Claim: large Antarctic polynyas to disappear, yet some are still found in satellite imagery

This PR from McGill University  claims that the “deep ocean heat has been unable to get out and melt back the wintertime Antarctic ice”.  That might be true, but still, there are polynyas present in the location of interest (Weddell Sea) that they don’t mention. In fact, there’s even a large offshore polynya in progress in the Weddell Sea right now according to NSIDC imagery, and the Weddell sea has a lot more ice where it is not supposed to be according to “normals”. See below – Anthony

Global warming felt to deepest reaches of ocean

Study shows climate change has put a freshwater lid on the Antarctic ocean, trapping warm water in ocean depths

In the mid-1970s, the first available satellite images of Antarctica during the polar winter revealed a huge ice-free region within the ice pack of the Weddell Sea. This ice-free region, or polynya, stayed open for three full winters before it closed.

Subsequent research showed that the opening was maintained as relatively warm waters churned upward from kilometres below the ocean’s surface and released heat from the ocean’s deepest reaches. But the polynya — which was the size of New Zealand — has not reappeared in the nearly 40 years since it closed, and scientists have since come to view it as a naturally rare event.

Now, however, a study led by researchers from McGill University suggests a new explanation: The 1970s polynya may have been the last gasp of what was previously a more common feature of the Southern Ocean, and which is now suppressed due to the effects of climate change on ocean salinity.

The McGill researchers, working with colleagues from the University of Pennsylvania, analyzed tens of thousands of measurements made by ships and robotic floats in the ocean around Antarctica over a 60-year period. Their study, published in Nature Climate Change, shows that the ocean’s surface has been steadily getting less salty since the 1950s. This lid of fresh water on top of the ocean prevents mixing with the warm waters underneath. As a result, the deep ocean heat has been unable to get out and melt back the wintertime Antarctic ice pack.

“Deep ocean waters only mix directly to the surface in a few small regions of the global ocean, so this has effectively shut one of the main conduits for deep ocean heat to escape,” says Casimir de Lavergne, a recent graduate of McGill’s Master’s program in Atmospheric and Oceanic Sciences and lead author of the paper.

The scientists also surveyed the latest generation of climate models, which predict an increase of precipitation in the Southern Ocean as atmospheric carbon dioxide rises. “This agrees with the observations, and fits with a well-accepted principle that a warming planet will see dryer regions become dryer and wetter regions become wetter,” says Jaime Palter, a professor in McGill’s Department of Atmospheric and Oceanic Sciences and co-author of the study. “True to form, the polar Southern Ocean – as a wet place – has indeed become wetter. And in response to the surface ocean freshening, the polynyas simulated by the models also disappeared.” In the real world, the melting of glaciers on Antarctica – not included in the models – has also been adding freshwater to the ocean, possibly strengthening the freshwater lid.

The new work can also help explain a scientific mystery. It has recently been discovered that Antarctic Bottom Water, which fills the deepest layer of the world ocean, has been shrinking over the last few decades. “The new work can provide an explanation for why this is happening,” says study co-author Eric Galbraith, a professor in McGill’s Department of Earth and Planetary Sciences and a fellow of the Canadian Institute for Advanced Research. “The waters exposed in the Weddell polynya became very cold, making them very dense, so that they sunk down to become Antarctic Bottom Water that spread throughout the global ocean. This source of dense water was equal to at least twice the flow of all the rivers of the world combined, but with the surface capped by freshwater, it has been cut off.”

“Although our analysis suggests it’s unlikely, it’s always possible that the giant polynya will manage to reappear in the next century,” Galbraith adds. “If it does, it will release decades-worth of heat and carbon from the deep ocean to the atmosphere in a pulse of warming.”

The research was supported by the Stephen and Anastasia Mysak Graduate Fellowship in Atmospheric and Oceanic Sciences, by the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery programme, by the Canadian Institute for Advanced Research (CIFAR) and by computing infrastructure provided by the Canadian Foundation for Innovation and Compute Canada.

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To help readers understand what they are talking about, here is a pictorial via NSF.

What they don’t mention in this press release though, is that polynyas near the coast are often the result of Katabatic winds. The Turney Ship of Fools surely knows about what happens when the winds shift and the ice starts packing in when the polynya closes.

