I didn’t write a #WaveWatchingWednesday post last week. I think when my last blogpost ended with the Oslo ferry leaving Kiel for the last time in the forseeable future, it really hit me how far away so many of the people I love are, indefinitely out of reach. I had a couple really tough days isolated all by my self, with additional high fevers and a very active imagination, but not eligible to be tested. Anyway, things got better, I started being able to go out of my flat again, in the very early mornings to meet as few people as possible. I started taking pictures again and posting them to my Instagram. Initially, they were mainly pictures of sunrises (over water, of course ;-)) and I still didn’t feel like talking about waves. Anyway, today was the first day I felt the urge to talk about waves again, so here comes a bunch of pictures and then a real #wavewatching pic in the end!

From here on, things got better.

The way I felt about being in isolation changed drastically when I brought wave watching into my livingroom. Now I am actually quite content on my sofa, looking at the porthole and the view… Nice change when compared to the days before when I really felt isolated and not happy. Was it just being creative today that turned things around for me? I don’t know, but I’m happy with the result in any case

And then: My first snow this winter! :-)

And I built a snowman! :-)

Not a lot of water in Kiel fjord today, but: poolnoodle waves! When the water is very shallow compared to the wavelength, waves deform into this weird shape with very long troughs and these bulging crests that look as if poolnoodles were being pushed towards the shore.

And that’s it!


Here is last week’s summary of my #WaveWatching Instagram @fascinocean_kiel. Social distancing in Kiel isn’t so bad… At least until I started to take it seriously enough to stay inside full time, so this week we only have pictures until last Saturday. And there will probably be no wave watching in the near future. But I’m thinking about going through the archives and explaining some stuff better now that I have time. Does this sound interesting?

Anyway, let’s start.

So much going on in one picture! Can you explain all the different waves? Let me try below…

Red lines show the incoming waves; the wake of a ship that passed a minute ago and whose feathery wake is now reaching the sea wall.
As the feathery wake meets the sea wall (on whivh I am standing), it gets reflected. The reflected wave crests are marked in green.
With all these waves, the pontoon is bobbing up and down, making those waves that trace its contours & propagate away from it (blue).
And finally, the yellow waves radiate from the edge of a pontoon that you can’t see, which is also moving with the waves.
How super awesome is wave watching, please???

I love the contrast between the bright sky in the east that we are looking at, and the darkness behind me. That, plus simple geometric shapes like this pier, make for amazing wave watching because different sides of the waves are reflecting either the bright or the dark parts, and then the deformation of the geometric shapes in their reflection gives us a good idea of the shapes of the waves. Plus I just love being out for the sunrise ☀️

You think a little ice on the beach is going to keep me from a quick dip into the sea? Ha, think again! ‍♀️

Social distancing is not so bad when it means sitting in a beautiful sunny spot, looking at water.
But watching the Oslo ferry leave for the last time in at least the next couple of weeks is somehow really emotional for me. It’s not only the source of one of my favourite wave watching events (actually, several: Beautiful wakes, and the 180 degree turn in a really narrow part of the fjord befor backing up into its berth), it’s also what connects me to all my friends in Norway. And my mini escape when I need some time at sea without having time or opportunity for “serious” (i.e. research) cruises. God tur, hope to see you back in Kiel soon!

Yep, and that’s it. Be safe, everybody!

Reposting my “field report” for the DIYnamics blog

Reposting a guest post I wrote for the @DIYnamicsTeam‘s blog:

When we came across the DIYnamics article right after its publication, Torge and I (Mirjam) were very excited about the endless possibilities we saw opening up with an affordable tool like the DIYnamics rotating table. We applied for, and were granted, money for an “innovative teaching” project by Kiel University’s PerLe (1) and built four DIYnamics rotating tables (five if you count the one I built for personal use ;-)), which we’ve been working with for about a year now. Since we are using them in a slightly different context than we’ve seen described before, and also have modified and added some of the experiments, I thought I’d report on it here. If you have any comments or suggestions for us, please do get in touch!

