If Antarctica's ice sheets melted, the worlds oceans would rise by 200 - 210 feet, everywhere. Antarctica holds 6,957,470 cubic miles of ice. That represents over 90% of all the ice on the planet and between 60 to 70% of the worlds fresh water. The sea ice begins to expand at the beginning of winter, and eventually advances by 40,000 square miles per day, surrounding the continent and doubling the size of the ice in Antarctica. The snow that falls takes about 100,000 years to flow to the coast of Antarctica before it breaks off the marine extension of glaciers, or ice shelves, and becomes an iceberg. Once an iceberg breaks off the ice platform, any resistance that it provided to hold back the land ice is lost, and the continental ice can accelerate it’s flow to the southern ocean.
The Conversation notes that for the first time in 7,000 years a phenomenon known as upwelling (the upward flow of warm ocean water to the surface) is rotting the ice shelves from below. It is thought that the upwelling has caused the many ice shelf collapses and ice thinning that we have seen over the past decades.
The ocean surrounding Antarctica is extremely cold, but water over 300m deep, Circumpolar Deep Water (CDW), is about 3⁰C above the melting point of ice. Normally, the very cold water above keeps this away from ice shelves. But in some areas, CDW is spilling onto the shallow Antarctic continental shelf, causing the ice to thin.
Ice shelf thinning has accelerated in recent decades, but the picture is not the same everywhere. While the east of the Antarctic has shown modest gains in ice thickness, the west has outstripped this with significant ice loss – up to 18% in vulnerable areas like the Amundsen and Bellingshausen Seas.
The pattern of ice loss and other observations indicate that warmer water upwelling beneath these ice shelves is driving it. But what has caused this upwelling? Is it related to human activity? And how concerned should we be?
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This coincidence of timing with the onset of industrialisation shows it is possible that human made greenhouse gasses, thought to cause atmospheric warming, are having an impact on the position of the winds, the increase in warm water reaching the surface, and ultimately the melting of more ice in the Antarctic.
Irrespective of the causes of past changes in SHWW positions, the link between winds and ocean upwelling is cause for concern, as future projected global warming may shift SHWW belts and promote further upwelling and melting. More research is now needed to fully understand the link between CDW and past climate, and to estimate the strength of upwelling since the 1940s compared to upwelling before 7,000 years ago. But the emerging picture is one of the potentially increased vulnerability of West Antarctic ice sheets, and possible future sea level rise.
See NASA’s Jet Propulsion Laboratory news release from September of 2017 for an expanded review.
Hole the Size of Maine Opens in Antarctica Ice
A hole the size of Maine has opened in the wintertime sea ice surrounding Antarctica. Though these holes, called polynyas, are not uncommon around Earth's southernmost continent, one hasn't been spotted in this location since the 1970's, reports Heather Brady of National Geographic.
The polynya in question opened on September 9 in a relatively shallow area of water in the Weddell Sea. At its peak, it spanned roughly 30,000 square miles—about the size of Maine, writes Brady. The first hole in this location was spotted in 1974 and was roughly the size of Oregon. It stuck around for another two years, but then disappeared. Since that time, the region has remained largely quiet.
Then in 2016, a gap in the ice appeared, catching scientists attention. The latest hole is the largest the spot has been since the 70's, writes Brady.
These holes in the ice form thanks to Antarctic water circulation, reports Maddie Stone at Earther. Warm water rises toward the surface, melting the ice that sits atop the open ocean waters, creating the polynya "window." Heat is released from the water through this opening, causing the now cooler water to sink. This circulation pushes more warm water toward the surface, which keeps the polynya open. As Stone reports, the hole is expected to close when warm spring air or the addition of freshwater from melting sea ice, slows the circulation of the waters.
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The sinking, cold water helps drive parts of the oceanic conveyor belt that moves ocean water around the globe—a major force in regulation of Earth's climate, reports Stone. As climate warms there is concern that this conveyor belt could slow down or even halt as the input of cold fresh water increases from melting ice. Less dense than the underlying saltwater, the fresh water stubbornly stays on top of the ocean waters, slowing the churn of the system.
