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! :-))

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).

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! :-)

Teacher training at Lotseninsel

As I mentioned yesterday, I recently contributed to a teacher training on Lotseninsel, a tiny island on the Baltic Sea coast. The training was run by the Ozean:Labor of the Kieler Forschungswerkstatt, and we spent Friday to Sunday there. I’m going to show you some impressions of that weekend here.

At first, it did not look promising:

We had to pack A LOT of equipment on a small boat in pouring rain to bring everything over to the island.

After unpacking all that stuff, we went to test some instrumentation in the pouring rain. This is our cute ROV:

In the evening, when all the teachers had arrived, we started with the workshops and continued until late in the night. Below you see two groups of teachers working on 3×3 m stretches of the beach, collecting plastic to map the pollution of the beach.

The next day, the group was split up in two parallel groups. One doing stuff like this:

The other group, in which I was involved, doing stuff like this:

Obviously we had to do the melting ice cube experiment in a workshop on ocean physics!

But Johanna and Dennis did tons of other cool stuff, too, like for example this demonstration of salt inflow events into the Baltic Sea:

And again, the second time that same workshop was run in the afternoon for the second group of teachers. Amazing how quickly the weather changed!

But of course our group also did some field work: Water sampling and then analysing nutrients, salinity, oxygen concentration…

The next day, I got to see my first fish dissection. I know why I studied physics…

I am not showing you the gory pics here because that’s not what we do on this blog ;-)

Also really cool: Those are baleens, those filters that whales use! Never touched them before.

But we also got some time to enjoy the weather and play with our equipment: Those are Jeannine, Dennis and Johanna, who I had the pleasure to work with. It was great fun!

Even though the amazing weather only lasted for a short while, this is them arriving back on the main land with the last of three tours to shuttle everything back…

But I had a great weekend! And if you haven’t yet, go back and look at the lighthouse on Lotseninsel. I could spend years there, taking pictures from different angles and in different weathers… So pretty :-)

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 :-)

Considered exemplary: My “ice cubes melting in fresh water and salt water” in the “on the cutting edge” teaching collection! :-)

After reading recently that I am being considered the queen of the melting ice cube (aaaaw, thank you!!!), having my movies of the experiment featured in Elin Darelius and Petra Langebroek’s article on “fun in the kitchen”, and hearing that the activity I posted on the “On The Cutting Edge”‘s website using the very same experiment has been awarded “exemplary” status (so excited!), I simply had to talk about this experiment again. Even though just two days ago I talked about using it as a tool to let future instructors experience inquiry-based learning. One really cannot talk about this experiment enough!

Go check it out on On The Cutting Edge’s website, check out my own summary page with all the best tips and tricks, watch the movie below or look at all the posts tagged with “melting ice cubes experiment“. And then go and DO THE EXPERIMENT!

Using the “melting ice cube” experiment to let future instructors experience inquiry-based learning.

Using the “melting ice cube” experiment to let future instructors experience inquiry-based learning.

I recently (well, last year, but you know…) got the chance to fill in for a colleague and teach part of a workshop that prepares teaching staff for using inquiry-based learning in their own teaching. My part was to bring in an experiment and have the future instructors experience inquiry-based learning first hand.

So obviously I brought the ice cubes melting in fresh water and salt water experiment! (Check out that post to read my write-up of many different ways this experiment can be used, and what people can learn doing it). On that occasion the most interesting thing for me was that when we talked about why one could use this — or a similar — experiment in teaching, people mainly focussed on the group aspect of doing this experiment: How people had to work together in a team, agree to use the same language and notation (writing “density of water at temperature zero degree Celsius” in some short syntax is not easy when you are not an oceanographer!).

And this experiment never fails to deliver:

• you can be 100% sure that at least in one group, someone will say “oh wait, which was the salt water again?” which hands you on a plate the opportunity to say “see — this is a great experiment to use when talking about why we need to write good documentation already while we are doing the experiment!”
• you can also be 100% sure that in that group, someone will taste the water to make sure they know which cup contains the salt water. Which lets you say your “see — perfect experiment to talk about lab safety stuff! Never ever put things in your mouth in a lab!”
• you can also be sure, that people come up with new experiments they want to try. At EMSEA14, people asked what would happen if the ice cubes were at the bottom of the beaker. Today, people asked what the dye would do if there was no ice in the cups, just salt water and fresh water. Perfect opportunity to say “try! Then you’ll know! And btw — isn’t this experiment perfect to inspire the spirit of research (or however you would say that in English – “Forschergeist” is what I mean!). This is what you see in the pictures in this blog post.

So yeah. Still one of my favorite experiments, and I LOVE watching people discover the fascination of a little water, ice, salt and food dye :-)

Btw, when I gave a workshop on active learning last week and mentioned this experiment, people got really really hooked, too, so I’ll leave you with a drawing that I liked:

Oceanography PBL workshop and case

My awesome colleague Marisa ran another workshop on Problem-Based Learning (PBL) in which I was lucky enough to assist. For the last workshop for people who are planning to use PBL in their teaching, we used the solar eclipse to build a case around. Since this time we weren’t as lucky to have a solar eclipse happening on our second workshop day again, we were in need of a new case. We wanted something that was interesting and challenging enough to our audience of engineers to realize that PBL is a method that can definitely be used for hard science and engineering stuff, too, and that was obscure enough that none of the participants would know all the answers right away, but that on the other hand was solvable with only about an hour of individual research in step 6 between the first and second workshop day. So we were pretty much looking for a magic unicorn.

Enter the oceanography case!

