Melting Antarctic Ice Sheets Have Made Southern Ocean More Acidic, Warmer

According to a new study, the increased freshwater caused by melting ice sheets in Antarctica, combined with the increased Antarctic wind has decreased the oxygen level in the Southern Ocean. This has made the ocean warmer and more acidic. The study was headed by geoscientists from the University of Arizona.

Researchers used a fleet of microsensor-equipped robot floats to collect data on oxygen loss and warming in the Southern Ocean. Image Credit: Hannah Zanowski.

The scientists discovered the change in the Southern Ocean waters by comparing shipboard measurements obtained between 1990 and 2004, with those taken by a series of robot floats between 2012 and 2019. These robot floats were equipped with microsensors.

The warming and loss of oxygen around the Antarctic coast are greater than estimated by a climate model. These observations have further implications in predicting the melting of ice sheets.

This finding pushed the researchers to enhance the prevalent climate change computer models in order to better indicate the environmental changes occuring around Antarctica.

It’s the first time we’ve been able to reproduce the new changes in the Southern Ocean with an Earth system model.

Joellen Russell, Study Co-Author and Professor, Department of Geosciences, University of Arizona

This is the first-ever study to apply the increased freshwater of the Southern Ocean and additional wind to a climate change model, Russell added. The researchers utilized the ESM2M model of the National Oceanic and Atmospheric Administration.

According to Russell, the present chemical and physical changes occurring in the Southern Ocean were not predicted by global climate change models before. Russell also holds the Thomas R. Brown Distinguished Chair in Integrative Science.

We underestimated how much influence that added freshwater and wind would have. When we add these two components to the model, we can directly and beautifully reproduce what has happened over the last 30 years,” she added.

According to Brown, improved climate change models now are able to estimate upcoming environmental changes both in and around the Antarctic coast more efficiently. She further added that the Southern Ocean takes up a large portion of the heat generated by anthropogenic global warming.

One out of every eight carbon molecules that comes out of your tailpipe goes into the Southern Ocean,” Russell added. “Our model says that in the future, we may not have as big of a carbon sink as we were hoping.”

Ben Bronselaer, the first author of the study, headed the effort to enhance the climate models during his career as a postdoctoral research associate in Russell’s laboratory. Currently, Bronselaer is working as a meteorological and oceanographic engineer at the British multinational oil and gas company BP, based in London.

The researchers’ paper, titled “Importance of wind and meltwater for observed chemical and physical changes in the Southern Ocean,” was published in the Nature Geoscience journal on January 6th, 2020.

Researchers continually improve their global climate change models in order to gain deeper understanding surrounding the climate system of the Earth.

As part of this endeavor, the Southern Ocean Carbon and Climate Observations and Modeling Project, or SOCCOM for short, explores the Southern Ocean and its impact on climate.

SOCCOM is financed by the National Science Foundation, with further support extended by NASA and the National Oceanic and Atmospheric Administration (NOAA).

SOCCOM group, headed by Russell, enhances the way the Southern Ocean is represented in global climate computer models. For 25 years, Russell has been analyzing the ocean around the Antarctic region.

My first research cruise in the Southern Ocean was in 1994. It was in the winter in the deep South Pacific. I had grown up in Alaska, and I knew what a blizzard felt like—and I had never felt winds like that before.

Joellen Russell, Study Co-Author and Professor, Department of Geosciences, University of Arizona

Since that time, she has been “obsessed” by the adverse winter winds in Antarctica, Russell added.

Along with other researchers, Russell has been taking shipboard measurements in the oceans around Antarctica for many years. However, it proved difficult to take measurements, due to winter conditions. Furthermore, the level of the winter sea ice makes it impossible to take near-shore measurements from ships, she added.

That issue was solved when the SOCCOM robot floats were deployed in 2014.

The robot floats can go under the winter ice and work all winter long collecting data. The robot floats are the revolution in how we can even imagine looking at the evolution of the ice and the ocean. We had never seen the winter-time chemistry under the ice.

Joellen Russell, Study Co-Author and Professor, Department of Geosciences, University of Arizona

The robot floats showed the amount of Antarctic waters that had changed in the last several years—an advancement that was not predicted by the global climate change models.

Previously, Bronselaer, Russell, and their collaborators have introduced more freshwater from the melting ice sheets to the climate change models, but this modification did not recreate the new changes in the chemistry of the Southern Ocean.

The problem was solved by raising the freshwater and the extent of Antarctic wind in the climate model; currently, the model accurately represents the present state of Antarctic waters.

In addition, the researchers utilized the enhanced climate change model to predict the Southern Ocean conditions. The forecast indicates that in the days to come, the Southern Ocean is not likely to take up as much atmospheric carbon dioxide as assumed earlier.

Russell has planned to pursue the winter winds in the Antarctic coast.

We didn’t observe it—but the model says we need it,” she added. “I’m proposing to NASA a satellite to go hunt for the missing wind.”

Other co-authors of the study include Michael Winton and John P. Dunne from the NOAA Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey; Richard A. Feely from the NOAA Pacific Marine Environmental Laboratory in Seattle, Washington; Nancy L. Williams from the University of South Florida College of Marine Science in St. Petersburg, Florida; Robert M. Key and Jorge L. Sarmiento from Princeton University; and Kenneth S. Johnson from Monterey Bay Aquarium Research Institute in Moss Landing, California.


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