Category Archives: Oceanography

Oceanography of Nares Strait Ice Flushing

Posted on July 13, 2015 by | 4 comments

I need the ice out of Nares Strait, a 20 mile wide and 300 miles long pathway to the North Pole between northern Canada and Greenland. The ice blocks our way to Petermann Fjord where a large glacier pushes thick ice out so sea as a floating ice shelf. We plan to drill through the floating section of the glacier that is about as thick as the Empire State Building is high. The ship to get us there is the Swedish icebreaker Oden (Location Map). She is passing the Faroe Islands to the north-west of Scotland and will arrive in 2 weeks at Thule Air Force Base where we will meet her.

Image of northern Greenland (top right) and Ellesmere Island (center) showing open water as black, land as gray, and sea ice as gray/white. The two red dots are Thule Air Force Base in the south and Petermann Glacier in the north. Note the bands of black water along the coast of Ellesmere Island that result from east to west blowing winds that move ice offshore.

Image of northern Greenland (top right) and Ellesmere Island (center) showing open water as black, land as gray, and sea ice as gray/white. The two red dots are Thule Air Force Base in the south and Petermann Glacier in the north. Note the bands of black water along the coast of Ellesmere Island that result from east to west blowing winds that move ice offshore and reduce the southward flow in Nares Strait.

The voyage from Thule to Petermann usually takes about 2-3 days, but if the sea ice does not flush out with the generally southward currents, then it may take a week or two wrecking havoc to our busy science schedule. So, why is the ice still lingering in Nares Strait this year?

Nares Strait ice cover in July of 2015 (left), 2014 (center), and 2013 (right) from MODIS Terra.

Nares Strait ice cover in July of 2015 (left), 2014 (center), and 2013 (right) from MODIS Terra.

There are three parts to the answer: First, a sturdy ice arch at the southern entrance of Nares Strait has to break. It has done so only last week. Second, a strong and perhaps oscillating flow has to thoroughly collapse the large pieces of ice at a narrow choke point that is Smith Sound. This has not happened yet. And third, a persistent flow to the south has to flush out ice into Baffin Bay to the south faster than it enters from the Arctic Ocean in the north. This flow is much weaker at the moment than is normal, because winds in the Arctic Ocean have been from east to west right now. These winds moved water (and ice) offshore to the north, so sealevel along northern Greenland and Canada drops. We can see this in today’s satellite imagery as prominent black bands of open water along the coast of northern Canada.

Lets take a closer look of this same image and zoom in on the southern part of Nares Strait as it looked this morning.

Collapsing ice arch at the southern entrance to Nares Strait on 13 July 2015 from MODIS AQUA.

Collapsing ice arch at the southern entrance to Nares Strait on 13 July 2015 from MODIS AQUA.

What used to be a solid frozen mass of ice along the Greenland coast (bottom right) has become a broken and loose mass of smaller ice floes. The larger blocks farther from the coast are now sliding southward as the loose ice along the coast reduces friction or lubricates the edges. The sides lose their grip on the ice and the entire construction fails and collapses. A most beautiful video on the stability of arches is posted by Open University here about lines of action or thrust.

All we now need for the ice to flush out of Nares Strait is a weakening or reversal of the winds at the other northern entrances to Nares Strait. Much of the generally southward flow is caused by the ocean’s surface being higher in the north than it is in the south. There are details that I am skipping, but basically much of the flow rolls downhill like a ball. And with the winds up north being from east to west, there is not much of a hill that the water can flow down, so we got somewhat stagnant waters. I have actually measured the height of this “hill of water” many times over the many years with ocean sensors that measure how much water is above them. This figure summarizes 3 years of data collected every 3 hours or so

Graph showing how water flow (called “volume flux”) varies with the steepness of the hill (called “pressure gradient”). The “hill” is at most 10 centimeters or 3 inches) high. [Adapted from Muenchow, 2015]

Now there is more to the “hill” story that is modified near the surface by the earth’s rotation in a fluid that has different densities at different depths. In a nutshell, the surface flow is 2-3 times as strong as the depth averaged flow. Furthermore, the surface flow on the Canadian side of Nares Strait is often twice as strong as that closer to Greenland, but all these spatial variations in flow actually help to smash large pieces of ice by moving and rotating them different sides of the same large piece of ice differently.

