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Notes from the Arctic - SWERUS-C3 Expedition
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September 17-27, 2014
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A slightly splashy day on Oden. (Photo courtesy of Markus Karasti) |
These surveys revealed greater detail of the iceberg scouring (or lack thereof in certain regions) that will shed light on the glacial history of the ridge, and also gave us a peek at a possible ‘spillway’ for deep waters trapped in the basins on either side of the ridge. It will take much longer than just the transit back to Norway to start putting the big picture together, but all teams on board seem excited about the data and samples they’ve collected and the improved understanding of the Arctic Ocean they will bring.
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Our path through the new ice... |
For the CCOM team, we are planning to leave our split-beam water column mapping system in place until the dock lines are tight in Tromsø, hoping to catch some last-minute seeps wherever our data collection permits allow during transit on the continental shelf. We’ve had a few examples of seeps that clearly demonstrated our technology for this type of bubble detection, but overall we’ve come across fewer seeps than we had anticipated. That might not sound terribly newsworthy, but the dearth of bubble plume observations compared to Leg 1 will improve the collective understanding of where to expect gas seepage in the Arctic and inform future cruise plans for seep mapping. Over the next week we’ll finish up the cruise report and prepare to reenter civilization, while sincerely looking forward to rejoining our families who have been so patient during this cruise. Their much-appreciated support from shore means as much to the success of the scientific mission as the 24/7 efforts of those at sea.
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New ice forming with slightly older ice in the background. |
Until next time…
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Dark nights return as we head south, requiring headlights during the early morning watch. |
September 4-16, 2014
Kevin Jerram
A brief update from ODEN: we are alive and well! The last two weeks have been quite busy with numerous CTD, water sampling, and sediment coring transects up and down the continental slope in longitudes between 180-140° E. Of course, water column, seafloor, and subbottom mapping continue 24/7. While we haven’t come across quite the numbers of gas seeps we hoped to see, the echosounding systems continue to perform smoothly. The remarkable layering and sharp disturbances of ancient sediments recorded in the subbottom profiler (to depths of ~200 m) have become rather fascinating to my untrained geological eye, which has typically been focused on acoustic returns from bubbles rising on very different timescales. Each sediment feature (or featureless region, in some cases) brings a mix of reactions and speculations from the geologists and geophysicists on board – a welcome reminder that the data we collect are of sincere interest in the greater discussion on the history and, necessarily, the future of the Arctic Ocean.
One notable accomplishment, at least from the water column mapping perspective, is a second calibration of our wideband split-beam scientific echosounder. To provide some background information, the calibration method involves suspending a copper sphere beneath the ship and ‘viewing’ its acoustic returns in the split-beam echosounder. The copper sphere has a certain capability to scatter acoustic waves directed at it, enabling us to determine the echosounder’s sensitivity to this target over a wide range of viewing angles. These are important corrections because the ‘true’ acoustic scattering strengths of bubbles are strongly related to temperature, depth, gas composition, and bubble size, but the ‘observed’ strengths depend also on where the bubbles show up in our echosounder field of view. Thus, the calibration data are used to compensate our acoustic observations of bubbles for where they appear in our field of view, with the intent of improving estimates of bubble sizes and numbers at gas seep sites. These, in turn, are related to mass transport of gas out of the seabed and into the water column and atmosphere.
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Split-beam echosounder calibration, Arctic-style. |
As we discovered during our first calibration attempt at anchor in Barrow, even a small current relative to the ship will cause severe drag on the sphere and wreak havoc on the lines, poles, and reels used to control its position from deck. Despite snapping two of our three fiberglass rods and losing a sinker under strain from the current, we were able to collect calibration data at that time for several echosounder settings and then retrieve the copper sphere without further incident. (Note: we do have replacement spheres, but it’s a good feeling to have the original back on deck after its wild ride below the ship.) This initial calibration at anchor had not cost any ‘official’ ship time underway, so we planned to perform a second calibration while drifting under better conditions.
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Larry, Denis, and Rezwan carefully guide a sphere support line up one deck and around the widest, curviest section of the hull during our second split-beam calibration. |
We got our chance late last week when a break in the sampling schedule happened to coincide with a tentative window in the sea state. The early hour, dark skies, snow showers, and slippery deck didn’t slow down Rezwan and Denis, our volunteer deckhands from the first calibration who cheerfully signed up for another round of untangling lines and cranking reels in the cold. Thanks to their efficiency on deck and the reduced current relative to the ship, our second calibration proceeded much more smoothly and with vastly improved control over the sphere position. I dare say it was almost too easy. After sphere deployment and adjustment to the center of the echosounder field of view, we drank tea and made snowmen on the ship’s rail while Larry ran the software from the bridge, occasionally calling over the radio for slight adjustments to the sphere position. All in all, this was a much more comfortable and successful calibration experience and we are presently working on a document describing our method so future expeditions can include split-beam echosounder calibrations as a matter of course. (Many thanks – and apologies – to CCOM project engineer Carlo Lanzoni, who donated his calibration rod and reel setup for this cruise.)
