Tag Archives: research cruise

Deploying an oceanographic mooring

Do you want to know the full story behind the rope in the mystery picture the other day? On the recent Håkon Mosby cruise, we did a lot of mooring work, and that rope was part of a mooring that we recovered after it has been out in the Iceland Sea for two years.

So what are those moorings all about? The idea behind moorings is that it is super expensive to go out on research ships and that you can only stay out for a fairly short period of time compared to the amount of time you would like to cover with measurements. Therefore, installing instrumentation in the sea and leaving it out there for extended periods of time to measure and store data without anyone being close by, looking after it, gets you a lot of data that you could otherwise never obtain. Once a mooring is in the water, there is no communication with it at all until, after a year or two, we come back to pick up the instruments, read out the data and start on the science.

Moorings basically consist of a lot of rope. They are one or more long pieces of rope held down to the sea floor by a large metal anchor and then pulled in an upright position by large buoys that float at some depth underneath the sea surface. And then there are lots and lots of instruments attached to the ropes at different depths, most with their own buoyant orange floatation thingies [technical term] attached so that, if the ropes broke accidentally, they would float up to the surface and there is the (tiny) chance they might be recovered.

Below is a sketch of a mooring on the Kögur section (And check out the website http://kogur.whoi.edu for tons of information on that section!) to give you an idea of what those things look like (thanks, Kjetil, for letting me use the sketch, and thanks, Steinar, for the awesome work!). I was actually on both the cruise deploying that mooring in 2011 and recovering it in 2012 – check out the cruise blogs for those cruises, well worth a read even years later!

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So now without further ado: on to deploying a mooring!

Before a mooring can be deployed, though, a lot of work goes into preparing ropes of the correct lengths with shackles in between where instruments or floatation thingies go.

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On the day the mooring is deployed, instruments get attached to the ropes in the correct spots, so they end up at the right depths in the water.

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Since moorings are typically several hundred to thousands of meters long, instruments and floatation thingies cannot be attached beforehand and the whole thing then just be thrown out into the water. Instead, when a part of the mooring is ready, out it goes into the sea to make room on deck for the next one to be prepared to avoid creating a gigantic knot filled with very expensive instrumentation.

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The whole thing has to be very well coordinated, since there are several cranes and winches involved, and many expensive instruments that are all to end up at a specified depth to measure specific features.

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Below we see orange buoyancy floatation thingies being lowered into the sea, and still on deck there is an acoustic current meter that will be next.

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One thing I found super interesting on this cruise was to see the different generations of instruments all in use. For example, what we see being lowered into the sea in the picture below, above those orange flotation thingies, is a rotating current meter, predecessor to the acoustic current meter we saw in the image above. Rotating current meters work pretty similar to how we measure wind at home weather stations: The red vane will position the instrument in the current and the little wheel will turn with the current. Both the orientation of the instrument and the rotations of the wheel will be recorded.

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When all the instruments and orange floatation thingies are attached to the rope and it has all been lowered into the sea, everything is still floating on the surface. The final act is to drop the anchor that will pull everything under water and in an upright position. This, again, requires a lot of precision, because where the anchor is dropped determines the position in from all the data is going to be collected. So the way this works is that the ship is steaming pretty slowly towards the target position while instrumentation, floatation thingies and rope go over board, and if everything is timed well, by the time everything is out in the sea, the final position has been reached and the anchor can go out.

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Exciting stuff! One mooring we even deployed before breakfast (and I am showing this mainly because I like the colors in this pic).

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Next post will be on: So now how do we get those things back on deck again after their stint out at sea?

Reading the water – a new mystery picture for you!

Back by popular demand: Reading the water in my mystery pictures series!

Who knows what’s going on in the picture below?

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You might recognize a couple of details that might give you a hint: There are waves parallel to the rope and drops of water falling from the rope.

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And here is what happened: A floating rope was repeatedly being pulled up from the water’s surface and then sank back down as the research ship Håkon Mosby moved in swell (white). Each time the rope broke the surface, it caused waves that propagate away from it, the ones we see as lines parallel to the rope (yellow). And when it was pulled up, water dripped from it, so drops falling directly underneath the rope (green) cause the wave rings (red).

Like posts like these? Then you will love my upcoming book! Stay tuned! :-)

Measuring the concentration of dissolved oxygen in sea water – Part 3 of 3 – finding the titration volume by looking at the change in color

So now we have prepared our sea water sample and are ready to start titrating to figure out the concentration of dissolved oxygen. The sample itself changes color with added thiosulfate, it goes from yellow to lighter yellow to clear over a wide range of added thiosulfate. But determining the titration volume just based on this is a pain.

When measuring dissolved oxygen with automatic titration, the instrumentation that I used previously used a UV lamp and a detector: After each tiny volume of the titrant was added, the amount of UV light that made it through the sample as it changed it color from its original apple juicy-color to clear was measured and noted. Two lines were fitted to those data points: One while the color of the sample was still changing, the other when it wasn’t any more. The titration volume is found at the intersection of those lines.

