Category Archives: Oceanography

The Turbulence of Van Gogh and the Labrador Shelf Current

Posted on May 8, 2013 by | 2 Comments

Vincent Van Gogh painted his most turbulent images when insane. The Labrador Current resembles Van Gogh’s paintings when it becomes unstable. There is no reason that mental and geophysical instability relate to each other. And yet they do. Russian physicist Andrey Kolmogorov developed theories of turbulence 70 years ago that Mexican physicist applied to some of Van Gogh’s paintings such as “Starry Sky:”

Vincent Van Gogh's "Starry Sky" painted in June 1889.

Vincent Van Gogh’s “Starry Sky” painted in June 1889.

The whirls and curls evoke motion. The colors vibrate and oscillate like waves that come and go. There are rounded curves and borders in the tiny trees, the big mountains, and the blinking stars. Oceanographers call these rounded curves eddies when they close on themselves much as is done by a smooth wave that is breaking when it hits the beach in violent turmoil.

Waves come in many sizes at many periods. The wave on the beach has a period of 5 seconds maybe and measures 50 meters from crest to crest. Tides are waves, too, but their period is half a day with a distance of more than 1000 km from crest to crest. These are scales of time and space. There exist powerful mathematical statements to tell us that we can describe all motions as the sum of many waves at different scales. Our cell phone and computer communications depend on it, as do whales, dolphins, and submarines navigating under water, but I digress.

The Labrador Shelf Current off Canada moves ice, icebergs, and ice islands from the Arctic down the coast into the Atlantic Ocean. To the naked eye the ice is white while the ocean is blue. Our eyes in the sky on NASA satellites sense the amount of light and color that ice and ocean when hit by sun or moon light reflects back to space. An image from last friday gives a sense of the violence and motion when this icy south-eastward flowing current off Labrador is opposed by a short wind-burst in the opposite direction:

Ice in the Labrador Current as seen by MODIS-Terra on May 3, 2013.

Ice in the Labrador Current as seen by MODIS-Terra on May 3, 2013. Blue colors represent open water while white and yellow colors represent ice of varying concentrations.

Flying from London to Chicago on April 6, 2008, Daniel Schwen photographed the icy surface of the Labrador Current a little farther south:

Ice fields seen in Labrador Current April 6, 2008 from a plane. [Photo Credit: Daniel Schwen]

Ice fields seen in Labrador Current April 6, 2008 from a plane. [Photo Credit: Daniel Schwen]

Ice in the Labrador Current as seen by MODIS-Terra on April 6, 2008. Blue colors represent open water while white and yellow colors represent ice of varying concentrations.

Ice in the Labrador Current as seen by MODIS-Terra on April 6, 2008. Blue colors represent open water while white and yellow colors represent ice of varying concentrations.

The swirls and eddies trap small pieces of ice and arrange them into wavy bands, filaments, and trap them. The ice visualizes turbulent motions at the ocean surface. Also notice the wide range in scales as some circular vortices are quiet small and some rather large. If the fluid is turbulent in the mathematical sense, then the color contrast or the intensity of the colors and their change in space varies according to an equation valid for almost all motions at almost all scales. It is this scaling law of turbulent motions that three Mexican physicists tested with regard to Van Gogh’s paintings. They “pretended” that the painting represents the image of a flow that follows the physics of turbulent motions. And their work finds that Van Gogh indeed painted intuitively in ways that mimics nature’s turbulent motions when the physical laws were not yet known.

There are two take-home messages for me: First, fine art and physics often converge in unexpected ways. Second, I now want to know, if nature’s painting of the Labrador Shelf Current follows the same rules. There is a crucial wrinkle in motions impacted by the earth rotations: While the turbulence of Van Gogh or Kolmogorov cascades energy from large to smaller scales, that is, the larger eddies break up into several smaller eddies, for planetary-scale motions influenced by the Coriolis force due to earth’s rotation, the energy moves in the opposite direction, that is, the large eddies get larger as the feed on the smaller eddies. There is always more to discover, alas, but that’s the fun of physics, art, and oceanography.

Aragón, J., Naumis, G., Bai, M., Torres, M., & Maini, P. (2008). Turbulent Luminance in Impassioned van Gogh Paintings Journal of Mathematical Imaging and Vision, 30 (3), 275-283 DOI: 10.1007/s10851-007-0055-0

Ball, P. (2006). Van Gogh painted perfect turbulence news@nature DOI: 10.1038/news060703-17

Wu, Y., Tang, C., & Hannah, C. (2012). The circulation of eastern Canadian seas Progress in Oceanography, 106, 28-48 DOI: 10.1016/j.pocean.2012.06.005

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Posted in Oceanography

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Oceanography and Icebergs in Baffin Bay: LCDR Edward “Iceberg” Smith

Posted on March 27, 2013 by | 2 Comments

In 1928 Edward H. “Iceberg” Smith took the 125 feet long Coast Guard Cutter “Marion” on an 8,100 mile journey from Boston, MA to New York City, NY via Disko Bay, Greenland. Along the way he defined operational Arctic Oceanography to explain and predict iceberg entering the busy sea lanes off North-America. The Titanic was sunk in 1912, the International Ice Patrol was formed in 1914, and LCDR Smith sailed to Greenland in 1928. The data are priceless 85 years later still. I used them to place modern observations from 2003 into a context of climate variations. First, however, let me give credit to one of the pioneers on whose scientific shoulders I stand:

Edward H. "Iceberg" Smith of the US Coast Guard with reversing thermometer.

Edward H. “Iceberg” Smith of the US Coast Guard with reversing thermometer.

