282
Antarctic ice sheets have been shaping the ocean for millions of years, but recent discoveries show that icebergs existed even before the continent completely froze over. It’s not unusual to see icebergs break off Antarctica and drift across the ocean—just like the huge ice sheet currently moving toward South Georgia Island. But climate change is making this process happen more often, and the icebergs themselves are getting bigger.
Researchers from Utrecht University are studying the ways in which icebergs drifted during periods of rapid ice loss, such as at the end of ice ages. Their work is helping to understand how iceberg melting affects ocean conditions and what this means for the future. In the process, they have also stumbled upon a clue to an old mystery: the presence of ancient Antarctic material near the South Orkney Islands. Their findings provide new insights into how icebergs have shaped the planet over millions of years.
Ice sheets: a fragile balance
Ice sheets grow as snow accumulates. Gravity then pulls the ice toward the sea, where it loses mass as icebergs melt and break off, a process called calving. If new ice formation matches its loss, the ice sheet remains stable. However, in recent decades, rising air and ocean temperatures around the South Pole have accelerated the loss of ice. Melting water weakens the ice on top, while warmer ocean waters erode it from below. This causes icebergs to break off more frequently, and in some cases, huge blocks of ice can break off in a short period of time.
Iceberg Lane: A Story of Drifting Giants
The waters around South Georgia Island have long been an important region for iceberg research. This area, known as the Iceberg Passage, is a narrow strip of ocean filled with icebergs that break off from Antarctica and drift north, carried by winds and ocean currents. Once they reach warmer waters, they gradually melt and disappear. For about 34 million years, Antarctica has been home to a huge ice sheet, meaning that the Iceberg Passage has seen a continuous flow of drifting ice. But scientists studying the South Orkney Islands have stumbled upon a puzzle: evidence of icebergs that existed 3 million years before the great Antarctic ice sheet formed.
In 2017, researchers found fragments of Antarctic rocks on the seafloor around the South Orkney Islands. The only way this material could have traveled such a long distance is through iceberg drift. Glaciers scrape rocks off the Antarctic continent, and when icebergs break off and drift, they carry these fragments with them. When the iceberg melts, the fragments settle to the ocean floor. But how could these icebergs have existed before Antarctica froze?
Cold Enough: Solving a Glacial Mystery
Utrecht University student Mark Elbertsen has offered an answer to these questions in his master's thesis. Using computer simulations, he determined where the icebergs that reached the South Orkney Islands in the late Eocene could have come from, and how large they had to be to survive the journey.
He found that the Weddell Sea was cold enough to transport medium-sized icebergs over such a distance. Furthermore, the most logical place for their origin was precisely the part of Antarctica where the fragments found correspond to rocks found near the South Orkney Islands. This suggests that in the late Eocene, Antarctica already had an ice sheet that reached the coast and moved fast enough to form large icebergs that could survive the warm conditions of the Weddell Sea. Thus, the study confirmed that enough snow fell there to form glaciers and icebergs 3 million years before the great glaciation of Antarctica.
Freshwater and future climate change
Bijl and van Sebille are continuing their research. There have been many periods of intense iceberg calving in Earth's history, during the transition from glacial to interglacial periods. The new EMBRACER research program will involve a doctoral student to study these "deglaciation periods." Computer modeling will be used to determine the volumes of meltwater entering the Southern Ocean and their impact on ocean conditions.
Researchers also want to better understand the consequences of large volumes of freshwater entering the Southern Ocean in the future. Excess freshwater could affect deep ocean currents and the ocean's ability to absorb carbon. If climate change continues at this rate, the Southern Ocean will soon be faced with even larger and more numerous icebergs.
Drifting: The Journey of Iceberg A23a
In 1986, iceberg A23a broke away from the Filchner Ice Shelf in the depths of the Weddell Sea. This massive iceberg remained attached to the shallow waters for decades until it began drifting in 2020.
Scientists are closely monitoring its movements because South Georgia is an important breeding ground for penguins, seals and albatrosses. If an iceberg were to collide with the island, it could block the animals’ access to food. However, it is more likely to get stuck in shallow water, and its presence could even contribute to the emergence of additional resources in the surrounding waters. Ocean currents could push the iceberg out to sea, where it would gradually melt, continuing the long history of Antarctic icebergs.
