Fimbullisen is a relatively small ice shelf that overhangs the continental slope in the eastern Weddell Sea. The Norwegian Polar Institute (NPI) has three sub-ice shelf moorings installed there, and two years ago we added an APRES (a handy little thing that you place on top of the ice to measure time series of ice shelf thickness from which one can infer the basal melt rate) to one of their sites. The plan is now to – in collaboration with NPI – also measure what happens outside of the ice shelf cavity.
Going on a scientific cruise is mostly exciting, interesting and fun, but it is also linked to risks.
I participated in a survival suit course that prepares us for emergencies on the ship during which we have to use floating suites and life rafts to survive in cold waters far away from help. During the training we learned how to handle the suits, swim in them, build formations to stay close together and how to enter a life raft that contains all survival equipment. It was a lot of fun and we are now well prepared for our next cruise!
Do you remember our student cruise in the fjords south of Bergen some weeks ago? We brought students on the ship Kristin Bonnevie to deploy moorings and take CTD measurements (read about it here: https://skolelab.uib.no/blogg/darelius/2018/02/07/to-the-bjornafjord-with-students-from-gfi/).
Last week, we returned to Bjørnafjorden with Bachelor students on board of Kristin Bonnevie to recover the moorings and take more CTD sections. All four moorings were recovered smoothly and successfully without any loss, which made us very happy! During the whole cruise, the students took CTD measurements, also with miniCTDs, for which they had to drive out with a little boat to get into more shallow areas. The student definitely returned from the cruise with a lot of data to work with.
I’m still in the Bjørnafjord doing one last section before we head back to Bergen – but I just had a report from Svein Østerhus and Polarstern. They are now just north of the front of the Ronne Ice shelf in the Weddell Sea.
Scientist from British Antarctic Survey are onboard with “Boaty McBoatface” – an unmanned, autonomous (i.e. not attached to a cable) submarine with sensors for just about everything onboard – that they plan to send on a mission beneath the Ronne ice shelf! Truly exciting!!! I’d love to be there…
While being in the vicinity of the ice shelf front, Svein will deploy a couple of temperature recording LoTUS bouys (see previous post) within the ice shelf front polynya* for me. These will remain five years at the bottom before surfacing… so be patient!
*a polynya is an area within otherwise ice covered water. Tidal currents and wind typically keep the area just in front of the ice shelf front ice free during summer, and often also during winter.
A new day in the Bjørnafjord with the fjord oceanography students from GFI has begun – and we decided to check in on one of our moorings. The moorings are equipped with an “acoustic release”, a unit which we can communicate with using acoustic signals. Normally we only talk to it to tell it to release the anchor and come up to the surface, but you can also use it to find out where the mooring actually is… and that was what was on the schedule this morning.
The captain made three stops around the position where we let go of the anchor, and at each position we lowered a transducer down into the water and asked the release to tell us how far away it is*. There was some confusion about what codes to actually use (sorry Kristin for waking you up!), but once we got the right one the release responded promptly!
With three positions and three distances you can draw three circles – and if all is well they ought to cross each other in one location… which is where your mooring is! This time it was well and safe were we thought it was – which is good, because the captain had already reported the position to the navy who will do submarine training here in the weeks to come!
*what actually happens is that the deck unit measures the time it takes between emitting a signal and receiving a response, and knowing the speed of sound in the water you can calculate the distance.
You don’t have to go all the way to Antarctica to do exciting oceanographic fieldwork! This week I’m lucky enough to bring a bunch of enthusiastic students out on Krisitin Bonnevie to explore the fjord “Bjørnafjorden” just South of Bergen. Many of them have never been at sea before, but a week of CTD’s and moorings and they are ready to go just about anywhere!
One of the aims of the cruise is too try to solve the puzzle with the mysterious tidal currents in Lukksundet… Lukksundet is a narrow strait connecting the Bjørnafjord to the Hardangerfjord in the south. The tidal currents are very strong here – nothing strange with that – what’s strange is that they turn every two hours!
The tides along the coast of Norway are semi-diurnal; there are two high tides and two low tides a day. We’d expect the tidal currents to have the same periodicity (i.e. to change direction every sixth hour), but to be shifted in time so that maximum tidal currents occur in between high and low tides. Obviously, something more complicated is happening in Lukksundet! I’ve got an hypothesis about what is going on… do you?
The students have deployed moorings within and around the strait, and hopefully we’ll be able to resolve the riddle when we retrieve the data on another student cruise to the fjord a month from now!
The students have posted photos and a film from the cruise here!
Amongst the facebook birthday wishes in my inbox I also found this perculiar Message:
Transmit Time: 2018-02-02T13:41:59Z UTC
Iridium Latitude: -77.0799
Iridium Longitude: -33.8234
which means that at least one of the LoTUS buoys that I deployed last year did what it was told and surfaced today!
LoTUS stands for “Long Term Underwater Sensing” and it is a bottomlander that you more or less through over the side of the ship. It sinks to the bottom, where it measures the tempearture until it is programmed to let og of its weight and come to the surface. Once at the surface, it transmits the data back to us in the office via satellite. Very nice!
The number in the Message above are as in-understandable to me as they are to you – but hopefully the instrument devellopers from KTH will be able to transform them into understandable data… a one year long temperature record from a location just north of the Filchner Ice Shelf front in the Weddell Sea! There was one more buoy that was programmed to come up today and which didn’t yet report home – so keep your finger’s crossed!