“Iceberg” Smith entered the Coast Guard Academy at age 21 in 1910 and served during World War I as a navigator on Atlantic convoy escort duty. After this war his ship was detailed to the International Ice Patrol and he became one of its first scientific observers at age 32 in 1921. As such he was sent for a year to Bergen, Norway in 1925 to learn the latest theories in physical oceanography. Scandinavian explorers like Nansen, Ekman, Sverdrup, Bjerknes, and Helland-Hansen defined physical oceanography at this time by applying physics on a rotating earth to phenomena that they observed from ships sailing at sea or ships frozen in Arctic ice. Much of this revolutionary work is now elementary oceanography taught in introductory courses, but then, nobody knew much about why ice and ocean move they way they do. It was time to put ideas to a thorough test which is what “Iceberg” Smith did, when he got his ship and orders to explore in 1928.

USCGC Marion built in 1927 [from http://laesser.org/125-wsc/]

USCGC Marion built in 1927. Note the scale indicated by a person standing on the lower deck. [From
http://laesser.org/125-wsc]

Armed with new ideas, knowledge, and the tiny USCGC Marion “Iceberg” Smith set to out to map seas between Labrador, Baffin Island, and Greenland to explain and predict the number of icebergs to enter the North-Atlantic Ocean. During his 10 weeks at sea he mapped ocean currents from over 2000 discrete measurements of temperature and salinity at many depths. This was before computers, GPS, and electronics. In 1928 this was slow to work with cold water collected in bottles with “reversing thermometers” that cut off the mercury to preserve temperatures measured in the ocean at depth to be read later aboard. Salinity was measured at sea by tedious chemical titrations. Imagine doing all of this from a rocking and rolling shallow draft cutter that bounces in icy seas for 10 weeks within fog much of the time. No radar to warn of icebergs either, and you want to study icebergs, so you move exactly where they are or where you think they are coming from. And they though that the Titanic was unsinkable.

Iceberg in the fog off Upernarvik, Greenland in July of 2003. [Photo Credit: Andreas Muenchow]

Iceberg in the fog off Upernavik, Greenland in July of 2003. [Photo Credit: Andreas Muenchow]

USCGC Healy in northern Baffin Bay in July 2003 with iceberg. Ellesmere Island is in the background.

USCGC Healy in northern Baffin Bay in July 2003 with iceberg. Ellesmere Island is in the background.

The 1928 Marion Expedition was the first US Coast Guard survey in Baffin Bay while the last such expedition took place 2003. Unlike “Iceberg” Smith we then had military grade GPS, radar, and sonar systems. These sensor systems allowed me to directly measure ocean currents from the moving ship every minute continuously from the surface to about 600 meters down. Oh, we also took water samples in bottles, but temperature, depth, and salinity are all measured electronically about 24 times every second. As a result we can actually test, if the physics that had to be assumed to be true in 1928 actually are true. As it turns out, the old theory to estimate currents from temperature and salinity sections works well off Canada, but not so well off Greenland. Furthermore, we found several eddies or vortices in the ocean from the current profiling sonars.

And finally, it took Edward H. “Iceberg” Smith only 3 years to publish most of his data and insightful interpretations while I am still working on both his and my own data 85 years and 10 years later, respectively. Sure, I got more data from a wider range of moored, ship-borne, and air-borne sensors, but I do wonder, if I really consider my data and interpretations as careful and think as thorough as LCDR Smith did. Furthermore, he had no computers and performed all calculations, crafted all graphs, and typed all reports tediously by hand. I would not want to trade, but all this makes me admire his skills, dedication, and accomplishments even more.

Dr Helen Johnson on acoustic Doppler current profiler (sonar to measure ocean velocity) watch aboard the USCGC Healy in Baffin Bay in 2003. [Photo credit: Andreas Muenchow]

Dr Helen Johnson on acoustic Doppler current profiler (sonar to measure ocean velocity) watch aboard the USCGC Healy in Baffin Bay in 2003. [Photo credit: Andreas Muenchow]

P.S.: The New Yorker has three stories on the subject published in 1938, 1949, and 1959. I eagerly await to read those.

ResearchBlogging.orgSmith, E. (1928). EXPEDITION OF U. S. COAST GUARD CUTTER MARION TO THE REGION OF DAVIS STRAIT IN 1928 Science, 68 (1768), 469-470 DOI: 10.1126/science.68.1768.469

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Oceanography, Technology, and Ships

Posted on March 15, 2013 by | Leave a comment

Sea-going oceanography is in transition. Times are exciting as we developed new tools, sensors, and ideas on how to observe the ocean and the stuff that lives in it, floats on it, and is submerged below it. I just learned about an awesome interview with Eli Kintisch which is posted as a podcast at the American Association for the Advancement of Science:

Better technology, but less money: Eli Kintisch discusses the crossroads facing U.S. oceanography.(Podcast)

I will write more about this, but I have to run off to meet with an electrical engineer to discuss ideas on how we perhaps can get data from bottom-mounted sensors out of the ocean in ice-covered seas instantly, rather than waiting 2-3 years to get instruments back with a ship.

Kintisch, E. (2013). A Sea Change for U.S. Oceanography Science, 339 (6124), 1138-1143 DOI: 10.1126/science.339.6124.1138

Seal with ocean sensor.

Seal with ocean sensor.

Elephant seal off Antarctica with ocean sensor transmitting data via satellite [Credit Lars Boehme]

Elephant seal off Antarctica with ocean sensor transmitting data via satellite [Credit Lars Boehme]

CCGS Henry Larsen in thick and multi-year ice of Nares Strait in August 2009. View is to the south with Greenland in the background. [Photo Credit: Dr. Helen Johnson]

CCGS Henry Larsen in thick and multi-year ice of Nares Strait in August 2009. View is to the south with Greenland in the background. [Photo Credit: Dr. Helen Johnson]

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Shades of White as the Sun Rises over Nares Strait

Posted on March 5, 2013 by | 5 Comments

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]

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Posted in Ice Arch, Ice Cover, Ice Island, Oceanography, Uncategorized

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Storm Surges, Global Warming, and Delaware Beaches

Posted on November 4, 2012 by | 5 Comments

ADDENDUM (Nov.-7, 2012): Time lapse video from Delaware Sea Grant.

