Massive Icebergs Slowly Swerve, Threaten South Georgia Penguin Colony

An iceberg that broke off the Larsen C Ice Shelf in Antarctica in 2017 is slowly drifting off the coast of South Georgia Island, a British territory in the southern Atlantic Ocean. The iceberg, designated A68a by the National Ice Center, has even given birth to a smaller but still sizable chunk of ice, now known as A68B, and together they could threaten wildlife on the island if they wander too close and get stuck on the seafloor.

So far, the icebergs have not run aground on the shallow shelf area extending from the island, but scientists worry that ocean currents will carry them southeast, away from the island, but then turn them back to the west, grounding them on the island's eastern side. If this occurs, penguin colonies in that region, as well as other marine wildlife, could have a harder time foraging for food, having to divert around the ice to get to the best areas for fishing, for example.

This could cause sudden population declines of penguins and SEALs during peak breeding season. The island is home to millions of king and macaroni penguins, SEALs, sea birds and blue whales that feed on krill just off the coast.

The main tabular iceberg, characterized by a flat, plateau-like top and steep cliffs along its sides, is about the size of Rhode Island and more than 650 feet thick, with about nine-tenths of it underwater. The smaller chunk of ice would ordinarily be considered large in its own right, at about 12 miles long and 6 miles wide at its widest point.

When A68a broke away from the Larsen C ice shelf in Antarctica in July 2017, it measured nearly 2,300 square miles - about the size of Delaware. After shedding ice at its edges and breaking off chunks as it traveled through the rough waters of "Iceberg Alley," the iceberg is now smaller.

The Antarctic Peninsula, where the Larsen C Ice Shelf is located, is one of the fastest-warming areas in the world. In February, a temperature of nearly 70 degrees was recorded on Seymour Island in the Antarctic Peninsula, which may be the continent's highest temperature on record. As ice shelves like Larsen C melt, they free up inland ice to move into the ocean, raising sea levels.

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To better understand the process by which large icebergs break up and their effects on the surrounding ocean and ecosystems, the British Antarctic Survey (BAS) plans to lead a research mission to the iceberg via a ship that will set sail from the Falkland Islands in late January. Researchers will use robotic gliders that can cruise underwater to gather data about the iceberg and the surrounding waters.

Scientists aim to spend four months taking readings of ocean salinity, temperature and chlorophyll at different spots along the iceberg, as well as oceanic plankton concentrations.

"The team will investigate the impact of freshwater from the melting ice into a region of the ocean that sustains colonies of penguins, SEALs and whales. These waters are also home to some of the most sustainably managed fisheries in the world," the Antarctic Survey stated in a news release.

Gerant Tarling, an ecologist at the BAS, says he expects "devastation" if the iceberg were to make contact with the sea floor.

This would occur due to scouring of the seabed communities, damaging populations of sponges, brittle stars, worms and sea urchins, he said in the news release. "These communities help store large amounts of carbon in their body tissue and surrounding sediment. Destruction by the iceberg will release this stored carbon back into the water and, potentially, the atmosphere, which would be a further negative impact."

However, there would be some positive impacts of the iceberg's visit, as well, Tarling said. "For example, when traveling through the open ocean, icebergs shed enormous quantities of mineral dust that will fertilize the ocean plankton around them, and this will benefit them and cascade up the food chain.

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While it's not unusual to have icebergs, including one this large, drifting in the South Atlantic between Antarctica and South Georgia Island, new scientific research shows that tabular icebergs coming off ice shelves like A68a play a significant role in transporting freshwater from the Antarctic ice sheet into the Southern Ocean. Such icebergs are expected to increase in frequency as the region's air and sea temperatures increase, leading to a greater transport of ice into the sea.

In the Southern Ocean, the injection of freshwater from large, tabular icebergs can influence globally-significant ocean currents, which are powered by density differences between water containing different amounts of salt. Saltier water tends to sink, whereas slightly milder freshwater is lighter and stays near the surface.

According to a study published Dec. 16 in Science Advances, nearly half the freshwater the Antarctic Ice Sheet adds to the Southern Ocean each year comes in the form of large tabular icebergs calving from ice shelves, such as Larsen C. However, this freshwater transport is not represented properly in climate models, causing them to misrepresent the future ocean circulation of the Southern Ocean.

Mark England, the lead author of the study from the University of North Carolina at Wilmington and Scripps Institution of Oceanography, said the goal of the study is to simulate the breakup of large, tabular icebergs since current computer models show that happening close to the edges of Antarctica, which isn't the case.

"We want to simulate them since where you put this freshwater in the Southern Ocean is important," England said in an interview.

He and co-author Ian Eisenman, also of Scripps, said the Southern Ocean is a critical region for taking carbon out of the atmosphere and storing it in the ocean, and for determining ocean currents. Failing to accurately simulate large iceberg transport and breakup means that current models are not accurately predicting changes in currents and carbon absorption in coming years.

"The Southern Ocean is where a lot of the uncertainties lie," England said of climate change projections.

The calving of icebergs from ice shelves like Larsen C does not affect sea level rise since the shelves are already floating. However, it can speed the transport of inland ice to the sea, which does contribute to sea level rise.

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