A collegaue of mine, Svein Østerhus, is currently onboard Polarstern in the Weddell Sea, and he will deploy more of these buoys for me later during the cruise!
Below are a few Pictures from the LoTUS buoy deployment last year:
Guest blog by Karen Assmann
After our outing on to the eastern Getz Ice Shelf, the weather got a bit worse again we continued our way east with more moorings being recovered and deployed and three ocean gliders going in the water. These small autonomous underwater vehicles will spend the next year going in and out of the Dotson Ice Shelf cavity, if everything goes to plan. Getting ocean observations in the ice shelf cavities, rather than along their edges like we do with ships and moorings, is difficult. The few observations that exist come from drilling holes through several hundred meters of ice and deploying instruments through them or from sending bigger unmanned submarines into them. So sending ocean gliders that normally profile the surface ocean into the cavity under the ice shelf is rather daring. If the project by the University of Washington and Columbia University succeeds, it will mean that we will learn a huge amount about what happens in the ocean under the shelves, but the risk that the ocean gliders do not make it back out is high.
At this point the weather turned good again and we dashed east across the bay to start on the next lot of helicopter work. This was to include the replacement of an automated weather station (AWS), and two days of radar and magnetics surveys and ApRES deployments on Thwaites Glacier and Dotson Ice Shelf. We were crossing fingers for 3 days of good weather. The AWS replacement on the first day ended rather abruptly, when the old weather station couldn’t be found and the responsible scientist decided not to replace it with a new one. Preparations for the second day of air operations came to an abrupt halt when a leak in the hydraulic system of one of the helicopters was found. Despite best efforts and extensive spares kits the leak couldn’t be fixed and this spelled the end of any work that needed a helicopter. Two working helicopters are needed for safe operations as an emergency backup, so the fact that one of them was no longer safe to fly meant the other couldn’t fly either. After a brief pause to re-group, on we went with the ocean work on the schedule while considering what could be done with the time that has suddenly become available.
Guest blog by Karen Assmann
After we finished our mooring marathon at the western Getz ice shelf we started to make our way east towards the Amundsen polynya. One stop on the way was the last UIB mooring that was placed in one of the smaller openings of the ice shelf. The area where the mooring was located had been covered in fast ice and heavy sea ice since we started monitoring sea ice conditions at the start of the cruise. When we got there the mooring position was located in open water about 100 meters from sea ice that was tightly packed by strong winds. After a bit of deliberation we decided not to release and recover the mooring, because we were worried that the strong winds and surface currents were going to carry it into the sea ice. We did however talk to the acoustic release and worked out that the mooring was still where we had left it two years ago.
Then we turned further eastward to make use of a weather window that would allow us to complete some of the helicopter work that was on the schedule. As well as a joint KOPRI/University of Bergen/University of Gothenburg effort to deploy autonomous phase-sensitive radars ApRES to measure ice shelf basal melt rates, there was also a group from the University of Texas who had installed radar to measure the ice sheet structure and magnetics equipment to find out about the type of ground under the ice on one of the helicopters. After being windy, snowy and cloudy for a few days the weather turned sunny, clear and calm on 22 January that also happened to be my birthday. After a few delays we loaded our equipment into one of our helicopters, hopped in and away we went over the cliff of the ice shelf edge onto the white expanse of the eastern Getz ice shelf. I have been involved in research around ice shelves for 20 years and two years ago I finally got to stand on one. This time was just as exciting even though at the surface and ice shelf is just very flat and white and big.
We spent a bit of time setting up our first ApRES site, while the helicopter shuttled out more equipment and fuel drums for the other helicopter to refuel while doing its radar and magnetics surveys. Then we loaded everything into the helicopter and moved to the second site where the setup went much faster, partly because we now had the pilot to help as well, partly because we had now worked out how to do things efficiently. After a photo session we took the scenic route back to the ship.
In some ways it was lucky that Johan only realized quite how full the schedule was going to be at the western side of the Getz ice shelf two days before the cruise. Otherwise he might not have agreed to come on the cruise. The change of schedule had moved this work to the start of the second half of the cruise and there were only two stations before we started our first mooring recovery at 22.00 on 18 January.
After a few pings from the deck unit the release on the first mooring woke up and we got the okay from the bridge to release the mooring. Shortly afterwards we spotted the orange buoys at the surface and the ship inched up to them to catch the top float with grappling hooks and to start pulling the rope, floats and instruments onto the ship over the stern. The whole recovery took about an hour and by about 07.00 in the morning we had recovered two more moorings, the last rather close to the ice shelf edge. Mooring two didn’t tell us that it had released and just popped up to the surface. The top instrument on the third had been pushed to the next one below by an iceberg, but both were fine.
To get the new moorings into water we had to download the data from some of the instruments, change their batteries and give them a service as quickly as possible to not keep the ship waiting too long. Luckily we had help from the glider team and just after lunchtime we were ready to deploy the first of our new moorings. These first two deployments took us to dinner. The transit to the other side of the ice shelf gave us the opportunity to catch a few hours sleep before the last recovery and deployment. Those came and went without any problems as well and both us, and the deck crew were getting so efficient at the whole process that the time we were given on the schedule for each recovery and deployment was reduced from four to two hours. By the time it got to breakfast on 20 January we were finished, 34 hours after starting with all four moorings that we deployed in the area two years ago successfully recovered and three new ones in the water to take over their work.