Rising seas and flood waters cause most of the damage during storms such as Sandy did last week. Tides, waves, and storms all contribute. We can debate how global warming impacts any of the above, but the arguments are involved. So lets assume, that neither tides, waves, nor storms are impacted by global warming, but that the globally averaged rise in sea level over the last 50 or 100 years is. This global warming induced sea level rise is about half a foot in 50 years (3 mm/year), but why would we care about global averages, when we live in Delaware? Furthermore, why worry about the whimpy surges we get ever 2-3 weeks. We don’t, we worry most about the most extreme events like Sandy and want to know how often they occur. Below I show a Sandy-like event to occur about once every 10 years. Furthermore, over time Delaware’s most extreme storm surges are rising twice as fast as global averages do. So, how much does the global warming impact our local flooding in Delaware?

Market Street on the beach in Lewes is in one of the lowest lying areas of town and takes its good old-time draining. This photograph looks northeastward toward the beach, just west of the intersection with Massachusetts Avenue. [Credit: Cape Gazette]

More than I initially thought: the largest storm surge that has hit Delaware was the Ash Wednesday storm on March 6, 1962 which added 5.8 feet to the regular tides and waves. I wrote about this yesterday using public NOAA data. This same storm today would add 6.8 feet to the regular tides and waves. For comparison, Sandy’s storm surge added 5.3 feet. So Sandy was a weak storm by comparison. If it had hit in 1962, it would have added only 4.3 feet. The difference of 1 foot in 50 years is due to steadily rising sea levels:

Largest storm surge at Lewes, Delaware each year from 1957 to present. The red line is a linear fit to the data. The slope indicates that the largest storm surge increase by almost 3 inches every 10 years.

On average each year has a larger largest surge than the year before. While this steady increase by 2.8 +/- 1.7 inches each 10 years is statistically significant (95% confidence), picking the extreme each year is perhaps not the best statistic as extremes do not happen often. Please note that a 95% confidence means that there is a 5% chance that the true increase is either smaller than 0.9 inches/decade or larger than 4.5 inches/decade.

What about the mean or average surge each year? From hourly data, I pick the middle surge, that is, half the surges each year are larger and half are smaller:

This increase of 1.4 +/- 0.2 inches per decade (95% confidence) is more in line of the global average. The uncertainty in this trend is smaller than that of the trend for the extreme, because the median sea level varies little from year to year, while the extreme value varies more from year to year. So, from these results we can conclude, that while the mean or median sea level at Lewes increases by perhaps 1.5 inches in 10 years, the extremes increase twice as fast. So, storm surges like Sandy will become more common than they are today mostly because of global warming.

Over the last 50 years we had at least 5 such events in 1962, 1968, 1996, 1998, and 2012. So, on average we have a Sandy-type storm surge greater than 5 feet every 10 years. This contradicts a Wilmington News Journal article today which quotes John Ramsey to describe “… Sandy as a 1-in-200-years storm, unlikely to be repeated anytime soon. That could give coastal communities time enough to deal with the real threats and realities of sea level rise and climate change.” There is no such time, as it is mis-leading to describe Sandy as a 1-in-200-year event when it has happened about every 10 years during the last 55 years. Instead of a 0.5% percent chance of a Sandy-like event to hit Lewes each year, I would raise this chance to be larger than 10%.

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Posted in Global Warming, Oceanography

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Rising Seas, Storms, and Flooding

Posted on November 3, 2012 by | 2 Comments

Ocean waters are rising and flooding inland waters in Delaware and elsewhere. Some of this is perfectly regular and normal such as the up and down of the tides. Some of it is irregular and normal such as caused by storms, river discharges, waves, and weather. And some is caused by global warming as we continue to burn coal and oil to power our economies. Lets have a quick look at what all this looks like and try to put this into some perspective, but Sandy’s 5.3 feet surge last monday was second to the 5.5 feet surge that hit Lewes in 1962.

Cedar Street in Lewes flooded on Monday, October 29. (Photo by: Don Bland), as published by Cape Gazette.

The up and down of the tides each day is about 3 feet in Lewes, Delaware. This large change in sea level is so regular, normal, and predictable, that I remove it from all further discussion, because I want to know how extreme an event this week’s storm Sandy was. For this purpose I downloaded all the hourly tide gauge data from Lewes, Delaware from NOAA. The record starts in 1957 and is ongoing. Here is how the record looks for the last 4 weeks including the surge caused by Sandy last monday:

Sandy’s storm surge added 5.3 feet to the regular tide which is second-largest surge in the historical record. The largest surge at Lewes, DE was caused by the 1962 Ash Wednesday Storm that added 5.5 feet to the regular sea level:

So while Sandy was a very large surge, it was neither unprecedented nor a once in a century event. Furthermore, and this is where I come back to global warming, the 5.3 feet 2012 surge of Sandy includes the last 50 years of steady sea level rise which comes to about an inch every 10-15 years or about half a foot in the ~50 years between 1962 and 2012. So, a repeat of the 1962 storm system would cause a 6.0 feet and not the 5.5 feet surge that took place in 1962.

Furthermore, while the real size of the surge depends on where the center of the storm makes land-fall or where you are relative to the storm, the rising seas caused by global warming are much more uniform, that is, they are little different in Boston, New York, Lewes, Norfolk, or even San Francisco:

So, global warming and the rising seas it causes are both real and here to stay. Global warming provides the upward creeping background sea level to which larger tides, waves, and surges add. The combined effect of all these cause the coastal flooding. So 50 years from now, a rare, but perhaps perfectly natural freak storm like Sandy will cause a storm surge of 5.8 instead 5.3 feet on account of global warming. About 1/3 of this added sea level is caused by the oceans expanding as they warm, another 1/3 is caused by melting glaciers and ice sheets in Greenland and Antarctica, and the last 1/3 is caused by other processes. So, what happens on Greenland or China does not stay there, it impacts present and future sea level in Lewes, DE.

