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- Iceberg A23a continues to drift towards South Georgia, but there is a high probability that it will "get stuck" on a shoal before reaching the island.
- New scientific evidence suggests that Antarctic icebergs were plying these waters as early as 36 million years ago, changing our understanding of ice formation in the distant past.
- Analyzing ancient icebergs helps researchers more accurately predict changes in ice masses and subsequent impacts on climate.
Scientists are keeping a close eye on the massive iceberg A23a, which is drifting towards South Georgia Island. Some experts warn that if it were to hit land, it could damage the habitat of penguins, seals and albatrosses that inhabit this remote South Atlantic island. While the actual probability of a direct collision remains low, the consequences of such a scenario could be extremely negative for many marine animals, as the iceberg could make it difficult for them to access feeding grounds.
However, the journey of A23a, which broke away from the Filchner Ice Sheet in 1986 and remained aground for a long time before drifting again in 2020, is just one example of how climate change is affecting Antarctica. As new research from Utrecht University shows, icebergs have been making similar journeys for decades and even epochs - they could have happened as far back as 36 million years ago. This suggests that glaciers may have existed on the southern continent much earlier than previously thought.
Icebergs are millions of years older than the "official" Antarctica
For a long time, scientists assumed that the first major ice sheet in Antarctica formed around 34 million years ago, at the turn of the Eocene to the Oligocene. During this period, a sharp cooling occurred that transformed the southern tip of the Earth into the icy desert we know today. However, experts from Utrecht, using their analysis of ancient ocean sediments and modeling the movement of icebergs, are challenging this generally accepted chronology. They have found evidence that ice blocks were drifting in southern waters as early as 36 million years ago, at a time when, according to traditional ideas, the continent's ice cap should have been insignificant or nonexistent.
The main evidence is rock fragments brought by icebergs (so-called glacial debris or IRD). These fragments were found in sediments dating back 36,5 million years during offshore drilling in the microcontinent of South Orkney Province (site 696 of the Ocean Drilling Program, ODP). As the researchers suggest, the fragments came from Antarctic regions where solid glaciers capable of "chipping off" such large icebergs may have existed.
Tracking drift in the late Eocene
Utrecht University master's student Mark Albertsen and his supervisors Peter Bijl and Erik van Sebille used modern computer models to investigate how icebergs might have moved in the warmer atmosphere of the late Eocene. The results showed that only huge ice blocks weighing more than 100 megatons and several tens of meters thick could have "lived" long enough to reach the South Orkney province. Smaller icebergs melted quickly in relatively warm (compared to today) ocean waters, which could reach 10°C at the surface.
During the simulation, wave erosion played the biggest role in the rapid destruction of ice masses, which could “bite off” from 10 to 20 meters of iceberg per day. Therefore, even very large blocks usually melted completely within a few months. Despite this, some of the “giants” could well overcome the distance to the South Orkney Province if there were appropriate currents, similar to the modern “iceberg alley” along which icebergs from Antarctica drift to this day.
The results of the computer models match geological data - the mineral composition of the fragments found corresponds to rocks from the southern Weddell Sea, where these ancient icebergs likely came from. This supports the hypothesis that the coast of Antarctica may have had ice sheets much earlier than previously thought.
How could ice exist in a warmer climate?
Scientists believe that increased precipitation was the main factor. In a warmer climate, evaporation from the ocean is more intense, so the hydrological cycle is intensified. This means more snowfall, which, accumulating on the highlands of the continent, forms large glaciers. Eventually, these ice formations can descend to sea level, where the "birth" of icebergs occurs.
Such findings are consistent with a growing body of evidence suggesting that the formation of Antarctic ice was a more complex and gradual process than previously thought, likely occurring locally long before the continent's general glaciation.
Importance for modern understanding of climate
The results of this master's thesis, published in the journal Climate of the Past, help to better understand how ice sheets formed and responded to climate change in the past. By studying periods of rapid warming and how meltwater from icebergs affected the environment, researchers from Utrecht hope to improve predictions about current global warming and the future of the Antarctic ice sheet.
Elbertsen's supervisors, Peter Bijl and Erik van Sebille, are continuing to study past iceberg calving phases as part of the EMBRACER climate program. Studying the ancient journeys of icebergs can provide useful information about the thresholds at which Antarctic ice begins to expand or melt.
Fate of A23a
As for the current iceberg, A23a, experts suggest that it will most likely run aground around South Georgia without directly hitting the island's coast. If this happens, the situation may even benefit local animals - thanks to tidal and ocean currents around the huge ice floe, the influx of nutrients will increase, which will contribute to the development of marine ecosystems. However, scientists continue to monitor its movement, since even a relatively stationary iceberg of this size has a significant impact on the local biodiversity.
Ultimately, the Utrecht results confirm that Antarctica's ice sheets have a much longer history than previously thought. Understanding how sensitive these colossal ice systems may be to climate change is becoming increasingly important in light of current warming.
