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OutreachActivitiesHealy 09-05Notes from the Arctic
Daily Notes from the Arctic
A blog by Andy Armstrong
Physical Scientist/Co-director UNH Joint Hydrographic Center
The joint U.S.-Canadian Extended Continental Shelf project is underway, with OCS physical scientist Andy Armstrong onboard the U.S. Coast Guard icebreaker Healy. As explained in an article on the NOAA website, NOAA is taking the lead to collect bathymetric data to map the seafloor.
"The mission's primary purpose is to determine the full extent of the continental shelf," Armstrong explains, "but the data collected during this cruise will also help us learn more about seafloor processes, ocean circulation, the geologic origin of the Arctic basin, ecosystems, and navigation."
Andy will be sending in daily updates on their work, and we will be posting them here. These updates give us a fascinating insight into the project. Beyond that, we can share, at least vicariously, in the experiences of these men and women as they work through the inevitable challenges of the Arctic.
For more information about the Healy 2009 Leg 5 cruise see the Healy 09-05 page.
*Read the original account of the discovery of the seamount on August 25th, 2009.
Today was our final day of work in the Arctic on the U.S. Coast Guard Cutter Healy. We did some multibearm mapping along the foot of the slope north of Barrow. This is an area where the slope is cut with a regular pattern of ridges and canyons, much like those that might be seen cutting a similar slope on land.
During the 41 days of this cruise, we completed 5175 lineal nautical miles of multibeam seafloor mapping.
We only saw a little bit of ice today as we passed through a small tongue of 1/10 or 2/10 ice. Some of the pieces are very thick; the thick ones being the only ones that have survived the melting season in this part of the Arctic. As we went though this area, the ship slowed a bit from what has been our 15-knot mapping speed in open water to a more prudent 10 knots.
Early tomorrow morning we will approach Barrow cautiously, because the bowhead whales are starting their annual westward migration along the northern Alaska coast. After arriving offshore of Barrow, we will start our helicopter transfer ashore.
This morning began early with the redeployment of the first of 3 High Frequency Acoustic Recording Package (HARP) moorings. These are Scripps Institution of Oceanography hydrophone moorings that we recovered at the start of the cruise. During the cruise, passive acoustic recordings of natural ice and marine mammal sounds from the past year have been downloaded for analysis and the HARP packages have been refurbished. They packages are now in place on the seafloor for another year of recording. We expect to retrieve these moorings again on a 2010 Healy cruise. Following the 2nd and 3rd HARP deployments we recovered a University of Washington meteorological buoy that was put on station by a research team on an earlier Healy cruise this summer. The very limited opportunity for icebreaker ship time in the Arctic makes this kind of scientific cooperation essential. After the met buoy was safely aboard we began mapping a section the foot of the continental slope north of Barrow.
After completing our mapping in the pockmark area we continued south, choosing our path to acquire multibeam bathymetry in swaths adjacent to previous tracks. By running adjacent tracks, we can build seafloor coverage over wide enough areas to identify and map features of geologic interest. In the evening, we arrived at a rendezvous point to retrieve a Seaglider deployed early in the cruise by a U.S. Navy team who are riding with us. The glider, which is directed by satellite from the Navy's glider control center in Mississippi, has been diving and rising through the water column and transiting up and down the continental slope in this area, measuring water column properties and transmitting data ashore. The glider surfaced exactly as directed, and was retrieved successfully by small boat and A-frame.
After the dredge, we headed south, leaving the ice for the last time, to do some additional multibeam mapping in an area of the Chukchi Cap we have partly mapped on prior cruises. In this area, prominent parallel sets of seafloor scours at about 450 meters of depth suggest the grounding of a very large ice sheet. Individual icebergs create scour marks irregularly oriented on the seafloor. Ice sheets, by contrast, create extensive sets of parallel grooves on the seafloor. In one swath, we found a set of parallel ridges which are clearly related to the parallel scours, but different in character from other features we have seen. Another feature of this area is a very large field of very large sand waves on the seafloor. We extended the mapping of this large sand wave field to the south, hoping to complete the coverage of this area.