DIYnamics tables in undergraduate education

In contrast to using the DIYnamics rotating tables mainly for outreach purposes which is the most common application I am aware of, we are using them as part of a regular Bachelor-level class on “ocean and atmosphere dynamics” at Geomar, Germany. I have gained a lot of experience using a rotating table in undergraduate education at GFI, Norway, but there we only had one – much bigger – table available. Now we have four that can be used simultaneously! This is great for so many reasons:

Time efficiency for the instructor

With only one rotating table available, the typical setup I have used was to have small groups of students come in at different times over the course of a week or so, to do that week’s experiment with me. But that meant that I would spend a lot of time in the lab, and a large part of that time would be spent on waiting for the water on the rotating table to have spun up into solid body rotation, as well as prep time or cleaning, drying, putting away time.

Of course, wait times can easily be used for discussions of the upcoming experiment, of the concept of a “spun up” body of water, of how to judge whether or not a body of water is spun up or not, and many other things. But those are things that don’t necessarily have to be discussed in a setting of one instructor per each small student group, they could just as well be discussed in student groups and then in a larger plenum.

Exchange between student groups

In the setup with one table and student groups coming in one after the other, students would then write lab reports, submit them, and come back for the next experiment. While I am sure there was some exchange between student groups happening (which we could sometimes see from eerily similar ways of expressing things between groups, or errors propagating through several groups’ reports), that wasn’t an instructional design choice.

Now, however, when we have student groups working on the same experiment at the same time in the same room, it is very easy to have discussions both within individual groups and then across groups. There are many instructional methods to choose from that facilitate that kind of exchange, for example “think, pair, share”, where students first think about a question individually, then pair up with a partner (or the group at their tank) to discuss, and then results are shared with and discussed in the whole class.

Seeing many implementations of the same experiment

One reason why these discussions are especially fruitful if done in connection with simultaneously-run tank experiments is that, even if all student groups get the exact same instructions, two implementations of the same experiment do not ever look the same. There is always something that’s different. Maybe one tank is spun up less than the others, or a bit wobbly, because someone bumped into the table mid-spinup. Or the dye that is used as flow tracer has a different density for one group (less diluted? Different temperature?) and thus behaves differently. Or dye is put in a different spot in the tank and thus shows different features of the flow field. There are so many tiny things that can and will be different from experiment to experiment, and it’s a great learning experience to see an ensemble of different implementations and discuss what change in boundary conditions made results look different rather than just seeing one implementation and wrongly assuming that this is the one and only way this experiment always turns out.

Seeing many different experiments at the same time

And then, there is of course the opportunity to have different student groups work on different experiments simultaneously, which cuts down on total prep and spin-up time and enables students to see a larger variety of experiments. It also opens up the possibility that students pick what experiment they want to work on – either new ones or repeating older ones that they would like to take better pictures of or modify something in the boundary conditions. This seems to be very motivating!

Our group of students coming together at one tank to discuss observations. Note that in the background a square tank is sitting on a different rotating table, being spun up for the Rossby wave experiment described below

Why we are using higher-walled tanks

In contrast to the tanks we’ve seen used on the DIYnamics rotating tables before, we chose to invest in some high-walled tanks.

An interesting feature of rotating fluid dynamics is that the flow becomes 2D, so technically having a shallow layer of water is completely sufficient to give a good representation of those flows. And if we look at the aspect ratios of the oceans, they are in fact extremely shallow compared to their horizontal extent. But it’s easy to see a 2D flow in a shallow tank and assume that it’s 2D because of the shape of the tank, not because of the flow itself. So having an exaggerated third (depth) dimension that can be easily observed by looking into the tank from the side actually helps drive home the point that there is “nothing to see” on that dimension because the flow really is as 2D as theory told us it would be.

But then there are of course the cases where the flow isn’t 2D, and then a higher-walled tank is really convenient. For some experiments where there are exciting things to discover by looking into the tank from the side, check out this blog post over on my blog.

Students working with an experiment on the Ekman bottom boundary layer – one of the experiments that really benefit from a larger water depth because this allows for observations of the development of the boundary layer over time.