But the relationship of these polynyas to climate change remains hazy, and studying this latest opening could help provide scientists with some clues. “While many climate models tend to produce such a large open ocean polynya, the feature was viewed more as a disruptive model glitch than a true phenomenon in the past,” Torge Martin, a meteorologist at the Helmholtz Centre for Ocean Research in Kiel, Germany, tells Stone. “Its recurrence supports our hypothesis... that the Weddell Polynya was not a one-time event but possibly occurred regularly in the past.”
How openings in Antarctic sea ice affect worldwide climate
In a new analysis of climate models, researchers from the University of Pennslyvania, Spain's Institute of Marine Sciences and Johns Hopkins University reveal the significant global effects that these seemingly anomalous polynyas can have. Their findings indicate that heat escaping from the ocean through these openings impacts sea and atmospheric temperatures and wind patterns around the globe and even rainfall around the tropics. Though this process is part of a natural pattern of climate variability, it has implications for how the global climate will respond to future anthropogenic warming.
"This small, isolated opening in the sea ice in the Southern Ocean can have significant, large-scale climate implications," said Irina Marinov, a study author and assistant professor in Penn's Department of Earth and Enviromental Science in the School of Arts & Sciences. "Climate models suggest that, in years and decades with a large polynya, the entire atmosphere warms globally, and we see changes in the winds in the Southern Hemisphere and a southward shift in the equatorial rain belt. This is attributable to the polynya."
The study appears in the Journal of Climate. Marinov coauthored the work with Anna Cabre, a former postdoc in Marinov's lab and now an oceanographer with the Institue of Marine Sciences in Barcelona, and Anand Gnanadesikan, a professor in the Department of Earth and Planetary Science at Johns Hopkins.
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Their model indicated that polynyas and accompanying open-ocean convection occur roughly every 75 years. When they occur, the researchers observed, they act as a release valve for the ocean's heat. Not only does the immediate area warm, but there are also increases in overall sea-surface and atmospheric temperatures of the entire Southern Hemisphere and, to a lesser extent, the Northern Hemisphere, as well.
Changes in north-south temperature gradients lead to changes in wind patterns as well.
"We are seeing a decrease in what we call the Southern Hemisphere westerlies and changes in trade winds," Marinov said. "And these winds affect storms, precipitation and clouds."
Among these changes in precipitation is a shift in the Intertropical Convergence Zone, an equatorial belt where trade winds converge, resulting in intense precipitation. When a polynya occurs, this rain belt moves south a few degrees and stays there for 20 to 30 years before shifting back.
"This affects water resources in, for example, Indonesia, South America and sub-Saharan Africa," said Marinov. "We have a natural variation in climate that may be, among other effects, impacting agricultural production in heavily populated regions of the world."
Penguin disaster as only two chicks survive from colony of 40,000
In the colony of about 18,000 breeding penguin pairs on Petrels Island, French scientists discovered just two surviving chicks at the start of the year. Thousands of starved chicks and unhatched eggs were found across the island in the region called Adélie Land (“Terre Adélie”).
The colony had experienced a similar event in 2013, when no chicks survived. In a paper about that event, a group of researchers, led by Yan Ropert-Coudert from France’s National Centre for Scientific Research, said it had been caused by a record amount of summer sea ice and an “unprecedented rainy episode”.
The unusual extent of sea ice meant the penguins had to travel an extra 100km to forage for food. And the rainy weather left the chicks, which have poor waterproofing, wet and unable to keep warm.
This year’s event has also been attributed to an unusually large amount of sea ice. Overall, Antarctica has had a record low amount of summer sea ice, but the area around the colony has been an exception.
Ropert-Coudert said the region had been severely affected by the break-up of the Mertz glacier tongue in 2010, when a piece of ice almost the size of Luxembourg – about 80 km long and 40km wide – broke off. That event, which occurred about 250km from Petrels Island, had a big impact on ocean currents and ice formation in the region.