New scientific paper points to ozone depletion as well as greenhouse gas for warming of the southern ocean

A study points to OZONE DEPLETION in addition to climate change on the Southern Ocean

Look up the hole in the ozone layer in Antarctica in Google and you will find a plethora of articles saying the hole in the ozone layer is "healing".

Margo has been chronicling ozone levels in Antarctica and found extremely low levels which appear (if yesterday's figures are anyhting to go by) to be getting worse despite the fact that the sun is returning to the continent.

In the last day or so a new paper from Nature has identified ozone depletion as a secondary cause of warming of the southern ocean as well as some other factors.

What’s Causing Antarctica’s Ocean to Heat Up? New Study Points to 2 Human Sources

With help from floating data-collectors, a new study reveals the impact greenhouse gas emissions and ozone depletion are having on the Southern Ocean.

Inside Climate Change,

26 November, 2014

The Southern Ocean around Antarctica is warming at an alarming rate—twice that of the rest of the world's oceans. Now, researchers have developed more powerful evidence pointing to the human causes.

Though warming had been observed in the past, there was little historical data to allow scientists to pinpoint the causes with much certainty.

In a new study, researchers used climate models, the past observations that did exist and data flowing in from new ocean-going sensors to show how greenhouse gas emissions and the depletion of ozone in the atmosphere have led to both a warming of the Southern Ocean and an increase in its freshwater content. The findings also rule out natural variability as a major source of those changes.

"The observed warming is due to human influence," said oceanographer Neil Swart, a research scientist with Environment and Climate Change Canada who led the study, published Monday in the journal Nature Geoscience. "That may have been suspected or proposed before, but this is the evidence that really proves it."

Ocean-Going Floats and Climate Models

The Southern Ocean is notoriously inhospitable, clogged with ice and home to rough seas and weather. As a result, there weren't many measurements in the past.

In 2004, a partnership of 30 countries across the world launched the Argo program to improve what's known about the world's oceans, and now there are close to 4,000 programmable floats collecting data in the oceans worldwide. That is helping improve what's known, but the lack of complete data going back decades has, in the past, left researchers wondering if their conclusions were robust.

or this study, Swart and his colleagues used data collected in the Southern Ocean from 1950 onward, which showed the pattern of warming and freshening. Then they turned to computer models to try to replicate the cause.

"We sampled the model just the way the ships sampled the ocean so we could compare them," explained Sarah Gille, a physical oceanographer at Scripps Institution of Oceanography and a co-author of the paper.

So if a ship had taken a sample at a specific latitude and longitude on a certain date, the researchers could sample the model at the same location during the same month and year. Within the model, they were then able to turn off and on different influences, like natural variability (from solar radiation and volcanoes), the emissions of aerosols, greenhouse gas emissions and ozone depletion.

When they looked at natural variability and aerosol emissions, neither affected warming or freshening enough to explain what had been observed. But greenhouse gas emissions and ozone depletion did.

Because of global action under the Montreal Protocol, through which the world in 1987 committed to stop producing ozone-depleting substances that had been used in such products as refrigerants and aerosol sprays, it's expected that the role of ozone depletion will shrink. "That action—the Montreal Protocol—is often put forward as an example of, "Hey, as a society we can tackle these problems as they come up," Swart said.

The role that ozone depletion is playing in warming the Southern Ocean is far less than the role of greenhouse gas emissions, though, and so far, those emissions have been a stickier problem to fix.

"That signal of greenhouse gas emissions is just going to continue on intensifying as long as we keep emitting more and more," Swart said.

What's Causing the Freshwater Increase?

The study also suggested that most of the increasing freshwater content in the oceans is coming from precipitation, rather than melting ice from Antarctica.

Cecilia Bitz, a sea ice and climate scientists at the University of Washington who was not involved in the study, said she found the study's observations about the increased freshening particularly interesting. "According to their study, an increase in runoff of meltwater from Antarctica is not needed to explain the decrease in salinity in the upper ocean when considering the linear changes over the last 70 years," she said.

In the future, Gille said, the role that glacial melt is playing in the freshening of the Southern Ocean is "one of the enormous questions that the research community would like to address."

What Warmer Water Could Mean for the Ice

Another study published last week in Nature offers more insight into the future of East Antarctica's massive ice sheet.

David Wilson, a geochemist at Imperial College London, and his co-authors found that even 2 degree Celsius of warming above pre-industrial times had been enough to melt a significant part of the East Antarctic Ice Sheet in the past.