Experiment on planetary Rossby waves

One of the first experiments we tried on our DIYnamics rotating table was a “planetary Rossby wave” experiment. We hadn’t bought our cylindrical tanks yet (read more about those below), so using a clear plastic storage box was very convenient. Btw, this is one of the experiments where looking into the tank from the side gives a lot of interesting insights!

For the planetary Rossby wave experiment, we need a sloping bottom (easiest done in a rectangular tank, but we’ve also run the same experiment on a cone-shaped insert in a cylindrical tank) and a dyed ice cube. When the tank is in solid body rotation, a dyed ice cube is inserted in the shallow “eastern” corner of the tank (make sure it is sitting far enough from the edge of the tank so it can turn around its own axis unobstructed). For more details see this blog post, but in a nutshell: The cold melt water sinks, setting up a column of spinning water that sheds spinning eddies at regular intervals. Eddies and ice cube propagate westwards. This is a really easy and fool-proof experiment, and it looks beautiful!

Planetary Rossby waves in a square tank with a sloping bottom.

Presenting the DIYnamics tanks at an institute colloquium

In January, Torge and I gave a seminar presentation titled “you should really play more often! Using tank experiments in teaching” at our institute’s colloquium. In the abstract, we announced that we would give a brief overview over our project and then give people the opportunity to play – which we did. We had been expecting that maybe a handful of our loyal friends would stick around after the presentation to look at the tanks, but we were very surprised and excited to see that pretty much everybody in the audience wanted to stay. We had set up the four rotating tables with four different experiments and a student presenting at each in the back of the room, and we ended up running all the experiments repeatedly, until we were kicked out of the room because the next lecture was about to start. It was really motivating to see how everyone – students, PhD students, postdocs, staff, professors – got really excited and wanted to learn more about the tank experiments, discuss observations, modify and experiment. This goes to show that an affordable rotating table is an amazing tool at every level of education: There is always more to discover!

A snapshot of the audience of our seminar presentation interacting with the tanks and each other. We were running four experiments simultaneously.

Follow our experiences

If you want to follow our experiences with the DIYnamics rotating tables, there are several options for you:

Torge and I have recently launched the “Teaching Ocean Science” blog at https://www.oceanblogs.org/teachingoceanscience/, which is a joint effort of ourselves and other instructors, describing fun hands-on stuff they do in their teaching, and students, who write course assignments on what they are currently learning for the blog.

Additionally, all the outgoing links in my guest post above are to posts on my own blog, “Adventures in Teaching and Oceanography”, at https://mirjamglessmer.com/blog. I use that blog as my own archive and document every new thing I try on there, so you might want to sign up for email alerts or follow via my Twitter @meermini.

In addition to writing about the DIYnamics rotating tables and what we are up to with those (and you can be sure that if I played with a tank, you will read it on that blog right away ;-)), I write a lot about#KitchenOceanography (which are very easy hands-on experiments on ocean and climate topics that you can do with household items) and #WaveWatching (observing ocean physics everywhere, all the time). I also write about science communication issues.

Please feel free to check out those blogs and as I wrote in the beginning: Please get in touch if you have any comments or suggestions for us. I am always happy to chat!

(1) This project has been funded by the PerLe fund for innovative teaching through resources from the Federal Ministry of Education and Research, grant number: 01LP17068. The responsibility for the content of this publication lies with the authors.


Recap of last week’s posts on my #WaveWatching Instagram @fascinocean_kiel!

Starting off with two newts, because sometimes I actually look at stuff in the water, not just the waves on top ;-)

As much as I love being in Hamburg, especially with my job taking me to the heart of the city, it always just makes me super happy to be back home in Kiel!

…and then I looked at waterfalls in Lüneburg!

All in all not the most active wave watching week for me; too much life stuff going on. But things will get better again! :-)

#SciCommSunday: Tweeting about publications

In case you’ve been wondering why I’ve been tweeting so much about our recent Nature article: Yes, I am really this proud and need to tell the whole world about it! :-)

Of course there are more other good reasons to discuss articles on Twitter, to do it yourself, and to publish in journals that also tweet about articles.