So, lets all hope that we get a few days of strong winds from the north flowing south, that should clear Nares Strait quickly before Oden arrives there in 2 weeks time. Those winds from the north not only flush out ice from Nares Strait, they also keep it nicely on one, the Canadian side. Earth rotation does wonderful and magical things to fluids such as water and air.

Muenchow, A, 2015: Volume and freshwater flux observations from Nares Strait to the west of Greenland at daily time scales from 2003 to 2009. J. Phys. Oceanogr., re-submitted July 2015, .pdf

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Posted in Greenland, Ice Arch, Ice Cover, Oceanography

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Coastal Oceanography off North-East Greenland

Posted on July 9, 2015 by | 1 comment

Greenland is melting, but it is not entire clear why. Yes, air temperatures continue to increase, but what does it matter, if those temperatures are below freezing most of the time. What if the ocean does most of the melting a few 100 m below the surface rather than the air above? It means that gut feeling and everyday experience can be poor guides for science, it means that there is more than meets the eye, and it means that some of Greenland’s melting happens out of sight without the dramatic imagery of a rapidly disintegrating glacier that sends icebergs out to sea.

Floating section of 79N Glacier in north-east Greenland as seen from LandSat in march 2014.

Floating section of 79N Glacier in north-east Greenland as seen from LandSat in march 2014.

In order to “see” where changes may happen out of sight American tax payers supported me via the National Science Foundation (NSF) to use available University of Delaware ocean sensors from an available German ship to investigate the ocean near two large glaciers off north-east Greenland. The sensors are in the water for over a year now and will stay there for another to collect data every half hour. The data are stored on computers inside the sensors and it is a marvel of smart engineering that we can measure water temperature, salinity, and velocity at the bottom of an ice-covered ocean. Now what would I do with such data?

Two ocean sensor packages ready for deployment near Isle de France, Greenland 10 June 2014.

Two ocean sensor packages ready for deployment near Isle de France, Greenland 10 June 2014.

First, one needs to know that in the Arctic Ocean temperature increases as one moves a thermometer from the surface towards the bottom for the first 900 feet or 300 meters. This only make sense, if the warm water is heavier than the cold water above. This is the case in the Arctic, because the warm water at depth is also very salty. The cold waters above contain less salt and that’s why they float. The warmest waters originate from the Atlantic Ocean to the south-east of Iceland. Lets call it Atlantic Water for this reason. The surface waters contain sea ice and its fresh melt water and thus are always close to the freezing point, so lets call them Polar Waters.

Vertical profiles of temperature and salinity across Norske Ore Trough, Greenland. The insert shows station locations for profiles (small symbols) and moorings (large circles). The red dot marks the location of the red profile.

Vertical profiles of temperature and salinity across Norske Ore Trough, Greenland. The insert shows station locations for profiles (small symbols) and moorings (large circles). The red dot marks the location of the red profile.

All along the East Coast of Greenland, we find a strong southward flow of ice and Polar Water called the East Greenland Current. On a rare clear day one can “see” this flow as a beautifully structured undulating band separating the deep Greenland Sea from the shallow and broad continental shelves. Now recall that the warmest waters are in the Atlantic layer way down and somewhat offshore. How do these waters cross the East Greenland current and the very wide continental shelf to reach the glaciers along the coast? It is this question my project tries to answer with lots of help from NSF and German friends.

Satellite image 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.

Satellite image 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.

