You’ve heard us talk a lot about rotating swimming pools. Nadine has written about why we care about Antarctic ice shelf melting (link), why the ice shelf is melting (link) and how we are going to investigate it (link). Today, I am going to bring those explanations together with all that you’ve seen so far about our experiments in Grenoble. I hope! :-)
Let’s start with a technical drawing of our “Antarctica”, the topography we have in the middle of the tank. You have seen it in many of our previous posts: It’s the thing that used to be in clear plastic, but that one early morning got painted black.
Sketch of our topography and what currents we expect to see in our experiment
What we are going to investigate is how a current, introduced at the “source”, will behave. We expect that it will flow along the shelf break and that some of it will flow around the corner into the canyon, while some of it will continue on straight ahead. How large a portion of the current takes which part depends on several parameters, which we will systematically change over the next couple of weeks: How large the source’s flow rate is (we are starting with 50 liter per minute), whether there is a density difference between the source water and the ambient water (we are starting with no density difference) and what happens if we add a sharp corner to the nice and smooth corner of Antarctica and the shelf.
So far, so good. When we look down from the rotating first-floor office, things look a little different (an annotated version further down this page):
Woah! It is happening! Laser sheets and currents are on!
You see (parts of) the topography in the lower right corner of the image. And then you see a lot of green light: Our laser sheets! The laser sheets will illuminate thin layers of water, which we can take pictures of with cameras mounted perpendicularly to the sheets. That in itself isn’t so exciting, but we will have neutrally buoyant particles in the water, which light up when lit with the laser. If we take enough pictures of the particles, we can track individual particles as they get advected by the currents, and thus get a good idea of the flow field that is illuminated by the lasers.
Details of the experimental setup: Position of laser sheets, source, topography
And the cool thing is that we have not only one, but six vertical laser sheets, that are used sequentially. Below you see our first experiment and each picture in the animated gif is showing you a different layer, so you get an idea of the vertical shape of the flow field.
And these are the first current fields we are observing!
Isn’t this amazing? How lucky are we that we got the opportunity to travel to Grenoble to see all this? :-)
