Deep water renewal – finally!

It’s been almost ten years since the water in the deepest basin on Masfjorden was last renewed – but now it has finally happened! My colleague Lars Asplin from the Institute of Marine Research in Bergen do regular hydrographic surveys* of the fjords in western Norway– and the last profiles from Masfjorden show increased levels of temperature and oxygen at depth. Between April and August, the oxygen concentrations in the basin have increased from 2 ml/L to 4 ml/L, making life much, much easier for whoever lives down there!

The concentration of dissolved oxygen in Masfjorden in April (upper panel) and August (lower panel).The concentration in the MAsfjorden basin has increased from about 2 mL/L (dark blue) to about 4 mL/L (cyan). Figure courtesy: Lars Asplin, HI.

The oxygen concentrations at depth can only increase if new water enters the basin -i.e during a deepwater renewal. A deepwater renewal can take place if sufficiently dense water is lifted up to sill level outside the sill, for example, when northerly winds move the surface water off-shore** and denser water from below is pumped upward. The coastal records from Sognesjøen, suggest that water dense enough was present at sill level during the last part of April – so the deepwater renewal probably occurred around then.

The news about the renewal was waiting for me in the inbox when returning from holiday – along with an e-mail telling me that the UIB-biologists are heading to Masfjorden this week on a research cruise…. after a bit of frantic e-mail writing back and forth we managed to organize that they take a few extra samples of the new deep water for us!

We’ve got moorings on the Masfjorden sill and in the basin that are to be recovered by fjord oceanography students in February – they will tell us more about when and how the renewal happened!! The students will for sure have a lot of exciting data to write about in their report!

* i.e. they measure profiles of temperature, salinity, and oxygen with a CTD.

** due to the rotation of the Earth, the winds cause a transport of surface water to the right of the wind direction (in the northern hemisphere)

To Python or not to Python…

… is not a question anymore. All our students learn Python, starting the day they enter the university (and even before), and when teaching you are expected to integrate Python and programming whenever possible.

Of course, it makes sense for the university to promote the use of a free, open-source software rather than a commercial product like Matlab, but for all of us old (and not so old) lecturers at the university who – like me – have done your data analysis and plotting since the beginning of time in Matlab, it is not an easy switch.

I took a Python course more than a year ago, and I’ve done a bit of Python here and there, but for a long time now, it has been one of those uncomfortable “have-to-do” but “not-right-now” things that keep accumulating at the horizon. Until a month ago, when a twitter-thread by a colleague (Thanks, Angelica!) who had decided to take the step (and who enjoyed it!) finally got me to dive headfirst into the Python world… so, I read a Python – book (Python for Data analysis by W. McKinney) and set my mental default “program-to- open-when-time-for-science” to Python (or Jupyter, Python is a programming language, not a program). I did not go as far as to uninstall Matlab, but I’m only using it for emergencies…

I quickly realized that I’m Google-dependent – whenever I don’t know how to do something – Google is there to help, directing me to Stackoverflow or one of the thousands of Python tutorials that are available online. It seems like (almost) every question has been asked before – and that there is an army of Python-enthusiasts out there ready to answer and help*!

Now, Matlab and Python have much in common – it is not like I’m starting to learn programming from scratch. Maybe more like learning to speak Norwegian (rather than Chinese) when your mother tongue is Swedish? You understand what the Norwegians are saying (i.e. you can read and  – at least roughly – understand code that others have written), but to write your own Norwegian text and to speak… hmmmm, not so easy! You quickly get used to all the small differences – like that you have to start counting on zero and not on one, and that you have to use # and not % to comment out lines – but get accustomed to all the different types of variables in Python, to build up a vocabulary of commands and to  “think” in a python way, rather than “translating” your Matlab – way of doing things will take longer time.

I’ve lived more than a decade in Norway – but my children still laugh if I open my mouth and try to speak Norwegian… hopefully, it won’t take that long to be fluent in Python!

“Hytte” office!

The Norwegian word “hytte” means cabin, and as a foreigner in Norway, you easily get the impression that *everyone* has (or has access to) a “hytte” (if not two or three). That is of course not true, but to “blend” in (end to enjoy lazy weekends away from home) my husband and I bought a “hytte” on an island not far from Bergen a few years ago.

