Category Archives: Greenland

How to whisper under sea ice: Wireless Acoustic Sensor Network Design

I want to build a cell phone system under water. I want it to send me a text messages every 30 minutes from 200 feet below the ocean that is covered by sea ice next to a glacier in northern Greenland where polar bears roam to catch seals for food at -40 Fahrenheit. Why would I want to do this and is this is even possible?

The author measuring sea ice thickness in Wolstenholme Fjord, Greenland April-17, 2017.

The author measuring sea ice thickness in Wolstenholme Fjord, Greenland April-17, 2017.

Our project successfully showed that it is possible to move data as text messages from a computer in the ocean to another and on to another and then via a cable to a weather station and then on to a satellite and then on to my laptop at home somewhere, anywhere, really [Intellectual Merit]. The ocean data that we moved by whispering from modem to modem (my acoustic cell phone towers) under water can be anything that any scientist may want to study. It could, for example, detect pollutants in the water that seep out of the sediment like gas or oil or radioactive materials burried accidentally [Broader Impacts] such as a nuclear-tipped B-52 bomber that crashed into Wolstenholme Fjord on January-21, 1968 at the height of the Cold War. The propagation of sound under ice also has military applications, because our communication network operates in both ways, that is, if I can receive a text message, I can also send one [Broader Impacts].

Installation of Automated Weather Station on Mar.-23, 2017 near Thule, Greenland via snowmobile. The station includes a satellite connection to the internet and a cable to the ocean.

Installation of Automated Weather Station on Mar.-23, 2017 near Thule, Greenland via snowmobile. The station includes a satellite connection to the internet and a cable to the ocean.

While the problem sounds simple enough, it is hard, real hard, because it requires many different people with very different skill sets. Our project included mechanical, electrical, and computer engineers but also scientists who know about acoustics, oceanography, and sea ice, as well as technicians with common sense and practical abilities to keep machines and people moving and running safely. This includes guns that we had to carry while working on the sea ice via snowmobile to protect from polar bears and medically trained personnel who could spot frostbites before they bite. All of this has to come together in just the right way and right time. Good and successful science is more than just engineering and machines, there is a strong human element in all polar field work such as ours. 

A local volunteer is designing, building, and rigging the Research Sled R/S Peter Freuchen for profiling the ocean below the sea ice in March 2017 on Thule Air Base.

A local volunteer is designing, building, and rigging the Research Sled R/S Peter Freuchen for profiling the ocean below the sea ice in March 2017 on Thule Air Base.

The first step in our project involved the design of the acoustic modems that Lee Freitag of Woods Hole Oceanographic Institution did many years back. It took us about 2 years to select this design that Lee then modified for this application in 2014-15). The second step involved the selection of a study site where our small group of 6 people could work and experiment and learn by some trial and error without incurring extra-ordinary costs (2015-16). It helped that I was in and out of Thule Air Base on unrelated projects in 2015 and 2016 when we settled for the final experiment to take place in March and April of 2017. Satellite remote sensing tools where then developed to quantify sea ice conditions for safe operation and navigation traveling on the  ice. We uncovered a barely visible area of thin ice to the south of Manson Island that recurs at the same location every year. We stayed clear of this area.

Thule2017_CTD

Satellite image of ice-covered Wolstenholme Fjord, Greenland with water column profiling station (green dots) and acoustic modems (red dots). Blue lines are water depths in meters. Labels G1, G2, and G3 indicate three tide-water glaciers while Thule refers to Thule Air Base. Saunders Island is near the center left while the weather station is the red dot halfway between Saunders and Manson Islands.

Field work started with a survey of sea ice thickness on Mar. 18/19, 2017 by drilling 2” holes through the sea ice that varied in measured thickness from 0.12 m (4 inches) near Manson Island to 1.25 m (4 feet) near Thule Air Base. On Mar.-23, 2017 we deployed the weather station along with a tent and survival gear at the center of our study area. An ocean temperature mooring was deployed to complement in time a spatial survey of ocean sound speed profiles estimated from conductivity, temperature, depth (CTD) measurements. We drilled 10” holes through the sea ice for our profiling CTD operated via an electrical winch. Our CTD survey spanned the entire fjord from three tidewater glaciers in the east to the edge of the sea ice in the west. Concurrently ocean testing of acoustic communication between modems commenced Apr.-8, 2017 and the final array was deployed Apr.-14/15 to be fully operational Apr.-16/18. All gear was recovered and stored at Thule Air Base Apr.-18/19, 2017 before our departure Apr.-20, 2017.