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Posted in Global Warming, Oceanography

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Petermann Ice Island 2012 Breaking Up

Posted on September 2, 2012 by | 4 Comments

Dr. Preben Gudmandsen pioneered some of the early micro-wave remote sensors 30-40 years ago that are now used routinely to monitor sea ice, snow, and glaciers. Despite being “retired” for over 20 years, this Danish professor of Electrical Engineering is still very active in all things related to Nares Strait from sea ice, oceanography, glaciers, and winds. He is one of the main instigators to set up the automated weather station at Hans Island.

Nares Strait bottom depth (in meters) according to the International Bathymetric Chart of the Arctic Ocean (IBCAO, version 2, 2008). The black dot in the center of Nares Strait indicates Hans Island.

He also instigated the latest round of exchanges among “Friends of Nares Strait” about the fate of the ice island that broke off earlier this summer from Petermann Gletscher. He asked yesterday what may happen if PII-2012 reaches the sill separating northern Nares Strait and the Arctic Ocean from southern Nares Strait and the Atlantic Ocean. This sill is the deepest connection between the Arctic Ocean to the north and Baffin Bay in the south. The sill is in western Kane Basin off Ellesmere island and is about 220 meters deep.

So, to answer that question one needs to know three things: Where is the ice island, how deep is the water where it is, and how thick is the ice island. Before I could assemble these three things, however, the ice island has already broken into at least three pieces. Luc Desjardins of the Canadian Ice Service answered first by pointing this out. He has access to the commercial RadarSat data that few others have. So, here is the latest from MODIS which answers the first two questions:

Petermann ice island 2012 (PII-2012) breaking apart on Sept.-1, 2012 near the sill of Nares Strait. Faint black lines are bottom contours of 200, 150, 100, and 50 meter depth (IBCAO-2). Bottom left has clouds, top right is the mountainous terrain of Ellesmere Island. The most southerly part of PII-2012 is the thickest as it was attached to the glacier earlier this year. The most northerly section connected to PII-2010 which passed a moored array in place near Hans Island on Sept.-22, 2010.

Petermann Ice Island 2012 as one piece on Aug.-30, 2012 19:20 UTC in Kane Basin over contours of bottom topography.

From the above two MODIS images over contours of bottom topography, the shallowest water that PII-2012 has seen is the 150-m contour to the east towards Greenland. It is possible, however, that PII-2012 may also have hit some shallow topographic feature not properly charted in IBCAO-2008 (there is a 2012 version, I just learnt) or not properly contoured by me. Lets move on the next question, how thick is this ice island?

From data we recovered 3 weeks ago I can say, however, that PII-2012 is thicker than 144 meters. I base this estimate on the ice island that formed in 2010 and that passed over our moored array on Sept.-22, 2010. It hit two ice profiling sonars at 75 meters and damaged the stainless steel guard cage designed to protect the sensors (which they did), e.g.,

Two Ice Profiling Sonars (IPS) aboard the CCGS Henry Larsen in Aug.-2012. The bent stainless steel protective frame was bent by the 2010 ice island that hit both instruments in Sept.-2010. [Photo Credit: Andreas Muenchow]

Another instrument moored deeper at ~360 meter depth sends out acoustic pings and measures how much sound comes back. A weak scatter like some microscopic plankton or grain of mud or sand in the water reflects little energy, but a hard surface like the ice floating atop reflects lots. And here is how a time series of this backscattered energy looks like when an ice island passes over:

A 24-hour segment of acoustic backscatter from a bottom-mounted acoustic Doppler current profiler is show to vary with time and height above the bottom. The dark red represents the sea surface and/or the bottom of ice floating on it. Vertical resolution is 8 meters, temporal resolution is 30 minutes for a 3-year deployment. The main purpose of this instrument is to measure ocean currents at the same spatial and temporal resolution as shown here for backscatter. PII-2012-B passed over the instrument on Sept.-22, 2010 and is here estimated to be about 144 meters thick.

The exact place of the mooring and the time that PII-2010-B was on Sept.-22, 2010 is shown in this MODIS image of that day:

Location of ADCP mooring site (red square) with Petermann Ice Island 2010 segment B overhead on Sept.-22, 2010.

If you like puzzles, then you will like physical oceanography or any field of science or engineering. If you like puzzles, you will correctly notice, that the flat segment of PII-2010-B oriented parallel to the shores of Ellesmere Island fits the flat segment of PII-2012 that also has a hook to the north. These two segments were indeed connected before they separated from the glacier in 2010 and 2012. This is the reason, that the thickest part of the 2010 ice island is the shallowest part of the 2012 ice island, because the ice gets thicker towards the grounding line of Petermann Gletscher.

And finally, if you like puzzles, then you should consider a career in physical oceanography or physics or mathematics or electrical or mechanical or civil engineering. These are fields where jobs and careers are plentiful and people live long and happy lives: Preben chose Electrical Engineering 70 years ago in Denmark, I chose physical oceanography 30 years ago in Germany, and Allison chose physics 3 years ago in the U.S. of A. Sadly, few American students chose to compete for these jobs and lives, because they need to take a “difficult” undergraduate major. Allison did, she picked physics and oceanography, and so can you.

University of Delaware summer intern Allison Einolf from Macalester College, Minnesota in Nares Strait in Aug.-2012 aboard CCGS Henry Larsen. Allison studies physics. [Photo Credit: Jo Poole, British Columbia]

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Posted in Ice Island, Nares Strait 2012, Oceanography, Petermann Glacier

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Ice Thickness in Nares Strait 2008 and 2009

Posted on August 28, 2012 by | 1 Comment

[Editor's Note: Undergraduate Julie Jones of the University of Delaware summarizes her work that was supervised by Helga Huntley as part of an NSF-funded summer internship.]