South of the sand wave field, we added mapping coverage to an area of large seafloor pockmarks that we discovered and began mapping on earlier cruises. This area contains pockmarks of a variety of sizes, from 250 meters to 900 meters across and 50 to 100 meters deep, as well as several linear and circular troughs that may be the result of coalescing pockmarks-or may not.
Most of the day was devoted to a multibeam swath along a Louis S. St. Laurent seismic line from last year's cruise. The multibeam line and the subbottom profile from our ~3.5kHz chirp sounder will combine with the Louis' deep seismic profile to complete the seafloor picture along the track. In the afternoon, we redirected our track toward a dredge site in the north central part of the Chukchi Borderlands. We completed this final dredge of the cruise late in the evening, once again bringing up about 1000 lbs of rock. Our series of dredges has been designed to span the area that might be part of the U.S. Extended Continental Shelf.
Today was another map and dredge day. In our mapping, we filled in some areas along what may be the foot of the slope that we had skipped over in earlier mapping cruises. These were areas where this transition zone is deeply indented into the Chukchi Borderlands. As always, the seafloor relief is much more complex than the existing map shows. The existing maps are based on widely spaced single point depth measurements originating from ice islands, aircraft deployed ice soundings, and occasional ship tracks. While usefully conveying general depths, they can falsely convey the impression that the Arctic is already mapped.
We also dredged again on Healy Seamount. Today's dredge captured another excellent haul of rocks. As in yesterday's dredge, we came up with a mixture of ice-rafted rocks and rocks from the seamount itself. Rocks of both categories will go ashore to be archived.
Today was a lot like yesterday. Overnight, we mapped some previously unmapped areas on an elevated plain northwest of Healy Seamount. We found a group of 3 parallel ridges on the plain that look sort of dune-like, except that they are 5 miles long and 100 to 300 meters in height. After the overnight mapping, we moved into position for another dredge.
We dredged on a steep slope between the depths of 3300 and 2700 meters. The dredge came up full of rocks that appear to be local in origin. The Arctic seafloor has lots of ice-rafted debris including rocks of all sizes that were torn from the land and carried out to sea by ice. We got some of those rafted rocks in the dredge, but the great majority of the 1000-lb haul was similar rock of a common source. These rocks, like those brought up yesterday will be analyzed for origin, composition, and age. These analyses will help geologists unravel the geologic history of this part of the Arctic.
After completing our dredge last night we set off on a trackline to fill in gaps in the bathymetry and get us to the next dredge site. On the way, we found and mapped a couple of small elevations rising abruptly from the seafloor. Every line of mapping adds something to our knowledge of the Arctic Ocean. At about noon we started a dredge up the southeastern flank of Healy Seamount. Healy Seamount is a 30-nautical mile long pincer-shaped underwater mountain, rising from 3850 meters of depth to its peak at less than 900 meters, that we discovered and mapped on our first extended continental shelf mapping cruise in 2003.
Our dredge today got a little more complicated than we had hoped. At about 2400 meters of depth, the dredge--basically a steel basket dragged on the seafloor by a very long wire--got lodged on something and refused to budge. Good advance planning on the part of the Healy and the science team paid off, however, as we had a plan in place for just such a possibility. We were able to maneuver the ship around the dredge and successfully free it from the seabed. As in our dredge yesterday, we had a mix of mud and rocks. The rocks we recover will be archived as part of the extended continental shelf data set, and will be analyzed by experts at independent academic laboratories.
After we got the dredge and the rocks aboard, we started another mapping track to fill in some bathymetry gaps around Healy Seamount and take us to our next dredge site.
Today we crossed the Canada Basin in mostly open water, making as much as 15 knots when no patches of ice were around. This evening we reached the eastern margin of the Northwind Ridge (part of the Chukchi Borderlands), where we stopped to dredge the seafloor along one of the very steep slopes that are found on this margin. Our dredge came up with lots of mud, which isn't very helpful, and some rocks, which will be analyzed as part of the U.S. extended continental shelf program. Our rock experts, who had been anxious to get their part of the cruise started, were happy to have some samples to examine and catalog.