Paul: People always say that Arctic melting is a positive feedback loop. But I don’t think that’s true, that’s all part of the big climate conspiracy! When the ice melts, this decreases the salinity of the sea ice. If there is less salt in the water, though, the ice melts less fast. This means that the process stabilizes itself!

Marie: Come on, Paul, don’t believe everything people tell you! As a scientist you should really be less gullible. The melting of the Arctic is influenced by so many other processes, for example the different albedos of ice and open water. That must be at least as important as the salinity!

Now Paul starts looking for scientific proof for his theory. Marie starts researching as well, she tries to find something Paul can observe himself so her argument doesn’t rely on papers Paul might not trust.

Even more so than in the previous PBL workshop, it was absolutely fascinating how the discussion evolved. Also, this time people were talking about my favorite topic and it was super interesting to see what a crowd of PhD students and PostDocs in engineering knew – and didn’t know – about the climate system.

Steps 1-4 went uneventfully, as described in this post. In step 5, we ended up with four questions that the participants wanted to do research on during step 6, namely

• How does the albedo influence melting of Arctic sea ice?
• How is the salinity of Arctic sea water influenced by the melting of Arctic sea ice?
• How does the salinity of the water surrounding the ice influence the ice’s melting?
• How does atmospheric CO2 influence Arctic melting?

Faithful readers of my blog will have recognized from the case already where the whole PBL session was heading: I wanted them to do my favorite experiment! Just by doing the experiment they could have shown Paul that more salt in sea water doesn’t mean that ice floating in it will melt faster. Luckily they were all good sports and came up with more research questions than just that one, but after discussing their answers to their research questions, we obviously had to do the experiment.

As always, participants did the experiment in groups of 2 or 3. My ice cubes had suffered quite a bit during the day, so the experiment was quite quick. Usually I bring ice cubes in a huge thermos, but this time a) that thermos was at work and my ice cubes were at home on the day of, and b) I only needed so few ice cubes that I thought a thermo mug would do fine. Yeah. Suffice to say, next time I’ll use the thermos again.

In the previous PBL session on this case, there had been quite a long discussion about temperature gradients and stirring, so obviously we had to conclude the experimental part by stirring.

So that was that. How did PBL work for an oceanography case? I really loved it. The first session was really exhausting (as all first PBL sessions are, at least in my limited experience). There were a lot of discussions that went fairly deep into the topic of climate change, and also a broad range of topics related to the melting Arctic was covered. I was actually pretty surprised how far people went into formulating models and how much they knew about different aspects, yet how difficult it was to put everything together. When writing the case, I had expected a lot less of an in-depth discussion of the issue, especially since none of the participants had an explicit ocean/climate background. So really positive surprise here how well it went!

The second session, where everybody brought their results together was great fun, and not only for me (or at least that’s what I think). The goal of our workshop was to have instructors, who will likely use PBL in their own teaching soon, experience the method in a student’s role. Therefore we couldn’t solve all the burning questions of ocean and climate during that second session and had to focus on reflection and the how-tos of the PBL method. But I would definitely use this (or a slightly modified) case in oceanography teaching! And I would also use this case for the same purpose again, although then I would probably make it a little bit more confined in order to leave more time for the meta-aspects of the workshop.

Thanks, Marisa, for another great workshop, I always learn SO MUCH from watching you lead discussions! :-)

Ice cubes melting at the bottom of the beakers

Because surely there is one more post in this topic? ;-)

For those of you who haven’t heard about the “melting ice cube” obsession of mine, please check out the links to other posts at the end of this post. For everybody else’s sake, let’s dive right in!

When Kristin and I ran the workshop at EMSEA14, a couple of people asked very interesting questions. One that I totally had to follow up on was this: What would happen if the ice cubes were forced to the bottom of the beakers? Of course we knew what theory said about this, but who cares? I still had to try.

If you have ever tried holding down ice cubes with straws…

…you might know that that is quite difficult. So this is the experimental setup I ended up with:

Zooming out a little bit, this is my fancy equipment:

Zooming out a little more, this is the whole setup:

I know that some people want to try the experiment for themselves, so I’ll hide the rest of the experiment behind the cut, at least until Kristin tells me that she’s done it :-)

Why folic acid might be good for people, but not so good for tank experiments

I had to do the complete series of experiments, of course…

The other day I mentioned that I had used salt from my kitchen for the “ice cubes melting in fresh and salt water” experiment, and that that salt was the super healthy one that was both iodized and containing folic acid. And what happened is that the experiment looked like I was using milk. Not what I had envisioned.

Since I had often before used just regular table salt – which is usually iodized – I was intrigued by the opaqueness that seemed to be due to the addition of folic acid. Or was it? That I had never noticed the milky-ness of the salt water didn’t necessarily mean that it had not been milky before. So this is what the same experiment looks like if regular iodized table salt is used:

In the literature it is always recommended to use kosher salt for experiments. Kosher meaning in this context that the salt should be only NaCl with no other additions. I happened to have some at hand after having bought it for the “teaching oceanography” workshop in San Francisco last year (after the salt that I brought for the workshop didn’t make it to the US. Long story). So this is what that looks like:

In summary: Folic acid is what makes the salt water look opaque – but iodized salt is completely fine for tank experiments. I think it’s tiny air bubbles that cling to something folic acid-y, but I have no clue what is going on. I noticed that the dusty stuff settled down over night (so the top experiment here is a lot clearer than the experiment I ran with the same batch of water the day before), but even the next day the water wasn’t completely clear.

Anyway, now we know. And I came out of this series with more movies of ice cubes melting in fresh water and salt water!

Links to previous posts on the topic after the cut.

[Edit: Using my mom’s iodized, but not folic acid containing, table salt leads to milky water, too. So there you have it. I have no clue what is going on!]