Tag Archives: polynya

Formation of Nares Strait Ice Bridges in 2014

Darkness and cold covers North Greenland, Ellesmere Island as well as Nares Strait, the waterway that connects these two inhospitable places. And despite the darkness of the polar night, I can see that three beautiful arches made of ice connect Greenland to Canada. It is possible to walk across water, if the water is frozen. Stuck to land, ice arches or ice bridges shut down ice motion while the ocean under the ice keeps moving. Lets have a peek at how this looked from space yesterday:

Ice arches of Nares Strait on January 26, 2014 from MODIS thermal imagery.

Ice arches of Nares Strait on January 26, 2014 from MODIS thermal imagery. Surface temperatures in degrees Celsius are all below zero despite the missing “-” sign stripped by Adobe Illustrator.

The colors above show the temperature that satellite sensors “see” at the surface of the ice. Red is warm, blue is cold, and grey is land, but “warm” here is still below the freezing point of sea water near -2 degrees Celsius, so even the red or “hot” spots are covered by ice. The 300 deep ocean in Nares Strait generally flows from north to south without trouble under the ice, but just behind the fixed arching ice bridges, it sweeps the newly formed thin ice away to the south. The “warm” spots that form to the south of each ice arches have their own stories:

Farthest to the north a massive ice arch spans almost 200 km (150 miles) across. It faces the open Arctic Ocean to the north and it formed a few days before Christmas 4-5 weeks ago. It was still shedding large ice floes from its edge as it tried, and finally succeeded, I think, to find a stable location. Nevertheless, one of its larger pieces of ice moved into Nares Strait on January-3, 2014 where it became stuck on both Greenland and Ellesmere Islands:

The large floe from the edge of the first ice arch becames firmly lodged on both sides of the 30-km wide entrance to Nares Strait on January-4 (not shown), perhaps aided by strong winds from the north with wind speeds exceeding 40 knots (20 m/s). This second northern arch then aided the formation of the third ice arch in the south. All three arches became first visible on January-8:

Jan.-8, 2014

Jan.-8, 2014

A subsequent lull and short reversal of the winds brought warm southern air masses into Nares Strait while water and drainage pipes froze at my home in Delaware:

Weather record from Hans Island at the center of Nares Strait for January 2014. [Data from Scottish Marine Institute in Oban, Scotland.

Weather record from Hans Island at the center of Nares Strait for January 2014. [Data from Scottish Marine Institute in Oban, Scotland.

“Warm” here refers to -10 degrees Centigrade (+14 Fahrenheit). Air temperatures in Nares Strait today are -21 degrees Celsius (-5 Fahrenheit) while ocean temperatures under sea ice are near -1.8 degrees Celsius (+29 Fahrenheit). It is these “hot” waters that “shine” through the thinner ice as the satellite senses the amount of heat that the ice surface radiates into space. More details on this one finds elsewhere.

I enjoy these elegantly arching ice bridges across Nares Strait, because they challenge me each year anew to question how sea ice, oceans, air, and land all interact to produce them. Nobody really knows. It is a hard problem to model mathematically and many graduate theses will be written on the subject. A student in our own program, Sigourney Stelma, just presented first results and movies of computer simulations of ice bridges forming. Perhaps I can convince her to post some of them on these pages?

Kozo, T.L. (1991). The hybrid polynya at the northern end of Nares Strait Geophys. Res. Let., 18 (11), 2059-2062 DOI: 10.1029/91GL02574

Kwok, R., Pedersen, L.T., Gudmandsen, P. and Peng, S.S. (2010). Large sea ice outflow into the Nares Strait in 2007 Geophys. Res. Let., 37 (L03502) DOI: 10.1029/2009GL041872

Muenchow, A. and H. Melling. (2008). Ocean current observations from Nares Strait to the west of Greenland: Interannual to tidal variability and forcing J. Mar. Res., 66 (6), 801-833 DOI: 10.1357/002224008788064612

Shades of White as the Sun Rises over Nares Strait

After four months of total darkness the sun is back up in Nares Strait. It transforms the polar night into thousand shades of white as mountains, glaciers, and ice take in and throw back the new light. Our satellites receive some of the throw-away light as the landscape reflects it back into space. During the long dark winter months these satellites could only “see” heat, but this will change rapidly as Alert atop of Arctic Canada receives 30 minutes more sun with each passing day.

Surface temperature in degrees centigrade over northern Baffin Bay on March-4, 2013 16:20 UTC from MODIS Terra.

Surface temperature in degrees centigrade over northern Baffin Bay on March-4, 2013 16:20 UTC from MODIS Terra. Warm colors (reds) show thin and/or ice while cold colors (blues) suggest thick ice stuck in place.

A very strong ice arch at the southern entrance to Nares Strait separates thick (and cold) ice to north from thin (and warm) ice to the south. The thick and cold ice is not moving, it is stuck to land, but the ocean under the ice is moving fast from north to south. The ocean currents thus sweep the newly formed thin ice away to the south. This ice arch formed way back in early November just after the sun set for winter over Nares Strait.