But let’s start with a disclaimer: Even though it’s the measure most commonly used to capture the impact of an article, and the one that is used below, too, citations of course don’t actually tell us anything about the quality of an article, nor about its importance for bringing the field forward. And none of the articles referred to below look at mechanisms — correlation doesn’t imply causation! With that out of the way, let’s look at the impact of tweeting about an article on that article’s citations.

More tweets about an article mean more citations

In their 2016 article, Peoples et al. looked at Twitter and how it relates to citation rates in ecological research. Of course, the strongest predictor of the number of times an article is cited is time after publication: the older the article, the more time it has had to accumulate citations. However, Peoples et al. (2016) found a strong relationship between the number of unique tweets, i.e. Twitter activity, about an article and the number of citations that article received. It’s thus beneficial for authors to tweet about articles — it brings the article to a larger audience’s attention, and knowing of an article is the requirement for it being read and potentially cited.

Peoples et al. (2016) also found that how much twitter activity an article received was not related to the journal’s impact factor. Articles in journals with lower impact factors can be just as heavily tweeted, and cited, as articles in higher impact factor journals. And in fact, they found that twitter activity related to an article was a better predictor of how much articles were going to be cited than 5-year journal impact factor of the journal they were published in!

If you don’t tweet about an article, nobody will

Actually, that’s completely overstating what the literature says. But it brings across a point I’m always trying to make: It’s in your own hands to promote yourself and your science.

In their 2016 study, Ortega found that articles authored by Twitter users are tweeted about 33% more than articles that were authored by non-Twitter users. Which makes sense to me: Even though I occasionally tweet about articles someone else has published, I tweet about pretty much everything that I publish myself.

Interestingly, once someone — anyone — tweets about an article, citation numbers don’t depend on whether the authors tweeted about it themselves, or whether someone else did for an author that isn’t a Twitter user. But again, if you tweet yourself, it’s in your hands and you don’t have to rely on anyone else to disseminate your research output, making it more likely that it will be seen and cited.

The more you tweet, the more they’ll cite

It’s kinda obvious, but the more you tweet about an article, the more people have a chance to catch that tweet, read the article, and eventually cite it.

As Eysenbach (2011) found: Highly tweeted articles are 11 times more likely to be highly cited than less-tweeted articles. Number of tweets can even be used to predict highly cited articles within the first 3 days of publication of an article.

But: correlation doesn’t imply causation, so we don’t know anything about the mechanism, and they write: “Social media activity either increases citations or reflects the underlying qualities of the article that also predict citations”.

More followers mean more visibility for your paper, thus more citations

This result of the Ortega (2016) seems also fairly obvious: Many tweets citing an article are probably due to the authors promoting a newly published article. So the more followers an author has, the more likely, and the further, the message can be directly multiplied by followers’ retweets.

On the flip side: You yourself are also one of those followers that can multiply someone else’s work. Use your own followers to generate visibility for other people’s articles!

Journals that are on Twitter get tweeted about, and cited, more than those that aren’t

A 2017 study by Ortega investigates the relationship between the presence of academic journals on Twitter and how much articles in those journals get cited. Turns out that journals that have their own Twitter accounts are tweeted about about twice as much as journals without a Twitter account. Also, journals with twitter accounts do get 3 times more citations  than those without.

So even if you don’t want to tweet yourself, even just picking a journal that is active on Twitter is helping to make your article more visible to more people. Obviously this shouldn’t be the deciding factor for where to publish…

It even benefits the journal to be on Twitter

In a study on the use of Twitter by radiology journals by Kelly et al. (2016), it was shown that journals with Twitter profiles had a higher impact factor than those without a Twitter profile. There is, of course, the hen and egg problem here. But the study also found that 7 of 11 journals experienced increases in impact factor after joining Twitter, and that a greater number of followers on Twitter correlated with higher journal impact factor.

Btw, if you want to see an example of a journal’s Twitter done really well, check out Frontiers for Young Minds Twitter @FrontYoungMinds!