Research Sled

Research Sled “Peter Freuchen” with wooden CTD storage box, electrical winch, tripod, and electrical motor during deployment on Apr.-7, 2017. View is to the west with Cape Atholl on the left and Wolstenholme Island on the right background. University of Delaware technician operates the winch via joy stick while a student monitors the instrument’s descent through water column visually at the 10” hole and acoustically via a commercial Fish-Finding sonar.

Subsequent analysis in 2017/18 revealed a successful experiment as data from ocean sensors traveled along multiple paths to the weather station and on to the internet. All data were submitted to the NSF Arctic Data Center where after review they will become public at

https://arcticdata.io/catalog/view/urn:uuid:d2775281-3231-47d0-ab79-b2e506ea8d04

This graph is just one of many in desperate need of a proper peer-reviewed publication. There is always more work to do …

Time series of ocean temperature at the weather station from 10-m (top) to 100-m (bottom below the sea ice. The red line gives the -1.7 Celsius for reference. The temperature field dominates the speed of sound field. Note the presence and absence of tidal oscillations.

Time series of ocean temperature at the weather station from 10-m (top) to 100-m (bottom below the sea ice. The red line gives the -1.7 Celsius for reference. The temperature field dominates the speed of sound field. Note the presence and absence of tidal oscillations.

Northern Winds and Currents off North-East Greenland

I spent 6 weeks aboard the German research icebreaker R/V Polarstern last year leaving Tromso in Norway in early September and returned to Bremerhaven, Germany in October. We successfully recovered ocean sensors that we had deployed more than 3 years before. It felt good to see old friends, mates, and sensors back on the wooden deck. Many stories, some mysterious, some sad, some funny and happy could be told, but today I am working on some of the data as I reminisce.

The location is North-East Greenland where Fram Strait connects the Arctic Ocean to the north with the Atlantic Ocean in the south. We worked mostly on the shallow continental shelf areas where water depths vary between 50 and 500 meters. The map shows these areas in light bluish tones where the line shows the 100 and 300 meter water depth. Fram Strait is much deeper, more than 2000 meters in places. I am interested how the warm Atlantic water from Fram Strait moves towards the cold glaciers that dot the coastline of Greenland in the west.

Map of study area with 2014-16 mooring array in box near 78 N across Belgica Trough. Red triangles place weather data from Station Nord (81.2 N), Henrik Kr\o yer Holme (80.5 N), and Danmarkhaven (76.9 N). Black box indicates area of mooring locations.

There is also ice, lots of sea icebergs, and ice islands that we had to navigate. None of it did any harm to our gear that we moored for 1-3 years on the ocean floor that can and often is scoured by 100 to 400 meter thick ice from glaciers, however, 2-3 meter thick sea ice prevented us to reach three mooring locations this year and our sensors are still, we hope, on the ocean floor collecting data.

Ahhh, data, here we come. Lets start with the weather at this very lonely place called Henrik Krøyer Holme. The Danish Meteorological Institute (DMI) maintains an automated weather station that, it seems, Dr. Ruth Mottram visited and blogged about in 2014 just before we deployed our moorings from Polarstern back in 2014:

Weather station on Henrik Kroeyer Holme [Credit: Dr. Ruth Mottram, DMI]

It was a little tricky to find the hourly data and it took me more than a day to process and graph it to suit my own purposes, but here it is

Winds (A) and air temperature (B) from an automated weather station at Henrik Kroeyer Holme from 1 June, 2014 through 31 August, 2016. Missing values are indicated as red symbols in (A).

The air temperatures on this island are much warmer than on land to the west, but it still drops to -30 C during a long winter, but the end of July it reaches +5 C. The winds in summer (JJA for June, July, and August) are weak and variable, but they are often ferociously strong in winter (DJF for December, January, February) when they reach almost 30 meters per second (60 knots). The strong winter winds are always from the north moving cold Arctic air to the south. The length of each stick along the time line relates the strength of the winds, that is, long stick indicates much wind. The orientation of each stick indicates the direction that the wind blows, that is, a stick vertical down is a wind from north to south. I use the same type of stick plot for ocean currents. How do these look for the same period?

Ocean current vectors at four selected depths near the eastern wall of Belgica Trough. Note the bottom-intensified flow from south to north. A Lanczos low-pass filter removes variability at time scales smaller than 5 days to emphasize mean and low-frequency variability.

