Tag Archives: oceanography

Recovering an oceanographic mooring

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So in my previous post we deployed a mooring (in fact, those pictures were from the deployment of several different moorings). Now how do we get such a monster back on board again?

Recovering a mooring is always slightly nerve-wracking, because even though we’ve tried very hard to forget about this possibility during the year the mooring was out there in the ocean, it is never 100% certain that we will actually be able to recover it. It might not be there any more, or it might be out of batteries. I have been on cruises where we have had to give up on recovering moorings, or on another one where we had to dredge for a mooring (and found it!). Luckily, on this cruise things went smoothly and the way they were supposed to:

A sound signal is sent and establishes contact with a releaser that connects the anchor with the rest of the mooring. After establishing the position of the mooring, a signal is sent and the releaser lets go of the anchor: The mooring floats up to the surface!

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Then, the task is to spot the orange floatation thingies in the waves.

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And bring the ship close enough to actually connect a hook to it.

 

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Once it is on the hook, it needs to be brought on board.

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Remember, it’s hundreds to thousands meter of rope we are talking about! Luckily the Håkon Mosby is (as all research ships are) equipped with plenty of winches and cranes and a super helpful, knowledgeable and skilled crew.

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Instruments are brought on board individually (or, in this case, a releaser).

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After having been out in the ocean for a year or two, they are sometimes overgrown with stuff. And in this particular case, that bio stuff was stinky!

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But pretty, I have to admit. I think it’s some sort of cold water coral. I think. Any biologists here?

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But there is always a lot of stuff to be recovered.

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And also pretty interesting: This is the first time I got a good look into one of those orange flotation thingies. I knew there was a glass sphere inside, but it was nice to actually see one. I had previously seen one that had imploded – it ended up pretty much pulverized. But so this is what we knock around on deck and throw out into the ocean:

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But yeah. In a nutshell, this is how moorings are recovered.

Deploying an oceanographic mooring

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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?

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

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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

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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.

Oceanographic concepts and language (part 4)

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On how it always helps to speak the same mother tongue as your teacher.

As you might have realized from previous discussion on the topic of oceanography and language (part 1, 2, and 3), I have been thinking a lot about how me teaching in a foreign language to both me and most of my students affects my teaching, our interactions and their learning. I thought I was very aware of the difficulties that arise due to the second (or third or fourth) language issue, and that that awareness was helping me deal with it in a good way.

Recently though, I was supervising students writing the exam for the course I had taught. I was walking around, talking to individual students, and a german student asked me a question to clarify what I wanted them to do. Specifically, the student repeated the question back to me in German and asked me to confirm that their understanding was correct, which it was. And that was when I realized that even though I have always been teaching in English, and always tried to respond to students in one-on-one situations in whichever language they approached me in, german students really have an advantage in my class.

Similarly, when correcting exams, I understand the false friends that german students might use, or their weird choice of words. And while I always try to separate language problems from problems with the oceanographic concepts, I might not be doing such a good job for students whose languages I am not familiar with. Actually, not “I might not be doing such a good job” – there is no way I would do a good job if I was not familiar with the language and the false friends or weird sayings or typical mistakes that come with that language.

I don’t know how to resolve this. I don’t even know whether it is possible. I am sure that the effect is small in my courses and grades because I am aware and actively trying to make sure this isn’t unfairly helping or hindering students. But this is the first time that I think of being back in a primarily german-speaking environment as an advantage – at least I am not introducing unfair circumstances due to different languages.

What do you guys think? Have you come across these problems? How did you deal with them?

Mediterranean outflow

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Students demonstrating the mediterranean outflow in a tank.

As reported earlier, students had to conduct experiments and present their results as part of CMM31. Niklas chose to demonstrate the mediterranean outflow – warm and salty water leaving the Mediterranean and sinking to a couple of kilometer’s depth in the Atlantic Ocean.

