Corona is turning our lives up side down – but that’s no reason not to stand up and sing “Happy Birthday” to Prof. Emiritus Arne Foldvik who turns 90 years old today! (Those of you who read Norwegian can read about him here)
Arne started out his scientific carrier as a meteorologist, studying among other things the waves that are generated when wind blows over topography (he did that using the long tank down in the basement of GFI where I’ve taken my students to play with Nansen’s dead water) – but he later turned to oceanography. Around the time when I was born he led his first Norwegian oceanographic expedition to Antarctica and the southern Weddell Sea. During that expedition he found what the Americans had failed to find a few years later: The Filchner overflow, an enormous* under water river that carries cold and dense water from the Filchner-Ronne ice shelf cavity to the bottom of the Weddell Sea. This discovery is one of the reasons I’m working with polar oceanography today, as I spent the three years of my PhD revisiting the exciting data that Arne & co had collected in the outflow.
The last time Arne came by my office, we chatted about towed icebergs, melting ice and the experiment I did in my “Nansen’s memorial lecture” (which Arne attended). Arne has been involved in projects where the aim has been to tow icebergs from Antarctica to dry areas in demand of freshwater (originally the middle east, and just a few years ago, to South Africa ). Arne told me, that if one did that, one would get ice into water warm enough, that the results of my experiments would no longer hold.
The density of seawater is a non-linear function of temperature and salinity, and while salinity dictates the density for cold water (causing the lines of constant density to be almost vertical in the TS-diagram below), temperature is more important for warm water (causing the lines of constant density to tilt more). So, that means that while the (fresher and colder) melt water mixture is lighter than the ambient water if it is cold, it will actually be denser if the ambient water is warm enough! Off course we had to try this out – I never got around to doing so, but yesterday, Mirjam finally did!
Somewhat disappointing – we realized that the result is more or less the same, independent of the water temperature. Does that mean the physics (and Arne) are wrong??? Probably not, it probably just means that the molecular diffusion of heat is acting fast enough that the “cold” melt water mixture doesn’t stay cold enough to sink 🙁
Anyway, here’s a stratified toast to Arne Foldvik! HAPPY BIRTHDAY!
* 1.6 million cubic meters per second – that is almost ten times the Amazon river
A while ago I was asked by the university (#realfaguib) if I wanted to present myself and my work in a short movie that they want to show to future students – and a few days later I found my office occupied by cameras of different sizes and three very nice journalists/moviemakers/photographers that came along. I quickly realized that making a short movie – I think they only want a minute or two – takes a loong time! Repeat, repeat, repeat – look into the camera, walk faster, walk slower, one more time, slower, shorter, clearer, louder, start over, look that way, look here, smile, don’t smile… at the end of the day, I was quite happy that I’m not a Hollywood movie star but an oceanographer in Bergen
So what did we find out – well, to make a long story short – we oceanographers talk about two types of currents. They are both driven by pressure gradients – but for what we call barotropic currents, the pressure gradient is caused by differences in sea level (i.e. in how much water there is) while for baroclinic currents, the pressure gradient is caused by differences in density (i.e. how heavy the water is). The barotropic current is depth independent – this means that the current is equally strong from the surface down to the bottom, while the baroclinic current changes in strength (and potentially in direction) with depth. Our observations showed that the currents bringing heat towards the Getz ice shelf had both a barotropic and a baroclininc (bottom intensified) part. The barotropic part was the stronger one and the one carrying the majority of the heat. But when the current reached the ice shelf front (Anna was brave enough to deploy a mooring only 700m from the ice shelf front) – the strong barotropic current had to turn, and only the weaker baroclinic current was able to enter the ice shelf cavity. The experiments at the rotating table showed the same thing – barotropic currents turned at the front, while baroclinic currents could enter.
You can read more about what we did in the Coriolis lab here, and about when Karen recovered the moorings here
Congratulations to @MarkusMelin4 and @cisprague who has recovered four out of four moorings in the Amundsen Sea! Despite fishing vessel rescue-operations, iceberg-on-top-of-mooring-problems and strong winds the four moorings and all of the instrumentation are now safely on deck! One of the top boys had suffered from an iceberg encounter and the connector plug on my ADCP (A large instrument that measures the current velocity in the water column using acoustics and Doppler theory) had been leaking…. but that’s just little scratches when you consider that they’ve spent two years in the water!
I look forward to see what the records has to tell us about the currents and the hydrography around the Getz ice shelf. Stay tuned!
CTD – which is short for Conductivity-Temperature-Depth – is indeed a much appreciated instrument by every (sea-going) oceanographer. You send it down to the bottom of the ocean, and back comes nice profiles of temperature, conductivity (from which one can calculate salinty) – and whatever other sensor you’ve attached (oxygen, chlorophyll, and turbidity for example)
Most of the time the CTD is mounted on a rosette, which carries bottles so that one can also collect water samples from selected depths. But make sure to have the bottles open when you send them down – otherwise they will implode, and that is not a good thing, believe me!
Araon is steaming south for a new expedition to the Amundsen Sea and it’s now out of range on marinetraffic.com (unless you pay) … but @cisprague (Christopher Iliffe Sprague – one of two Swedish students on board who will hopefully recover the moorings Karen & co deployed two years ago) is still on Twitter so internet connections onboard must have improved since I was onboard in 2016… the icebergs look the same, though!
Have a happy cruise – and good luck with recoveries & science!
… and happen to be in Bergen 12 or 13 December, 2019? Then you shouldn’t miss out on the concert in Grieg Hallen where the Bergen philharmonic orchestra and researchers from University of Bergen joins up on the stage to take us on a cultural&scientific journey to the the depths of the oceans! You can read more about the concert series here (in Norwegian only).
On Friday I’ll be in the entrance during the pause together with a couple of “Nansen water catchers” and Snotra, one of UiB’s amazing gliders – see you there!
Nadine just made me aware of this book on the Antarctic treaty – written (by J. H. Berkman & A. Pope) for children and illustrated by children from all over the world! It is available in different languages: Swedish, Norwegian, English, French, Spanish, Arabic, Japanese … and many more! Isn’t that the perfect way to celebrate Antarctica day?
You can download the pdf (or order a paper copy) here