Georgia in December 2020 before being swept back into deeper water south of the island.
It has begun to disintegrate and is no longer a continuous island of ice. There are now 12 named iceberg fragments from A-68 and countless smaller icebergs. The largest of these, dubbed A-68A, is 50 kilometres long and 200 metres thick in places, and covers an area of around 900 square kilometres, similar to that of the Isle of Mull in the UK.
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Ships have to be very cautious around icebergs due to the damage that can be caused by the hard, freshwater ice, so we keep a distance of 1 nautical mile from the largest icebergs, and the crew navigate carefully around the smaller pieces. But we can still hear when larger parts break off, even above the sounds of the ship鈥檚 engines and machinery.
Whether in one piece or dozens, A-68 could have a large impact on the ocean and ecosystems around South Georgia, which sustain large colonies of penguins and seals, as well as whales.
The cooling and freshening that takes place as the giant iceberg breaks up and melts might affect the lifeforms at the very bottom of the food chain: tiny algae called phytoplankton. At the same time, large icebergs can also stir up nutrients from the deep, increasing biological productivity in their wake.
To find out, I am here in the Southern Ocean, which surrounds Antarctica, on the research ship RRS James Cook. We will monitor the temperatures, salinities and plankton concentrations in the water, and compare the findings to long-term data from oceanographic studies in the region.
Leading an oceanographic expedition to the Southern Ocean is always exciting and unpredictable. It is even more so when the target of your observations is spinning around in meandering currents while gradually breaking up.
Due of the pandemic, we have a reduced team of just 11 scientists, engineers and technicians from the National Oceanography Centre in Southampton, UK, and the British Antarctic Survey in Cambridge, UK, in addition to the ship鈥檚 crew and a doctor.
After two weeks of quarantine, we are trying to fit our research into the iceberg into a short time window between our other work carrying out annual monitoring of the ecosystems and climate of the Southern Ocean. Luckily the A68-A iceberg has ended up in a location that doesn鈥檛 require a large detour.
Icy impact
We are spending three days near this iceberg as part of five intensive weeks of research at sea. The weather is typical for the Southern Ocean at this time of year: cloudy, windy and chilly, with daytime temperatures just above freezing.
After admiring the iceberg briefly, we carry on with our measurements. On our second day, we deploy an underwater robotic glider. This 1.5 metre-long submersible will continue monitoring the ocean around the iceberg for months after we leave. We can barely see the iceberg through the fog, and hope that our third day affords us better views.
The ship circles around the iceberg overnight, and this time we approach it from the north as the weather clears, only to find that the many fragments of ice, large and small, that have broken off the iceberg impede our passage. In the end, we deploy our second glider near A-68P, the newest named iceberg, which is 鈥渙nly鈥� 100 square kilometres big. It will make its way to A-68A, through iceberg-infested waters where the ship cannot safely navigate.
As we start heading north to our next study area, I look back on the vast field of icebergs in the sunset. One small iceberg has a few penguins on it, and albatrosses and smaller seabirds are flying around the ship. The oceans around Antarctica are a remarkable place to work, constantly changing.
Although icebergs are a fact of life in these parts, who knows what we will find when we next return.
