Arctic

The earth’s changing climate is characterized by warming temperatures, a rising sea level, and changes in the intensity and frequency of extreme events. Average temperatures are increasing all over the globe, but in the Arctic this warming is much more rapid. The Arctic is the north polar region and is primarily comprised of a large ocean basin: The Arctic ocean, which is the smallest of the world’s five oceans, encompassing only 3% of total ocean surface area and only 1% of total ocean volume. It’s a nearly enclosed ocean basin surrounded by North America, Greenland, Europe, and Russia, with only one small inlet from the Pacific Ocean and one outlet into the Atlantic Ocean. Because of its enclosed nature, when waters enter the Arctic Ocean they can stay there for hundreds of years. One of the other special properties of the Arctic is that about 50% of its total area is composed of shallow regions called continental shelves that extend hundreds of kilometers out from the continents with an average depth of only 150 meters. These shelf regions allow for significant exchange of Arctic seawater with continental sediments, rivers, and biological communities, giving the Arctic a unique chemical composition.

More importantly, however, these continental shelves become factories for the production of sea ice from Arctic seawater. This ice grows so much that about 93% of the surface Arctic becomes ice-covered each winter. This ice can reach several meters in thickness, and its snowy expanse is historically home to native Inuit communities and also large populations of seals, walruses, and, of course, polar bears. Over the next weeks we will talk about the real-time threat of a changing climate to Arctic communities and how Texas A&M University oceanographers are working to study this rapidly changing environment.

In this series we are discussing the Arctic ocean, the region of the planet that is warming fastest in response to global climate change. Air temperatures in the Arctic Ocean have increased about 7°F in the last 50 years, which is the fastest temperature increase recorded anywhere on the planet, and is about twice the rate of global temperature increase.

One of the most series consequences of this temperature rise is the melting of Arctic sea ice, which traditionally covers most of the surface of the Arctic each winter. Arctic sea Ice thickness has decreased by 15% in the last 50 years, and the duration of winter ice coverage has decreased by more than 2 months. Staggeringly, sea ice extent has dropped 20% over the last 30 years alone. Not only do these changes affect the lives of people living in the North - for example, this year’s Iditarod sled race was forced to move its starting line 225 miles farther north due to lack of snow – but the organisms who make homes of these sea ice flows, such as polar bears, seals, walruses, and seabirds are finding their natural habitats shrinking and moving.

There is, however, another reason that the loss of Arctic sea ice is dangerous. The melting of sea ice causes a climate feedback that encourages more melting. Sea ice has a high albedo, which means that its white surface is very reflective of energy from the sun, while the ocean has low albedo, absorbing relatively more energy. The reflectivity of sea ice helps keep the earth cool, but as global warming reduces sea ice coverage, more heat is absorbed by the ocean causing more ice melt and even more heat absorption. Some scientists predict that this feedback loop could lead to a complete loss of summer sea ice by year 2100.

We’ve been discussing the Arctic Ocean and its position in a warming climate. This week our focus is on the freshwater systems in the Arctic.

Glaciers are large bodies of ice with an average thickness of 7000 feet that are built up from precipitation over land in very cold areas. Glaciers flow downhill over land towards the ocean under their own weight. Arctic glaciers cover parts of Alaska, Canada, Greenland, Scandinavia, and Russia, and include the second largest glacier in the world: the Greenland ice sheet. Since 1979, summer melt on the Greenland ice sheet has increased in surface area by 30%. The melting of Arctic glaciers alone is projected to result in sea level rise of at least 5 cm by the year 2100, while total sea level rise from climate change over this time is expected to be between 10 and 90 cm, depending on many factors.

Additionally, while the Arctic Ocean only encompasses 1% of total ocean volume, 10% of the global river discharge flows into the mostly enclosed Arctic Ocean basin. The Arctic watershed, or land surface area over which freshwater converges into the Arctic, is nearly double the surface area of the Arctic Ocean itself. With increasing Arctic temperatures, tropical moisture is predicted to move from the tropics toward the poles, resulting in increased precipitation over the Arctic by nearly 20% by the year 2100. This will result in freshening of the Arctic Ocean which will impact global ocean circulation, a part of which is driven by the sinking of very cold and salty seawater in the polar North Atlantic.

In 2015, Texas A&M oceanographers deployed in the Arctic Ocean as part of a multi-institutional, multi-million dollar research initiative funded by the National Science Foundation through the International GEOTRACES program. The goal of the 65-day research cruise was to establish the most comprehensive understanding of the Arctic Ocean’s chemical composition, with 51 scientists and 94 Coast Guard personnel deployed to the task. U.S. ships have only reached the true north pole a total of 4 times. This research cruise aboard the world-class U.S. Coast Guard iceabreaking ship Healy was the fourth.

Due to thinning ice in recent years, the Healy was able to break through the Arctic ice by itself, while in previous Arctic ventures at least two ships were required to supply sufficient power and fuel. Texas A&M oceanographers were aboard the Healy when it made history becoming the first unaccompanied U.S. ship to reach the true north pole.

The goals of the Arctic GEOTRACES cruise were to constrain chemical inputs to the Arctic Ocean from the Pacific, as well as explore the changing chemical inputs to the Arctic from rivers, sea ice, snow, and continental shelf sediments. Texas A&M scientists focused on measuring dissolved metal concentrations in Arctic seawater, snow, and ice. One metal of interest was iron which is an important nutrient for phytoplankton. Another was lead which has minimal contributions from natural sources but has an increasing human input from the use of fossil fuels.

Though the Arctic is rapidly changing, this chemical inventory will serve as a baseline against which future change can be compared.