Measuring the concentration of dissolved oxygen in sea water – Part 1 of 3 – taking samples

Since my task on the recent Håkon Mosby cruise was to measure dissolved oxygen, I will give an overview over how that is done over the next couple of posts. Starting with today’s post on how to sample (because this isn’t as simple as just filling a bottle with sea water!)

In fact, sampling oxygen requires great care and I am very grateful to Ailin and Steffi for the excellent job they did. Ailin kindly agreed to let me take pictures of her sampling to illustrate this blog post.

Water is sampled in Niskin bottles on a CTD (For how the CTD and the water sampling in Niskin bottles works, see this blog post). We’ll start when the CTD comes back to the surface and sea water from various depths is trapped inside the Niskin bottles.


The rosette is brought back on deck, and things are about to get busy for us!


Oxygen has to be sampled as soon as the CTD is back on deck in order to avoid that the dissolved oxygen in the sample starts outgassing due to changed pressure, equilibrating with atmospheric oxygen, or do anything else that would change the oxygen concentration we are interested in measuring.

In order to not contaminate the sample, the hose which we use to sample needs to be free of air bubbles, too.


The sample flask is rinsed, as is the top, with water from the respective Niskin bottle the sample will be drawn from. The bottle is then filled until overflowing while care is taken that there are no bubbles trapped in the flask.


Next, two reagents are added (more on those in my next post, which will be on measuring dissolved oxygen concentrations). Adding more volume to an already overflowing bottle means that some of the sample is going to be displaced and flow out.


Then, the top is placed on the sample flask, again taking great care that no air bubbles are trapped in the flask.


And then the fun part (for the first about three samples, afterwards this part gets really really annoying) begins: Shaking! Until the sample and the reagents are very very well mixed.


We’ll end up with crates of sample bottles, all filled with something that looks like cloudy apple juice:


And we’ll talk about how we can measure those samples in the next blog post.

Joys of a sea-going oceanographer

So you might have noticed that the last 6 weeks or so all posts had been scheduled ahead and that I was strangely absent. Yep. That’s because I was on a research cruise in the Nordic Seas. But be assured – we’ll be talking about that for the next couple of posts!

First, let’s get some stuff out of the way, like: Did we see whales? Yes, we did! First, an orca.


It was so close to the stern of the ship that I couldn’t get a better picture since it was really THAT close.


Then the guy below. He surfaced out of nowhere when I was standing on the bridge, having a chat. And then he was gone again, never to be seen again. Just like that. (See the handrail of the ship in lower left corner of picture? Yes, that’s how close he was)


But most whale sightings looked like that one:


Or that one.


Next couple of posts: How to measure dissolved oxygen in sea water. `Cause that’s the reason I got to go on the cruise in the first place… :-)

A touristy post about my trip to Heligoland

I recently went on a trip to Heligoland, Germany’s only island that is far away from the mainland (70 km in this case). It was a great trip, and I know you’ll be reading about it for some weeks to come :-)

Today, we’ll just do the touristy parts, though, and get into the oceanography later.

The trip started out super awesome. I went on a ferry and got the chance to see ships being greeted by Wilkomm Höft, the Ship Welcome Station, by dipping the Hamburg flag and playing the national anthem. I’ve seen this before, but only from land (this is a place that I love going to for birthdays, mine and other people’s). Sitting on a ship and being bid farewell this way is really touching! I loved it and got a little teary-eyed.

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Being bid farewell (by dipping the Hamburg flag and playing music) at Wilkomm Höft in Wedel on the Elbe river.

The ferry itself is a high speed catamaran, which, as you might have guessed, produces an amazing wake.

Wake of the Halunder Jet, the high-speed ferry going from Hamburg to Heligoland.

Unfortunately, the ship is set up such that the rescue boats obscure the view of the wake a little. How inconsiderate ;-) Please ignore the outboard engine…

On Heligoland itself, there are the famous red cliffs, and tons of birds. Let me just show you a few:


The best-known part of Heligoland is the Lange Anna — a red rock called “long Anna”. You see it on the picture below. What I liked most about it — besides the beauty of the rock and the birds, obviously — was the wave breaker build there to protect the coast, and what it did to the waves.

“Lange Anna”, the famous red rock on Heligoland in the German Bight

Zooming in on the wave breaker’s edge, there is clearly very strong winds coming around that corner:


To be fair, it was a super windy day.

They also have a very nice beach on Heligoland, where you can see the bending of waves due to changes in topography that we talked about before.