My 2 cents on tweeting about publications

I hear all the time that people (usually those neither actively nor passively involved with Twitter) feel like tweeting about articles is somehow a repulsive way of selling something that should be recognized for its scientific value alone, not for how much publicity the authors or someone else is generating for it. And while I kinda see the point — I agree that articles should be cited based on their scientific value, not their authors’ Twitter skills — I kinda don’t see it. In this day and age, there is so much research published every single day that it’s not a realistic expectation to be fully aware of everything being published that might be relevant to ones own research and interests. So assuming that not everybody for whom my articles might be relevant will be see it, I feel that it’s a service to the community to help them come across my work, that I of course believe is interesting, relevant, and sound. If I can let people know that I’ve published something that is worth reading, and I can even give them a brief idea what it’s about, either in a tweet or a thread, I am making it easier for people to find what they might have been looking for (or even what they would have been looking for had they known there was something like this out there to look for). And if they are not at all interested, I wonder how much of a different scrolling past my 280 characters will make? Surely not enough for them to cite something irrelevant.

Anyway, my take-away from all the research I’ve summarized above:

  • Tweet about your publications, and repeatedly!
  • Make your co-authors, your journal, your network tweet about articles!
  • But also: Tweet about / retweet other people’s relevant articles to make that information visible to your own network!


Eysenbach G. (2011). Can Tweets Predict Citations? Metrics of Social Impact Based on Twitter and Correlation with Traditional Metrics of Scientific Impact, J Med Internet Res 2011;13(4):e123, DOI: 10.2196/jmir.2012

Kelly, B.S., Redmond, C.E., Nason, G.J., Healy, G.M., Horgan, N.A., Heffernan, E.J. (2016). “The Use of Twitter by Radiology Journals: An Analysis of Twitter Activity and Impact Factor”, Journal of the American College of Radiology, Volume 13, Issue 11, Pages 1391-1396, ISSN 1546-1440,

Ortega, J.L. (2016) To be or not to be on Twitter, and its relationship with the tweeting and citation of research papers. Scientometrics 109, 1353–1364. https://doi.org/10.1007/s11192-016-2113-0

Ortega, J. (2017), “The presence of academic journals on Twitter and its relationship with dissemination (tweets) and research impact (citations)”, Aslib Journal of Information Management, Vol. 69 No. 6, pp. 674-687. https://doi.org/10.1108/AJIM-02-2017-0055

Peoples, B. K., Midway, S. R., Sackett, D., Lynch, A., & Cooney, P. B. (2016). Twitter Predicts Citation Rates of Ecological Research. PloS one, 11(11), e0166570. https://doi.org/10.1371/journal.pone.0166570


Our Nature article in 20 tweets

(Not true, there were 22 tweets, but apparently I can’t count! :-D)

For those of you that don’t follow my Twitter, here is what I posted over there the day our Nature paper got published:

Published online in @Nature today: “Ice front blocking of ocean heat transport to an Antarctic ice shelf” by @a_wahlin @nadsteiger @dareliuselin @telemargrete @meermini (Yes! That’s me!!! :-)) @ClnHz @ak_mazur et al.. What is it all about? A thread. 1/x

And here is the link to our Nature article!

The Antarctic ice sheet has been losing mass recently. Ice sheets consist of the “grounded” parts that rest on land or sea floor, and the parts that float on the sea. If the floating part get thinner, the grounded part “flows off” land much more easily (pic by @dareliuselin) 2/x

Floating parts of ice shelves break off&melt. But why are ice sheets thinning? Mainly because of melting from below. We are thus concerned with what controls how much warm(-ish) water is transported across the Antarctic continental shelf towards the ice (Sketch: Kjersti Daae) 3/x

I’m writing “Warm(-ish) water”, because the water is only 1-2°C “warm”, but that’s still warmer than the freezing point. IF this warm(ish) water gets in contact with ice, it will nibble away at it. But that’s a big IF, that we set out to investigate 4/x

From existing data, it seemed that the shoreward heat flux is much larger than what would be needed to cause the observed melting. But this is a heat flux that was measured not right where the melting is happening, but a lot further offshore 5/x

