Category Archives: Oceanography

East Greenland Current Instabilities

The coast off north-east Greenland is a grey, cloudy, and icy place. I spent 4 weeks on a ship earlier this summer to place sensors on the ocean floor to measure water currents, salinity, and temperature. The data shall uncover the mystery of how ocean heat 300 m below the surface gets to glaciers to melt them from below year round. My contribution is a small part of a larger effort by German, Norwegian, Danish, American, and British scientists to reveal how oceans change glaciers and how oceans impact Greenland’s ice sheet, climate, and weather.

So, for months now I am watching rather closely how this ocean looks from space. Usually it is cloudy with little exciting to see, but for 4 days this week the clouds broke and displayed a violently turbulent ocean worthy of a Van Gogh painting:

Satellite image ocean current instabilities on Aug.-19, 2014 as traced by ice along the shelf break, red lines show 500, 750, and 1000 meter water depth. Small blue triangles top left are ocean moorings.

Satellite image of ocean current instabilities on Aug.-19, 2014 as traced by ice along the the shelf break, red lines show 500, 750, and 1000 meter water depth. Small blue triangles top left are ocean moorings.

A wavy band of white near the red lines indicates the East Greenland Current. The red lines show where the water is 500, 750, and 1000 m deep. All waters to the left (west) of the red lines are shallow continental shelf while all waters to the right (east) are deep basin. Some islands and headlands of Greenland appear on the left of the image as solid grey. The image covers a distance about the same as from Boston to Washington, DC or London to Aberdeen, Scotland. Black areas are ocean that is clear of ice while the many shades of white and gray are millions of ice floes that act as particles moved about by the surface flow. Using a different satellite with much higher resolution shows these particles. The detail is from a tiny area to the north-west of the red circle near 77.5 North latitude:

Individual ice particles as seen on the north-east Greenland shelf from LandSat 15-m resolution from Aug.-21, 2014 near 77.5N and 10 W.

Individual ice particles as seen on the north-east Greenland shelf from LandSat 15-m resolution from Aug.-21, 2014 near 77.5N and 10 W.

Strongly white areas indicate convergent ocean surface currents that concentrate the loose ice while divergent ocean currents spread the ice particles out in filaments and swirls and eddies.

This is how many real fluids look like if one takes a snapshot as satellites do. Stringing such snapshots together, I show the fluid motion as comes to life for about 3 days:

Output

Notice how the large crests seaward of the red line between 74 and 75 North latitude grow and appear to break backward. This is an instability of the underlying East Greenland Current. It starts out as a small horizontal “wave,” but unlike the waves we watch at the beach, the amplitude of this “wave” is horizontal (east-west) and not vertical (up-down). The mathematics are identical, however, and this is the reason that I call this a wave. As the wave grows, it become steeper, and as it becomes too steep, it breaks and as it breaks, it forms eddies. These eddies then persist in the ocean for many weeks or months as rotating, swirling features that carry the Arctic waters of the East Greenland Current far afield towards the east. The East Greenland Current, however, continues southward towards the southern tip of Greenland. The wave and eddy processes observed here, however, weaken the current as some of its energy is carried away with the eddies.

I could not find any imagery like this in the scientific literature for this region, but similar features have been observed in similar ocean current systems that transport icy cold waters along a shelf break. The Labrador Current off eastern Canada shows similar instabilities as does the East Kamchatka Current off Russia in its Pacific Far East. And that’s the beauty of physics … they organize nature for us in ways that are both simple and elegant, yet all this beauty and elegance gives us complex patterns that are impossible to predict in detail.

Beszczynska-Möller, A., Woodgate, R., Lee, C., Melling, H., & Karcher, M. (2011). A Synthesis of Exchanges Through the Main Oceanic Gateways to the Arctic Ocean Oceanography, 24 (3), 82-99 DOI: 10.5670/oceanog.2011.59

LeBlond, P. (1982). Satellite observations of labrador current undulations Atmosphere-Ocean, 20 (2), 129-142 DOI: 10.1080/07055900.1982.9649135

Solomon, H., & Ahlnäs, K. (1978). Eddies in the Kamchatka Current Deep Sea Research, 25 (4), 403-410 DOI: 10.1016/0146-6291(78)90566-0

Of Moorings, Elephants, Norwegians, and Codswallop

The oceans are cruel, unforgiving, and destructive. Microbes, algae, plankton, fish, and whales all evolved slowly to make the seas their home. We men and women of science and technology race to catch-up Continue reading

Deep Sea Biology and Chemistry: Muddy Business

Mud, mud, and more muddy mud was hauled from the bottom of the ocean for
the last five days from depths of one, two, and even three miles below the
icy surface. The biologists aboard are having a Continue reading

Wild Women Working Science Aboard Polarstern

My wife of 20 years teaches at Padua Academy, a private catholic High
School for girls only. It mostly serves families where the girls will
become the first in their families to go on to college. I am thinking of
them right now, as an hour ago there was a flurry of activity on the deck
of FS Polarstern after 2 days of endless grinding and breaking ice. And it
was predominantly women Continue reading

Day-3: Working on Ocean Physics, Chemistry, and Biology

Position: 65:36’N and 00:23’W
Time: June-9, 23:33
Temperature: 9.6 C Air and 9.8 C Water

More than 5 different groups finished moving and unpacking the content of
15 or more containers filled to the brim with gear that was packed months
ago. Continue reading