Melting Glaciers Cool the Southern Ocean – Might Explain the Recent Antarctic Cooling and Sea Ice Expansion

Earth Antarctic Region

MIT scientists suggest sea ice extent in the Southern Ocean may increase with glacial melting in Antarctica. This image shows a view of the Earth on September 21, 2005, with the full Antarctic region visible. Credit: NASA/Goddard Space Flight Center

Research suggests glacial melting might explain the recent decadal cooling and sea ice expansion across Antarctica’s Southern Ocean.

Tucked away at the very bottom of the globe surrounding Antarctica, the Southern Ocean has never been easy to study. Its challenging conditions have placed it out of reach to all but the most intrepid explorers. For climate modelers, however, the surface waters of the Southern Ocean provide a different kind of challenge: It doesn’t behave the way they predict it would. “It is colder and fresher than the models expected,” says Craig Rye, a postdoc in the group of Cecil and Ida Green Professor of Oceanography John Marshall within MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS).

In recent decades, as the world warms, the Southern Ocean’s surface temperature has cooled, allowing the amount of ice that crystallizes on the surface each winter to grow. This is not what climate models anticipated, and a recent study published in Geophysical Research Letters attempts to disentangle that discrepancy. “This paper is motivated by a disagreement between what should be happening according to simulations and what we observe,” says Rye, the lead author of the paper who is currently working remotely from NASA’s Goddard Institute for Space Studies, or GISS, in New York City.

“This is a big conundrum in the climate community,” says Marshall, a co-author on the paper along with Maxwell Kelley, Gary Russell, Gavin A. Schmidt, and Larissa S. Nazarenko of GISS; James Hansen of Columbia University’s Earth Institute; and Yavor Kostov of the University of Exeter. There are 30 or so climate models used to foresee what the world might look like as the climate changes. According to Marshall, models don’t match the recent observations of surface temperature in the Southern Ocean, leaving scientists with a question that Rye, Marshall, and their colleagues intend to answer: how can the Southern Ocean cool when the rest of the Earth is warming?

This isn’t the first time Marshall has investigated the Southern Ocean and its climate trends. In 2016, Marshall and Yavor Kostov PhD ’16 published a paper exploring two possible influences driving the observed ocean trends: greenhouse gas emissions, and westerly winds — strengthened by expansion of the Antarctic ozone hole — blowing cold water northward from the continent. Both explained some of the cooling in the Southern Ocean, but not all of it. “We ended that paper saying there must be something else,” says Marshall.

That something else could be meltwater released from thawing glaciers. Rye has probed the influence of glacial melt in the Southern Ocean before, looking at its effect on sea surface height during his PhD at the University of Southampton in the UK. “Since then, I’ve been interested in the potential for glacial melt playing a role in Southern Ocean climate trends,” says Rye.

The group’s recent paper uses a series of “perturbation” experiments carried out with the GISS global climate model where they abruptly introduce a fixed increase in melt water around Antarctica and then record how the model responds. The researchers then apply the model’s response to a previous climate state to estimate how the climate should react to the observed forcing. The results are then compared to the observational record, to see if a factor is missing. This method is called hindcasting.

Marshall likens perturbation experiments to walking into a room and being confronted with an object you don’t recognize. “You might give it a gentle whack to see what it’s made of,” says Marshall. Perturbation experiments, he explains, are like whacking the model with inputs, such as glacial melt, greenhouse gas emissions, and wind, to uncover the relative importance of these factors on observed climate trends.

In their hindcasting, they estimate what would have happened to a pre-industrial Southern Ocean (before anthropogenic climate change) if up to 750 gigatons of meltwater were added each year. That quantity of 750 gigatons of meltwater is estimated from observations of both floating ice shelves and the ice sheet that lies over land above sea level. A single gigaton of water is very large — it can fill 400,000 Olympic swimming pools, meaning 750 gigatons of meltwater is equivalent to pouring water from 300 million Olympic swimming pools into the ocean every year.

When this increase in glacial melt was added to the model, it led to sea surface cooling, decreases in salinity, and expansion of sea ice coverage that are consistent with observed trends in the Southern Ocean during the last few decades. Their model results suggest that meltwater may account for the majority of previously misunderstood Southern Ocean cooling.

The model shows that a warming climate may be driving, in a counterintuitive way, more sea ice by increasing the rate of melting of Antarctica’s glaciers. According to Marshall, the paper may solve the disconnect between what was expected and what was observed in the Southern Ocean, and answers the conundrum he and Kostov pointed to in 2016. “The missing process could be glacial melt.”

Research like Rye’s and Marshall’s help project the future state of Earth’s climate and guide society’s decisions on how to prepare for that future. By hindcasting the Southern Ocean’s climate trends, they and their colleagues have identified another process, which must be incorporated into climate models. “What we’ve tried to do is ground this model in the historical record,” says Marshall. Now the group can probe the GISS model response with further “what if?” glacial melt scenarios to explore what might be in store for the Southern Ocean.