And if you look over to the second island, you can very nicely compare and contrast the upwind and downwind coasts of islands:

See how there are lots of breaking waves (well, you probably only see the foam) on the upwind coast of the island in the back of the image, and how there are absolutely no waves in the lee of the sea wall in the foreground of that picture?


Btw, the downwind side of that same second island looks also a lot calmer as it is sheltered by the island itself:


Unfortunately, I couldn’t take a picture of the whole island at once, I really need to upgrade my camera… But can you spot the rainbow above?

Also there is some more, pretty spectacular weather to be seen:


If you go over to the other island, there are TONS of seals. Like several hundred, right on the beach! Obviously, I only have pictures of seals when there are also nice waves happening at the same time :-)


Oh, and birds.


And more seals! This one is cute, I have to admit…


Oh, and I was lucky (lucky means bold enough to ask!) enough to hitch a ride on the local research vessel, Aade. Below, they just finish a plankton trawl. We weren’t allowed out on deck because the weather was so rough…


What looks like a calm and serene morning really wasn’t one. It was super windy and wavy! Good thing I don’t get sea sick.


It turns out it’s super difficult to take pictures of waves that look as impressive as the waves are in reality. I really need to learn how to do that! But even if you don’t see the size of the waves, at least you get a different look at “lange Anna” below.


And these are white caps on the “open” sea, not waves breaking on a shore.


And for a nice comparison: The Aade (the research vessel I was on) and the catamaran that took me home later that night.


Anyway, it was a great trip!

Can you make “boring” math or physics exciting by relating it to the adventures of a research cruise in Antarctic? Elin can!

My friend Elin is currently on a research cruise in Antarctica and you really need to check out her blog. She is writing about life at sea, including the most beautiful photos of sea ice. Today’s post is called “ice or no ice” and describes the first couple of days of the research cruise. Elin combines the catching narrative with exercises and experiments that will be conducted by at least 30 schools all over Norway! And maybe you can use some of her posts, exercises and experiments in your teaching, too?

Today, for example, the exercises are all about ice. Depending on how much brain power you want to invest and how much prior knowledge your students have, you could for example do an exercise about Archimedes’ principle, calculating how much of an ice floe is visible above the water’s surface, and how many scientists you could put on it before people start getting wet feet. Or, more challenging, you could work with real data that Elin provides to practice your statistics and look at the annual cycle of sea ice in Antarctica. Or you could even set up differential equations for how ice thickness increases over time.

There will be new exercises every Monday for the next two months. How exciting!

Elin’s blog, “På tokt i Antarktis“, is available in English, Norwegian and Swedish. So you can use it not only to practice your maths and physics, but also your language skills! :-)

Btw, if you got hooked and can’t nearly get enough of reading about that research cruise, there is a second blog that tells you, for example, about the different kind of New Year’s Eve the scientists and crew had before heading off to Antarctica. Also very much worth a read!


Pinging, so we don’t hit the ground

I’ve been thinking about an old friends recently. I met Anton on a RV Knorr-cruise I was on in 2011, and we spent many fun night watches running CTDs. Together with Sindre, this was our favorite toy: The echo sounder. Many CTD packages have an altimeter on them so they don’t accidentally hit the bottom, and if the package is deep enough, funny pictures develop.

In the picture below, for example, you see the CTD at its deepest at the very left of the screen. The x-axis is time – as new time steps are added on the right, old ones eventually vanish to the left. The y-axis is time in milli seconds, which is more or less proportional to the distance of the pinger to the receiver on board the ship.


So on the left you see those two lines very close together – the top line being the CTD that is sending the chirps, the bottom line is the sea floor. As the CTD comes up again, its own signal rises to the top of the screen (because it’s coming closer to the receiver and hence the run times get shorter) and the sea floor sinks away (because the signal now has to travel down further and further before it is reflected up again).

Then what you see at the right of the plot are more parallel lines emerging. And those occur because the run length of the sound signal is longer than the time between two chirps, so the receiver registers both the actual reflection from the bottom as well as the reflection from a previous chirp.untitled

This is fine when the CTD is going up, but when it’s going down you have to pay close attention because you might have to cross what looks like a reflection from the sea floor a couple of times before you come close the actual sea floor. Unnerving if you aren’t as nerdy as Sindre and me and enjoy playing with this equipment!

In the plot below you can see more funny features: The left half of the screen shows the ship’s echo sounder (so the sea surface and sea floor staying in more or less the same place over time), and on the right we played with different scalings and zoomed in. Obviously, the smaller the units on the scale, the larger the magnification.untitled5So yeah. It was fun. And thanks for all the good times, Anton.