The two ships got underway again late in the evening after the barbeque, and Louis fell in behind Healy on a westbound track. In the morning, the ice had diminished to the point that Healy could part company with Louis. The two ships will complete their cruises operating independently, Louis continuing with seismic profiling and Healy with bathymetry and seafloor sampling. After we parted from Louis, our track took us back into the margin of the pack ice. The ice cover was near complete, but the ice was relatively thin and broken into small floes. The wind was blowing about 35 knots, and there was a large swell coming from the west that continued into the pack. It was fascinating to watch the ice surface undulating in 10 to 12 ft. swells.
The ice thinned even more today as we traveled farther south. The thinner ice allowed us to lead the Louis along a more eastward track than anticipated, which provided an opportunity to acquire data in a gravity "low" anomaly. Gravity data that have been acquired over the years by aerial, helicopter-deployed, and shipborne gravity meters often provide clues to where significant seafloor and subbottom features may exist. Obtaining both bathymetry and seismic subbottom profiles at these anomalies can provide very useful information for the U.S. and Canadian extended continental shelf projects. About midday, as we reached our farthest south point, Louis pulled their seismic gear and came alongside Healy to raft up. While rafted, the science parties and crews enjoyed an afternoon barbeque aboard Healy, with a variety of dishes provided by the galley staffs of each ship. After the barbeque, there were tours of each ship, some games and contests, and some scientific and operational planning meetings.
After Louis S. St. Laurent got their seismic gear back in the water and operating, following Thursday's repairs, we resumed our sediment thickness profiling line toward the south. As we got farther south, the ice thinned significantly, both in coverage and in thickness. Only occasionally were we jarred by breaking the ice. The depth diminished and we began to see small bits of seafloor relief with Healy's multibeam echo sounder as we got closer to the Canadian margin of the basin.
We spent today sitting in one place in the ice while Louis S. St. Laurent made repairs to their seismic system. While waiting we took the opportunity to take a Conductivity/Temperature/Depth (CTD) cast and periodically drop Expendable Bathythermographs (XBT). We take these observations primarily to make sound speed corrections for our multibeam echo sounder. As it turned out, we didn't need those too much today, but the observations also get sent ashore for incorporation into operational oceanographic models and for archive at the National Oceanographic Data Center where they will be available for a variety of oceanographic and climate applications. There are relatively few oceanographic observations from the Arctic, so each of these provides some tangible value.
Also today, the scientists from the National Ice Center who are piggy-backing along with us on this cruise took advantage of the unplanned stop and the Louis' helicopter to deploy an ice beacon on a large floe. They had hoped to find a multi-year ice floe, but had to settle for a thick first year ice floe. The beacon will report its position and the atmospheric pressure and temperature at 2 meters above sea level regularly via satellite to the National Ice Center. Several of these beacons, which are intended to last about 4 years, are in service in the Arctic. We use the ice beacon position reports aboard Healy to assist to estimate ice drift direction and speed as we plan our mapping routes.
Today we continued our southerly multichannel seismic profiling line, simultaneously acquiring seismic data from Louis S. St. Laurent and multibeam data from Healy. While these seismic lines have been a little tedious for those of us aboard Healy, our icebreaking in the lead has resulted in very high quality seismic profiles that will be of great value to both the U.S. and Canada in establishing our respective extended continental shelves. And, even though the seafloor has been flat along many of our lines, we now have much improved depth data for the base bathymetric map of the Arctic.
Although the temperature continued to drop, reaching -9°C (16° F), the ice cover steadily thinned from the 9/10 we had yesterday to the 7/10 - 8/10 cover we had today.
The big event today was the arrival onboard Healy of Davey Jones along with King Boreas Rex and his court, who came aboard to initiate neophyte bluenoses into the Realm of the Arctic Circle. After some rather chilling experiences, the neophytes were duly accepted into the realm.