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Winkler titration: What an automatic titration system measures

 

When measuring oxygen with manual titration, like I did on this cruise, we can’t take all those individual data points and then fit lines, we can just take one single reading the moment we think the titration volume has been reached (well, we can note down volumes when we think we are close, and then just use the one we think was closest to something actually happening. But we don’t have a good account of how close we were at each of those volumes, and we can’t go back in time to compare values, so it still comes down to either getting it right or not). Having a good indicator that clearly shows when the titration volume (I.e. the point at which the amount of thiosulfate solution added to the sample is proportional to the concentration of dissolved oxygen in the original sample) is reached is key.

Luckily, Kristin prepared an awesome starch mixture which I got to use that makes it a lot easier to determine the point when titration is done. You add it when the yellow of the sample has become so light that it gets difficult to see whether it is still yellow or clear already, and the sample turns a deep, dark purple. As you come closer to the titration point, color changes little until you are very close, when it changes very rapidly (that’s why you only put it in once you are fairly close, otherwise the looooong time with no changes would likely lead to you becoming too impatient, adding too large volumes at a time, and over-titrating [at least if you are like me at all]). Adding starch late and then having it change very sensitively to added thiosulfate makes it very easy to determine the exact volume of thiosulfate needed.

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Winkler titration: Sketch of the color changes of just the sample, or a sample with an added starch solution, during titration. Note how it is a lot easier to find the titration volume when starch is added at the right moment!

And here are a couple of impressions of what it looks like for real:

 

Winkler titration: Sketch + photos of the color changes of just the sample, or a sample with an added starch solution, during titration. Note how it is a lot easier to find the titration volume when starch is added at the right moment!

Winkler titration: Sketch + photos of the color changes of just the sample, or a sample with an added starch solution, during titration. Note how it is a lot easier to find the titration volume when starch is added at the right moment!

When writing this post and showing it to people, I have been warned repeatedly to not make myself redundant by making it too easy for other people to just print this blog post and go take my spot on the next cruise to measure oxygen. So I just want to state: Clearly there is more to measuring oxygen than what was shown here! For example, you need to measure standards to calibrate your measurements, which I am too lazy to write about right now. And most importantly: If something goes wrong, you need to be able to figure out how to fix things. And that’s not always a piece of cake, I can tell you… So please don’t use this as a manual. But I’m happy to talk about my experiences if anyone is interested!

And Kjetil and Emil, I really want to go on that winter cruise! :-)

Measuring the concentration of dissolved oxygen in sea water – Part 2 of 3 – the measuring part

So how do we actually measure dissolved oxygen concentrations from the samples we took in the last post?

We are using a method called “titration” to determine the unknown concentration of dissolved oxygen in our sea water sample. And this is how titration works in general: During titration, we add known volumes of a chemical, called “titrant”, to the sample until all of our unknown amount of the substance we want to measure has reacted with the second chemical. The volume of the titrant that we needed to add until all of the substance-to-be-measured is used up is called the “titration volume” and it is proportional to the volume of the substance-to-be-measured we had in the sample and that we want to figure out. Since the chemical reactions of the substances are well known, the factor that needs to be used to convert one substance into the other is known, too.

Unfortunately, when attempting to measure oxygen, we can’t add the titrant directly to the water sample, but a couple of other steps have to happen before. Remember the last post? We ended by adding reagents to the sample:

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To be precise, we add manganese sulfate first and then a mixture of sodium iodide and sodium hydroxide. This is shaken really well to mix everything. A white manganese hydroxide precipitate forms but is quickly oxidized by the oxygen in the sample. When this happens, the sample turns the color of brownish cloudy apple juice. This is where it is important that we don’t have air bubbles in the sample – the oxygen contained in those would also take part in the reaction which would later look like there had been a higher concentration of dissolved oxygen in the sample.

After a little while, a yellowish-brownish precipitate falls out. This is what we later want to measure, as the dissolved oxygen is bound in there and can’t take part in any further reactions for the time being.

A sample then looks like this:

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Or, for a full crate of samples:

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Next, using a syringe, we need to carefully, take about 20ml of water off of the top of the sample flask (because we will measure inside the sample flask and need to make room for the magnet stirrer and chemicals to be added later). This works surprisingly well without disturbing the precipitate at the bottom of the bottle!

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Next, we add acid (sulfuric acid in our case) to the sample to dissolve the precipitate back into solution.

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Where in contact with the acid, the apple juice becomes clear.

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It will become clear everywhere once the magnet stirrer starts mixing the acid and the rest of the sample.

And now we are ready to start titrating!

In titration, we add known amounts of the titrant, thiosulfate solution in our case, to our sample until we reach the “titration volume”, where all oxygen has reacted. The task is figuring out the titration volume. This can be done for example by adding an indicator that changes color when the sample changes from acidic to basic. Then we need to note down the volume of the titrant, the titration volume, at the exact point that happens. The titration volume of thiosulfate solution is then proportional to the concentration of dissolved oxygen in the original sample (again, provided there were no air bubbles trapped in the sample).

We’ll talk about what this looks like in practice in the next blog post :-)

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.

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

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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.

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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.

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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.

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

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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.

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

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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.

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

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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)

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But most whale sightings looked like that one:

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Or that one.

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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.

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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:

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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.

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“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:

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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.

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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?

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

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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:

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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 :-)

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Oh, and birds.

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

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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…

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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.

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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.

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

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

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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!

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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.

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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.

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