After spending several decades sedentary, an ice block twice the size of Greater London is adrift on the high seas.
Breaking free from its position north of the South Orkney Islands, A23a’s current journey actually began in 2020, when it came loose from a position on the seabed it had occupied for nearly 30 years.
Weighing nearly 1trillion tonnes, and calved from the Antarctic Filchner Ice Shelf in 1986, the giant iceberg was settled in the Waddell Sea until the beginning of this decade, when it naturally broke off and began heading north. However, this colossal odyssey has taken longer than expected, revealing some scientific phenomenon en route.
For example, A23a spent several months trapped in a Taylor Column. This rare oceanographic occurrence involves water rotating above a seamount, preventing objects from escaping. Remarkably, given the berg’s scale and weight, this system of currents kept the enormous hulk of ice spinning on the spot, delaying its northbound trajectory.
As it moves up the Earth, it will encounter warmer waters once in the sub-Antarctic region, likely close to the island of South Georgia. This will trigger a breaking down of the mass, forming smaller icebergs which will eventually melt. The path has been mapped based on the route of the Antarctic Circumpolar Current.
‘It’s exciting to see A23a on the move again after periods of being stuck. We are interested to see if it will take the same route the other large icebergs that have calved off Antarctica have taken. And more importantly what impact this will have on the local ecosystem,’ said Dr Andrew Meijers, an oceanographer at British Antarctic Survey, and co-lead on the OCEAN:ICE project.
‘We know that these giant icebergs can provide nutrients to the waters they pass through, creating thriving ecosystems in otherwise less productive areas. What we don’t know is what difference particular icebergs, their scale, and their origins can make to that process,’ added Laura Taylor, a biogeochemist on the BIOPOLE cruise. ‘We took samples of ocean surface waters behind, immediately adjacent to, and ahead of the iceberg’s route. They should help us determine what life could form around A23a and how it impacts carbon in the ocean and its balance with the atmosphere.’
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