Now that the sun is up, we can also “see” more structures in the ice by the amount of light reflected back to space. A very white surface reflects lots while a darker surface reflects less. We are looking at the many shades of white here … even though I color them in reds and blues:

Surface reflectance at 865 nm in northern Baffin Bay on March-4, 2013 16:20 UTC from MODIS Terra.

Surface reflectance at 865 nm in northern Baffin Bay on March-4, 2013 16:20 UTC from MODIS Terra. A true color image (which this is not) would show only white everywhere. Hence I show the very bright white as red and the less bright white as blue. This artificial enhancement makes patterns and structures more visible to the eye.

Zooming into the area where the ice arch separates thick ice to the north that is not moving from thin ice in the south that is swept away by ocean currents, I show this image at the highest possible resolution:

Surface reflectance at 865 nm at the southern entrance to Nares Strait on March-4, 2013. Contours are 200-m bottom depth showing PII2012 grounded at the north-eastern sector of the ice arch.

Surface reflectance at 865 nm at the southern entrance to Nares Strait on March-4, 2013. Contours are 200-m bottom depth showing PII2012 grounded at the north-eastern sector of the ice arch.

Note, however, that the sun is far to south and barely peeking over the horizon. This low sun angle shows up as shadows cast by mountains. And since the sun is still far to the south, the shadows cast are to the north. This “shadow” makes visible the ice island from Petermann Gletscher that anchors this ice arch as it is grounded. I labeled it PII2012 in the picture.

From laser measurements we know that the ice islands stands about 20 meter (or 60 feet) above the rest of the ice field. This height is enough to cast a visible shadow towards the north (slightly darker = less red) as well as a direct reflection off its vertical wall facing south (brighter = more red) towards the sun. At its thickest point, PII2012 is about 200 meters (~600 feet) thick. For this reason, I also show the 200-m bottom contour that moves largely from north to south along both Ellesmere Island, Canada on the left and Greenland on the right.

The sun brings great joy to all, especially those hardy souls who live in the far north. The sun’s rise also shows the delicate interplay of light and shadows that we can use to solve puzzles on how ice, oceans, and glaciers work. At the entrance of Nares Strait the playful delights of the sea ice, ocean currents, and ice islands gives us a large area of thin ice. The thin ice will soon melt and perhaps has already started to set into motion a spring bloom of ocean plants. Ocean critters will feed on these to start another cycle of life. Whales, seals, and polar bears all depend on it for 1000s of years now.

Sketch of the biological pieces that a large area of open water near a fixed ice edge like that of a polynya may support. [From Northern Journal>/a>]

Sketch of the biological pieces that a large area of open water near a fixed ice edge like that of a polynya may support. [From Northern Journal]

Ice Arches and Gothic Cathedrals

Soaring towards heaven awash in light, Gothic Cathedrals awed medieval kings, jesters, and peasants alike. Their upward pointing arches allowed walls of stained windows to filter light into these massive buildings when most dwellings from royal castle to decrepit hut were dark, damp, and filthy. While the power of god was both invoked and abused, it was physics and engineering that allowed these cathedrals to scrape the skies. A delicate balance of forces is of the essence to avoid accelerations and collapse.

Arched windows within an arch inside the Cathedral of Reims, France.

Hence it should not surprise that ice arches buttressed by land show similar elegance and stability, but also dramatic collapse. When these ice arches form and collapse is one factor to determine when the Arctic Ocean will be free of ice in summer.

June-10, 2012 ice arch in Nares Strait between northern Greenland and Canada. The arch has been in place since Dec.-8, 2011.

Nares Strait Jun.-10, 2012 image showing land-fast ice between northern Greenland and Canada as well as the ice arch in the south (bottom left) separating sea ice from open water (North Water).

The Nares Strait ice arch forms between December and April most winters. Unlike the medieval cathedrals it consists of blocks of ice. Once in place, the arch shuts down all ice movement. The ocean water under the ice moves undisturbed southward sweeping newly formed ice away. This creates the North-Water polynya, first reported by William Baffin in his ship logs in 1616. The North Water supports wild life for millenia providing food and trading items for people. Even viking remnants from the time the first Gothic Cathedrals were built in Europe were found here: sections of chain mail, iron point blades, cloth, and boat rivets.

I want the ice arch in Nares Strait to collapse as soon as possible so that a Canadian ice breaker can get us to where we like to recover instruments and data that we deployed in 2009. And while I researched the stability of ice arches and studied Moira Dunbar’s 1969 satellite imagery, I came across a wonderful NOVA broadcast on medieval skyscrapers of glass and stone.” PBS stations will show it on Sept.-9, 2012.

Digging a little deeper, I also found a series of Open University podcasts and videos. My favorite 3-minute segment covers lines of thrust where barely connected irregular blocks of wood form a surprisingly stable yet wobbly arching bridge. If you want to build your own arch, then play interactively for fun with the physics of stone arches.

Since I want to understand and predict when the ice arch of Nares Strait collapses, I must understand how medieval architects and engineers designed their Gothic Cathedrals. I will also need understand why some cathedrals are still standing while others collapsed. My icy building blocks in Nares Strait are not as solid as the stones of Reims Cathedral, but unlike the medieval scientists, today we have computers and mathematics to help … as well as more than 800 more years of experience in science and engineering.