Three years ago in 2009 Andreas Muenchow left from Delaware for Greenland with students Pat Ryan and Berit Rabe to recover instruments that recorded salinity, temperature, current velocities, and ice thickness in Nares Strait since 2007.  This summer, I used those observations to estimate ice thickness for April through June in 2008 and compare them to estimates for the same spring period in 2009.  An ice bridge had formed in 2008 but not in 2009.  Working as a group, we wanted to investigate the effect of ice arches on the ice thickness.  Allison Einolf, another summer intern who focused on ocean currents during the same time periods and Andreas produced these maps that introduce the study area, spatial ice cover, and mean ocean currents:

Image

Nares Strait MODIS satellite imagery of the study area and ice arch April 21, 2008. Red dots are instrument locations. Arrows show current velocities.

Image

Nares Strait MODIS satellite imagery of the study area and ice arch April 22, 2009. Red dots are instrument locations. Arrows show current velocities. Note the lack of the southern ice arch, but the presence of one north of the study area.

I used Matlab for most of the data processing, more specifically the Ice Profiling Sonar (IPS) Processing Toolbox for Matlab provided by the manufacturer of the instrument that collected the data: ASL Environmental Sciences, Inc. First I transformed the data from the IPS instrument into a range time series.  I then manually “despiked” the data, taking out any data points that were likely due to bubbles or fish within the acoustic path from the sensor system to the ice above and back.  In a second step I wrote a function using sound speed data from Andreas, atmospheric pressure from Dr. Samelson at Oregon State University, and pressure (depth) data from the IPS instrument to get a time series of the thickness of the ice.  In a third step I applied a Lanczos raised cosine filter that was taught as part of a 2012 Summer Intern Page Workshop. Hence I finally had some nicely filtered data for the periods of the April-June of 2008 and 2009.

Now the results:  Just as we expected, there was much thicker ice in the 2008 spring with a southern ice arch present than there was in the spring of 2009 when no such ice arch was present:

Histogram for April – June 2008 ice. There is a peak at 3 meters, with almost 25% of the ice that thick.

Histogram for April – June 2009 ice. The ice does not get thicker then 2 meters with most of the ice thinner than one meter.

The histograms show thicker ice in 2008, about 2-6 meters on average and with some ice even reaching 10 meters.  In 2009, the ice doesn’t get thicker than 2 meters with most of the ice being thinner than 1 meter.  More specifically, the mean ice thickness for April – June 2008 (2009) is 3.8 (0.58) meters with a standard deviation of 1.8 (0.29) meters.  This further shows that there was thicker ice in 2008 than there was in 2009.  I attributed the cause for the thin 2009 ice to ice flowing freely through Nares Strait all winter and spring as no ice arch in the south blocked such flow.  The ice, thus, did not spend enough time in the high Arctic to thicken.

I noticed something else in my histograms when the 2008 ice bridge collapsed.

April 2008 ice thickness

May 2008 ice thickness

June 2008 Ice Thickness

The monthly histograms show that the ice in April and May is thicker than the ice in June.  We know that the 2008 ice bridge collapsed near June 6th, so it is interesting and it makes a lot of sense that the ice in June would be thinner than the ice two months earlier.

The mean ice thickness for April 2008 was 4.6 meters with a standard deviation of 2.40 meters.  In May 2008 the mean ice thickness was 3.5 meters with a standard deviation of 1.40 meters.  Lastly, in June the mean ice thickness was 3.5 meters with a standard deviation of 1.30 meters.  The ice thickness decreased after April and the variability decreases in June, which helps detect the bridge collapse in the data.

Lastly here are the filtered time series of April – June of 2008 and 2009.

Filtered time series for April – June 2008

Filtered time Series for April – June 2009 with the same scale as 2008 (above figure)

Filtered time series for April – June 2009 with a different scale to see the variability over time more clearly.

Hopefully we can see more interesting and exciting results from the instruments that the Nares Strait team picked up this summer even though they were hit hard by the 2010 Petermann Ice Island!

Two Ice Profiling Sonars (IPS) aboard the CCGS Henry Larsen in Aug.-2012. The protective stainless steel frame was bent by the 2010 ice island that hit both instruments in Sept.-2010. [Photo Credit: Andreas Muenchow]

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New Ocean Observations in Petermann Fjord

Posted on August 22, 2012 by | 10 Comments

A new ice island separated from Petermann Glacier on July 16, 2012 as reported here first. Less than 4 weeks later, the Canadian Coast Guard Ship Henry Larsen reconnoitered the ice island on Aug.-9 when it blocked the northern half of the entrance of the fjord.

Petermann Ice Island 2012 (PII-2012) as seen Aug.-11, 2012 at the entrance of Petermann Fjord. The view is to the north-west. [Photo Credit: Canadian Coast Guard Ship Henry Larsen.]

I was aboard this ship when Captain Wayne Duffett decide to break into the largely ice-free fjord behind the ice-island after consultations with Ice Services Specialist Erin Clarke. The ice observer had just returned from her second helicopter survey in 2 days with pilot Don Dobbin to assess both ice cover and its time rate of change. From the time the ship entered the fjord behind the ice island, hourly flights to a fixed point at the south-western corner of the ice island ensured that its movement would not cut off the ship’s exit. This approach worked and it gave the science crew of 8 aboard about 18 hours to conduct the very first survey of a previously ice-covered ocean:

Petermann Glacier, Fjord, and Ice Island as seen by MODIS at 865 nm on Aug. 07, 2012 overlaid with survey lines of CCGS Henry Larsen on Aug.-9/10/11, 2012 in red.

We were not funded to do enter the fjord, but our main mission to recover an array of ocean moorings with 3-year long data records covering the 2009-12 period about 100 km to the south in Nares Strait has already been accomplished. So, what does a physical oceanographer do when in uncharted and unknown territory? He drops a number of CTDs, that is, measuring conductivity (C), temperature (T), and depth (D, pressure, really) as the instrument (the CTD) is lowered at a constant rate from the surface to the bottom of the ocean at a number of stations. The results from such work next to the present front of Petermann Glacier was a surprise for which we do not yet have a satisfactory explanation: The waters inside the fjord are much warmer at salinities 32.5-34.25 than they are outside the fjord:

Temperature as a function of salinity from 9 stations across Petermann Fjord next to the current seaward edge of Petermann Glacier on Aug.-10, 2012 in red. For comparison I show in blue a station done outside the fjord on Aug.-9, 2012. Note that temperatures increase with increasing salinity which is expected for waters that are a mixture of cold and fresh polar and saltier and warmer Atlantic waters. Density deviations from 1000 kg/m^3 are shown as solid contours along with the freezing temperature that decreases with increasing salinity.

