Polar Connections: Exploring Antarctic ice, and why it matters

Editor’s note: This is the first in a series of monthly columns called Polar Connections. The columns explore how the Arctic and Antarctic regions are changing and why it truly matters.

 

Sir Ernest Shackleton and his men watched the Endurance crumple under the pressure of sea ice in the Weddell Sea over 100 years ago. Since then, the story of these 28 men and their survival in the icescapes of Antarctica has lived on through books, films and imaginations across the world. So it is not surprising that as a group of researchers plan the “Weddell Sea Expedition 2019,” where they will use autonomous underwater vehicles to map the ocean floor, they’ve added Endurance hunting to the list of things to do.

Next February, this international research team will head south to 68 degrees latitude with a primary purpose of exploring the area around the one trillion ton iceberg that broke off from the Larsen C ice shelf last summer. This iceberg covers 2,240 square miles. It would only take three and a half icebergs of this size to completely fill Cook Inlet.

This past February I traveled into the northern edge of the Weddell Sea. I was there at the end of the southern hemisphere’s summer season so most of the sea ice that had formed during the winter had melted. The Antarctic region has an average maximum sea ice coverage of over 7 million square miles – more than a million more than the Arctic. But by summer’s end, the 3 million square miles of remaining sea ice is just half of what is left in the Arctic. This is just one of the ways that the ice of the polar regions is different. However, this comparison is changing as recent Arctic sea ice patterns are showing a decline of both maximum and minimum extents.

Unlike the Arctic region, which is an expanse of ocean surrounded by continents, Antarctica is a continent surrounded by oceans. Since there is no northern boundary of land to contain Antarctic ice, it is free to float north into warmer waters and melt. In the Arctic, the sea ice moves around the polar region but is more hemmed in by land masses and stays in colder waters. As a result, Arctic sea ice is typically 6 to 9 feet thick, while Antarctic ice tends to be only 3 to 6 feet thick. But as Shackleton found out, Antarctic sea ice combined with fierce winds can conspire into pack ice that can crush the strongest of ship hulls.

My ship was a former National Oceanic and Atmospheric Administration vessel. It was twice as long (278 feet) and wide as the Endurance and my shipmates were all women. I was onboard as part of Homeward Bound – a global leadership initiative for women in science. We were there to learn new skills and to build a network of women focused on influencing policy and decision making as it shapes our planet. I was also there to see how changes to our earth’s climate system are altering the southern polar region and to share with the 77 other participants from 18 different countries what I know about changes in Alaska’s Arctic and subarctic regions.

As we entered the Weddell Sea, we motored past huge tabular icebergs. Some of these slabs were no doubt from the collapsing Larsen ice shelf. Ice shelves are tongues of ice that extend out from grounded glaciers attached to land and surround 75 percent of Antarctica’s coastline. Similar to sea ice, ice shelves are floating ice, like ice cubes in your lemonade, and they don’t contribute to sea level rise.

But the ice shelves play an important role of holding back the movement of the Antarctic ice sheet. Once an ice shelf collapses, the sheet behind it can move more quickly. That sheet of land-based ice that will act like a water faucet and add to sea level rise. After another part of the Larsen ice shelf broke off in 2002, researchers concluded that the loss of the Larsen B ice shelf will speed up the flow from the West Antarctica ice sheet by 10 times. The Larsen C ice shelf that calved in 2017 is twice as big as Larsen B. Recent modeling efforts indicate the Antarctic ice sheet may add an additional 31.5 inches of global sea level rise by 2100.

Although the collapse of the Larsen B and C ice shelves doesn’t increase sea level rise directly, they have added significant amounts of freshwater into the marine environment. This freshening of the surface waters from ice shelf melt will actually impact the movement of nutrient rich bottom waters to the world’s oceans.

In fact, the bottom of the Weddell Sea, where the remains of the Endurance likely sit at 9,850 feet, has some of the densest waters of the world. This dense seawater is both extremely cold and extra salty and is the result of salts being released into the surface waters as sea ice forms. The salts increase the water’s salinity and, because salt water is heavier, the denser water sinks.

This movement of the dense, salty water to the ocean bottom is an important part of the global circulation system pumping oxygen- , carbon- and nutrient-rich waters out into the Southern Ocean. The freshening of the surface waters from the melting of the ice shelves stabilizes the water column by reducing the amount of cold, salty, bottom water being produced and thus, effectively, slowly turns off the circulation pump. We have much to learn about these processes and what the implications mean for our planet.

More than a century has passed since the early years of polar exploration. For the modern adventurer, only faster and quirkier ways to get to the poles are left. Not surprisingly, someone already kite-skied to the South Pole. For scientists, with tools like autonomous underwater vehicles and satellite imagery, the age of exploration is in full swing. For me, traveling to the other end of the earth is just the start of my journey exploring how women in science can shape and lead the conversation about our earth’s changing climate and ensure a just energy transition that allows Alaska communities and Arctic species to thrive.

Sue Mauger is Science Director for Cook Inletkeeper and lives in Homer.

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