#polynya

Shivers got a new mom and their name is Polynya.

In their paper, What caused the remarkable February 2018 Greenland Polynya?, Moore, Schweiger, Jinlun Zhang and Mike Steele identify the polynya's cause to be strong surface winds catalyzed by a dramatic warming in Earth's upper atmosphere known as a Sudden Stratospheric Warming.

"During these events, temperatures in the stratosphere – about 30km above ground level—can warm by 10° or 15°C in just a few days," Moore says.

"This causes a change in air circulation that includes a reversal in the winds in the stratosphere. These high altitude winds blow against the west-to-east direction of the jet stream, descending toward the Earth's surface. In February 2018, this caused winds from Siberia to blow cold air into northern Europe, creating a weather system that became known as the 'Beast from the East'. It brought temperatures of minus 20°C to northern Europe, and the same weather pattern moved warmer air northwards up the east coast of Greenland."

Strong southerly winds forced mild air to Greenland and beyond, but it wasn't their warmth that caused the polynya.

Antarctica in a changing climate: Increasing sea ice DOES NOT mean that the Earth has stopped warming.

As you probably know, 2013 saw the Arctic summer sea ice reach its minimum extent since records began. It was recorded at 4.1 million square kilometres; around 50% lower than the 1979-2000 average. (see post here: http://on.fb.me/URg3KE)

Interestingly, over the same period, a study by the British Antarctic Survey (BAS) and NASA found that sea ice in the Antarctic has been increasing; hitting a 35-year record high in September 2013.

The key words here are “sea ice”.

Unlike the Arctic, Antarctica is composed of both sea and land ice. This consideration is the most important thing we must remember when talking about the effects of climate change on the Antarctic. Sceptical arguments which suggest that Antarctica is “gaining ice” are relying on an error of omission; essentially ignoring the fundamental differences between land and sea ice.

The Antarctic land ice sheet is the largest single mass of ice on our planet, covering an area of almost 14 million square kilometres. It contains an enormous 30 million km3 of ice, encompassing around 90% of fresh water on Earth- the equivalent of 70 metres of water in the world’s oceans. (British Antarctic survey, 2012). It is this land ice mass that is the best representation of how climate change is affecting the continent. A study published in the journal Nature based on GRACE (Gravity Recovery and Climate Experiment) satellite data, has found that some areas of the Antarctic are not only losing ice mass rapidly, but also at an accelerating rate. Also, NASA scientists are currently keeping a close eye on a huge crack in the Pine Island Glacier in the Antarctic. Should this calf, it will produce an iceberg the size of New York City and will be the largest contribution to sea level rise from Antarctica to date.

On the other hand, it is true that while the land ice mass is decreasing, the sea ice extent is increasing. This is not unprecedented.

The oceans around Antarctica consist of layers of cold water at the surface and a layer of warmer water below. Water from the warmer layer rises up to the surface, melting sea ice. However, as air temperatures increase, the amount of rain and snowfall also increases. This “freshens” the surface waters, leading to a surface layer less dense than the saltier, warmer water below. The layers become more stratified and mix less. Less heat is transported upwards from the deeper, warmer layer. Hence less sea ice is melted (Zhang 2007)

Another reason for an increase in sea ice is attributable to another environmental problem; the hole in the ozone layer. The drop in ozone levels over the Antarctic has caused cooling in the stratosphere (Gillet 2003). As stratospheric temperatures affect wind velocity, the cyclonic winds that circle the Antarctic have strengthened (Thompson 2002). The wind pushes sea ice around, creating areas of open water known as polynyas. More polynyas lead to increased sea ice production (Turner 2009).

The message to take away today is that the Antarctic is not the Arctic. It is a continent, surrounded by water, while the Arctic is a sea, surrounded by land.

You don’t have to be a scientist to understand that despite being polar; they are extremely different regions and each will be affected by a changing climate in different ways.

-Jean

Information and references:

British Antarctic Survey: http://www.antarctica.ac.uk/press/press_releases/press_release.php?id=1967

NASA Climate Change: http://climate.nasa.gov/news/?FuseAction=ShowNews&NewsID=813

Previous TES post: http://on.fb.me/SNT7f3

Turner, J., J. C. Comiso, et al. (2009). "Annular atmospheric circulation change induced by stratospheric ozone depletion and its role in the recent increase of Antarctic sea ice extent." Geophys. Res. Lett. 36(8): L08502.

Zhang, Jinlun, 2007: Increasing antarctic sea ice under warming atmospheric and oceanic conditions. J. Climate, 20, 2515–2529.

Strange Science: Holey Ice in Antarctica

Holes that open up in the ice pack in Antarctica are nothing new. They’re called polynyas, and they can be caused near coastlines by warmer water or wind.

Scientists have recently identified a polynya in Antarctica that is hundreds of kilometers inland, an unusual place for a polynya to form. It’s also roughly the size of the state of Maine (over 35,000 square miles).

From NASA Earth Observatory Image of the Day; March 1, 2017:

Grounded in the Caspian Sea

On February 4, 2017, the Operational Land Imager (OLI) on Landsat 8 acquired natural-color images that beautifully demonstrate the variety of ice types that can form in the northern Caspian Sea.

The Caspian stretches about 1,000 kilometers (600 miles) from Kazakhstan to Iran. In the north, temperatures are colder, and the water is fresher (less saline) and shallower. As a result, northern areas are more prone to freezing in wintertime.

The first image shows the northwestern Caspian where it meets western Kazakhstan. The brown areas are part of the Volga Delta. Just offshore, in the shallowest parts (only meters deep), a well-developed expanse of consolidated ice appears white. Farther offshore, a large field of old, hummocked, white and gray-white ice has detached. (When pieces of ice are pushed together, some ice is forced upward and downward into so-called ‘hummocks.’) This ice is slowly drifting in a giant polynya which is covered by young, thin ice (nilas).

The second image shows a detailed view of the nilas ice, which appears dark. Perhaps most notable, however, is the white, diamond-shaped piece of ice parked right in the middle. “This ‘island’ of white ice is most probably a piece that detached from the ice field,” said Alexei Kouraev, a scientist at the Laboratory of Geophysical and Oceanographic Studies (France). He notes that a likely point of origin is the “dent” of similar size in the boundary of the white ice (mid-right of the top image).

It might look like that ice diamond is on the move, cutting a path through the thinner cover. But it’s more likely that the chunk of ice broke away from the thicker sea ice and became grounded—anchored to the bottom of the sea. The grounded ice (‘stamukha’ in Russian) is not moving, according to Kouraev. Instead, the wind is pushing the thin ice around this grounded ice, creating a ‘shadow’ of open water behind it.

Grounded ice is particularly apparent in the third image. This false-color image shows thermal data: orange depicts where the surface is warmer, which tends to be where the ice is thinnest; blues and whites are colder areas, including the main ice pack and grounded ice.

With the advance of spring and rising temperatures, ice on the Caspian will soon disappear. All of the ice is first-year ice, meaning that it should not survive the summer. But with the melting of the ice, a different picture can emerge: the keels of hummocked ice that once reached all the way to the seafloor can leave behind scour marks.

References and Related Reading:

Kouraev, A. et. al (2004, June) Sea ice cover in the Caspian and Aral Seas from historical and satellite data. Journal of Marine Systems, 47(1), 89-100.

NASA Earth Observatory (2016, April 23) Ice Scours the North Caspian Sea.

NASA Earth Observatory (2013, March 30) Ice on the Caspian Sea.