Another way to show the same data is to actually plot the section, that is, the distribution of temperature and salinity in physical space across the fjord as a function of depth:

Section across the seaward edge Petermann Glacier on Aug.-10, 2012 for salinity (left panel) and temperature (right panel). Symbols indicate station locations from which color contours are drawn. Note that the display is cropped to the top 300 meters while real recordings extend to the bottom which exceeds 1000 meters. The view is eastward towards the glacier with north to the left.

Note the doming salinity contours which to classically trained oceanographers suggest a flow out of the page on the right and into the page on left with maximum at about 90 meter depth relative to no flow at, say, 500 meter depth. Another way to view this distinct property distribution is that the flow above 90 meters is clockwise (outflow on left, inflow on right) relative to the more counter-clockwise flow below this depth. This feature, too, comes as a surprise and requires more thought and analyses to explain.

There is much more work to be done to figure out what all this means. I feel like scratching the surface of a large iceberg half-blind. The data from below 300 meter depth, too, contain clues on how some this glacier interacts with the ocean. As for the purpose of this post, I merely wanted to report that the ice island is presently having a hitting or scratching tiny Hans Island. The latter is unlikely to move, but Petermann’s Ice Island will slow on impact, swivel counter-clockwise, bump into Ellesmere, and pretend nothing has happened on its merry way south. This is the latest image I have:

Petermann Ice Island 2012 on Aug.-22, 2012 as seen by MODIS Terra at 21:45 UTC. The tiny red dot marks Hans Island, the location of a weather station in the Kennedy Channel section of Nares Strait. Petermann Fjord is towards the top right out of view.

ADDENDUM Sept.-1, 2012: PII-2010B had a maximum thickness of at least 144 meters as it passed over a mooring that measures ocean currents from the Doppler shift of acoustic backscatter that is shown here for one of four beams:

Time-depth series of acoustic scatter from a bottom-mounted acoustic Doppler current profiler for 24 hours starting Sept-22, 2010 9:30 UTC. Red colors indicate high backscatter from a “hard” surface like ice. The vertical axis depth in meters above the transducers while the horizontal is ensemble number into the record (0.5 hours between ensembles). The 2010 ice island from Petermann Glacier (PII-2010B) passed over the mooring. When PII-2010B was attached to the glacier it was adjacent to the segment that became PII-2012 this year.

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Nares Strait 2012: Renske’s Blog on Data Collection (and other adventures)

Posted on August 14, 2012 by | 1 Comment

Dr. Renske Gelderloos, from Oxford University, has posted more accounts of data collection from the CCGS Larsen (including a description of rosette operations by our own Pat Ryan).  Read her copied posts below, or follow her accounts at her blog directly (where there are additional photos from the area, taken in 2009).

CTD sections…

7/8 August 2012:

Two days of CTD sections. We actually need to work on the weather stations as well: there is a weather station on Cape Baird that needs to be dismantled and relocated to Joe Island on the other side of Nares Strait. Access to a weather station, however, requires a helicopter and the weather has changed from its lovely sunny side to a cloudy and windy variety. There is either far too much wind for the helicopter to fly, or it is foggy and then we can’t fly either. The main activities are therefore centered around taking CTD profiles, which, by the lack of other activities and the need for a deck crew for the rosette system, is now a daytime activity. We take one section just south of Petermann Fjord, and one further north in Robeson Channel. The latter section is extra nice because this part of Nares Strait was often too much ice covered to access for taking measurements in previous years.

In the late afternoon of 8 August the FRC (the small boat) is sent out into Discovery Bay to try and recover a tide gauge pressure mooring that had been there since 2003. In that year, a diver from the American ship ‘Healy’ installed this mooring. In 2006, when the first next ship for scientific purposes came up here, the bay could not be reached because of heavy ice conditions. In 2007, during the expedition thereafter, the science crew flew to the bay by helicopter and successfully talked to the mooring and released it, but it has never come to the surface. In 2009, on the third expedition after deployment, heavy ice conditions again inhibited access to the bay. Now, in 2012, we decided to take the absolute longest of long shots in trying and recover this mooring (if the bay would not be frozen over) using a sinking line and try and ‘catch’ the mooring. As we knew the exact location, it was at least worth trying. So, the FRC was sent into Discovery Bay and came back later that evening, to everyone’s astonishment, with the mooring on board that had been happily recording data for the full nine years it had been there in the water! (In an attempt to be creative I naively inquired whether it would be an option to land the FRC on the beach below Cape Baird and walk to the weather station. Given the steep slope and significant height of the plateau, this idea was quickly discarded.) The success with the Discovery Bay mooring was later celebrated at the bar.

…and water sample collection

During some of the CTD profiles we also take water samples. As I am in the ‘CTD command centre’ almost full time during the sections, I asked Pat Ryan to write something about the water sampling. Here is her story:

Water Sample Collection, by Pat Ryan, University of Delaware

One of the ways oceanographers study the sea is through the collection of water samples.  Chemical oceanographers evaluate the characteristics of water to provide information on the source of the water, contaminants and conditions of the sea to sustain life among other things.