Today Healy and Louis S. St. Laurent traveled south-southeasterly, with Healy leading as the seismic team on Louis measured sediment thickness with their multichannel seismic reflection system. The multibeam echo sounder system on Healy continued to reveal the extremely flat bathymetry of the Canada Basin Abyssal Plain.
An Arctic high pressure system dominated our weather today, and we enjoyed bright sunshine and clear skies. The ice continued to cover more than 90% of the sea surface, but was thinning somewhat as we traveled south. We occasionally encountered small pressure ridges and floes of thick ice, but for the most part the ice was about 1 meter thick--easy for Healy to break.
It is difficult to capture the extraordinary vista of nothing but ice from horizon to horizon in a photograph.
Today we spent the day crossing the Canada Basin, with Healy in the lead and Louis S. St. Laurent following with multichannel seismic profiling gear streaming behind. As expected, the multibeam echo sounder revealed a featureless abyssal plain.
We had a change in the weather today, with the sun coming out, the wind coming up, and the temperature dropping. It was very cold outside with the air temperature at about -5°C (21°F) and the wind blowing at 20 to 25 knots for a wind chill around -25° C. The clear weather and full ice cover provided the opportunity for our embarked Coast Guard public affairs specialist to get a ride in the Louis' helicopter and film Healy breaking ice. A little later, the weather closed in and it started snowing.
Photos by U.S. Coast Guard.
Photos by U.S. Coast Guard.
Today was a little more interesting than Saturday, as we reached our 3rd 2500-m contour point in this 4-day bathymetric loop of the project. We found and mapped two distinct seafloor elevations with 2500-m contours. The first was a small rise to the seaward of the main elevation, with a bathymetric saddle connecting this smaller rise to the second, and larger, high area. The multibeam echo sounder on Healy was extremely valuable in locating and developing these key bathymetric features. The 5-nautical mile wide swath allowed us to pinpoint the important depths and define the 2500-m contours in this poorly mapped region without the need to pass directly over the top of the feature. While it is not unusual to use the real time multibeam display to guide a survey ship's path, that process is complicated significantly by the need to guide an icebreaker's path a mile in advance. This evening, after completing the primary bathymetric goals of this part of the cruise, Healy retook the lead icebreaking position and Louis redeployed their seismic gear for more sediment thickness mapping.
Throughout the day and overnight, we slogged southward through very heavy ice, making very slow headway as the Louis was forced to stop, back, and ram frequently to break the ice ahead of us.
Although we thought we had reached the northern limit during the night, ice conditions drove us a little further to the north en route to a second salient of the 2500-m contour. We mapped to latitude 84°15' N. In doing so, we encountered some of the heaviest ice we have seen so far, with some patches of multi-year ice around 3 meters thick. Late in the afternoon, we obtained the necessary sounding data and turned southward with Louis still in the lead.
After the Louis S. St. Laurent retrieved their seismic equipment and took the lead yesterday, we have been able to increase our speed without degrading the quality of our multibeam echo sounder data. Last night we crossed directly over two very large charted seamounts, obtaining greatly improved bathymetry on these major features. After crossing the seamounts, we continued our northward track toward the farthest north limit of our cruise, where at midnight (in full daylight) we obtained soundings across the 2500-m contour. The 2500-m contour (isobath) is one of the principal features involved in delineating an extended continental shelf.
After our discovery and mapping of the isolated seamount yesterday, we have returned to our transects across the Canada Basin. Although the Arctic as a whole is probably heading for another near-record minimum summer ice extent, we are headed into an area where the winds and currents have concentrated and packed the ice.
This afternoon we completed our eastward line and turned north. As the ice thickened this evening, and it became more difficult for Healy to clear ice sufficiently well to keep the seismic gear operating effectively on Louis S. St. Laurent, the U.S. and Canadian chief scientists made the decision to pull the seismic gear and shift to a bathymetric survey. Louis will now lead northward and break ice as Healy follows and maps the seafloor with our multibeam echo sounder. With Louis in the lead, we should be able to both increase our speed and improve our data quality.