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A moment of discovery on the Lomonosov Ridge. |
After our calibration, we steamed to the Russian end of the Lomonosov Ridge, a submarine mountain chain which stretches across the entire Arctic Ocean and almost bisects the North Pole, to begin surveying a deeper section connecting the ridge to the continental shelf. It is believed this deeper section acts as a ‘spillway’ between the basins on both sides of the ridge, facilitating mixing of deep waters that are otherwise divided in the Arctic Ocean. We were surprised and excited to find large parallel scours across the ridge, probably created by massive icebergs grounding and plowing through the upper sediment layers during a period of extensive glaciation over 100,000 years ago. It was one of those ‘moments of discovery,’ chief scientist and advisors all crowded around the mutlibeam, that brings new life to a survey.
It’s difficult to believe, but we are now more than half-way through the cruise and have fewer than 14 days remaining for planned science before we must start the lengthy transit to Norway. It promises to be another couple of busy weeks!
August 26-September 3, 2014
Kevin Jerram
Well, here we are in ODEN’s natural habitat: the ice. The ship and her crew wasted no time escorting us north from Herald Canyon last week, steaming at a full 10 knots into the edge of the ice pack. Many ships might take a more leisurely pace at the first sight of ice, but not ODEN. Her hull was carefully designed to submerge, slice, and divide the ice ahead without a fuss, leaving an ice-free path astern that is slightly wider than necessary to ease maneuvering, deployment of instruments, and towing. (A sample of the hull material is available for inspection on the bridge; its heft is surprising and, admittedly, a bit reassuring.) Compared to our earlier transits in open water, the ship rides much more comfortably in the ice where wind-driven waves have little chance to build and the swell from the south is extinguished.
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Into the ice... |
We have been treated to a wide variety of ice types and coverage over the last few days. The region of our entrance to the pack consisted of scattered bits of all sizes and ages, from young, ragged, white chunks less than a meter in any dimension to older, blue bergs the size of small buses. Blue ice is created over several years and aptly named ‘multiyear’ ice. The blue bergs we’ve seen have been sculpted and exposed by wave action during their slow descent into the open ocean, often becoming the smoothest and most colorful natural objects in sight. As we steamed further north toward lower air and sea temperatures, we encountered increasing ice coverage (surprise, surprise) and spent a particularly snowy day surrounded by a sea slowly transforming its surface from liquid to solid. In general, the first stages of freezing at the surface yield a slushy layer that coagulates and behaves like a slick on the water - hence its name, ‘grease ice.’ Our grease ice was whipped into broad streaks by the wind and, in its slushy stickiness, preserved the shape and turbulence of the ship’s wake as we passed.
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Ship wake turbulence frozen into the grease ice. |
Our first intensive sampling study in the ice occurred over several days in ‘Box 2,’ an area along the International Date Line at the continental shelf break where gas seepage was thought to be likely. (By coincidence, this was also the setting for the book I was reading last week, In the Kingdom of Ice by Hampton Sides, which tells the story of a US Navy Arctic expedition aboard the steamer Jeanette in the early 1880s. Captain George De Long and his crew were stuck in the ice for over a year in our present area before the Jeanette was crushed and sank, leaving 33 men and 40 dogs with no choice but to hike, sled, row, and sail to Siberia as winter set in over the next several months. The book provided excellent context for appreciating the advances in Arctic exploration, mapping, and science that have been made over the last century, but you’ll have to read it yourself to find out how their journey ended. Let’s just say it’s good to be on the ODEN.)
‘Box 2’ included the first ‘planned’ multibeam survey designed to cover a certain region with a given level of coverage. ‘Planned’ is in quotes because the noise from icebreaking and presence of ice beneath our echosounders typically reduce the quality of our soundings, so we must frequently stray from our planned lines to avoid the thickest of the ever-shifting ice and improve our picture of the seafloor. The mates who steer the ship have been exceptionally responsive, frequently adjusting the speed and heading to improve data quality in each particular patch. In fact, most steering during surveys is done by watching the multibeam to keep an eye on the seafloor coverage in the given ice conditions – an approach much appreciated on our end. Our survey in ‘Box 2’ naturally included multiple crossings of the dateline, an event which has occasionally thrown our bathymetric processing software for a bit of a loop. Thankfully, the galley staff were not fazed: Thursday night’s traditional Swedish meal of pancakes and pea soup was served with New Hampshire maple syrup (courtesy of Larry) despite a dinnertime dateline crossing which knocked us briefly into Friday.