The collection of water aboard the Larsen is done in a contraption we call a rosette.  It’s comprised of a number of Niskin bottles (large cylindrical plastic bottles), in our case 12, held upright in a large round metal frame.  Our rosette is about as tall as I am (170 cm).  As the device is lowered into the ocean, all of the bottles are open at both the top and the bottom so that there are more cylinders than bottles. As the rosette is lowered, water flows freely through the open bottles as if they were pipes… stoppers at each end are connected to a tension-based triggering device that can close both ends instantaneously – thereby capturing the seawater residing at the depth of the rosette at the time of firing.  On the deck, connected via wire to the rosette, is a computer that sends a signal to each of the bottles when the operator wants to capture water.

Our rosette is typically lowered at a controlled rate to the bottom of Nares Strait collecting samples on its descent and then quickly brought back up.  Attached to the rosette is also a CTD device that continuously provides salinity, temperature and depth information to the operator.  Physical oceanographers use these data to analyze aspects of the sea and for the water collection purpose this information is vital to collect samples (that is to trigger the closure of bottles) at specific depths.

All of the heavy work of wrangling the rosette off and then back onto the deck of the ship is done by the deck crew of the Henry Larsen.  Garbed in bright orange jumpsuits and hard hats, the crew pilot the heavy and cumbersome rosette to a gentle landing after each cast.  They are a great group of guys who regale us with tales of the sea, and places back home (Newfoundland for most of them) and make us laugh to the point that we sometimes even forget how cold our hands are!

While the deck crew is managing the heavy work of the rosette, one of the science team members, Jo, mans the winch, hoisting, lowering and then raising the rosette up as directed by another member of our team, Renske.  She operates the computer, carefully monitoring the graphics which tell her where the rosette is at all times.  It’s Renske who determines when each of the bottles fire.

As soon as the rosette is safely back aboard, the piddlers get to work.  We are members of the science crew assigned to get the samples from each Niskin bottle into the pre-labeled sample bottles.  First, we check that the bottles have fired properly and that there are no signs of leaks that would indicate a sample was compromised.  Then a group of us (3 is a nice number – as it speeds up the process and is not so many that there are traffic jams on the deck) set about the task of filling various glass and plastic vials with very cold ocean water, these will be shipped to a lab for analysis when we port.  The label in each bottle indicates the location and depth at which the sample was collected as well as which type of analysis is to be performed.  On this trip we are sampling for O-18, Barium, Salinity and Nutrients.   Protocols to insure the integrity of the sample for each analysis are followed – some of the samples must be immediately frozen and kept at very cold temperatures.  Others require specialized gaskets to prevent oxygen transfer.  Duplication of some samples provides for quality control check performance.   Every time the rosette is deployed, we typically fill about 50 bottles.  Each of the bottles is rinsed with the sample several times prior to being filled – as we dump this rinse water onto the deck, this process can lead to wet shoes and socks when the wind is blowing hard as it was yesterday. In the Arctic, this water piddling as it is “affectionately” dubbed can be chilly, wet work.  Your hands can feel like you might not get sensation back for days and on a windy day (as we had yesterday) the water can be blowing in sheets to soak you.

That being said, it can also be an enjoyable group endeavor.  Our lead scientist often joins us filling bottles and Renske will lend a hand as time permits.  There is a frenzy of activity when the rosette alights upon the deck that feels like work but the camaraderie of the piddlers and the tendency to easy laughter among the group actually makes it some of the fondest (if perhaps coldest) memories of my Arctic experience.

An Arctic Hike

9 August 2012

When I woke up this morning, the wind had not settled down. Quite the opposite to be honest: For the first time since we left Thule the boat was significantly moving in other directions than forward. Taking the helicopter to Cape Baird was absolutely out of the question, and the usual 8-o’clock science meeting was cancelled because it did not seem we would be able to do anything in this weather.

I took a cup of coffee to my cabin and wrote a bit on this blog. After finishing I decided to go up to the bridge to get the latest info on the state of affairs. At the bridge it turned out that the idea to take the FRC to shore and climb up the cliff was being considered more seriously. Apparently, something that is considered impossible one day is suddenly not such a bad idea the next one out here. I was asked to come along and immediately agreed! I knew it would be a tough climb and a windy exercise on the plateau, but this unique opportunity to walk up a glacial outlet and be part of this, admittedly, somewhat absurd plan, I did not want to miss for the world. The carefully-put-together list of absolute essentials to dismantle a weather station was, figuratively speaking, thrown overboard and replaced by a light-weights-only list, as we would have to carry everything up the hill. The magnitude of the team was now determined by the number of people required to carry tools up the hill and tools and a dismantled weather station down the hill. The science team was therefore expanded to four (Humfrey, Dave, Andreas and me) and a crew member with a shotgun (Melvin) was added to the team in case of a polar bear attack. Chief officer Brian, aided by seaman Derick, skillfully maneuvered the FRC from the ship to the beach below the cliffs (while making sure we all got absolutely soaked were it not for our waterproof floater suits),  where we jumped out of the boat onto the beach with our backpacks.

From the beach the least steep route (but still steep) to the plateau where the weather station was situated was through a dry glacial valley. The ground was covered in loose gravel and stones, which made the climb up not an easy hike. In some less covered spots small mosses and tiny plants had been able to find a habitat to flourish, really amazing! I am not a biologist and know little about plants, but this surely is not an easy environment for most life I know. Humfrey later explained that some of the plants we had seen were actually even tiny trees. While sliding backwards we made progress upwards (being Dutch I am not really used to steep slopes anyway) and finally the weather station came into sight. The wind conditions up here were far from ideal to do anything at all! Wind gusts down at the ship reached well over 30 knots, up here they were a lot more severe. We had to strongly lean into the wind and secure everything we laid on the ground with heavy rocks to prevent them from being blown away. Some of the dismantling had already been done for us by local animals (one of the damaged items was definitely the work of a polar bear; cut wires could have been done by other animals). We wrapped the sensors in bubble wrap and put them in my backpack. The tools went back into other backpacks and the battery box and the solar panel had to be carried down while holding them in our hands. Humfrey decided we would take the short way back, which meant sliding down the steep side of the hill straight to the beach. Being only a little over sixty kilos, and very aware of the insanely expensive equipment on my back, the combination of this route and the wind made me go down very slowly. We all made it down to the beach safely, and quickly afterwards Brian and Derick came to pick us up. With a tail wind the ride back to the ship was a lot more comfortable than the way out. Time for a shower and some laundry…