Tonight we are surveying over two very large seamounts shown on existing maps of the northern end of the Canada Basin. Because these seamounts have been charted on the basis of only a few soundings, we will run our multibeam over the top of the features to confirm their location and depth, and to improve the detail with which they are mapped.
Today we began on what appeared would be a long and unremarkable transit across the Canada Basin Abyssal Plain. Louis S. St. Laurent would be measuring sediment thickness with their seismic profiling system and Healy would be measuring depth on the featureless plain. Our track was to take us close to an area shown as slightly shallower than the general basin depth--3600 meters in surrounding 3700-meter depths. The chief scientists aboard both Louis and Healy agreed to alter our track about 2 miles to pass over the charted rise. As we approached the area, the depth did begin to decrease, with the seafloor rising about 50 meters very gradually over several miles. Because we were in the middle of an extraordinarily flat basin, this was all we expected.
Just to the south of the charted position, however, the multibeam echo sounder began detecting an abrupt reduction in depth. After some hurried discussion among the Louis' and Healy's science teams, we agreed to divert from our planned track and devote 4 hours to a survey of the surprising feature. As we followed the seafloor terrain to the south, it became apparent that this was a very large target, probably large enough to be categorized as a seamount. Limited to 4 knots because of the seismic gear streaming behind Louis, our mapping of the eastern flank proceeded quite slowly. Even so, the mapping lab on Healy was full of people watching the plot develop on the computer screens. When the time constraints demanded it, we turned west and then back north to map the spine and the western flank of the feature. This final pass confirmed the seamount status and established a least depth of about 2630 meters. Although we didn't quite get the southernmost extent of the feature covered and there was a small rise developing to the north, we believe that the main part of this newly discovered seamount has been mapped. It rises over 1000 meters from the seafloor, is about 12 nautical miles long and 6 nautical miles across.
Today, and over the weekend, we have alternated between breaking ice for the Louis S. St. Laurent on seismic reflection tracklines and mapping seafloor features with Healy's multibeam echo sounder. On Friday night, we completed mapping the ridge described in the 20 August update, finding a least depth of about 3140 meters. While this previously unmapped feature rises impressively almost 700 meters above the surrounding seafloor, it does not rise the 1000 meters necessary to qualify as a seamount.
After completing the survey of the ridge, we resumed the seismic track toward the east. On Saturday, while the Louis was performing some maintenance on their seismic equipment, we ran some small bathymetric surveys to fill in gaps in our 2008 survey of the southern margin of the Alpha-Mendeleev Ridge complex. While we were able to improve our map of the ridges and valleys along of this part of the seafloor, we found no real surprises. Sunday was more eastbound seismic track. Sunday evening brought us close to the southeast corner of the Alpha-Mendeleev Ridge complex, and we decided to take advantage of the opportunity and fill in some bathymetry. Although the goal of this diversion was primarily bathymetry, Louis followed us around the 1-day survey loop with their seismic gear operating. The bathymetry and seismic data taken together will almost certainly improve our understanding of the geology of the Arctic and will be of significant value to the scientists of both nations on this joint U.S.--Canada project.
Athough considerable more bathymetry remains to be done in this area, this afternoon Healy and Louis resumed our eastward seismic trackline to obtain sediment thickness information across the Canada Basin.
Today we did some multibeam bathymetric mapping over areas of high seafloor relief. We are still breaking ice in front of the Canadian Coast Guard icebreaker Louis S. St. Laurent, but instead of sounding over the very flat abyssal plain, our track took us over some interesting areas on the Alpha-Mendeleev Ridge complex, 625 nautical miles north of the Arctic coast of Alaska.
