Our latest paper from the Amundesn Sea was highlighted by eos.org! You can read what they Write about Our work here!
Our latest paper from the Amundesn Sea was highlighted by eos.org! You can read what they Write about Our work here!
My phone rang twice yesterday – the first time it was Anna Wåhlin, who had just sat her feet on land again in Punta Arenas, Chile after two months in the Amundsen Sea With Ran.
The second time it was a local, Bergen number and I was very surprised to hear Nadine’s voice on the line! It still amazes me, that (when things work) you can talk to someone on a ship in Antarctica and it sounds as if they are in the room next door…
She had bad news, there were too much ice, the captain couldn’t go nearly as far south as we had hoped for to deploy Our moorings and we have to move them further north to deeper water. 1500m instead of 800m. Where should we add the extra line? Should we rearrange the instruments? We discussed a bit and agreed on a solution.
When I woke up this morning there were five missed calls from the same Bergen number – and there was soon a new call from Nadine.
– More bad news. The captain couldn’t make it even to 1500m, they were now about to deploy the NPI mooring at 2000 m. What should we do with ours? No point in going deeper, we don’t have more lines to add and many of the instruments can’t be deployed that deep. Deploy it on Maud Rise? Move instruments over to the NPI mooring and bring the rest home? Bring them all home? Not an easy decision!
While Nadine is wathing icebergs drift by in the Southern Ocean, I brought the students in GEOF232 back to Masfjorden, a fjord just North of Bergen. No icebergs to be seen there (luckily), and the only thing we saw drift by was Our own DIY drifters that we had deployed in the fjord!
A drifter is simply an Object that drifts With the Ocean currents and then on a regular basis reports its position back. Now, you can pay a lot and buy a fancy drifter… or you can build Your own (almost as fancy). That’s what Our handy technician Helge Bryhni did! All you need is some paint trays, a bucket, flotation, some rope and chain – and one of these devices that you are supposed to put on your (expensive) car so that you can find it again if it gets stolen. To be on the safe side, Helge opted for a radar reflector and a water proof container.
Video by Algot Peterson, UiB
The students got to decide where and how to deploy our four drifters – spread out or together? in pairs with different depths*? near a river outlet? on rising tides or sinking tides? – and once they were in the water they could sit back and follow the drift on their mobile phone!
*by adjusting the length of the rope we could Place the bulky plastic part of the drifter on the Depth we wanted, and the drifter would then follow (and show us) the water motion at that Depth.
Dear Dr. Darelius,
The editors of Geophysical Research Letters have selected your paper “Warm Circumpolar Deep Water at the Western Getz Ice Shelf Front, Antarctica” (MS# 2018GL081354) to be featured as a Research Spotlight on https://Eos.org and on the journal’s website. Congratulations!
I’ll post the links when they are out!
The new Swedish AUV (autonomous underwater vehicle) heroine Ran has returned from her second mission beneath Thwaites ice shelf! Just in time for the international women’s day tomorrow!
An AUV is sent down in the water with a pre-programmed mission, e.g. “dive down to 500 m depth, swim 2 km to the east while measuring salinity and temperature and then come back here so that I can pick you up”, while a “ROV” (Remotedly operated vehicule) is connected to and steered from the mother ship via cables.
The name Ran is borrowed from Nordic mythology, where she is the goddess of the deep sea. According to the legend (and wikipedia), Ran catches seamen in big nets and then keeps them with her at the bottom of the sea. Luckily Ran escaped both the nets and the sea ice that was closing up around her pick up spot… and made it safely back to the mother ship were Anna Wåhlin and the rest of the AUV-team was waiting. I bet they were nervous!
On her second trip, Ran ventured three kilometers in under Thwaites, and brought back information on the sub-ice shelf hydrography and currents but also water samples that will be analyzed back in the laboratory.
Ran and I have one thing in common – neither she nor I would be where we are today without Anna’s support and stubborness. I’m so happy Your “baby” is successfull, Anna. You’ve worked so hard for this to happen! Congratulations!
You can read more about Ran and the expeditions (in Swedish) here!
… if you don’t know what to do on Friday afternoon… then maybe drop by the library in “Realfagsbygget”, Bergen!… and yes, that’s me jumping with the penguins!
Guest blog by Karen Assmann
Maybe you remember the blog posts I wrote a year ago about the cruise to the Amundsen Sea onboard the South Korean icebreaker Araon? (If not, see here!) Maybe you have even been wondering what we have been doing with all the data we recovered? About two weeks ago we had our first paper using these data published in a journal called Geophysical Research Letters: Warm Circumpolar Deep Water at the Western Getz Ice Shelf Front, Antarctica
Our two years of data show that there is a constant flow of warm water towards the western Getz Ice shelf and that this flow is pretty fast (20 cm/s). The distance from the shelf break, where the warm water comes from, to the ice shelf front is just 110 km so it takes only about a week to get from the deep ocean basin to the ice shelf front and the water does not have time to cool down much along its way. Temperatures in the inflow reach up to 1.59°C at the ice shelf front which makes this water the warmest that has been observed at any ice shelf front in the Amundsen Sea. The water reaching the Getz ice shelf cavity is hence warmer than the water reaching the fast melting Pine Island and Thwaites Ice Shelves further east!