It’s difficult to measure the heat flux right up to the ice shelf, because Antarctica isn’t the friendliest of environments for research ships, gliders, moorings, etc, especially in winter. Cool toys like floats, or CTDs on seals give a lot of data, but not enough yet 5/x

But @a_wahlin, @dareliuselin & team put moorings closer to the ice shelf than ever before, the closest one of three only 700m from the ice shelf front. There was absolutely no guarantee that the moorings would survive (Pic by @a_wahlin showing @dareliuselin) 6/x

Luckily, despite being threatened by storms, ice bergs etc, the moorings recorded for two years, right next to the ice shelf, giving us better estimates of heat fluxes than were available ever before 7/x

While the moorings were out in Antarctica, we went to LEGI in Grenoble and worked on the Coriolis rotating platform, basically a 13-m diameter swimming pool on a merry-go-round. SO EXCITING! (Pic by Nadine Steiger) 8/x

It’s really an amazing experience to sit in an office above a swimming pool when both are rotating together. As long as it’s dark outside the tent that covers both, you don’t really notice movement. But when the light comes on it’s very easy to get dizzy! (Pic Samuel Viboud) 9/x

We were not playing on the merry-go-round for two months just for fun, though. Rotating the large water tank is important to correctly represent the influence of Earth’s rotation on ocean currents, which is very important for this research question 10/x

In the rotating platform, we built a plastic “ice shelf” that was mounted at the end of a v-shaped plastic “canyon”. We could set up a current and then modify parameters to investigate their influence on the transport towards and underneath the ice shelf (Pic @a_wahlin) 11/x

If you are interested to read a lot more about this (also about how parts of the team went for a swim in the rotating tank, and about how sick you can get when sitting on a merry-go-round all day every day for weeks), check out @dareliuselin’s blog 12/x

Link to Elin’s blog!

In a nutshell: We put particles in the water and lit them, layer by layer, with lasers. We took pictures of where the particles in each layer were, and with the “particle image velocimetry” (PIV) technique, we got a 3D map of particle distributions over time 13/x

And what we found both from the data that we got from the moorings in Antarctica, that we were lucky enough to recover, as well as from the tank experiments at the rotating platform was really interesting: Ice front blocking of ocean heat transport to the Antarctic ice shelf14/x

The ice shelf, at its most offshore part, still reaches down to 250-500m. That means that the depth of the water column changes drastically at the front of the ice shelf. And that has important consequences for depth-independent part of the current 15/x

The barotropic, i.e. depth-independent part of the current is blocked by the step shape of the ice front (as well as the plastic front in the tank). Only the baroclinic (depth-varying) part can flow below the ice, but that part is much smaller 16/x

In the tank we changed the shape of the ice front to see that it’s really the large step that blocks the current. Other configurations lead to different flow pattern. But the large step shape is what the Getz Ice Shelf system looks like, and other systems, too 17/x

What that means is that looking at the density structure of the water column, thus the relative magnitude of barotropic and baroclinic components of the current, is a better indicator of ice shelf melting than the heat transport onto the continental shelf 18/x

It also shows the importance of accurately representing the step of the ice shelf front accurately in models in order to simulate the heat transport towards the ice as well as the melting of the ice shelves 19/x

TL;DR: Article published @Nature on ice front blocking of ocean heat transport to an Antarctic ice shelf, and I contributed to the exciting study and feel so honored to have been part of this amazing project with @a_wahlin, @dareliuselin, @clnhz et al. (Pic Samuel Viboud) 20/x


Here’s another #WaveWatchingWednesday overview over my Instagram @fascinocean_kiel! Enjoy!

Sun glint can be so helpful to make waves visible more clearly, like this morning. I love the combination of the turbulent wake, the feathery usually V-shaped (and in this case quite wonky) wake, the sun. Always fun to watch!

Just moments later and the feathery wonky V is a lot more difficult to recognize (its remnants are reaching the shore at the very bottom of the picture). But the turbulent wake looks a lot more interesting now with that cloud-like appearance!

And one last look at the billows of the turbulent wake. I mean it’s quite impressive for such a large ship to do a 180 turn in such a narrow fjord. But it’s also really cool to see it like this, documented in the wave field!