This part of the track is designed to obtain multichannel seismic reflection profiles over areas where we dredged rock samples from the seafloor last year. The dredge samples and seismic profiles will help us analyze the geology of the Arctic region in support of the U.S. delineation of its Extended Continental Shelf. As a bonus, though, our planned route has taken us within a few miles of an unsurveyed feature vaguely depicted--probably from 1 or 2 isolated soundings--on Russian contour maps of the area, and represented as a single circular contour on the International Bathymetric Chart of the Arctic Ocean (IBCAO). In an exploratory deviation from our planned track, we are running a bathymetric survey to precisely locate and define the feature. We found and began mapping a north-south trending 14-nautical mile long ridge rising abruptly at least 500 meters out of the seafloor. Having mapped the eastern flank on our first pass, our path over the next two hours will take us along the spine of the feature and back to our originally planned track line. As we turned to run the northbound leg of our survey, we saw a hint of some additional seafloor relief to the south. That will have to wait for next year.
More of the same today. We are still leading the Louis S. St. Laurent through 9/10 first year ice. Although the ice is often 1-2 meters thick, we are generally breaking it fairly easily. The Louis continues to acquire high quality seismic reflection data and the Healy continues to acquire multibeam bathymetry over the abyssal plain.
Our seismic lines continue over flat areas of the Arctic Ocean, but we will be crossing into an area of significant relief tonight. Earlier this evening we crossed over an area that showed as a deeper spot on Russian bathymetric maps of the area. As we passed over the area, however, we found no change in the depth. The existing maps and charts of the Arctic are based on very sparse soundings from a wide variety of sources, with depth contours that reflect the very subjective judgment of the compiler.
Today began on the same northwestward track as yesterday, with Healy multibeam echo sounding in the lead and Louis S. St. Laurent towing their multichannel seismic reflection gear astern. Although we had expected ice conditions to remain about the same, the ice actually got a little more closely packed, with more ridges and thick areas. On a couple occasions we had to back up and ram the ice to break through and to make a path for Louis.
Our survey and mapping progress was also slowed a bit by some of the inevitable problems that arise in a major project like this. The Louis was experiencing intermittent problems with their seismic gear and decided to haul the gear in for service. Louis' helicopter was sent aloft to find open water where the sled and streamer could be safely retrieved, and the two ships steamed about 7 miles east of our track to the opening. With Louis temporarily out of service, Healy took advantage of this time to do some equipment repair of our own. About a week ago during the first CTD cast of the cruise, the CTD winch level-wind malfunctioned and mis-wrapped some of the wire on the drum. The result of that mishap was that the wire was jammed at about 1300 meters out. The Coast Guard engineers and science technicians have spent the past few hours carefully paying out wire and clearing the jam. We should be on our way back to the track in about an hour. Because we want continuous lines of seismically determined sediment thickness, we will return to where we left off on our original track before heading northwestward again.
We should complete this leg of the track sometime tomorrow morning, and turn eastward to cross some of the bathymetric features on margin of the Alpha-Mendeleev Ridge complex. Seismic profiling of this area will help us interpret the geologic history and structure of the region.
Today was more of the same--breaking ice and multibeam echo sounding ahead of Louis S. St. Laurent. We are in the midst of the Arctic melting season, and the ice is becoming thinner and sparser daily. Since last night we have been on a northwestward track, traveling from the center of the Canada Basin to the area north of the Chukchi Borderlands. The Chukchi Borderlands is a complex underwater plateau of the continental shelf projecting northward into the Arctic Ocean. This prolongation of the continental shelf is one of the foundations of the U.S. Extended Continental Shelf (ECS) in the Arctic.
On this track we are moving towards an area of irregular seafloor where we hope to obtain additional bathymetry. Our earlier cruises have located numerous previously unknown seafloor features that may bear on the delineation of our ECS. If the ice conditions continue to improve, we may have the opportunity to divert from our escort role to further develop the complicated bathymetry in this area.
USCGC Healy continues to break ice for the Canadian Coast Guard Icebreaker Louis S. St. Laurent, following astern of us. We are obtaining valuable multibeam bathymetry in parts of the Arctic Ocean that have never been mapped, but multichannel seismic profiling from the Louis remains the primary goal for now. On Friday and Saturday we were on an eastward upslope track toward the Canadian shelf. Last night we reached the end of that track and turned southwestward to profile and sound back down the slope. Tomorrow we expect to turn northwestward toward the areas of more interest to the U.S.
