Melting ice cubes experiment — observing the finer details

If you don’t know my favourite experiment for practically all purposes yet (Introduction to experimenting? Check! Thermohaline circulation? Check! Lab safety? Check! Scientific process? Check! And the list goes on and on…), check it out here. (Seriously, of you don’t recognize the experiment from the picture below, you need to read up on it, it’s awesome! :-))

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Susann and I got funding from PerLe (our university’s project to support teaching innovation) to add a couple of cool new features to Susann’s “intro to meteorology” lecture, and doing a hands-on experiment with 50 students in a lecture theatre in their second lecture was only one of the first of many more to come.

We used the experiment to introduce the students to oceanic circulation, and this experiment is, in my experience, very engaging and sparks curiosity, as well as being very nicely suited as a reminder that things are not as easy as they seem to be when you see those nice plots of the great conveyor belt and all the other simplified plots that you typically see in intro-level lectures. Especially understanding that there are many different processes at play simultaneously, and that they have different orders of magnitude and might act in different directions helps counteract the oversimplified views of the climate system that might otherwise be formed.

I usually use dye to make it easier to observe what’s going on in the experiment (either by freezing it directly into the ice cubes as shown in the picture on top of this blog post, or by dripping it onto the melting ice cubes when students have started to observe that — counter to their intuition — the ice cube in the fresh water cup is melting faster than the one in the salt water cup).  We had dye at hand, but I decided on the spur of the moment to not use it, because the students were already focussing on other, more subtle, aspects that the dye would only distract from:

The shape of the ice cubes

In many of the student groups, the most prominent observation was that the shape of the melting ice cubes was very different in the fresh water and salt water case. In the fresh water case, the ice cube melted from the sides inwards: as a cylindrical shape with a radius that was decreasing over time, but in any instance more or less constant for all depths. In the salt water case, however, the ice cube melted upwards: The top did not melt very much at all, but the deeper down you looked the more was melting away. Why?

Condensation on the sides of the cup

Another observation that I prompted was in what regions the cups showed condensation. In the fresh water case, there was a little condensation going on everywhere below the water line, and sometimes there were vertical streaks down from where the ice cube was touching the wall. In the salt water case, there was only a small band of intense condensation close to the water level.

This, not surprisingly, looks very similar to what a thermal imaging camera sees when observing the experiment (as described in this post).

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Taken together, those two observations are quite powerful in explaining what is going on, and it seemed to be a fun challenge for the students to figure out why there was condensation on the outside of the cups in the first place (does condensation occur in warmer or colder places?), what it meant that different places ended up being warmer or colder, and how all of that is connected to global ocean circulation. Definitely an experiment I would recommend you do! :-)

Melting ice cubes & thermal imaging camera

I haven’t talked about my favourite experiment in a long time (before using it last week in the MeerKlima congress and suddenly talking about it all the time again), because I felt like I had said everything there is to say (see a pretty comprehensive review here) BUT! a while back my colleagues started playing with a thermal imaging camera and that gave me so many new ideas! :-)

I showed you this picture yesterday already:

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Here we see ice cubes melting in fresh water and salt water (and my very fancy experimental setup. But I am pretty proud of my thermal insulation!). Do you know which cup contains which?

Here are some more pics: The ice cubes before being dropped into the cups. Clearly dark purple is cold and yellow/white is warm (see my fingers?)

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After a while (5ish minutes), the cold meltwater has filled up the bottom of the freshwater cup while floating on top of the salt water cup:

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Looking in from the top, we see that the ice cube in salt water hasn’t melted yet, but that the other one is gone completely and all the cold water has sunk to the bottom of the beaker.

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When you check out the movie at the bottom of this post, you will notice that this experiment doesn’t work quite as well as I had hoped: In the saltwater cup, the ice cube floats against the wall of the cup and for quite some time it looks like there is a plume of cold water sinking in the salt water. I’m not quite sure what’s going on there. If it’s showing up like that because the cup is such a good thermal conductor, then why is the “plume” directional and not spreading in all directions? If there really is a plume, then how did it get there? It shouldn’t be! So many questions!