Oh, and then I did some #FriendlyWaves for Christina on a super cool picture taken from a plane off Panama. Check it out!

…And a little wave watching on my way to work!

Christina’s #FriendlyWaves from Panama!

Christina writes on Twitter: “#wavewatching from a plane, approaching #Panama. @Meermini, do you know what causes those regular ‘wrinkles’?” and how could I resist writing a blog post about what I think might be the explanation?

Below is the picture Christina shared on Twitter.

Picture by Christina Oettmeier @sulfurium

What I think we see here are basically two wave fields: The regular “wrinkles” and then a lot of small crinkle.

The small crinkle are boring: local, wind-generated waves. They are not what Christina asked about.

But the wrinkles are swell: Waves that were formed in a storm far, far away and that have propagated here over a long distance. While propagating from the area where they were formed to the beach where Christina took these pictures, the waves got sorted by wave length. The longer a wave, the faster it propagates in deep water. So long waves from a distant storm will arrive first, and over hours or days the wave lengths of the waves arriving at the beach will get shorter and shorter. The wave lengths we see here seem to be about the height of the high rise buildings we see on the shore. The highest high rise in Panama is almost 300m high, so the wave lengths might not be that long, but at least 100+m.

Why do they look so “wrinkly” and not like proper breakers? When waves are in water that is shallow compared to their wave length (so say water depth would be less than 50m for these waves if we assume they are 100m long, which I think are both reasonable estimates), their shape changes from the normal sine-shape that they would show in deep water, to steep crests and loooong troughs. You might have observed waves with this shape for example in the very shallow waters of a beach on the wadden sea coast or any other beach with a really small slope, where waves look like sausages or pool noodles that are being shoved onto the beach (compare for example to pictures in this post).

What makes me confident that we are really seeing what I’ve just described above? Mainly that I can see the interaction of the waves with the sea floor. If you look at the pic above, do you see the area where the waves bend? That’s where the water is shallower. I’ve tried to sketch that below: The red lines are — in first approximation — the wave crests (I’ve only drawn in every third or so for clarity). Red dashed lines are kinda the second approximation of the wave crests: Those are the deformations that I want to talk about. And those deformations are caused by a shallower area, which I’ve drawn in with the green dashed line. This little submerged headland slows that part of the waves down that runs above it (because in shallower water the wave’s speed only depends on water depth, not on wave length any more), but not the rest of the waves that propagate towards the beach with the straight crests intact.

It’s even easier to be confident when we look at the next two pictures that Christina shared with me. Now we are a little closer to the beach and can see the area where the waves break and where it is shallow enough that the wave lengths drastically decrease (since the waves are slowed town more and more the closer they come to the beach, waves that are further out are still faster and can catch up to waves in front of them). This is very typical for the parts of a beach where the depth changes rapidly.

Picture by Christina Oettmeier @sulfurium

And on the next pic, we see even more clearly that the waves change from pool-noodle shaped offshore to breaking waves close to the beach:

Picture by Christina Oettmeier @sulfurium

In case you don’t see what I am trying to point out, here an annotated version of the pic above. Green dashed circles: Smudges on the window, or possibly reflections on the window, but nothing to do with the waves. Red circles: Here we see foam on the back side of breaking waves, so there was definitely some wave breaking going on here. And blue circle: Cool structures in the flow of water that is retracting downslope from the beach, back into the ocean.

So much for now. No idea if that made any sense to anyone except myself. Please let me know! :-)

Playing in a 13-m-diameter pool on a merry-go-round results in Nature article

A long, long time ago (ok, in fall of 2017) I got the chance to join Elin Darelius and Anna Wåhlin’s team for a measuring campaign at the Coriolis platform in Grenoble for several weeks. I was there officially in an outreach officer-like role: To write and tweet about the experiments, conduct “ask me anything” events, write guest posts newsletters and websites, etc.. A lot of my work from that time is documented on Elin’s blog, that I blogged on almost daily during those periods. And we had so many amazing pictures to share (mostly green, that’s because of the lasers we used).