They also don’t mention that a large polynya appeared in November 2011 in the Weddell sea they are wailing about that might be “… the last gasp of what was previously a more common feature of the Southern Ocean…”.

From NASA Earth Observatory:

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this natural-color image of a polynya off the coast of Antarctica, near Ross Island and McMurdo Station on November 16, 2011. The polynya was likely caused by katabatic winds, which derive their name from the Greek term for “descent.” The winds blow off Antarctica’s high interior toward the ocean and can attain hurricane strength—up to 200 miles (320 kilometers) per hour.

Strong winds have pushed sea ice away from the coast in this image, but not uniformly. Ross Island and the mountains to the west block some winds, so sea ice lingers near those landforms. Along the lower-elevation area east of Ross Island, winds clear the ice from a large stretch of ocean. North of the polynya, sea ice shows varying degrees of thickness, perhaps the result of alternating windy and calm spells.

Here is another from 2008:

And, there’s even a large polynya in progress in the Weddell Sea right now according to this NSIDC image via the WUWT Sea ice page:

(image annotated by A. Watts, click image for original) Source: http://nsidc.org/data/seaice_index/images/daily_images/S_bm_extent_hires.png

The orange lines indicate the “normal” sea ice extent for this time of year, and clearly there is more ice than normal in the Weddell sea, but somehow an offshore polynya managed to open up.

The paper: Ocean-atmosphere heat fluxes at the Ronne Polynya, Antarctica by UEA’s Anna Fiedler suggests that the Ronne Polynya, while wind-driven, still has an important role in heat flux transport, and that they actually help manufacture more sea ice:

The Ronne Polynya is a coastal polynya, a region of thin ice or open water in sea ice, caused by the offshore transport of the ice

by strong winds from the land (Figure 1). As soon as the ice is transported offshore, new ice forms on the exposed ocean surface and is also advected offshore in a continual process,

earning this type of polynya the nickname ‘ice factory’. These polynyas have an important impact on the regional meteorology and oceanography of the high latitudes

as well as on the global ocean circulation.

One wonders what role these features may have in building up the sea ice increase around Antarctica.

Source: Cryosphere Today – Arctic Climate Research at the University of Illinois – Click the pic to view at source

While it is certainly possible that the 1970’s polynya was caused by warm water upwelling, it is also equally possible that it was at least aided by a persistent wind pattern. Wind has an equal if not stronger effect on sea ice than upwelling.

And, it seems that according to a NOAA researcher (Robert Grumbine) who setup a tracking page, there was an event in 1998 that was of interest:

In 2000, we had no noteworthy polynas in the Weddell Sea.  There was only a small area of reduced ice concentration between approximately 26 August 2000 and 2 September 2000. 2001 and 2002 were even more boring. Not even an attempt to form a polynya.

In 1999, the Weddell Sea was quiet until mid-July. Towards the end of the month, a sizeable area of reduced ice concentration opened up. This was preceded (in time at least) by the formation of a large polynya in the Cosmonaut Sea in early-mid July. Interesting times! 29 July 1999. 4 August 1999: I’ve got to stop looking at the area. As soon as I wrote the above, the proto-polynya began closing back up. I’ll quit looking for a while, so you may find something happening again.

In 1998, while not a full-blown (large area of zero ice) polynya, there was less ice than usual in the Weddell Sea, in the same area as the giant Weddell polynya of the ’70’s.  Because the polynya is such a spectacular feature when it does occur, we have established this page to make it easier to keep track of the current state of the Weddell Sea ice pack.

Here is the June 1998 polynya (I’ve made a small change to the GIF animation to make it loop, previously it played only once):

What I find most interesting about their claim is they act as if the 1974-1976 giant polynya was part of a “normal” activity there, saying it was “a more common feature of the Southern Ocean”, yet we only have a scant 40 years of satellite data to monitor such events. Suggesting that it is likely to never reappear based on modeling is just as nonsensical as the pronouncements we saw in 2000 that “snowfall is a thing of the past”.

The Earth’s mechanisms operate at much longer and slower timescales than 30-40 years, it has often made fools of climate scientists making projections of “phenomena disappearance” before, and I suspect it will again.