There really can’t be a plume of cold melt water in the salt water cup. For my workshop last week I made the plot below (which, btw, I don’t think anyone understood. Note to myself: Explain better or get rid of it!). So unless the plume is cold salt water, there is no way anything would sink in the salt water cup.

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So maybe we are cooling the salt water around the ice cube which then sinks and shows up because it is close to the wall of the cup? We can’t look “into” the cup with a thermal imaging camera, we can only see the surface of the cup (See, Joke? Maybe it is useful after all to learn all that stuff in theoretical oceanography ;-)). That’s also why we don’t see a plume of cold melt water in the freshwater case like we see when we have dyed ice cubes and see the melt water plume, like below:

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Anyway. Here is the video, in which you sometimes see my finger, pushing the ice cube away from the beaker’s wall to finally get to a state that looks like what I wanted to show you above:

My workshop at MeerKlima.de

Today I ran a workshop at the MeerKlima.de congress in Hamburg: A congress for high school students, organised by a student committee. The large lecture theatre of the chemistry department at the University of Hamburg was crowded for the opening lecture by Mojib Latif:

For my workshop, however, we set a limit of 40 participants due to the size of the room (and the amount of stuff that I had lugged in from Kiel. Yesterday’s ice cubes did very well, btw!). And there were two TV crews and a photographer documenting the awesome ice cube experiment.

You can watch documentaries of the workshop here and here (both in german).

Sneak peak of those two documentaries, obviously only of the tiny little sequences featuring me:


And thanks to Johanna and Dirk for their support before, during and after the workshop!

I also got to watch another workshop by a colleague, who used the Monash Simple Climate Model (which I have talked about here) and I have got to say: That is such an awesome tool for teaching about models and/or the climate system! You will definitely hear more about it in the future as I incorporate it into my own teaching.

And last not least we had a phone call to the Meteor off Peru which rounded off a day full of bumping into people I hadn’t seen in a while. Always great to reconnect with old friends and colleagues!

It was great fun to be part of this congress, and it was a great way to experience first hand how science outreach can work in such a format. Since the congress was curated by the students themselves, many students were very interested and asked great questions. Also, the topics of the workshops corresponded closely to what students really wanted to see and hear. It would be amazing to see this scaled up next year, maybe over several days and with more parallel sessions, so that participating students really get to pick and choose exactly what topic they are interested in and that even more students get the opportunity to experience such an amazing congress!

Workshop prep and a riddle

Looking at the picture below, can you guess which experiment I am going to do at the MeerKlima.de workshop? Yep, my favourite experiment — melting ice cubes! :-)

And I am obviously prepared for several extensions of the classic experiment should the students be so inclined…

Now I only need to get the ice cubes from Kiel to Hamburg — and as ice cubes, not a colourful, salty, wet mess :-)

Having gotten that backstory as a hint, any idea what’s going on with the spoons below?

Yep. Freshwater on the left, salt water on the right. Different refraction indices due to different densities. Neat :-)

Air-sea gas exchange inhibited by oil layer on water? Yes, but not always

I have been brainstorming hands-on experiment ideas for a project dealing with the influence of oil films on air-sea gas exchanges, and one idea that I really liked was this one: Use sparkling water, pour oil on top, observe how outgassing stops.

Now. I should probably have realised that this was a stupid idea before trying it, but in my defence: I have a really really busy week at work and I just wanted a quick and dirty experiment.

As you probably know, sparkling water bottles are under a lot of pressure. Especially when you have been carrying them home right before opening them. As you will see from all the drops on my backsplash shown in the movie below, mine exploded all over my kitchen when I opened it…

But even that wasn’t enough of a clue for me to realise that the process that drives CO2 out of sparkling water probably isn’t just a gradient in concentrations between the water and the atmosphere, but that the CO2 can only be kept in solution under high pressures. So yeah, my oil film doesn’t inhibit gas exchange at all, my sparkling water with oil on top is outgassing just as happily as the one without. I suspect the oil film will only have an impact once outgassing doesn’t happen via bubbles any more, and hence isn’t visible any more. Fail!

