Antarctic seals are helping scientists learn more about melting glaciers

 /  2021-5-26

(CNN) Known as the Earth's "thermostat," Antarctica plays a vital role in regulating the planet's complex climate system.

Scientists are investigating how environmental changes in Antarctica will impact the rest of the world, but the continent's remote location and hostile climate, with winter temperatures that plummet to well below -100°F, make it an incredibly challenging environment for humans.
That's why a team from the Sea Mammal Research Unit at the University of St Andrews, in Scotland, enlisted the help of some of Antarctica's permanent residents: seals.
The furry, aquatic mammals thrive year-round in the freezing climate and can dive up to 3,000 feet below the water's surface says Lars Boehme, an oceanographer and one of the project's leaders.

By fitting the seals with sensors, the researchers gain insight into the seals habits and ecology, while also gathering data from inaccessible parts of the ocean.
Scientists around the world are now drawing on this data to learn more about the Antarctic environment and how it could impact climate change.

Animal assistants

Researchers have been tagging seals since 2004 to gather environmental information from around Antarctica. However, little was known about the Amundsen Sea in West Antarctica, where two of the continent's fastest melting glaciers -- Pine Island Glacier and Thwaites Glacier -- are located. So in 2014, Boehme led a team to tag seals there.
While six seal species live in Antarctica, only Weddell and southern elephant seals dive into the deeper layers of the ocean -- the main reason these species were chosen for data collection, says Boehme. The seals are hunted by orcas and other seals in the water, but have no land predators, so the scientists can approach them easily. "They're not running away," says Boehme.
The team members sedate the seals with a blow dart and glue a smartphone-sized sensor to the fur on the backs of their heads. The process doesn't hurt the animals or impact their social lives, says Boehme. Seals molt annually, so the device falls off after a year.
Boehme says the team are careful to minimize their interactions with the seals. Tagging up to 14 seals per trip in 2014, 2019, and 2020, the team have got the process down to just 10 minutes per seal he says, and are working to reduce the size of the devices.
As the seals swim through the ocean, the device collects information about the depth, temperature, and salinity of the water at different locations. When the seals come to the surface for air, the "data profiles" are transmitted via satellite.
When the project started in 2014, Boehme says there was less than 1,000 data profiles available for the Amundsen Sea area. Now, with the help of the seals, the team has more than 20,000 data points from thousands of locations around Antarctica.

This information is compiled by Marine Mammals Exploring the Oceans Pole to Pole (MOEP), an international consortium that runs a giant online database. The data is incorporated into daily reports by weather forecasting organizations such as the UK's Met Office and European Centre for Medium-Range Weather Forecasts (ECMWF) and is being analyzed by scientists from multiple disciplines.

In hot water

Yixi Zheng, who is undertaking a PhD in environmental sciences at the University of East Anglia, in the UK, has used data collected by seals in the Amundsen Sea in 2014 to investigate melting at Pine Island Glacier.
Previously, it was thought that the "meltwater" that flows out beneath the ice shelf at around 1,470 feet (450 meters) below the surface stays there, in the deep twilight zone of the ocean.
But Zheng's study, published in March this year, found that some meltwater actually rises to the upper sunlight zone of the ocean, around 650 feet (200 meters) below the surface. The meltwater has a unique "fingerprint" that makes it easily traceable in the surrounding seawater, says Zheng: it is nearly 3°C warmer than the water around it and contains less salt.
Moving from the lower to upper zone of the ocean, this warm meltwater causes the surface water's temperature to rise, which leads to more sea ice at the surface melting. The meltwater forms relatively warm lagoons, called polynyas.
While melting ice contributes to rising sea levels, the polynyays do have some environmental benefits, says Zheng.
Rich in nutrients and minerals from the land, the meltwater promotes growth of algae, which absorbs CO2 and attracts tiny creatures like krill, that form the basis the ocean food chain.
Zheng says the exact size and numbers of polynyas is difficult to pin down, but that permanent polynyas are forming in front of Pine Island Glacier, where this data was collected.
Pine Island Glacier, where this data was collected, is one of the fastest melting ice shelves in the region and could be a major contributor to global sea levels rising. Zheng's discoveries about glacial meltwater rising suggest that the rising meltwater could be exacerbating the melting of surface sheet ice. However, Zheng says that more study is needed before any firm conclusions can be drawn about its impact of melting at Pine Island Glacier and the climate at large.

Precise predictions

Antarctica boasts 90% of the world's ice and 80% of the planet's freshwater. But since the 1950s, temperatures in Antarctica have increased by 3°C and in February 2020 the continent logged its highest temperature since records began. The rising temperatures are causing rapid ice loss: between 1992 and 2017, the continent lost around 2.7 trillion tons of ice at an accelerating rate.
Scientists know melting ice will have a knock-on effect on the global environment -- but there's a lot of debate and uncertainty about what that will look like. For example, sea levels are expected to rise in the next century due to melting ice in the polar region and sea water expanding as it gets warmer, but estimates range between one to eight feet, depending on the levels of future greenhouse gas emissions.
Using seals to collect data and analyzing it, as Zheng has, can help narrow those predictions, and give scientists a clearer idea of what we're up against, Boehme tells CNN.
"For me, that's the exciting bit: when Yixi started to talk about what she found, then we begin to better understand these processes that might impact the melting of these glaciers," he says.

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