Tag Archives: Arctic Ocean

Sea ice and 2016 Arctic field work

The sea ice in the Arctic Ocean is quickly disappearing from coastal areas as we are entering the summer melt season. This year I follow this seasonal event with nervous anticipation, because in October and November we will be out at sea working north of northern Alaska. We plan to deploy a large number of ocean sensors to investigate how sound propagates from the deep Arctic Ocean on to the shallow Chukchi Sea. This figure shows our study area with the ice cover as it was reported yesterday from space:

Ice concentration for June 14, 2016 from SSM/I imagery. Insert show study area to the north of Alaska and planned mooring locations (red box).

Ice concentration for June 14, 2016 from SSM/I imagery. Insert show study area to the north of Alaska and planned mooring locations (red box).

Zooming in a little further, I show the coast of Alaska along with 100 and 1000 meter contour of bottom depth over a color map of ice concentrations:

Ice concentrations from SSM/I to the north of norther Alaska with planned mooring locations across the sloping bottom. The 100 and 1000 meter contours are shown in gray with blue and red symbols representing locations of ocean and acoustic sensors, respectively.

Ice concentrations from SSM/I to the north of norther Alaska with planned mooring locations across the sloping bottom. The 100 and 1000 meter contours are shown in gray with blue and red symbols representing locations of ocean and acoustic sensors, respectively.

My responsibilities in this US Navy-funded project are the seven densely packed blue triangles. They indicate locations where I hope to measure continuously for a year ocean temperature, salinity, and pressure from which to construct sections of speed of sound and how it varies in time and space. I will also measure ice draft as well ice and ocean currents from which to estimate the roughness of the sea ice over time. Sea ice and ocean properties both impact sound propagation from deep to shallow water and vice versa.

A first question: What will the ice be like when we get there? This is the question that has the 40 or so people all working on this project anxiously preparing for the worst, but how can we expect what challenges are to come our way?

Doing my homework, I downloaded from the National Snow and Ice Data Center all gridded maps of ice concentrations that microwave satellites measured almost daily since 1978. Then I crunch the numbers on my laptop with a set of kitchen-sink Unix tools and code snippets such as

set ftp = 'ftp://sidads.colorado.edu'
set dir = 'pub/DATASETS/nsidc0081_nrt_nasateam_seaice/north'
...
wget -r -nd -l1 --no-check-certificate $ftp/$dir/$year/$file

along with fancy and free Fortran and General Mapping Tools to make the maps shown above. With these tools and data I can then calculate how much sea ice covers any area at any time. The result for custom-made mooring area at almost daily resolution gives a quick visual that I use to prepare for our fall 2016 expedition. The dotted lines in the top panel indicate the dates we are in the area.

Time series of daily ice concentration in the study area for different decades from January-1 through Dec.-31 for each year from 1980 through 2015. Panels are sorted by decade. The red curve is for 2015 and is shown for comparison in all panels.

Time series of daily ice concentration in the study area for different decades from January-1 through Dec.-31 for each year from 1980 through 2015. Panels are sorted by decade. The red curve is for 2015 and is shown for comparison in all panels.

The story here is well-known to anyone interested in Arctic sea ice and climate change, but here it applies to a tiny spec of ocean between the 100 and 1000 meter isobath where we plan to deployed ocean sensors for a year in the fall of 2016. For the two decades of the last century, the ice cover looks like a crap shoot with 80% ice cover possible any month of the year and ice-free conditions unlikely but possible here or there for a week or two at most. The situation changed dramatically since about 2000. During the last six years our study area has always been free of ice from late August to early October, however, our 2016 expedition is during the transition from ice-free October to generally ice-covered early November, but, I feel, our saving grace is that the sea ice will be thin and mobile. I thus feel that we probably can work comfortable on account of ice for the entire period, but the winds and waves will blow us away …

Weather will be most uncomfortable, because fall is the Pacific storm season. And with little or only thin ice, there will be lots and lots of waves with the ship pitching and rolling and seeking shelter that will challenge us from getting all the work done even with 7 days for bad weather built into our schedule.

I worked in this area on larger ships in 1993, 2003, and in 2004. Here is a photo that Chris Linder of Woods Hole Oceanographic Institution took during a massive storm in the general vicinity in October of 2004. The storm halted all outside work on the 420 feet long USCGC Healy heading into the waves for 42 long and miserable hours:

Icebreaker taking on waves on the stern during a fall storm in the Beaufort Sea in October 2004. [Photo Credit: Chris Linder, Woods Hole Oceanographic Institution]

Icebreaker taking on waves on the bow during a fall storm in the Beaufort Sea in October 2004. [Photo Credit: Chris Linder, Woods Hole Oceanographic Institution]

Oh, I now also recall that during this four-week expedition we never saw land or the sun. It was always a drizzly gray ocean on a gray horizon. The Arctic Ocean in the fall is an often cruel and inhospitable place with driving freezing rain and fog.