During the Pleistocene era, roughly 125,000 years ago, sea levels were as much as 20 to 30 feet higher than they are now. Wilson and his co-authors focused on the Wilkes Subglacial Basin and how it responded to warming then. Unlike the land-based glaciers, the Wilkes Subglacial Basin is built up from the ocean floor, which can make it particularly susceptible to warming waters. Their findings suggested that 2°C warming now, if sustained over a couple of millennia, could begin melting that location.  

"If we wish to avoid the worst consequences—and you can think, this can have effects on coastal regions, agriculture, island nations—clearly we need to make efforts to change our behavior patterns and decarbonize the economy," Wilson said. "This is clearly what it's pointing towards."

Antarctica’s ‘moss forests’ are drying and dying

With help from floating data-collectors, a new study reveals the impact greenhouse gas emissions and ozone depletion are having on the Southern Ocean.

the Conversation,

26 September, 2018

The lush moss beds that grow near East Antarctica’s coast are among the only plants that can withstand life on the frozen continent. But our new research shows that these slow-growing plants are changing at a far faster rate than anticipated.

We began monitoring plant ecosystems 18 years ago, near Australia’s Casey Station in the Windmill Islands, East Antarctica.

Casey Station is on East Antarctica’s coast. Click map to zoom. Australian Antarctic Data Centre

As we report in Nature Climate Change today, within just 13 years we observed significant changes in the composition and health of these moss beds, due to the drying effects of weather changes prompted by damage to the ozone layer.

Living on the edge

Visitors to Antarctica expect to see a stark landscape of white and blue: ice, water, and sky. But in some places summer brings a surprisingly verdant green, as lush mosses emerge from under their winter snow blanket.

Because it contains the best moss beds on continental Antarctica, Casey Station is dubbed the Daintree of the Antarctic. Individual plants have been growing here for at least 100 years; fertilised by ancient penguin poo

Antarctic mosses are extremophiles, the only plants that can survive the continent’s frigid winters. They live in a frozen desert where life-sustaining water is mostly locked up as ice, and they grow at a glacial pace – typically just 1 mm a year.

These mosses are home to tardigrades and other organisms, all of which survive harsh conditions by drying out and becoming dormant. When meltwater is available, mosses soak it up like a sponge and spring back to life.

The short summer growing season runs from December to March. Day temperatures finally rise above freezing, providing water from melting snow. Overnight temperatures drop below zero and mosses refreeze. Harsh, drying winds reach speeds of 200 km per hour. This is life on the edge.

Tough turf

When we first began monitoring the moss beds, they were dominated by Schistidium antarctici, a species found only in Antarctica. These areas were typically submerged through most of the summer, favouring the water-loving Schistidium. But as the area dries, two hardy, global species have encroached on Schistidium’s turf.

Like tree rings, mosses preserve a record of past climate in their shoots. From this we found nearly half of the mosses showed evidence of drying.

Healthy green moss has turned red or grey, indicating that plants are under stress and dying. This is due to the area drying because of colder summers and stronger winds. This increased desertification of East Antarctica is caused by both climate change and ozone depletion.

class="caption" style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 11px; vertical-align: baseline; background: transparent;"Moss beds, with moss in the foreground showing signs of stress. Sharon Robinson, Author provided

Since the 1970s, man-made substances have thinned Earth’s protective sunscreen, the ozone layer, creating a hole that appears directly over Antarctica during the southern spring (September–November). This has dramatically affected the southern hemisphere’s climate. Westerly winds have moved closer to Antarctica and strengthened, shielding much of continental East Antarctica from global warming.

Our study shows that these effects are contributing to drying of East Antarctica, which is in turn altering plant communities and affecting the health of some native plant species. East Antarctica’s mosses can be viewed as sentinels for a rapidly drying coastal climate.

But there is good news. The ozone layer is slowly recovering as pollutants are phased out thanks to the 1987 Montreal Protocol. What is likely to happen to Antarctic coastal climates when ozone levels recover fully by the middle of this century?

Unlike other polar regions, East Antarctica has so far experienced little or no warming.

Antarctic ice-free areas are currently less than 1% of the continent but are predicted to expand over the coming century. Our research suggests that this may isolate moss beds from snow banks, which are their water reservoirs. Ironically, increased ice melt may be bad news for some Antarctic mosses.

East Antarctica is drying – first at the hands of ozone depletion, and then by climate change. How its native mosses fare in the future depends on how we control greenhouse gas emissions. But with decisive action and continued monitoring, we can hopefully preserve these fascinating ecosystems for the future.