At the end our eastward line last night, we stopped briefly for engineering maintenance on both ships, and some maintenance on the seismic equipment. While stopped, we were able to complete a CTD cast to measure the conductivity (salinity) and temperature versus depth and thereby to establish a sound speed profile for correcting the multibeam echosounder depths. This CTD cast through the ice was a first for me, but is one of the things Healy does fairly routinely.
One of the remarkable aspects of this cruise is the cooperation and collaboration between the U.S. and Canada. Both nations need these seismic profiles for our respective Extended Continental Shelf projects, but they are almost impossible to obtain with the single icebreaker each of us has available. By operating jointly, we can both get the data we need. The project team includes personnel from the Office of Coast Survey-NOAA/UNH Joint Hydrographic Center, The National Ice Center, the National Geophysical Data Center, the U.S. Department of State, the U.S. Coast Guard, the U.S. Navy, the U.S. Geological Survey, the Canadian Hydrographic Service, the Geological Survey of Canada, and the Canadian Coast Guard. Also aboard are two teachers at sea, a National Science Foundation scientific support team from Lamont-Doherty Earth Observatory, and several individual scientists from other collaborating institutions.
We have had an uneventful day steaming northward at about 4 knots. Astern of us, the Louis S. St. Laurent is towing multi-channel seismic reflection gear for measuring the sediment thickness here in the Canada Basin. Our main job for this part of the cruise is to clear a path through the ice so that the seismic profiling can go on smoothly. Without a clear path through the ice, the towed seismic equipment would be destroyed in short order.
While we are clearing the path, we are also doing multibeam echo sounding. Our multibeam data has hardly varied from about 3800 meters of depth, either across the 5-nautical mile wide swath or along the 75 nautical mile track, all day. This part of the Beaufort Sea is one of the flattest seafloors in the entire world. It is flat because sediment has been drifting down and settling evenly in this basin for thousands of years.
The reason we are doing seismic profiling in this area is precisely because of the thick sediment. Both the U.S. and Canada will use the sediment thickness data collected by Louis in delineating the limits of our respective extended continental shelves.
Much of last night was spent in coordinated operations with Louis S. St. Laurent, the Canadian icebreaker that is working with us on this joint U.S.-- Canada ECS mapping project. The Louis and Healy conducted a calibration experiment to characterize the sound field of the Louis' seismic source. This 3-dimensional absolute sound pressure level information is required for both data processing purposes and environmental assessment purposes. Having a well-measured sound field will improve our ability to interpret the seismic data and allow us to avoid harm to any marine mammals that may come near our ships during seismic operations.
In this experiment, Healy sat motionless and quiet with a 4 hydrophones suspended about a 100 meters down in the water while Louis passed close (very close) by in a figure-eight pattern. Both ships recorded the seismic source sound levels continuously as the range between the ships decreased and then increased.
After the test, we headed north toward the start of our first seismic profiling line. We expect to come on line and begin profiling about midday tomorrow. The sketch shows the Healy track (red) and the Louis' AIS track (green) for the source calibration experiment.
Although we have known it was up there, the sun came out of the clouds for a while today. In the short period of the cruise so far, we have had fog, snow, overcast, and finally some sun.
Today we began the primary work of this joint U.S.-Canada Extended Continental Shelf mapping project. After a night and morning of steaming north in company with the Louis S. St. Laurent, we reached the starting point of our first seismic profiling line. At 77-11.2 N, 148-16.1 W, Healy moved into the lead to begin clearing a path through the ice, and the Canadian team on Louis deployed their seismic gear. This starting point coincides with the end of a line from last year's work. Not surprisingly for such a complex operation as multi-channel seismic profiling in ice-covered waters, some of the deployed equipment did not work properly and Louis had to retrieve and its gear as the two icebreakers doubled back to the start point for another try. Everything worked this time, and we began acquiring both bathymetry and seismic profile data.
We are presently moving north through the Beaufort Sea at about 4 knots, easily clearing the way though melting 6/10 - 7/10 ice (60% - 70% ice cover of ice).
