Rogue icebergs the size of Somerset may determine the fate of the planet

By Dasha Scanlan-Oumow

Three years ago, a 6,000 square kilometre iceberg broke off the western side of the Antarctic Peninsula. Since then, it has been a subject of oceanic currents, the wind, the waves – and has slowly meandered its way north.

For an iceberg the size of Somerset, that moves its own length in one day, its path could prove fatal to a poorly navigated ship, or indeed, a badly positioned island.

The island we’re talking about is South Georgia. An Antarctic oasis and wildlife documentary hotspot, where there is more wildlife per square foot than other place in the planet, South Georgia is home to 95% of the world’s fur seals, 50% of the world’s southern elephant seals (a male can weigh 4,000 kg), and 30 million pairs of breeding seabirds, including the wandering albatross.

Its moods are mercurial, wildlife plenteous and vegetation mystical with Himalaya-like peaks and bare rocks smothered in tundra-like shrubs. December brings around the most important time of the year for the mammoth populations of seals and penguins: mating.

But 2020 has in store another trial: the potential convergence of South Georgia with a giant iceberg, nicknamed A-68a. Usually icebergs ground on the island shelf, but A-68a boats a shallow depth of only 200m, meaning it could make it all the way to the island.

This would have catastrophic consequences to the endemic breeding populations that use coastal areas both for mating and raising young offspring. The lack of open access to the ocean, and the vast reserves of krill on which seals and penguins feed, could cause a plummet in mating and offspring success. For a Macaroni penguin, even a small detour over an iceberg could use up precious energy reserves, leading to negative consequences in reproductive ability. 

For an iceberg the size of Somerset, that moves its own length in one day, its path could prove fatal to a poorly navigated ship, or indeed, a badly positioned island.

This section of ocean is an iceberg motorway; through their initial calving from Antarctic glacial shelves, to their eventual dissolution in warm Equatorial seas. But situations like this are only increasing. Whilst a giant iceberg used to calve only once a decade, the warming Antarctic peninsula is causing an increase in ice loss.

The Larsen ice shelf, stable for the majority of the Holocene, has been deteriorating since the 1990’s, and has lost 20,000 of the original 85,000 square kilometres. A-68a broke off Larsen C: a subsection of the ice-shelf which is estimated to raise global sea levels by 10cm if fully melted. Global warming can be held directly accountable for the reduced growth of ice sheets, and increased melt of the Antarctic peninsula. As Antarctic seas warm up, currents eat away into the ice-shelves, whilst meltwater gathering on the ice warms in the sun and leverages open cracks. This entire continent has enough frozen water to raise global sea levels by 58 metres. 

The increased rate of iceberg formation has scientists coming to differing conclusions, emphasising the multi-faceted complexity of this issue. Firstly, an unexpected positive; icebergs have the potential to act as floating carbon sinks, breathing life into Antarctic seas.

It is impossible to predict the exact outcome of global warming on every ecosystem on the planet

As icebergs cruise their way through the Atlantic waters, they grind on bedrock and gather large amounts of organic material and trace elements, such as iron. These minerals are gradually released, ‘fertilising’ the ocean and resulting in large phytoplankton blooms. These phytoplankton feed off carbon dioxide and are crucial organisms at the bottom of marine ecosystem food chains. Once they die, they float to the bottom of the ocean and create a carbon sink. The increased productivity of the Southern Oceans, due to the passing of icebergs, could be seen as an offset for the freshwater released by their melting as well as reducing the rate of exchange of CO2 between ocean and atmosphere. 

But this silver lining is hiding a sinister storm cloud. Thermohaline circulation – global ocean currents driven by differences in temperature and salinity – is the linchpin to climatic security, but it is at risk. The increased proportion of freshwater in the oceans is changing oceanic salinity, and thus changing the density of these waters. Thermohaline circulation relies on density differences to move water around the globe. Warm surface water from the southern hemisphere moves northwards, cooling and sinking into the deep ocean where it flows back south. The current carries heat north, and effectively maintains a suitable climate in Western Europe and Northern America. The shutdown of this system would lead to unpredictable climatic consequences; radically effecting global winds, rainfall patterns and potentially dropping global temperatures by 10°C. 

A-68a represents a dawn in a new era, where unpredictable events cause a cascade of uncontrollable results. It is impossible to predict the exact outcome of global warming on every ecosystem on the planet. What we can be sure of is that climatic events are already spiralling beyond the speed that scientific research can predict, and as custodians of the Earth we must try and minimise the catastrophic impacts that our species wreak on the sophisticated systems of our planet.

Image: Anastasiia Orlova from Pixabay

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