We think that the warm and salty waters flow near the bottom below the East Greenland Current at deep bottom depressions such as canyons. Testing this idea, we placed our sensors in a line across the canyon with a small ice-capped island called the Isle of France on one side and Belgica Bank on the other. We deployed seven instrument as an array across the canyon to measure the speed and direction of the flow as well as its temperatures and salinities. Our canyon connects the deep Greenland Sea 150 miles to the east with two glaciers another 100 miles to the north-west. We all anxiously hope that no iceberg wiped out bottom moorings and that they all record data faithfully until the summer of 2016 when we plan to recover instruments and data.

Section of temperature across Norske Ore Trough with Isle de France, Greenland on the left and Belgica Bank towards Fram Strait on the right. The view is towards 79N Glacier.

Section of temperature across Norske Ore Trough with Isle de France, Greenland on the left and Belgica Bank towards Fram Strait on the right. The view is towards 79N Glacier.

Before and after the placement of our moored instruments, however, we did survey the section from the ship and I show the temperature and salinity across our canyon. We now see that the water below 200 m depth are indeed very warm and salty as expected, but there is a detail that I cannot yet explain: notice the slight upward sloping contours of salinity near km-80 at the rim of the canyon and the downward sloping contours on the other side near km-10. Such sloping contours represent a flow out of the page at km-80 and into the page at km-10 which is exactly the opposite of what I expected. All I can say at the moment is that this snapshot does not resolve motions caused by the tides, the winds, and the seasonal cycles properly, but our moorings do. So, there are still mysteries to be solved by the data sitting on the bottom of the ocean guarded by towering spectacles of ice.

Tabular iceberg and sea ice cover near Isle de France 10 June 2014

Tabular iceberg and sea ice cover near Isle de France 10 June 2014

[This entry will be submitted to NSF as a Final Outcome Report for award 1362109 “Shelf-Basin Exchange near 79N Glacier and Zachariae Isstrom, North-East Greenland.” The work would not have been possible without the generous support of NSF as well as the German Government as represented by the Alfred Wegener Institute who sponsored the expedition to North-East Greenland in 2014. Torsten Kanzow, Benjamin Rabe, and Ursula Schauer of AWI all deserve as much and even more credit for this work than do I.]

Budéus, G., & Schneider, W. (1995). On the hydrography of the Northeast Water Polynya Journal of Geophysical Research, 100 (C3) DOI: 10.1029/94JC02024

Hughes, N., Wilkinson, J., & Wadhams, P. (2011). Multi-satellite sensor analysis of fast-ice development in the Norske Øer Ice Barrier, northeast Greenland Annals of Glaciology, 52 (57), 151-160 DOI: 10.3189/172756411795931633

Reeh, N., Thomsen, H., Higgins, A., & Weidick, A. (2001). Sea ice and the stability of north and northeast Greenland floating glaciers Annals of Glaciology, 33 (1), 474-480 DOI: 10.3189/172756401781818554

Wadhams, P., Wilkinson, J., & McPhail, S. (2006). A new view of the underside of Arctic sea ice Geophysical Research Letters, 33 (4) DOI: 10.1029/2005GL025131

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Posted in Greenland, Ice Island, Oceanography, Polarstern

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Sweden’s Icebreaker for Petermann Gletscher 2015

Posted on June 22, 2015 by | 2 comments

Sweden’s icebreaker I/B Oden will sail for Greenland this summer to pick up about 50 scientists to work the ice, land, water, and glaciers of north-west Greenland with Petermann Gletscher as its focus. I will be working with Celine Heuze of Gothenburg University, Jari Kruetsfeldt of Stockholm Technical University, and Christina, a Swedish High School teacher. Together we are responsible to run the water sampling and ocean sensing.