With the kids away on scout camp this week, we took the opportunity to turn the hytte into “Hytte office”. With laptops, food, and an upgraded data deal with our mobile operator in the trunk we headed out to Øygarden earlier this week – and it’s amazing!

I do appreciate the changes in communication that the pandemic has forced upon us – from my “hytte office” I’ve participated in a Ph.D. defense in Paris (Congratulations, Ph.D. Lucie!), discussed figures and results from the Fimbul ice shelf with colleagues in Tromsø and checked in on what our seals in the Weddell Sea are up to… all while enjoying this wonderful view!

… it’s also a real treat to just step outside and munch a few blueberries (yes they are blue already!) while your Python script is munching away on the commands!

Have a nice summer!

 

When the winds are strong north of Siple islands during winter…

… the flow of warm water into the Getz ice shelf cavity is reduced! Wonder why? Well, Ph.D. Nadine Steiger (who successfully defended her thesis yesterday! Yippie and congratulations, Dr. Nadine!) nicely explains it in a newly published paper:

Intermittent reduction in ocean heat transport into the Getz Ice Shelf cavity during strong wind events (GRL)

Here’s a short version:

1) Eastward wind will (in the southern hemisphere) cause the surface water to move southward. (Oceanographers call this the “Ekman transport”). Water will hence pile up along the coast, along the green lines in the figure below.

Map showing winds (red arrows), Ekman transport (black arrows) and areas with coastal downwelling (green). Courtesy: N. Steiger

2) When surface water piles up along the coast, it will press down the warmer water below (Oceanographers call this “coastal downwelling”)

Ekman transport towards the coast will press the warm water deeper down. Courtesy: N. Steiger

3) The disturbance (i.e. the signal with depressed warm water) will travel along the coast (Oceanographers would call this a coastally trapped, internal wave. The wave is “internal” because the signal is traveling on the interface between two water masses, not on the ocean surface) and reaches the western Getz ice front 3 days after the storm! The figure below shows the observed temperature& salinity in the vicinity of the ice front, and below you see the wind and sea ice concentration. Each time the temperature at depth drops (marked by green triangles) there has been a storm just before!

4) When the wave arrives at the ice front, two things happen. Firstly the thickness of the warm water layer is greatly reduced (see above) and, secondly, the current changes direction so that the flow at depth is aligned with the ice front rather than to enter the ice shelf cavity like it normally does.

Observed mean currents (and temperature) during a) the cold events and b) the deployment period. Courtesy: N. Steiger

During the winter of 2016, this happened at least eight times – causing a reduction of the heat transport into the cavity by about 25%!

Well done, Dr. Steiger!!!

PhD. Nadine Steiger and a proud, ex. supervisor. Photo Andreas H. Opsvik

 

 

 

 

Good news from NFR!

What a morning! Scrolling through the newly published list of funded projects from the Norwegian Research Council while sipping your breakfast tea and finding this:

is even better than learning that Sweden qualified for the quarter-finals yesterday!

… and further down on the list I found this:

where I’m also involved!

I’m super excited to lead/join these interdisciplinary projects on Norwegian/Greenlandic fjords and climate change!

Masfjorden, here we come! The Bjerknes Center will fund our multi-disciplinary fjord project!

Yesterday the Bjerknes administration announced which of the “internal projects” they are to fund during the next four years – and I was very excited and happy to learn that our multi-disciplinary fjord project (led by Mari Myksvoll) was one of them!

Together with paleo-oceanographers and biologists, we will dive deep into the basins (and the mud/sediments) of Masfjorden to study how (and why) oxygen concentrations have varied in the “recent past” (the last 400yrs or so) and how that affects the ecosystem in the fjord.

I’m really looking forward to working locally – not only “locally” as in a nearby fjord, but also “locally” as in “together with colleagues in neighboring offices and buildings”! It’s is such a great team!

Proposal-funding-celebration outside GFI earlier today with parts of the new “Fjord-team”!

 

 

Do you miss Ninja?

Well – don’t worry! Dr. Ruth Mottram, a Climate scientist at the Danish Meteorological Institute is on her way to the Greenland Ice sheet and she is bringing “Ice Man” and “Bat Girl” (likely friends of our Ninja) along! Read her cool story here! (The story “Ninja goes South” is still on Flickr.com!)

