Total internal reflection

Have you ever wondered why at some angles the sea looks blue (or whatever the color of the sky that day) and at others you can actually look into the water? That’s the phenomenon of total internal reflection. There is a critical angle at which you switch from “being able to look into water” to “total internal reflection”, i.e. the sky being reflected off the water’s surface and reaching your eye. Below you see a nice example of this: The more perpendicular you look at the water surface (i.e. those sides of the wave facing you), the better you can look into the water. Whereas all those parts of the sea surface that face away from you look blue and you can’t look into the water there.

I think this is totally fascinating! Don’t those pictures look almost fake?

And, btw, this doesn’t only happen if you look in parallel to the direction of wave propagation. Although it looks even weirder at an angle:

Can you see how all those tiny ripples on the wave each show the same phenomenon of either reflecting the sky or being transparent and showing the sea floor underneath? How cool is that? :-)

A #scipoem on upwelling of tropical OMZ waters in a warmer climate

“Simulated reduction in upwelling of tropical oxygen minimum waters in a warmer climate”*

Let’s pick apart this article’s title,
inaccessible to most people out there.
Even though we know it as vital
to communicate clearly, be able to share,
what goes on in iv’ry towers detrital,
to whom it is relevant, as well as where.
Since taxpayers pay for us, science and all,
we need to inform them without any brawl.

“Sim’lated” just means a model predicts.
“Warmer climate”, then, is scientists’ code
for “some time in the future”, but nothing fix.
Which means if we continue down this road
of putting more CO2 in the mix
“upwelling”, whatever that is, will be slowed.
“Upwelling” means that waters from the deep
up to the surface of the ocean creep.

“Tropical” means “going on in the tropic’”.
“Oxygen minimum waters” contain
low levels of oxygen, which are a topic
of discussion in the science domain,
because if levels sink down to “hypoxic”,
almost no life in the sea can remain.
Fate of dead animals and plants, in the end,
does on the oxygen levels depend.

Dependent on oxygen, chemicals form,
that can change climate as does CO2,
if they reach the atmosphere in a storm
or just by “upwelling”, out of the blue,
they make that further the climate will warm.
Therefore, it’s nice to know that the brew
of “oxygen minimum waters” will leach
more slowly to continents’ western beach’.


*This poem is in the “Ottava Rima” form and it explains the title of an article by Glessmer, Park & Oschlies (2011). The title of this article was also chosen as title to this poem.

Mussel filtering water

And something more from the teacher training at Lotseninsel: A mussel that sucks in water dyed with food coloring and then pumps it out on the other side again. Very fascinating for a physical oceanographer who has never dealt with anything living in the water before :-)

Flatfish and mud

Here is something else I filmed during teacher training at Lotseninsel: how some flatfish (that the other group caught close to the island) digs itself into the mud. Pretty cool to watch!

Double the trouble — a poem about double-diffusive mixing in the ocean

On my blog’s fourth Birthday (!!!), it’s time to try something new. How about some celebratory oceanographic poetry? Obviously the topic has to be my oceanic pet process, double-diffusive mixing


Double the trouble

Heat mixes by molecules bumping
into each other and clunking
momentum transfers
so fast it all blurs
the warmer the faster they’r’all jumping

A different story for salts
where ions — through not their own faults!
must change their location
which leads to palpation
resembling a fairly slow waltz

Now heat and salt mix simultaneous
-ly without ‘ny extra extraneous
stirring or shaking
fish swimming, waves breaking,
which leads to effects miscellaneous

The ones I like best are salt finger:
structures that form and then linger,
tricking unsuspicious
oc’nographers vicious
-ly into assuming not threat to the thinker

This process includ’d in simulations
leads to much better foundations
of climate prediction
that is my conviction
you can read here* about the causations

Not only the currents o’the ocean
that consequently change their motion
but also biology
chemistry, geology
and last, not least, atmospheric transpos’tion

To sum up, this double diffusion,
those fingers that are no illusion
when climate has changed
the ocean’s been deranged
def’nitly deserve an inclusion :-)



Happy Birthday, my little blog! :-)


*Glessmer, M. S., Oschlies, A., & Yool, A. (2008). Simulated impact of double‐diffusive mixing on physical and biogeochemical upper ocean properties. Journal of Geophysical Research: Oceans113(C8).

Amplification of waves when they run into shallower water

It’s one thing to know that waves build up as they run from the open ocean over the shelf onto a beach, and that they build up as the water gets shallower and shallower. But we are so used to seeing exactly that (because that’s what the sea is supposed to look like!) that we don’t really notice it any more, at least most of the time. But below is an interesting case: Waves are running onto the beach, but there is also a headland going out into the sea. So in addition to running onto a beach, there is also a depth gradient along each wave crest (do you know what I mean?).

Watch the movie below to see that there are hardly any waves visible when you look at the open water on the left, but that the crests and troughs become clearly visible as soon as you are close enough to the headland where the water is shallow enough: One and the same wave crest builds up a lot more the closer you look to the headland than it does in open water.