But the movie is pretty, anyway.

I guess we would actually have to measure gasses in the atmosphere and water in order to run such an experiment… Which makes it a lot less appealing. I would really have liked to be able to stop sparkling water from sparkling just by pouring oil on top. Bummer! :-)

Using real time data of ship positions in teaching?

This morning I was looking for the current position of a research vessel on MarineTraffic.com and noticed something that should maybe not have been surprising, but that I had never really thought about: How all the fishing vessels (orange) are sitting right on the shelf break! I guess that’s where they should be when we think about currents and nutrients and primary production and fish, but how cool is it to actually see it?

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And see that area west of Lofoten where there are a lot of fishing boats in a circle? An unnamed inside source told me that that’s where cod is spawning right now, so everybody is going there to fish. Tomorrow, the cluster might be in a completely different place. And even now, some 10 hours later, it seems to have migrated a little northward? Will definitely check again tomorrow!

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I obviously had to look whether fishing on the shelf break was just a thing in Northern Norway and turns out that it’s the same on the Greenland Shelf.

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Now that I got into playing, I found it also really interesting to see that there is a lot of fishing in the equatorial Pacific going on. And how clearly you can see major traffic routes even in just the distribution of ships.

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And then, ShipTracker even offers a density map of ship traffic:

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Which I had to screen-shoot in two parts because of reasons:

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This site would be such a great tool for all kinds of teaching purposes. Realtime data on shipping is just a click away, even with the free version! There are so many things that students could do estimates on using this site, on transport, fishing, pollution, just pick your topic! And using authentic data makes the whole thing a lot more interesting than looking at maps or numbers a teacher would provide. Pity I’m not teaching right now!

Fictitious forces (2/5): Experiencing frames of reference on a playground

How can you be moving in one frame of reference, yet not moving in another?

We talked about the difficulty of different frames of reference recently, so today I want to show you a quick movie on how the seemingly paradox situation of moving in one frame of reference, yet not moving in another, can be experienced on a playground.

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My dad on a playground rotator. Moving relative to the rotating disk, yet staying in the same spot relative to the playground.

This is maybe not what you would do with a bunch of university students, but on the other hand – why not?

Fictitious forces (1/5): Record players and Coriolis deflection

An experiment showing how seemingly straight trajectories can be transformed into curly ones.

One of the phenomena that are really not intuitive to understand are fictitious forces. Especially relevant in oceanography: The Coriolis force. The most difficult step in understanding the Coriolis force is accepting that whether or not a trajectory appears straight or curved can depend on the frame of reference it is observed from.

Or to say it with John Knauss in his Introduction to Physical Oceanography: “Even for those with considerable sophistication in physical concepts, one’s first introduction to the consequences of the Coriolis force often produces something analogous to intellectual trauma”.

One way to show that the apparent change of shape is really due to different frames of reference, is to take a trajectory that is objectively AND subjectively straight and watch it being transformed into something curly.

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Trajectories for different voltages driving the record player.

We did this at JuniorAkademie by taping a piece of paper on a record player, putting it into motion and then, at as constant a speed as possible, drawing along a ruler’s edge straight across. (if you don’t have a record player or rotating table at your disposal, you could also use a Lazy Susan and turn it as uniformly as possible).

Of course, this approach has a lot of potential pitfalls. For example, if you change the speed while you draw, you get kinks in your curls (as the child drawing in the video below points out when it happens). Also, by drawing on a flat paper rather than a spherical Earth, this isn’t completely equivalent to the Coriolis force.

And, more importantly, I think this experiment is only helpful for an audience that doesn’t “know” about fictitious forces yet. A problem we have experienced with oceanography students is that they “know” that moving objects should be deflected, and that they “see” a deflection even when there is none (for example when they are watching, from a non-rotating frame of reference, an object move across a rotating table). In that case, sliding the pen along the ruler might be perceived as forcing an otherwise curly trajectory to become a straight line, hence cheating by preventing a deflection that should occur.