Of cupcakes and ice cores

For a popular science presentation on climate change, I needed a simple illustration for how ice cores can be used as archives of past climates. Luckily, my sister and family were excited to do some early Christmas baking for climate science!

And playing with food colors is always fun…

I think I had too much fun playing, actually, the “ice core data” would have been a lot easier to interpret if the different layers were just laying flat!

I should probably noticed here already that the color pattern wasn’t as regular as it should have been for easy interpretation of the core data later…

But it was fun! And they rose beautifully even though we were a little afraid that the time between mixing in the baking powder and actually baking the muffins was kinda long (because we had to mix in all the different dyes…)

The really difficult part, it turns out, was the coring itself. I had wider-than-usual straws, but instead of just cutting out the core, it was really difficult to have them pierce through the crust, and they compressed the core much more than I had hoped.

You can kind of see where the core goes in the cross section, and how the different colors correspond to their old locations inside the cupcake. But somehow this worked much better in my imagination than it did for real!

And I have a new-found appreciation for food bloggers. It’s really difficult to take good pictures of food!

But in case you were wondering: They taste just like boring, non-rainbow muffins. And my niece liked them! :-)

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:


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?)


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:


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.


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.


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:


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 :-)

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.

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.

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.

Evaporating sea water

How much salt is there in sea water? What concentration do you need before crystals start forming? What will those crystals look like? I am sure those are the kind of questions that keep you awake at night!

Of course this can easily assessed experimentally. On a visit to the University of Bergen’s Centre for Science Education just now, I was shown the result of such an experiment: A litre of water was mixed with 35 grams of salt to simulate sea water with its typical salinity. Below, you see what the beaker looked like after sitting out for three months.

You can see that salt crystals are forming at the walls of the beaker, but that their structure depends on depth below the initial water level (see the 1000 ml mark on the beaker).

When there is still a lot of water in the beaker, crystals look like ornate flowers. Then, the less water is left in the beaker, the more square the crystals become. And at the bottom of the beaker, you see the typical salt crystals you would expect.


Actually, even though they look like the kind of salt crystals I would expect, apparently someone who knows about crystallography commented that there must be other stuff in there than just cooking salt since the crystals don’t look the way they should. I need to read up on this! :-)

Anyway, this is an experiment that I want to do myself, so maybe in three months time there will be more pictures of this!

Thanks for a very nice lunch, Olaug, Frede, Andreas, Morven and Elin! Looking forward to working with you a lot more in the future! :-)

P.S.: with this blog post I am testing to blog pretty much “real time” from my mobile phone, so if you notice anything odd, please let me know!

Taking the hydrostatic paradox to the next (water) level

How well do people understand hydrostatics? I am preparing a workshop for tomorrow night and I am getting very bored by the questions that I have been using to introduce clickers for quite a lot of workshops now. So I decided to use the hydrostatic paradox this time around.

The first question is the standard one: If you have a U-tube and water level is given on one side, then what is the water level like on the other side? We all know the typical student answer (that typically 25% of the students are convinced of!): On the wider side the water level has to be lower since a larger volume of water is heavier than the smaller volume on the other side.

Clearly, this is not the case:


However, what happens if you use that fat separator jug the way it was intended to be used and fill it with two layers of different density (which is really what it is intended for: to separate fat from gravy! Your classical 2-layer system)?

Turns out that now the two water levels in the main body of the jug and in the spout are not the same any more: Since we filled the dense water in through the spout, the spout is filled with dense water, as is the bottom part of the jug. Only the upper part of the jug now contains fresh water.


The difference in height is only maybe a millimetre, but it is there, and it is clearly visible:

Water level 1 (red line) is the “main” water level, water level 2 (green line) is the water level in the spout and clearly different from 1, and water level 3 is the density interface.

We’ll see how well they’ll do tomorrow when I only give them levels 1 and 3, and ask them to put level 2 in. Obviously we are taking the hydrostatic paradox to the next (water) level here! :-)