To investigate what drives changes in the temperature and thickness of the warm bottom layer, we compared our ocean observations to wind data from the area and found that stronger easterly winds in the area make it harder for the warm water to reach the ice shelf front, because they depress the warm bottom layer over the shelf break. Climate projections indicate that these easterlies will weaken in future, making it easier for the warm water to get to the ice shelf base. We also find that gradients in the wind field over the shelf break control the thickness of the warm layer on longer time scales. This is a mechanism that previous studies have used to link changes in the wind field to changes in ice shelf flow velocities and melt rates, but these studies have lacked oceanic observations to support their hypothesis. Our observations close that gap and prove that the ocean does indeed react in the way that these studies imply
There is more science using these and the other mooring at the western Getz Ice Shelf moorings in the pipeline, so watch this space!
Yesterday the weather finally allowed the technicians from the Nowegian Polar Institute (NPI) to leave the research station Troll and fly out to go treasure hunting on the Fimbull ice shelf! Two years has gone by since they last visited the sites where NPI installed sub-ice shelf moorings more than ten years ago… and where we two years ago installed an “ApRES”. While the sub-ice shelf moorings measure the temperature and the currents in the water beneath the ice shelf, the APRES measures how fast the ice thins, and we can then calculate the basal melt rate. When combining the records we can hopefully learn a lot!
Like most Places in Antarctica, the snow that falls on the Fimbull iceshelf never melts away, so there was a few meters of snow to dig through in order to reach the instruments and to download the oh so precious data – a true treasure hunt!
Judging from the photos, the solar panel system that Helge Bryhni, a technician here at GFI, helped me design in order to power my APRES, appear to have survived two Antarctic winters… and we are now eagerly waiting for the report on how they’ve performed… and to have a look at the new data!
More stories from the successful treasure hunt at the Fimbul ice shelf will appear at @oceanseaicenpi soon!
The Santa Claus at the Norwegian Research Council distributes his gifts already during the first weeks of December… and this year one of them landed on our desk! Our Project iMelt (which is short for “Ocean-ice shelf Interaction and channelized Melting in Dronning Maud Land”) led by Laura de Steur at NPI got funded!
10 MNoK to service moorings and installations on the Fimbull ice shelf, to hire a PhD-student and posdocs to analyse all the data we are and will be collecting and to numerically model the system we are studying 🙂
This is the Project summary form the Application:
The recent increase in the Antarctic contribution to global sea-level rise is a major concern given that the majority of the world’s population lives along the coastlines. This increase, which is now thought to be irreversible in West Antarctica, is triggered by ocean-induced melting beneath the floating parts of the ice sheet known as ice shelves. Most basal melting occur near the ice-sheet grounding lines and the ice-shelf fronts, as well as within basal channels underneath the ice shelves. This project will quantify the processes and importance of ocean-ice shelf interactions and channelized basal melting in Dronning Maud Land, East Antarctica. The main focus will be on Fimbulisen ice shelf which has a complex network of basal channels in the central part of the ice shelf and a tongue that extends seaward of the continental shelf. Under-ice shelf data has been collected at Fimbulisen since 2010 and new, planned infrastructure along the coast of Dronning Maud Land will allow us to investigate ocean processes outside the ice shelf. Three autonomous radars are also deployed on Fimbulisen and Nivlisen ice shelves to monitor ice-shelf basal melting directly. The Project will quantify the relationship between far-field ocean dynamics, ocean-ice interactions and basal melt rates through these concurrent oceanographic and under-ice shelf measurements. This interdisciplinary research combines in-situ measurements, satellite remote sensing, and high-resolution modeling of ice-ocean interaction in Dronning Maud Land and will provide fundamental new knowledge on processes related to basal melting, essential for a better understanding of the stability of the Antarctic ice sheet.
… and this is the Fimbull ice shelf!
(by: Torunn Sandven Sagen, Petter Ekrem, Eirik Nordgård)
In 1893, during the Fram expedition, Fridtjof Nansen and his crew encountered a phenomenon where the velocity of the ship was reduced significantly, even though the engine was working at full speed. Nansen described this phenomenon as “dead water” (Brady, 2014). This dead water effect can happen when the ship creates an internal wave as it moves through water. The water must be stratified, meaning that the top layer is less dense than the bottom layer. At the same time, the draught of the ship must have the same depth as the top layer. The internal wave produces a drag, reducing the velocity of the ship. The speed of the wave is only dependent of densities and depth of the layers, not the velocity of the ship. (Grue, 2018).
We performed an experiment (as seen in the video) where we recreated the ocean conditions and created an internal wave. Then we explored how and when the internal wave could influence the velocity of the ship. To simulate the conditions Nansen experienced, a wooden boat was pulled with constant force across a tank filled with water. The water had two layers, one fresh layer on top (clear), and one saline underneath (purple). The depth of the saline layer must be much greater than the depth of the fresh layer.
The experiment was performed several times with the boat being pulled with constant, but different, force. We expect that if the speed of the boat is larger than the speed of the internal wave, the boat will not feel the wave because it moves faster than the internal wave. If the speed of the boat is smaller than the speed of the internal wave (as seen in the video), the wave will catch up with the boat, and the speed of the boat will be much reduced.