I am missing institute seminars! Or: Why we should talk to people who use different methods

You probably know that I have recently changed my research focus quite dramatically, from physical oceanography to science communication research. What that means is that I am a total newbie (well, not total any more, but still on a very steep learning curve), and that I really appreciate listening to talks from a broad range of topics in my new field to get a feel for the lay of the land, so to speak. We do have institute seminars at my current work place, but they only take place like once a month, and I just realized how much I miss getting input on many different things on at least a weekly basis without having to explicitly seek them out. To be fair, it’s also summer vacation time and nobody seems to be around right now…

But anyway, I want to talk about why it is important that people not only of different disciplines talk, but also people from within the same discipline that use different approaches. I’ll use my first article (Simulated impact of double-diffusive mixing on physical and biogeochemical upper ocean properties by Glessmer, Oschlies, and Yool (2008)) to illustrate my point.

I don’t really know how it happened, but by my fourth year at university, I was absolutely determined to work on how this teeny tiny process, double-diffusive mixing (that I had seen in tank experiments in a class), would influence the results of an ocean model (as I was working as student research assistant in the modelling group). And luckily I found a supervisor who would not only let me do it, but excitedly supported me in doing it.

Double-diffusive mixing, for those of you who don’t recall, looks something like this when done in a tank experiment:


And yep, that’s me in the reflection right there :-)

Why should anyone care about something so tiny?

Obviously, there is a lot of value in doing research to satisfy curiosity. But for a lot of climate sciences, one important motivation for the research is that ultimately, we want to be able to predict climate, and that means that we need good climate models. Climate models are used as basis for policy decisions and therefore should represent the past as well as the present and future (under given forcing scenarios) as accurately as possible.

Why do we need to know about double-diffusive mixing if we want to model climate?

Many processes are not actually resolved in the model, but rather “parameterized”, i.e. represented by functions that estimate the influence of the process. And one process that is parameterized is double-diffusive mixing, because its scale (even though in the ocean the scale is typically larger than in the picture above) is too small to be represented.

Mixing, both in ocean models and in the real world, influences many things:

  • By mixing temperature and salinity (not with each other, obviously, but warmer waters with colder, and at the same time more salty waters with less salty), we change density of the water, which is a function of both temperature and salinity. By changing density, we are possibly changing ocean currents.
  • At the same, other tracers are influenced: Waters with more nutrients mix with waters with less, for example. Also changed currents might now supply nutrient-rich waters to other regions than they did before. This has an impact on biogeochemistry — stuff (yes, I am a physical oceanographer) grows in other regions than before, or gets remineralized in different places and at different rates, etc.
  • A change in biogeochemistry combined with a changed circulation can lead to changed air-sea fluxes of, for example, oxygen, CO2, nitrous oxide, or other trace gases, and then you have your influence on the atmosphere right there.

What are the benefits of including tiny processes in climate models?

Obviously, studying the influence of individual processes leads to a better understanding of ocean physics, which is a great goal in itself. But that can also ultimately lead to better models, better predictions, better foundation for policies. But my main point here isn’t even what exactly we need to include or not, it is that we need a better flow of information, and a better culture of exchange.

Talk to each other!

And this is where this tale connects to me missing institute seminars: I feel like there are too few opportunities for exchange of ideas across research groups, for learning about stuff that doesn’t seem to have a direct relevance to my own research (so I wouldn’t know that I should be reading up on it) but that I should still be aware of in case it suddenly becomes relevant.

What we need is that, staying in the example of my double-diffusive mixing article, is that modellers keep exploring the impact of seemingly irrelevant changes to parameterizations or even the way things are coded. And if you aren’t doing it yourself, still keep it in the back of your head that really small changes might have a big influence, and listen to people working on all kinds of stuff that doesn’t seem to have a direct impact on your own research. In case of including the parameterization of double-diffusive mixing, oceanic CO2 uptake is enhanced by approximately 7% of the anthropogenic CO2 signal compared to a control run! And then there might be a climate sensitivity of processes, i.e. double-diffusive mixing happening in many ore places under a climate that has lead to a different oceanic stratification. If we aren’t even aware of this process, how can we possibly hope that our model will produce at least semi-sensible results? And what we also need are that the sea going and/or experimental oceanographers keep pushing their research to the attention of modellers. Or, if we want less pushing: more opportunities for and interest in exchanging with people from slightly different niches than our own!

One opportunity just like that is coming up soon, when I and others will be writing from Grenoble about Elin Darelius and her team’s research on Antarctic stuff in a 12-m-diameter rotating tank. Imagine that. A water tank of that size, rotating! To simulate the influence of Earth’s rotation on ocean current. And we’ll be putting topography in that! Stay tuned, it will get really exciting for all of us, and all of you! :-)

P.S.: My #COMPASSMessageBox for this blogpost below. I really like working with this tool! Read more about the #COMPASSMessageBox.


And here is the full citation: Glessmer, M. S., Oschlies, A., & Yool, A. (2008). Simulated impact of double‐diffusive mixing on physical and biogeochemical upper ocean properties. Journal of Geophysical Research: Oceans, 113(C8).