Since I happened to be around, they allowed me to document the experiments and blog about it, but there is a great description, including a movie, to be uploaded on the webpages of the University Centre of the Westfjords.

When the guys were done with the experiment, I couldn’t help but suggest to tip the tank so that the densest water would spill back into “the Mediterranean”. Check out the movie below if you fancy playing!

Rogue waves in a bath tub

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Trying to create rogue waves in the bath tub of the infamous “red house”.

As a part of their projects, students in the CMM31 in Isafjördur course had to conduct an experiment, document and interpret it. One of the students, Silvia, chose to create rogue waves in the bath tub of the “red house”, one of the student houses, and I was invited to participate and eat delicious cupcakes.

Since rogue waves can have devastating effects on ships they encounter, clearly we had to have a ship. None were to be found, so we had to make our own.

Since most studies of rogue waves in wave tanks had a hard time actually producing the waves (and a bathtub might not be the most ideal setup) we did not have high hopes that our experiment would be successful. And we did not manage to produce rogue waves in the strict sense – but we managed to avoid major spillage of the tub and still sink a couple of the paper boats, so at least we were getting some results.

Great to see students do experiments on a Sunday afternoon!

Types of breaking waves depending on steepness of slope – small scale

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Video of different types of breakers – small scale.

In this recent post we talked about types of breakers depending on the steepness of the slope. But even on a single stretch of coast line you can easily observe several kinds of breakers. My friend E lend her cabin on an island just outside of Bergen to me and another friend E for the weekend, and just sitting on the rocks we could observe at least two types of breakers.

Different types of “breakers” depending on the slope of the beach. Also see video below where it might become more clear…

In the movie below, you see surging breakers on the first little headland – the water level just raises and falls and no breaking occurs – whereas in the small bay behind the headland and on the next headland the slope is much less steep and here spilling breakers develop. Spilling breakers can also be seen about halfway through the movie on the right hand side beach. Isn’t it awesome how you can see so many concepts on the smallest scales once you start looking for them?

Waves breaking depending on steepness of the slope

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Waves breaking on slopes of different steepnesses.

Depending on a slope’s steepness, waves can break in very different ways. On nearly horizontal beaches, spilling breakers develop. On steeper beaches, plunging breakers, the kind of breakers that form the tunnels that people surf in, form. And on very steep beaches, the breakers don’t actually break, but surge up and down.

Types of breakers developing on beaches depending on the beach’s slope.

This can be seen on  the large scale when different beaches are known for different kinds of breakers, and one impressive example are Oahu’s North Shore plunging breakers that my friend Tobi took me and a couple of friends to see in 2010.

Plunging breakers on Oahu’s North Shore in September 2010.

 

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Another plunging breaker on Oahu’s North Shore. See surfer for scale.

More awesome breakers were to be seen on the Big Island a couple of days later:

Plunging breakers on Big Island in September 2010.

And of course I have movies of those breakers for you, too, first Oahu and then Big Island:

 

Hydrothermal springs

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Hydrothermal springs that you can visit without a deep-sea submersible.

When teaching about hydrothermal springs, I usually use a video a friend of mine took of hydrothermal vents on the mid-Atlantic ridge on the WHOI submersible Alvin. But being on Iceland now, there is much better material available which students can even go and experience themselves.

In the Blue Lagoon close to Reykjavik.

I am too chicken to take my camera under water in the Blue Lagoon to film the hot springs, but there are other hot springs all over Iceland that are less scary, for example this one that my friend Astrid found in the middle of a meadow.

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View from the top into the hot spring – do you see the bubbles breaking the surface?

And here I even dared take my camera under water.

View of the hot spring under water – that’s where the bubbles come from!

Granted, this is not quite as impressive as a black smoker or the Blue Lagoon. But the water in the whole little lake was warmer than about 40 degrees Celsius, and the hot spring is sitting randomly in a field. That’s hand-on geothermal heating for you!