First sight of the Petermann ice island

9 August

Ever since a large piece of the glacier tongue of Petermann Glacier broke off on the 22nd of July (now commonly referred to as ‘the ice island’), we have been anxiously monitoring the movement of this island. The event gives us both opportunities and threats: We are studying the ocean circulation (and its effect on glacial melting) in this fjord. This piece of the glacier breaking off may give us the opportunity to take measurements in a previously covered and therefore inaccessible area. The last time a ship went here to take measurements was in 2009, and incidentally two large calving events have taken place since then (the first one being in August 2010), so really a large part of the fjord that was previously covered under ice is now accessible by ship. On the other hand, the island can block the entrance to the fjord altogether and we may not be able to get in at all.

We are close to the ice island now and are very curious to see it. The news of the piece breaking off made the TV news all over the world, but we are probably the first people to see the island in real life. The captain announces this long awaited moment by: “All ship personnel, all ship personnel; there is a little piece of ice next to the ship if you’re interested”. The bow quickly crowded with people with cameras taking lots of pictures. By the time this ice island will reach the more inhabited part of the world (say Newfoundland) it will have been broken into smaller pieces and not be so gigantic anymore.

This ice island breaking off of the ice tongue of Petermann Glacier is not necessarily a dramatic and life changing event. This glacier tongue loses 80 to 90% of its ice through melting from below, because the ocean water is relatively very warm (don’t get too excited now, it is only about 0.2 degrees Celsius so not particularly hot-tub temperatures). Calving of ice from the edge is only responsible for a tiny fraction of the total ice loss. That being said, if the glacier continues to calve off ice, this may be different in the future.

After the ice-island sight-seeing moment it was time for dinner (or ‘supper’ as it is called on the ship). Supper time is quite early, from 16.30 h to 17.30 h. Chief scientist Humfrey decided on a night-time CTD section (up to about midnight) in the alongside direction of the fjord, away from the ice island and away from the fjord. Tomorrow we will see whether we can go into the fjord and do the rest of this section and another one. Things don’t look good though: the ice island is completely blocking the northeast side of the entrance, while the southwest side is stuffed with thick multi-year ice. But first to bed, and we will see what happens in the morning.

Data collection in Petermann Fjord

10 August 2012

After a short night I woke up this morning for regular breakfast hours between 7 and 8 am. It became clear that we would not be taking measurements in at least the next few hours, so I took the opportunity to catch up on some sleep. After about two hours I was woken up in a not-so-gently manner by the ship’s crushing the thick multi-year ice in the southwestern part of the Petermann Fjord entrance. After an ice reconnaissance flight by helicopter the captain had decided that it was safe to go into the fjord, provided the ice flights were repeated every hour to make sure the ice island did not rotate southwards and close off the whole entrance. This was the first time I saw the boat in action as a real ice breaker: breaking ice. Quite an experience I must say! Thick floes of ice were crushed by the ship’s bow and pushed sideward. The landscape around us is breathtaking: steep cliffs on both sides of the fjords, on top of the cliffs theGreenland ice sheet, large ice bergs that have calved off from Petermann Glacier in the ocean around us, smaller glaciers flowing into the fjord, and the rest of the ocean around us covered in thick ice floes. The wideness and calmness is amazing. The passengers on the helicopter flights today get a real treat. Apart from the amazing landscape a large group of narwhals (whales with long pointy noses) is spotted. I stay on deck for a long time just to admire in silence.

It takes to halfway the afternoon for the boat to break its way through the ice to the vicinity of the edge of the glacier tongue, where we start a CTD/rosette section across the fjord. I asked Humfrey to add some stations to the schedule, even it would only be the top few hundred meters, to better resolve possible finer structures in the fjord. He agreed and added a ‘shallow’ station in between every planned station, warning us though that the whole operation would then take up to 1 or 2 o’clock in the morning. As I really wanted this data I was willing to stay up that late. Apart from the CTDs and rosettes, which tell us something about the water properties and currents in the fjord, we also want to know what the underwater topography (known as bathymetry) looks like. The only information we have is from previous ships in this area, and that information is extremely limited. We basically don’t know more than that the fjord is at least over 1100m deep and that around the entrance the deep part is separated from Nares Strait by a shallow sill, probably no deeper than 450m deep. Therefore we zigzag from station to station, while recording the depth soundings from the ships. The ship’s echo sounder sends a sound signal out to the bottom and waits till this signal returns. From the time it takes to go to the bottom and back, combined with the speed of sound through the water, the depth of the water under the ship is calculated. So, while covering as much ground as we can, we basically map the bathymetry of Petermann Fjord. Knowledge about the bathymetry is of vital importance to be able to make reliable computer models of the ocean circulation in the fjord.

The zigzagging had one minor disadvantage: it took almost an hour to get from one station to the next. Most of the science team had gone off to bed or for a drink at the bar around 10 o’clock in the evening, while Andreas handled the winch and I monitored the CTD-recordings on the computer screen. Humfrey was also still dedicated to the science being done, but after being satisfied that the depth recordings of the bridge went well around 3 am, he went to bed as well. Although the deep stations were a bit boring to perform (looking at a wire unrolling for 20 min, and then rolling up for 20 min), the data was very exciting and we spent the time in between stations plotting the data, discussing, and going back and forth between the processed data and the rough profiles to see what features were real and which ones may be an artificial side effect of the plotting procedure used. When the last station was finally completed and we finished moving equipment into the container, it was 5 o’clock in the morning (slightly later than the scheduled end time). I decided skipping breakfast in the morning would be an excellent idea and went to bed for a good morning of sleep.

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Posted in Ice Island, Nares Strait 2012, Oceanography, Petermann Glacier, Polar Exploration

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