Ghosts of Discovery Harbor: Digging for Data

Death by starvation, drowning, and execution was the fate of 19 members of the US Army’s Lady Franklin Bay Expedition that was charged in 1881 to explore the northern reaches of the American continent. Only six members returned alive, however, they carried papers of tidal observations that they had made at Discovery Harbor at almost 82 N latitude, less than 1000 miles from the North Pole. Air temperatures were a constant -40 (Fahrenheit or Celsius) in January and February. While I knew and wrote of this most deadly of all Arctic expeditions, only 2 days ago did I discover a brief 1887 report in Science that a year-long record of hourly tidal observations exist. How to find these long forgotten data?

My first step was to search for the author of the Science paper entitled “Tidal observations of the Greely Expedition.” Mr. Alex S. Christie was the Chief of the Tidal Division of the US Coast and Geodedic Survey. He received a copy of the data from Lt. Greely. His activity report dated June 30, 1887 confirms receipt and processing of the data, but he laments about “deficient computer power” and requests “two computers of standard ability preferable by young men of 16 to 20 years.” Times and language have changed: In 1887 a computers was a man hired to crunch numbers with pen and paper.

Data table of 15 days of hourly tidal sea level observations extracted from Greely (1888).

Data table of 15 days of hourly tidal sea level observations extracted from Greely (1888).

While somewhat interesting, I still had to find the real data shown above, but further google searches of the original data got me to the Explorer’s Club in New York City where in 2003 a professional archivist, Clare Flemming, arranged and described the “Collection of the Lady Franklin Bay Expedition 1881-1884.” This most instructive 46 page document lists the entire collection of materials including Series III “Official Research” that consists of 69 folders in 4 Boxes. Box-4 File-15 lists “Manuscript spreadsheet on Tides, paginated. Published in Greely (1888), 2:651-662” as well as 3 unpublished files on tides and tide gauges. With this reference, I did find the official 1888 “Report on the United States Expedition to Lady Franklin Bay” of the Government Printing Office as digitized from microfiche as

https://archive.org/details/cihm_29328

which on page 641 shows the above table. There are 19 more tables like it, but at the moment I have digitized only the first one. Unlike my colleagues at the US Coast and Geodedic Survey in 1887, I do have enough computer power to graph and process these 15 days of data in mere seconds, e.g.,

Hourly tidal observations at Discovery Harbor taken for 15 days by Greely in 1881 and Peary in 1909.

Hourly tidal observations at Discovery Harbor taken for 15 days by Greely in 1881 and Peary in 1909.

A more technical “harmonic” analyses reveals that Greely’s 1881 (or Peary’s 1909) measured tides at Discovery Harbor have amplitudes of about 0.52 m (0.59) for the dominant semi-diurnal and 0.07 m (0.12) for the dominant diurnal oscillation. My own estimates from a 9 year 2003 to 2012 record gives 0.59 and 0.07 m for semi-diurnal and diurnal components. This gives me confidence, that both the 1881 and 1909 data are good, just have a quick look at 1 of the 9 years of data I collected:

Tidal sea level data from a pressure sensor placed in Discovery Harbor in 2003. Each row is 2 month of data starting at the top (August 2003) and ending at the bottom (July 2004).

Tidal sea level data from a pressure sensor placed in Discovery Harbor in 2003. Each row is 2 month of data starting at the top (August 2003) and ending at the bottom (July 2004).

There is more to this story. For example, what happened to the complete and original data recordings? Recall that Greely left Discovery Harbor late in the fall of 1883 after supply ships failed to reach his northerly location two years in a row. This fateful southward retreat from a well supplied base at Fort Conger and Discovery Harbor killed 19 men. Unlike ghostly Cape Sabine where most of the men perished, Discovery Harbor had both local coal reserves and musk ox in the nearby hills that could have provided heat, energy, and food for many years.

It amazes me, that a 1-year copy of tidal data survived the death march of Greely’s party. It took another 18 years for the complete and original records to be recovered by Robert Peary who handed them to the Peary Arctic Club which in 1905 morphed into Explorer’s Club of New York City. I suspect (but do not know), that these archives contain another 2 years of data that nobody but Edward Israel in 1882/83 and the archivist in 2003 laid eyes on. Sergeant Edward Israel was the astronomer who collected the original tidal data. He perished at Cape Sabine on May 29, 1884, 25 years of age.

Edmund Israel, astronomer of the Lady Franklin Bay Expedition of 1881-1884.

Edmund Israel, astronomer of the Lady Franklin Bay Expedition of 1881-1884.

References:

Christie, A.S., 1887: Tidal Observations of the Greely Expedition, Science, 9 (214), 246-249.

Greely, A.W., 1888: Report on the Proceedings of the United States Expedition to Lady Franklin Bay, Grinnell Land, Government Printing Office, Washington, DC.

Guttridge, L., 2000: The ghosts of Cape Sabine, Penguin-Putnam, New York, NY, 354pp.

Oceanography of Nares Strait Ice Flushing

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

Coastal Oceanography off North-East Greenland

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

Heartbeat of Ocean and Air of Greenland

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.