We met 3 weeks ago on the ship in Landskrona, Sweden where we loaded all our boxes filled with computers, electronics, bottles, rubber hoses, and some more computers. We also met the ship’s crew and a larger group of scientists and engineers from Oregon State University in the US, Gothenburg and Stockholm Universities in Sweden, and the Swedish Polar Research Secretariat that runs the ship. For 3 days we worked, ate, slept (somewhat), and worked some more to get ourselves and our equipment unpacked and organized.

There is nothing romantic about working in an industrial area lugging boxes and stuff up and down stairs from back to front and back again. Despite all the cranes, winches, fork lifts, A-frames, and other tools, it is still back-breaking labor as much is still carried to and fro by hand while watching for heavy loads overhead, sharp corners below, and tight corners to maneuver around. Hard-hats and steel-toed boots are NOT optional. The only positive here is that shared pain brings people together to lower the pain via teamwork.

While most people seem fresh and happy, this wears off after 3 days of intense work not captured in photos. Sleep deprivation sets in as everyone tries to cram too much work into the 24 hours available. And yet, it is during these short and intense work periods, that new friendships and scientific collaborations emerge quickly even though people do not always look their best.

As an example, here is me as a zombie after about 4 nights with little sleep

As always, I try too much as I perform my duties on the water sampling and ocean sensing during the day and fight a nasty Iridium satellite communication problem  at night.  At the University of Delaware we designed, assembled, and shipped off to Sweden an air and ocean weather station to be deployed above and below the floating tongue of Petermann Gletscher. There was no time for testing as all gear to deployed on Petermann Gletscher in August had to be in Landskrona in May.

Despite the looks, I was ecstatic on the inside, because I had just solved a crucial sub-problem when an e-mail reached me that a small NASA grant was coming my way to actually pay for the science that I hope to do during this summer. This, however, is another story for another day.

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Posted in Greenland, Oceanography, Petermann Glacier

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Tribal Interactions and Arctic Research

Posted on February 27, 2015 by | Leave a comment

Arctic field work connects people of different backgrounds, disciplines, and tribes. Last week I spent 3 days in Maine where I met with Arctic archeologists, anthropologists, and students of all ages. Susan Kaplan and Genevieve LeMoine run the Arctic Peary-McMillan Museum and do extensive field work in Labrador, Cape Sheridan atop Ellesmere Island (Canada), and northern Greenland. A class of smart sophomore asked more questions than I could answer in the morning and a diverse group of citizen did the same in the evening. I represented the “physics tribe.”

We learnt of each other after I posted an illustrated essay “Ruins of Fort Conger” that contained this image taken near Petermann Fjord in 2012

Fort Conger rebuilt 1900 by Peary

Carl Rose on the left was a seaman on our last 2012 expedition while Jonathan Poole is a marine field technician with whom I work often. They stand before a hut built by Admiral Robert Peary in 1900 on one of his early excursions to reach the North Pole. The 2012 photo bears remarkable similarity to one taken in 1909 that Genevieve LeMoine describes on her blog with title “Tides of the Arctic.”

Donald MacMillan and Jack Barnes at Fort Conger, spring 1909 [From LeMoine, 2013]

Donald MacMillan and Jack Barnes at Fort Conger, spring 1909 [From LeMoine, 2013]

It shows Donald McMillan and Jack Barnes in 1909 during a later Peary expedition. The pictures and histories are displayed at the “Glimmer of the Polar Sea” exhibition at the Bowdoin’s Peary-McMillan Arctic Museum. These huts are the closest “shelter” to Petermann Fjord about 50 miles to the east. The men visiting Fort Conger in 1909 and 2012 look towards the ocean which in 2012 looked like this

Discovery Harbor off Fort Conger, Ellesmere Island as seen from helicopter in 2012.

Discovery Harbor off Fort Conger, Ellesmere Island in 2012.

