I am a PhD-student (defending my thesis now in June – puh!) working with Elin at the Geophysical Institute, University of Bergen, working on the exchange of water masses between the continental shelf and the deep ocean in the Southern Weddell Sea, Antarctica.
Based on idealized modeling and moored observations, I study mechanisms that can bring warm water of oceanic origin onto the continental shelf and contribute to basal melting of the ice shelves. Furthermore, I study the production and export of cold and dense shelf waters, which overflows the Filchner sill, mixes with off-shore water masses and forms Antarctic bottom water. Antarctic bottom water is an important driver of the global thermohaline circulation, and is found near the bottom, in the large oceans.
Tomorrow I’ll tell you about one of the articles in my PhD-thesis that just got published!
…Hurray! We got money from the university to send Nadine (and some instrumentation) onboard “Kronprins Håkon” (KPH amongst friends) to Antarctica next season! KPH is the brand new Norwegian icebreaker and she will sail down to Dronning Maud Land and Fimbullisen in February, 2019.
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.
Map over Antarctica with the Fimbull ice shelf marked in red. From npolar.no.
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!
Those of you who understand Swedish (or is it “Svorsk”?) can listen to me trying to explain what we do in Antarctica to a Swedish journalist here: Radio Halland
In February last year we recovered a mooring at the Filchner Ice Shelf front (See map below) that we since long had consider lost. The large German ice-breaker Polarstern had failed to reach it twice due to sea ice, and it had now been in the water for more than four years. When we reached the location with (the much smaller) JCR last year, the mooring was only a few hundred meters from the advancing ice shelf front, and the captain was somewhat hesitant to go there – but he did, and the acoustic release on the mooring SA responded and released as promptly as if it had been deployed the day before! Most of the instruments had run out of battery and thus stopped recording – but one of them were still running, providing a four year long data record!
The mooring had several temperature and salinity sensors, and the records from them showed that there is a pulse of very cold (-2.3C!) ice shelf water (see explanation below) leaving the cavity during late summer and autumn each year. The water has been cooled down so much through interaction with the ice shelf base at depth, that there are ice crystals forming within it as it rises and leaves the cavity (I’ll write about what the ice crystals did to our instruments in a later post). The salinity of the cold water was relatively high – telling us that the water most likely entered the ice shelf cavity in the Ronne Depression, west of Berkner Island (see map).
In an earlier paper**, we had shown (using a numerical model) that ice shelf water flowing northward along the Berkner island would turn east when it reaches the ice shelf front (because conservation of potential vorticity hinders water to flow across the ice shelf front where the water depth suddenly changes by hundreds of meters) and exit the cavity in the east. But now the data showed that water was exiting the cavity in the west anyway?! What about the potential vorticity?? Our data also show that when cold water is flowing out of the cavity in the west during late summer, there is layer of less dense (and warmer) water present above it. In the paper we suggest that the presence of the upper, lighter layer breaks the potential vorticity constraint. The layer of less dense water reaches down roughly as deep as the ice shelf itself – and you can imagine that to the outflow it acts as a continuation of the ice shelf.
We now know that water leaves the ice shelf cavity also in the west – but where does it go then? Is there a flow of dense ice shelf water also along the western part of the Filchner trough?
Map over the southern Weddell Sea. The yellow dots show where our moorings were deployed, and the blue arrow show the path of the ice shelf water. From Darelius & Sallée, 2018.Temperatures at the front of the Filchner ice shelf. Note that the temperature scale goes down to -2.3C! At the surface seawater can not be colder than -1.9C, then it freezes. Modified from Darelius & Sallée, 2018.Density profiles at the ice shelf front. Red and green profiles are from periods with outflow – you see that the density decreases around 400 meters, roughly at the level of the ice shelf base. The black profiles are from a period without outflow – the density does not change at the depth of the ice shelf base. From Darelius & Sallée, 2018.
