In the Northern Hemisphere, a lot of radars are trained on the North Pole right now, trying to catch sight of a Santa and his sleigh. But this year, scientists in the Southern Hemisphere have a different target. They’re tracking A68a, a giant slab of ice that cracked off Antarctica’s Ross Ice Shelf more than three years ago. 

The iceberg is drifting close to South Georgia Island, a critical biodiversity hotspot in the vast Southeastern Atlantic Ocean, more than 1,000 miles from the spiny twin tips of South America and the Antarctic Peninsula. 

Christmas week the berg split into three main sections, still drifting close together, and scientists said the biggest pieces might get stuck near the shore and disrupt wildlife. The British Antarctic Survey has launched a mission to study the berg with drone submarines and other instruments, said Andrew Fleming, who has been tracking its exact position via satellite.

“If it gets grounded there, it might stay for a long time,” Fleming said. And as it breaks up, thousands of smaller bergs could float north into shipping lanes, he added.

There is also concern that if global warming breaks up more of Antactica’s ice shelves, the fresh water from flotillas of melting bergs could disrupt climate-regulating currents in the Southern Ocean.

A Very Big Iceberg

A68a is no ordinary iceberg. It was one of the 10 biggest bergs ever to break off the Antarctic shelf, about as big as Rhode Island and about 650 feet thick, with most of that heft below the waterline. So far, it’s floated nearly 1,000 miles toward South Georgia, an island about the same size as the berg.

Topped by 9,629-foot Mount Paget, South Georgia is a United Kingdom Overseas Territory. On the boundary of the Atlantic and Antarctic oceans, it became famous after the explorer Sir Ernest Shackleton scrambled over its icy crags to a whaling station on the last leg of his mission to summon help for the crew of the Endurance. The ship, which he captained, was crushed by Weddell Sea ice in early 1915.

As the only significant patch of land for 1,000 miles in any direction, South Georgia is a critical crossroads for wildlife. Animals have colonized the island in huge swarms, with about 5 million seals and 65 million seabirds, including several species listed as endangered on the International Union for the Conservation of Nature’s Red List. The surrounding sea is important for whales.

It is not a coincidence that A68a is on a collision course with the island. The main currents in that region have steered many other bergs that direction, but few so large. In 2003, a large iceberg got stuck on the north side of the island for a while, Fleming, the BAS expert said.

“They make such a difference to the water around them. When they melt, they release fresh, cold water, loaded with nutrients,” he said. The researchers will measure water temperature, salt levels, chlorophyll and plankton all around the iceberg and compare those readings with long-term measurements taken near the island to see how the system changes.

BAS ecologist Professor Geraint Tarling said that if the bottom of the iceberg drags along the ocean floor, it could damage communities of sponges, brittle stars, worms and sea-urchins in one of the world’s largest marine protected areas, with more marine species than the Galapagos Islands.

Learning From Icebergs Past

One melting iceberg by itself can disrupt local ecosystems, but it’s not enough to make a big difference to the climate. Already, melting icebergs contribute about half of all the freshwater produced by Antarctica, the other half coming from surface runoff.

From traces on the North Atlantic seafloor, scientists know that there were big surges in iceberg activity thousands of years ago linked with abrupt climate shifts. In some cases, the icebergs left behind distinct ridges of sediments that fell out of the melting ice to the bottom of the ocean. Researchers have also discovered seafloor gouges off the coast of Florida suggesting that giant bergs also drifted there.

And although the data is sparse, there does appear to be a trend in the past few decades toward more icebergs drifting away from the Arctic, as well. In 2018, the commander of the U.S. Coast Guard iceberg monitoring program described an “extreme” iceberg outbreak that disrupted shipping and drilling platforms in the Arctic. 

Together with other paleoclimate clues, the record from the Arctic suggests there were extreme climate fluctuations in the era that left the gouges and ridges on the sea floor, including big swings in temperatures and shifts in ocean currents. But there are not really similar records from the relatively unexplored Southern Ocean, so A68a will give scientists a chance to learn more about iceberg behavior in that region.

Clues to Climate Disruption

Those past iceberg events show that coastal ice shelves can become unstable very quickly, said Grant Bigg, an iceberg researcher at Sheffield University. The current era of rapid global warming, research shows, is putting some of the shelves around Antarctica at risk, Bigg said. If they disintegrate, they could unleash enough icebergs to alter existing layers of fresh and salty water enough to affect critical currents, he added. 

Those layers are important to the climate system because they move massive quantities of heat energy through the world’s oceans, and also determine how much carbon the oceans can take out of the atmosphere.

“If we can understand what the climate was like in past times, it gives us more confidence in what climate models project for the future,” Bigg said. One of the underlying anxieties raising interest in West Antarctica are unstable ice shelves that are only tenuously anchored to the ground, he added.

Looking at icebergs around both poles also gives a more complete picture of large-scale global climate shifts, helping scientists get an idea of the relative rates of temperature change between hemispheres. The paleoclimate evidence suggests that some sudden shifts in climate had unexpected effects. For example, during the iceberg surges in the Northern Hemisphere in the last ice age, there was warming in the Southern Hemisphere. Data showing that is important to understanding how the global climate system will respond to today’s warming, Bigg said. 

The BAS mission to A68a can help show exactly how fast one individual iceberg melts, and that new information could help make more accurate, larger-scale climate projections, said Ian Eisenman, an ice researcher with the Scripps Institution of Oceanography at the University of California, San Diego, and a co-author of a study on iceberg melt published Dec. 17 in the journal Science Advances.

“Right now, icebergs play a role in the climate system, but not a huge role,” Eisenman said. “A typical climate model doesn’t treat icebergs at all, but there are scenarios when all of a sudden we have a lot more icebergs out there. Where they go, where they deposit their freshwater affects the climate system.”

Encircling Antarctica is a huge pool of water so cold and dense that it pushes aside lighter and warmer water, acting as a pump for global ocean currents. The speed of those currents and the associated layers of sea water also affect how much carbon is stored deep down in the ocean, and how much is stirred up to mix back into the atmosphere as carbon dioxide.

The new study focuses specifically on how giant icebergs like A68a disintegrate and how their freshwater is distributed in the Southern Ocean, said co-author Mark England, a climate researcher at Scripps and the University of North Carolina Wilmington.

“Anything you do in terms of moving around the freshwater flux on the surface can have an effect on the ocean circulation, which is relevant to the carbon uptake,” Eisenman added.