Turbulence in a rotating system is 2D, therefore the whole water column is rotating in this eddy that we accidentally made when moving parts of the structure in the tank

But I was extremely lucky: Neither Elin nor Anna nor anyone else on the team saw me as “just the outreach person”, which is a role that outreach people are sadly sometimes pushed in. Instead, they knew me as an oceanographer and that’s how I was integrated in the team: We discussed experiments all the way from the setup in an empty tank (below you see Elin with her “Antarctica”)

No matter how carefully you planned your experiments, once you start actually conducting them, there is always something that doesn’t work quite the way you imagined. But since time in facilities like the Coriolis platform is limited, it is hugely important to think on your feet, come up with ideas quickly, and fix things. Which is the part of science that I enjoy the most: Being confronted with a problem “in the field” and having to fix it right then and there, using whatever limited equipment and information you have available.

Speaking of “limited information”: Sometimes you have to make educated guesses about what’s in the data you are currently collecting in order to make decisions on how to proceed, without being able to know for sure what’s in the data. We took tons of pictures and videos and obviously also observed by eye what was happening in the tank, but in the end, the “real” data collection was happening with images that we couldn’t analyse on the spot (and that’s what the research part is about that took place in between fall of 2017 and now: many many hours of computing and analysing and discussing and rinse and repeat).

Grenoble was also an amazing experience just because of the sheer size of the Coriolis platform. Below you see the operations room, an office that is built above the tank and rotates with it. And let me tell you, being on a merry-go-round all day long isn’t for everybody!

I really also enjoy the hands-on work. Below is me in waders in the 13-m-diameter rotating pool (while it’s rotating, of course), using a broom to sweep up “neutrally buoyant” particles that we use to track the flow that over night settled on the topography (so much for “neutrally buoyant”, but close enough). Sometimes it comes in handy to be an early bird and doing this work before everybody else gets up, so the tank has the chance to settle into solid body rotation again before experiments start for the day.

Here you see the layer of particles in different stages of disturbance, and me having fun with it (it might not be obvious from the picture, but I’m standing in waist-deep water there)

But then we weren’t playing all day long for weeks. There were times of intense discussions of preliminary results. Exciting times! And of course, those discussions only intensified when all the data was in and could be analysed in more depth.

I loved being part of the whole process and contributing to this exciting publication now!


Welcome to the recap of my #WaveWatching Instagram @fascinocean_kiel! Starting off strong:

My standard #KitchenOceanography overturning circulation experiment (recognize the tank & the cool pad?) put into a very different light by @davidcarrenohansenfor the upcoming issue of @sciencenotes5x15! Can’t wait to see how the pictures turn out — definitely not the “snap a pic with my phone in my kitchen” I always do!

#FlumeFriday with pretty much the opposite approach to my usual kitchen oceanography: Yesterday I got to visit @lufi_luh and see all their super cool flumes and wave tanks. Unfortunately without water, but you bet that I’ll be back! Can you imagine the endless possibilities?

Some things make me happy every time. Like watching hydraulic jumps in a sink. What’s your guess why in the second picture the radius of the shooting water circle is smaller even though the flow out of the tap is the same in both pics?

Interesting: distinct ripples on the sandy seafloor, but not all the way up to where the plants start. Why not? It’s not a change in water depth. I think it must be because of some plant wave interaction that dampens the waves enough that they can’t move the sand any more. Or possibly some reflection from the sea wall that messes something up? What do you think?

#SciCommSunday: Did you notice how I am always writing how much _I_ am fascinated by wave watching or kitchen oceanography or that stuff? Head over to my blog post on a recently published study in which it was found that writing in first-preson style is actually helpful in #SciComm because it makes you be perceived as more authentic and helps build a connection with your audience!⁠⠀
Picture taken on my last trip to Bergen (when P & I met up to go watch the tidal current you see in the background).⁠

Then one day on my way to work: Shear flow (see the essies?) between two watermasses. The muddy brown water coming out of Alsterfleet, the other one is “normal” brackish Elbe water in the Port of Hamburg. I saw this from the train station and had to go investigate & document! :)

And that’s it for this week! :-)