Ice shelf water: We define water that has a temperature below the surface freezing point (which is about -1,9C for sea water) as “ice shelf water”. The water leaving the cavity was as cold as -2.3C (See figure 2 above)! How can it be so cold? It is a combination of two physical facts: 1) The freezing point decreases as pressure increases and 2) water in contact with ice will have a temperature equal to the freezing point. In an ice shelf cavity we have ice in contact with water at large depth ( i.e. at large pressure) and the water will then be cooled down (the heat given off by the water is used to melt ice) to the local freezing point – and voila, you’ve got ice shelf water!
* I say my, but it’s a team effort: many thanks to J.B. Sallée who co-authored the paper and to all the people involved in deploying and recovering the moorings!
**Darelius, E., Makinson, K., Daae, K., Fer, I., Holland, P. R., & Nicholls, K. W. (2014). Circulation and hydrography in the Filchner Depression. Journal of Geophyscial Research, 119, 1–18. http://doi.org/10.1002/2014JC010225
As scientists it’s not enough to only do research alone in our little office, but we also need to get among other scientists to find out what new research is being done, to network and to make other’s aware of our important piece of work. Each year, there is a big European geoscience conference (EGU) in Vienna which again took place last week. 15000 scientists attended from more than 100 different countries and I (Nadine) was among them! In my luggage: A poster presenting our experiments at the Coriolis platform and some first results. This was very exciting, because it is a unique opportunity to talk to other scientists doing similar research. I was even co-convener in a session about the Southern Ocean which means I got to pick the talks and helped preparing everything in advance! After that week I was very exhausted, but happy! The program was stuffed with interesting talks and posters about Antarctica, oceanography, ice shelves, ice shelf—ocean interaction and glaciers and I got to talk to many skilled, interested and motivated scientists. All of them loved our experiments on the water-filled mary-go-round!
Happily presenting our poster at this year’s European geoscience conference (EGU) in Vienna!
Writing a scientific article is a long process – you collect the data, you calibrate them, process them and you analyze them. You plot them, think about them, discuss them, think about them again until hopefully, at some point, the data give you results that you can understand and – publish. So you write the paper – in between meetings and teaching you somehow manage to squeeze your outstanding results and neatly prepared figures into the template provided by the journal. Then you submit – and forget about it all until you hear back from the editor three months later: the REVIEWS are back… sometimes it’s like this:
i.e. you quickly find out that your results were not that outstanding and your figures not that neat… the reviewers have filled page after page with “Did you consider…”, “why didn’t you calculate…” how does this compare to..”, “can you really ignore the effect of….” and “you ought to refer to the paper by mr so and so”…so you start over, you do all the extra analyses that reviewer three asked for, you make new figures, you clarify and expand and include a citation of mr so and so (the reviewer?). You read and write the text over and over and at some point you realize that you’ve done all that they ask for… and that version 6.2 of the paper is indeed much better than version 1.0. So you write a very polite letter to the editor, where you respond to each and every comment from the reviewers and explain what you’ve changed – and then you resubmit. And you wait. Again. For three months.
… but then sometimes, you get three short lines from the editor stating that you paper is accepted! It will be published!!! YES!!!
I received one of these e-mails the other day – and once the paper get online in a couple of days I’ll let you know what it is all about!
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://elindarelius.no/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.
Recovery of moorings in Bjørnafjorden during a student cruise. Moorings are arrays of instruments that are brought to the see floor by heavy weights. A release and floating elements are used to bring the instruments back to the surface.With this little boat, we went further into the fjords in shallower areas to take measurements with miniCTDs.
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.
Polarstern 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.
Waiting for the ship to get in position (Algot, Vår and Carola)
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!
Transducer going down!Is there anyone out there? Vår listening for the acoustic release to respond
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.
I am a PhD-student (defending my thesis now in June – puh!) working with Elin at the Geophysical Institute, University of Bergen, working on the exchange of water masses between the continental shelf and the deep ocean in the Southern Weddell Sea, Antarctica. 