“Antarctic Glacial Melt as a Driver of Recent Southern Ocean Climate Trends” by Craig D. Rye, John Marshall, Maxwell Kelley, Gary Russell, Larissa S. Nazarenko, Yavor Kostov, Gavin A. Schmidt and James Hansen, 9 April 2020, Geophysical Research Letters.
DOI: 10.1029/2019GL086892

“Fast and slow responses of Southern Ocean sea surface temperature to SAM in coupled climate models” by Yavor Kostov, John Marshall, Ute Hausmann, Kyle C. Armour, David Ferreira and Marika M. Holland, 17 May 2016, Climate Dynamics.
DOI: 10.1007/s00382-016-3162-z

13 Comments on "Melting Glaciers Cool the Southern Ocean – Might Explain the Recent Antarctic Cooling and Sea Ice Expansion"

  1. Clyde Spencer | June 13, 2020 at 1:07 pm | Reply

    “and westerly winds — strengthened by expansion of the Antarctic ozone hole …”

  2. Ever stopped to think that it was possibly the sun that has the most influence?

  3. David K Hilderman | June 14, 2020 at 1:50 am | Reply

    Is it necessary to find ways to make every observance fit the narrative that the climate models are correct in predicting catastrophic warming? If antarctic sea ice disputes the model why are the models not questioned?

  4. Because, David, if one’s a partisan and supports partisan politicians, then one must agree with their party stance. One party says all life on earth will go extinct; another says some life may but other life will arise in its place; and yet another party says nothing will change. People don’t support scientists, they support their party. So whatever their party claims, THAT is the research people will support.

    Long live the sheeple in all parties.

  5. How about solar minimum? Yep. Why are dinosaur bones radioactive? Astroid, lol. Scientists ingore facts and make there own reality. I thought Miami was supposed to be under 12 feet of water by now. Al Gore made a fortune off people.

  6. Hi,
    So that means glaciers are growing or retreating. I am a little confused about this because I read certain news which says glaciers are melting very fast because of greenhouse gases.

  7. John-Paul Hunt | June 15, 2020 at 6:28 am | Reply

    if water and sun are in the upper atmosphere then it could be reaired or controlled from space using shades to help cool the air and water to maintain the ice caps. As you have to cool the oceans themselves soon not just clean up thr soil and air people of CO2.

  8. Richard Ivonen | June 15, 2020 at 8:24 am | Reply

    Glacial melt water is less saline than sea water and reduces the density of the oceans surface water. It also freezes at a higher temperature than more saline water.

    Deeper layers may be warmer than the surface layers because of the difference in salinity.

  9. This could be because global warming / climate change is bullshit Orwellian propaganda to bring in UN agenda 21/30 & world govt tyranny.

  10. Ocean ice is growing, news to me. Sea ice is calving and the cap is melting. What is the expansion of ocean ice, by vollume, hight, thickness, and age?

  11. Quickfire responses to above comments:

    Koob: The level of heat/energy the sun has been radiating and thus providing to the earth in the past 50-100 years has been slowly decreasing (likely part of sun’s own cycles), while the heating of Earth has increased significantly. This is common assumption without measurements or data to support it.

    Clyde: As noted in the Article, the study was done in 2016 while the link talks of particularly low hole in 2019. With some quick googling you can find that the studies mentioned look at data from 1970 onward before the measures to protect the ozone were implemented, and purpose was to see if the ozone reduction had impact in the pole.

    Prab: SEA ICE (which by melting does not increase sea level as it’s already in water) in particular areas on Antarctica appears to be increasing (what the article mentiones), while the overall ice sheet on the ground on Antarctica (which does contribute to the sea level rise) is decreasing slightly. When including all glaciers around the globe, the overall ice sheet melting has hugely increased. When global climate changes, it affects different areas of the earth differently due to changed weather patterns, causing some areas to heat up while others cool down. It’s the overall impact that matters on a global scale to sea water rise.

    Ironically, while talking of fitting the narrative, most commenters never read any of the articles or the papers under them in any detail. Just reading the few lines that happen to fit their narrative and beliefs and going with it as proof of something. Picking and choosing parts of a study or an article that support your view, when hundreds of studies every year are published that actually tell what actually is happening on our planet. This is disingenuous and purposefully ignorant behavior.

  12. Clyde Spencer | June 21, 2020 at 8:15 am | Reply

    ND W
    There was a study published in 2016; however, this 2020 study is supposed to be a follow up, starting with 1992 data, not 1970. The Montreal Protocol (1987), while off to a slow start, has commonly been credited with a reduction in size of the southern ‘ozone hole,’ albeit erratic in trend. At issue is the claim “According to Marshall, models don’t match the RECENT observations of surface temperature in the Southern Ocean, …” Thus, in order to explain the mismatch, one needs to look at RECENT behavior of the ‘ozone hole.’ The support for the claim that westerly winds are being strengthened by an expanding ‘ozone hole’ is not in evidence for RECENT activity.

    I completely agree with you that “Picking and choosing parts of a study or an article that support your view, when hundreds of studies every year are published that actually tell what actually is happening on our planet. This is disingenuous and purposefully ignorant behavior.” Thank you for demonstrating the point. Incidentally, science isn’t about consensus. That is a political activity.

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