Ice Man desperately needs to get to the Arctic – read the story by Ruth Mottram here! Photo: R. Mottram.

 

A76 – the largest iceberg in the world (at the moment)

My lunch out in the sun ended abruptly when my husband (also in home office) casually asked if I’d heard about the new iceberg in the Weddell Sea. If my husband – an economist – has heard about an iceberg it’s likely to be big… so I shuffled the rest of my pancake into my mouth and ran in to read!

And yes, a quick google revealed that a huge chunk (4320 km2, to be precise) of the Ronne ice-shelf has broken off! A76, as it is called, is now the largest iceberg floating around Antarctica – but (according to NewScientist) it would not make it onto the top ten of historical giant icebergs.

Will A76 end its days here, in the iceberg graveyard off South Orkney Islands?

It will be exciting to see where it drifts off to – and how it will influence the circulation on the continental shelf in the southern Weddell Sea. One of its old relatives, A23, that broke off from the neighboring Filchner ice-shelf in 1986, is still (!) stranded on the continental shelf, affecting e.g. the sea-ice distribution in the region.

 

The southern Weddell Sea with the location of A76 (not to scale) and the old A23. Modified from Ryan et al, 2017.

Into the “grand canyon”

You might have heard on the news a few weeks ago that a large iceberg
broke off from the Brunt Ice Shelf, in the Weddell Sea. If you follow
the “Antarctic” news – and have a good memory – you might also remember
that a few years ago (2016), the UK research station Halley, that used
to be situated on what is now an iceberg, had to evacuate scientists and
personnel and  move the relatively newly built station as the crack
suddenly started propagating faster than anyone expected. Halley is the
only research station that I know about which is built on skis, so it
was “simply” pulled to a new, safe location on the other side of the
crack!

Ninja and I watching the position of the iceberg as the ship (colored line) heads into “Grand Canyon”.

Anyway – the iceberg, which got the official name A74, finally broke
off, and it has now drifted a couple of nautical miles away from the
remaining iceshelf, leaving a “canyon” between the shelf and the iceberg
that is wide enough for Polarstern to enter. The scientists studying the
ocean floor – benthic ecosystems and sediments – where very eager to get
there to sample what was until recently a sub-iceshelf (and thus very
difficult to access) system.

Ice berg or ice shelf?

We were all excited about circumnavigating A74, and to enter what we
quickly named the “Grand Canyon” – and most of us have followed the
motion of the iceberg on the satellite pictures that we receive every so
often. Is the “canyon” widening or shrinking? Are there smaller icebergs
blocking the passage? Can we get through? The sun, which we haven’t seen
much of during this expedition, obviously were just as excited as we
were, because it decided to join us for most of the day in the canyon
offering a spectacular view of the glittering bluish ice walls around
us!

We got to do three stations in the “canyon” – with intensive sampling of
both the water column and the bottom sediments. The AWI OFOBS team sent
down their camera system, and we could watch the ocean floor beneath us
live on their screens. To me, a non-biologist who are just about able to
distinguish a fish from a sponge it looked mostly like the open ocean
stations we’ve occupied earlier, but to the experts, things were
apparently different. Hopefully they get to repeat the station in the
years to come, to study how the community evolves now that it no-longer
has an ice shelf roof over its heads.

The OFOBS screens showing live video from the ocean floor beneath us were drawing a larger than usual audience

The CTD-profiles we made in the “canyon” all looked more or less the
same – a straight line from surface to bottom (i.e. close to constant
salinity and temperature). Supercooled Ice shelf water (a lighter
version than what we find in the Filchner Trough) was flowing out of the
Brunt ice shelf cavity, and the formation of buoyant  ice crystals at
depth  were clearly visible in the images from the OFOBS team! The ice
crystals had also clearly aggregated on the “geo-bio-chemical-lander*”
line, which were deployed for about 8 hours at one of the stations. When
the lander was recovered, there was a 1 cm thick layer of ice on the
line!

*a big thing full of instruments (for bio-geo-chemical process studies)
that looks like something that would land on the moon.