Quantcast
Environmental News for a Healthier Planet and Life

Melting of Antarctic Ice Sheets Is Making Southern Ocean Less Salty

Popular

Melting Antarctic ice sheets are measurably reducing the salinity of the Southern Ocean. The research, published Thursday in Nature, notes that more freshwater entering the ocean "is more important for changes in global climate than has been appreciated so far."

Ocean salinity patterns from Dec. 2011 to Dec. 2012 as seen by Argentina's SAC-D satellite.NASA/GSFC/JPL-Caltech

Scientists have seen a reduction in salinity of the waters around Antarctica over the past decades. They haven't understood why until now. The study—by researchers from ETH Zurich, the GEOMAR Helmholtz Centre for Ocean Research Kiel and the University of Hamburg—describes a process whereby sea ice forms each winter, releasing salt in the seawater, then drifts northward and melts in the summer, spreading fresh water over a wide area.

On average, seawater is about 3.5 percent salts, mainly sodium chloride. Salt water is denser than fresh water, and the freezing point of water goes down as the amount of dissolved salts goes up. If all the salt in the world's oceans were removed and spread over the Earth, it would cover the planet in a 500-foot thick salt lick.

But salinity is not uniform across the world's waters. The highest salt content is generally found in the center of ocean basins, away from continents and the fresh water flowing from their rivers every day. Equatorial waters, where evaporation is highest, also boast above-average salinity. But these are not constant throughout the year.

Ocean circulation is driven by surface winds, temperature and salinity. Cooler, high-salinity water sinks to great depths, while lower-salinity water, which is less dense, rises. Over a long period—about 1,000 years—the Global Conveyor Belt moves water around the oceans in response to temperate and salinity.

In contrast to the Arctic Ocean, where the sea ice is declining at a rate of 13.4 percent per decade, the Antarctic ice sheet added 112 billion tons of ice per year from 1992 to 2001.

The maximum seasonal ice cover in the Southern Ocean now reaches further north than it did 30 years ago. The German and Swiss study explains, "This expansion is mainly due to a stronger transport of sea ice that has pushed the sea-ice edge further to the north." The northernmost edge of the ice at maximum is at about 60 degrees south.

That may seem paradoxical in the face of a warming planet, but NASA explains: "Just as the temperatures in some regions of the planet are colder than average, even in our warming world, Antarctic sea ice has been increasing and bucking the overall trend of ice loss."

The significance of the greater mass of Antarctic sea ice is that, as it melts each summer, the fresh water sinks to a depth of about 600 to 1,500 meters, a region known as the Antarctic Intermediate Water. It then spreads north to the equator, into the eastern Atlantic and as far as the Iberian Peninsula.

As the water in the upper layers of the ocean become fresher and less dense, they may block the heavier, saltier waters below from rising to the surface. This is a process known as stratification.

James Hansen, the former NASA scientist, pointed to stratification as a potential wild card in the climate disruption process. He thinks that it could accelerate the melting of the Greenland and Antarctic glaciers, and perhaps change current patterns in the Atlantic. Research published Aug. 23 in Nature found evidence that stratification is occurring in Prydz Bay in East Antarctica.

In announcing the German and Swiss study, the researchers noted, "So far, the Southern Ocean has acted as a climate regulator and carbon sink: climate models show that this ocean has absorbed around three quarters of the excess heat. The Southern Ocean has also taken up around half the total amount of anthropogenic carbon dioxide absorbed by the world's oceans."

NOAA

Further studies will test these theories, and new satellites will help researchers better observe the ocean and sea ice. The Southern Ocean will get more attention in the years to come.

EcoWatch Daily Newsletter

A pangolin at a rescue center in Cambodia. Rhett A. Butler / Mongabay

By Malavika Vyawahare

China has banned the trade and consumption of wild animals in the wake of the coronavirus outbreak that has claimed more than 2,700 lives and infected more than 81,000 people, most of them in China, according to the state-run Xinhua News Agency.

Read More
A man carries plastic shopping bags in Times Square on May 5, 2018 in New York City. Kena Betancur / VIEWpress / Corbis / Getty Images

Nearly one year after New York became the second state in the nation to pass a ban on grocery store plastic bags — the law is going into effect on Sunday.

Read More
Sponsored
White gold man-made diamond solitaire engagement ring. Clean Origin

While keeping track of the new trends in the diamond industry can be hard, it is still an essential task of any savvy consumer or industry observer. Whether you are looking to catch a deal on your next diamond purchase or researching the pros and cons of an investment within the diamond industry, keeping up with the trends is imperative.

Read More
Rep. Alexandria Ocasio-Cortez (D-NY) (C) chants with housing and environmental advocates before a news conference to introduce legislation to transform public housing as part of her Green New Deal outside the U.S. Capitol Nov. 14, 2019 in Washington, DC. Chip Somodevilla / Getty Images

Rep. Alexandria Ocasio-Cortez (D-N.Y.) took to the floor of the House of Representatives yesterday to chide Republicans for not reading the Green New Deal, which she introduced over one year ago, as The Hill reported. She then read the entire 14-page document into the congressional record.

Read More
Anti Ivan Duque's demonstrator is seen holding a placard with the photos of social leader Alirio Sánchez Sánchez and the indigenous Hector Janer Latín, both killed in Cauca, Colombia during a protest against Ivan Duque visit in London which included a meeting about fracking, environmental issues, the peace process implementation, and questioning the risk that social leaders in Colombia face. Andres Pantoja / SOPA Images / LightRocket / Getty Images

Colombia was the most dangerous nation in 2019 to be an environmental activist and experts suspect that conditions will only get worse.

Read More