We visited the site in 2012 to recover an ocean sensor that, so we hoped, had measured tides and temperatures for 9 years earlier. For 9 long years we had no way to tell, if either sensor or data existed. Only after recovery in 2012 did we jubilantly find sensors and data. At the time we deployed this sensor in 2003 technology did not exist to get data out from the ice-covered ocean. We are trying to develop technology to change this. The non-trivial goal is to get such data out as it is collected without waiting for 9 years. That’s what my crowd-funding project is about: Develop new technologies and share all data, results, and excitement.

If funded, this project will produce results immediately as ocean temperatures (and salinities) will be transmitted to the word wide web for anyone to use as she or he sees fit. Please help and be part of the cutting edge of Arctic Oceanography: Tell your friends, tell your family, and tell your colleagues about the science, about the Arctic, about the beauty, about the climate, and about the physics of the ocean.

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Posted in Greenland, History, Oceanography, Petermann Glacier, Polar Exploration

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Heartbeat of Ocean and Air of Greenland

Posted on February 12, 2015 by | 1 comment

While cables are designed at a small company in southern California,while instruments are shipped to friends at the British Antarctic Survey in England, while instrument locations are contemplated by a small group of scientists, technicians, and graduate students, I am also on a journey back in time to check up on the heart beat of the air we breath and the oceans we sail. The Arctic heartbeat to me is the annual change from the total darkness of polar night to total sunlight of polar day. This cycle, this heartbeat takes a year. There is 24 hours of day in summer the same way that there is 24 hours of night now. Let me first show, however, where we are heading before I look at the heartbeat.

I love making maps and this is a rich and pretty one that shows North America from the top where Petermann Fjord and Glacier are (tiny blue box on left map). The colors are water depths and land elevations. The thick dotted red line is where a very large iceberg from Petermann traveled within a year to reach Newfoundland. Teresa, one of the contributors to my crowd-funding project, sailed up there to Newfoundland to see this iceberg. And she made a movie out this voyage. So, what happens up there in northern Greenland only takes a year, maybe two, to reach our more balmy shores. What happens in Greenland does NOT stay in Greenland. Vegas, Nevada this is not.

Figure1

Now on to the map on the right. This is the tiny blue box made much larger. It looks like a photo, and in a way it is, but a photo taken by a satellite, well, only one “channel” of this specific satellite, the many shades of gray are mine, it is NOT the real color. The glacier is in the bottom right as the white tongue sticking out towards 81 N latitude. Red lines there are water depths of 500 and 1000m. The blue dot in the top-left is where I had to leave an ocean sensor in a shallow bay for 9 years, because we could not get there to retrieve it for 6 years. Lucky for me (well, some smart design helped), the instrument was still there, collecting and recording data that we knew nothing about for 9 long years. It took smart and hardy fishermen from Newfoundland aboard the CCGS Henry Larsen to dangle my sensor out of the icy waters. And here is the heart beat it revealed:

AlertDiscTemp

Top graph is ocean temperature, bottom panel is air temperature nearby. And as you go from left to right, we move forward in time starting in 2002 until the end of 2012 when the last ocean measurements were made. The red lines are a linear trend that represents local (as opposed to global) warming. Both go up which means it gets warmer, but careful, the bottom one for air is no different from a straight line with zero slope meaning no warming. It does go up, you say correctly, but if I do formal statistics, this slope is no different from zero just due to chance. The top curve for the ocean, however, is very different. It does not look different, but the same statistics tell me that the warming is NOT due to chance alone. Oh, in case you wondered, the two dashed lines in the top panel are the temperatures at which seawater freezes and forms ice for the salinity range we see and expect at this embayment. As you add salt to water, it freezes at a lower temperature. This is why we put salt on our roads in winter, it makes the water freeze less fast.

I am a doctor, so here is my conclusion: Ocean heart beat is a little irregular and the trend is not good news for the ice. Air heart beat looks normal, the trends may need watching, but I am not too worried about that just yet. Watch the oceans … that’s where the heat and the action is these days.

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Posted in Global Warming, Greenland, Oceanography, Petermann Glacier, Uncertainty

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