Ocean currents and winds have nothing in common. While the winds are from north to south, the ocean currents are usually in the opposite direction. This becomes particular clear as we compare surface currents at 39 meters below the sea surface with bottom currents 175 or even 255 meters below the surface. They are much stronger and steadier at depth than at the surface. How can this be?

Image of study area on 15 June 2014 with locations (blue symbols) where we deployed moorings a few days before this satellite image was taken by MODIS Terra. The 100-m isobath is shown in red.

Well, recall that there is ice and for much of the year this sea ice is not moving, but is stuck to land and islands. This immobile winter ice protects the ocean below from a direct influence of the local winds. Yet, what is driving such strong flows under the ice? We need to know, because it is these strong currents at 200 to 300 meter depth that move the heat of warm and salty Atlantic waters towards coastal glaciers where they add to the melting of Greenland. This is what I am thinking about now as I am trying to write-up for my German friends and colleagues what we did together the last 3 years.

Oh yes, and we did reach the massive terminus of 79 North Glacier (Nioghalvfjerdsfjorden) that features the largest remaining floating ice shelf in Greenland:

We recovered ocean moorings from this location also, but this is yet another story that is probably best told by scientists at the Alfred-Wegener-Institute who spent much time and treasures to put ship, people, and science on one ship. I am grateful for their support and companionship at sea and hopefully all of next year in Bremerhaven, Germany.

Two Years Ocean Observing Below Petermann Glacier Greenland

A year ago today I last set foot on Petermann’s floating ice shelf. The 28th of August 2016 was a drizzly, cloudy day with water running over the surface of the glacier in small streams emptying into larger streams to form small rivers that merged into larger channels carved into the ice. Two years ago Keith Nichols and I set-up a weather station atop the glacier. Many friends helped. We connected copper wires, ocean sensors, and a surface station to collect data from sensors 100-m below the ice in 800-m deep water. The small 2015 project of opportunity keeps giving us hourly ocean data. I am still stunned by our luck and technology.

My Petermann story started in 2010 when a first Manhattan-sized ice cube broke off the glacier. Two days after a University of Delaware press release, the US Congress asked me to appear before one of its inquiring committees. I humbly acknowledged how little I knew then, but everyone else knew even less. In 2012 another Manhattan-sized glacier piece broke off. While satellite a image shows what happens, only hard ocean data and modeling explains why it happens. Two research proposals were rejected, sadly, to probe ocean physics with carefully designed experiments, but in 2016 Alan Mix invited me to an expedition to Petermann aboard the Swedish icebreaker Oden. I gladly accepted, but I wanted to contribute something. That “something” became the Petermann Glacier Ocean Weather Observatory.

Alan needed holes drilled through the 100-m to 400-m thick glacier. Actually, he needed mud from 800 meters below the glacier. Keith Nichols of the British Antarctic Survey drilled those holes for Alan and collected the mud. My plan was to recycle the hole, that is, we dropped kevlar line, copper wire, and ocean sensors into the ocean and connected all to a weather station. David Huntley and I designed the system that included an Iridium satellite phone. Iridium phone calls ceased in February 2016, but a “service call,” that is, a helicopter site visit fixed the station. Chris Mooney and Whitney Shefte told the story for the Washington Post on 30 December 2016.

Ocean temperature at 95-m, 300-m, and 450-m below the sea surface as well as pressure at the bottom sensor near 810-m depth (~810 dbar pressure) updated through 27 August 2017.

The graph shows the entire 2-year long data record. Each gray vertical bar indicates a month between July 2015 and December 2017. The top record shows ocean temperatures just below the floating glacier ice. It was a surprise to see the data change from -0.3 Celsius to -1.6 degrees Celsius. The latter is close to the freezing point of salt water. Hence I interpret low-temperature events as meltwater pulse that swoosh past our sensor.

At 300-m we find a smaller range of temperatures near +0.1 degrees Celsius. Note the steady increase of temperature. Fluctuations are similar, but their absolute values increase with time. The linear warming trend becomes clear at 450-m depth, because the fluctuations diminish, but the warming does not. Temperatures at all depths increased over the entire two years of hourly observations.

The pressure record of the bottom-most sensor on the kevlar line perplexes me: During the first year the sensor slides into deeper water, because the kevlar stretches as all lines do when weighted down. In July 2016 the sensor sharply rises by almost 3 meters from 810.5 to 808.5 dbar to just as rapidly drop again to the 810.5 dbar value. The same feature occurs in the summer of 2017 also. It relates to the summer melt season, but how? I do not know.

