SOURCE: University of Arizona News

DATE: January 6, 2020

SNIP: The increased freshwater from melting Antarctic ice sheets plus increased wind has reduced the amount of oxygen in the Southern Ocean and made it more acidic and warmer, according to new research led by University of Arizona geoscientists.

The researchers found Southern Ocean waters had changed by comparing shipboard measurements taken from 1990 to 2004 with measurements taken by a fleet of microsensor-equipped robot floats from 2012 to 2019. The observed oxygen loss and warming around the Antarctic coast is much larger than predicted by a climate model, which could have implications for predictions of ice melt.

“It’s the first time we’ve been able to reproduce the new changes in the Southern Ocean with an Earth system model,” said co-author Joellen Russell, a professor of geosciences.

The research is the first to incorporate the Southern Ocean’s increased freshwater plus additional wind into a climate change model, she said. The team used the National Oceanic and Atmospheric Administration’s ESM2M model.

Previously, global climate change models did not predict the current physical and chemical changes in the Southern Ocean, said Russell, who 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 said.

Now, models will be able to do a better job of predicting future environmental changes in and around Antarctica, she said, adding that the Southern Ocean takes up most of the heat produced by anthropogenic global warming.

“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,” she said. “We had never seen the winter-time chemistry under the ice.”

The floats revealed how much Antarctic waters had changed in the last several decades – a development global climate models had not predicted.

The team also used the improved model to forecast conditions in the Southern Ocean. The forecast suggests that in the future, the Southern Ocean may not take up as much carbon dioxide from the atmosphere as previously predicted.