All in all, we are settling into our watchstanding routines and enjoying both the work and the life on board. I spent a day last week reviewing and renewing our split-beam echosounder calibration equipment so we can take advantage of the next break in weather and sea ice for another calibration. All echosounders are pinging happily together and producing high quality data given the ice conditions. Our survey in Box 2 wrapped up a few days ago and just this morning we finished a survey on the Arlis Plateau. After a round of sediment and water sampling, we used our multibeam and subbottom profiler to cover a region of deep iceberg scouring on the plateau where two previous surveys revealed scouring in significantly different directions on the eastern and western sides of our study site. We filled in the unmapped region between those previous surveys and hope that a bit of post-processing will shed some light on when and how the scouring changed course. Now we have departed the western hemisphere – for good, this time – en route to the next sampling and surveying site in our eastward march along the Siberian continental shelf break.
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A curious polar bear mother and cub approach the ship. |
On the non-work side of things, a major source of entertainment is watching for the wildlife that thrives in this harsh climate. Several seals were spotted in the looser ice pack and we’ve been accompanied by a few ‘ice gulls’ circling the ship for the last week; they seem to appreciate the fishing opportunities in the temporary open water left behind. Of course, the greatest excitement comes from polar bear sightings. We happened to see several bears on multiple occasions while running our back-and-forth survey patterns over the last week, but yesterday we were treated to an entirely different scene: a mother polar bear and cub ambling toward the ship while we were holding station for sediment coring. The whole science party and crew turned out to the starboard rail to watch the approach of our inquisitive visitors. After coming within a few hundred meters, the bears then stayed nearby so long that we all eventually had to get back to work and start our transit to the Arlis Plateau.
Just another day aboard the ODEN…
August 26, 2014
Kevin Jerram
Larry Mayer and I are taking part in the second leg of SWERUS-C3, a joint Swedish-Russian-US expedition aboard the Swedish icebreaker ODEN. The 'big picture' motivation is to better understand methane sources and pathways from the seafloor to the atmosphere in the Arctic Ocean. So, we're looking up, down, and sideways for methane during our cruise along the eastern Siberian continental shelf. The ship's atmospheric monitoring systems run around the clock, and it's not uncommon to see sediment cores and water samples being retrieved on different ends of the ship while a weather balloon is launched from the helicopter deck. Being from the Center for Coastal and Ocean Mapping, our specific responsibilities are acoustic mapping of the seafloor and water column using a multibeam echosounder and scientific split-beam echosounder. Additionally, we have a subbottom profiler which gives us a peak into the sediment structure.
Aside from collecting bathymetric data in regions of the Arctic which have likely never been surveyed, we are searching for the acoustic signatures of gas bubbles rising from the seabed toward the surface. These features help us to better focus our sampling sites. This cruise also presents an ideal opportunity to test new equipment. Courtesy of CCOM's Dr. Tom Weber, we've brought along an innovative transceiver that lets us run the split-beam echosounder over a relatively wide range of frequencies. This system helps us to 'see' a broader assortment of bubble sizes and will likely improve gas transport estimates from acoustic data alone.
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Boat transfer from Barrow, with ODEN visible on the horizon. |
We departed Barrow, Alaska last week and will gradually make the Northeast Passage to Trømso, Norway, arriving in early October. Trømso seems a long way off, but the first ten days or so have breezed by. Larry and I arrived in Barrow on Monday the 18th with all limbs, all luggage, and the ODEN anchored just a mile offshore. There is no port in Barrow, so all transfers to ships are carried out using small boats, landing craft, or helicopters. The seas cooperated fully with our plans to use a landing craft, giving us a chance to get out on board a day early and integrate our new transceiver with the existing network and transducer. With notes from Dr. Weber and superb assistance from the ship's system engineer, Axel, we were pinging with our new system in just a few hours.
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Larry hard at work in his fancy new office. This is our transceiver installation in the narrow space between the (heated) fuel tanks and the main deck. At least no one will be walking by and poking at it! |
After a split-beam echosounder calibration that ran all night at anchor in Barrow (with many thanks to fellow watchstanders Denis and Rez), we set sail for our first waypoint: Herald Canyon, northeast of the famed Wrangel Island. A number of gas seep observations had been made in this area during Leg 1 and we followed up with a series of surveying and sampling transects. The joint efforts of many CCOM and ODEN personnel in planning, testing, traveling, setup, and surveying came together as our first gas seep observation scrolled onto the screen of the new split-beam echosounder. The transects produced several additional seep observations and a variety of sediment and water samples before we wrapped up operations in this region and started steaming north.
Now we head through the fog and into the ice...