The 2-year record is not perfect as the many gaps indicate. These result from electronic and mechanical failures that, I feel, are caused by long and harsh winters when temperatures dropped below -40 degrees Celsius or Fahrenheit. These cold temperatures challenge the best batteries during the 4-5 months of total darkness. On 20. December 2016 our batteries ran out and shut down the station. The sun revived our data gathering when the solar panels recharged batteries in March 2017.

The glacier also melts about 1-2 meters at the surface each summer. This surface melt tilted and almost crashed the station that we repaired last year today. In 2015 we had 2-m of pipe to fix into the glacier ice. In 2016 we replaced this with a 4-m pole that should survive two year’s of surface melt, I hope.

There are many, many people who all contributed in ways both small and large. It takes a village to raise a station on Greenland:

Is Petermann Gletscher Breaking Apart this Summer?

I am disturbed by new ocean data from Greenland every morning before breakfast these days. In 2015 we built a station that probes the ocean below Petermann Gletscher every hour. Data travels from the deep ocean via copper cables to the glacier surface, passes through a weather station, jumps the first satellite overhead, hops from satellite to satellite, falls back to earth hitting an antenna in my garden, and fills an old computer.

A 7-minute Washington Post video describes a helicopter repair mission of the Petermann data machine. The Post also reported first result that deep ocean waters under the glacier are heating up.

Sketch of Petermann Gletscher’s ice shelf with ocean sensor stations. The central station supports five cabled sensors that are reporting hourly ocean temperatures once every day. Graphics made by Dani Johnson and Laris Karklis for the Washington Post.

After two years I am stunned that the fancy technology still works, but the new data I received the last 3 weeks does worry me. The graph below compares ocean temperatures from May-24 through June-16 in 2017 (red) and 2016 (black). Ignore the salinity measurements in the top panel, they just tell me that the sensors are working extremely well:

Ocean temperature (bottom) and salinity (top) at 450-m depth below Petermann Gletscher from May-25 through June-16 2017 (red) and 2016 (black). Notice the much larger day-to-day temperature ups and downs in 2017 as compared to 2016. This “change of character” worries me more than anything else at Petermann right now.

The red temperature line in the bottom panel is always above the black line. The 2017 temperatures indicate waters that are warmer in 2017 than in 2016. We observed such warming for the last 15 years, but the year to year warming now exceeds the year to year warming that we observed 10 years ago. This worries me, but three features suggest a new ice island to form soon:

First, a new crack in the ice shelf developed near the center of the glacier the last 12 months. Dr. Stef Lhermitte of Delft University of Technology in the Netherlands discovered the new crack two months ago. The new rupture is small, but unusual for its location. Again, the Washington Post reported the new discovery:

New 2016/17 crack near the center of Petermann Gletscher’s ice shelf as reported by Washington Post on Apr.-14, 2017.

Second, most Petermann cracks develop from the sides at regular spaced intervals and emanate from a shear zone at the edge. Some cracks grow towards the center, but most do not. In both 2010 and 2012 Manhattan-sized ice islands formed when a lateral crack grew and reached the central channel. The LandSat image shows such a crack that keeps growing towards the center.

Segment of Petermann Gletscher from 31 May 2017 LandSat image. Terminus of glacier and sea ice are at top left.

And finally, let’s go back to the ocean temperature record that I show above. Notice the up and down of temperature that in 2017 exceeds the 2016 up and down range. Scientists call this property “variance” which measures how much temperature varies from day-to-day and from hour-to-hour. The average temperature may change in an “orderly” or “stable” or “predictable” ocean along a trend, but the variance stays the same. What I see in 2017 temperatures before breakfast each morning is different. The new state appears more “chaotic” and “unstable.” I do not know what will come next, but such disorderly behavior often happens, when something breaks.

I fear that Petermann is about to break apart … again.

Only in Thule Greenland

… do you find a machinist working metal to take photos while I do oceanography the old-fashioned way by pulling up 100 meters of kevlar line to recover an ocean probe.

Wolstenholme Fjord March-26, 2017. [Photo by Mogens Werth Christensen]

The data were subsequently used by ocean acousticians to test speed of sound propagation as part of an NSF project on testing an underwater communication system to move data from A to B via C or D. The automated weather station reports ocean temperature and saltiness as well at

http://ows.udel.edu/ice

Web-site is low-bandwidth to be used operationally by Air Force personnel in Greenland and local communities where internet access and speeds are severely limited.