The mystery of Lokksund. Mysterious as ever, and I am still intrigued…

Forget climate change and all the big questions, there is this one thing that is really bugging me because I haven’t figured it out yet, but I really want to: This morning, when I was searching my old backup drives for data for my friend, I came across my favorite oceanography riddle of all times (which is still, as far as I know, unsolved!).

In 2012 and 2013, I went on cruises in the area of Hardangerfjorden, and there is one place that I find very intriguing: A narrow straight, connecting Hardangerfjorden in the south to Bjørnafjorden in the north. This straight is called Lokksund, and in its narrowest bit it’s only something like 20 meters wide and 30 meters deep. Which, as soon as water levels on both ends of the street are not exactly the same, leads to pretty strong currents.

In the description of Norwegian shipping lanes, it says about Lokksund “in the narrow part of the straight, the tidal current can be strong, up to 3-4 knots during spring tides, shifting direction every two hours. It goes southward for two hours before high tide, stops at high tide, goes north for two hours after high tide, and so on. … If there is constant wind from the south, the current can go continuously northwards. For wind from north or west, the same situation can happen with southward currents” (Den norske los 3, Farvannsbeskrivelse, Jørem Rev-Stad, 2006).

That the current is very strong in the straight was fairly obvious, and captain and crew were understandably not too happy that we wanted to spend a lot of time there (funnily enough, it’s Lokksund you see on the map on the screen in the picture below! Clearly, I really wanted to go there!).

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On the bridge, discussing the scientific plan for the next day. Picture courtesy of Angus Munro.

However, the current directions that we observed didn’t seem to agree with the farvannsbeskrivelse, but they also did not seem to agree with tides from mooring data we had from north and south of the mouths of Lokksund. So we ended up doing a repeat CTD station just north of Lokksund. The CTD data is very interesting:

Above, you see a plot for salinity, and below for temperature. And there is a strong interface in both S and T — approximately at sill depth! — that is oscillating with the same frequency as described in the farvannsbeskrivelse, although from what I remember the timing was somehow different from what we expected based on the tides from the mooring data we had available.

Also, looking at how narrow the straight is, even with peak speeds of 3-4 knots, the volume of water that can actually go through Lokksund is actually very small. So even though the mixing in the narrow spots with high speeds is probably very high, the volume of displaced water is still very very low, and it’s not even clear how big its influence on mixing between the two fjords is.

But that’s not what makes me so intrigued: It should be such an easy system to understand: A narrow straight and water levels on either end driving the flow through the straight. Right? Except there is clearly more to it, and I wish I could go back there and figure out what that is!

I know for a fact that to this day, some of the crew vividly remember the time we spent in Lokksund during that cruise, and that they don’t have the fondest memories of being in a narrow straight in a strong current in the dark. But I still think it was good we spent all that time there, and luckily Elin is taking on this riddle now, hope you will keep us posted on what you find! :-)

Student cruises (part 5 of many, or – thank you to a great mentor)

The first student cruise I ever taught while being taught by one of the greatest teachers myself.

As you might have noticed from the last four or so blog posts, I really enjoy teaching student cruises and I think they are a super important part of the oceanography education.

So let me tell you about the first student cruise I taught. I was lucky enough to co-teach it with one of the most experienced and knowledgeable oceanographers out there, who was excited about sharing with me all there is to know about cruise planning, cruise leading, teaching at sea and many other topics.

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Me and Anne on watch during that student cruise. Picture courtesy of Angus Munro.

From the first day of the first cruise onward, my ideas and contributions were welcomed, and I got to heavily influence the scientific program of the cruise. On the second day of the first cruise, I was told to just walk up to the captain and tell him if I wanted to change the course and go measure somewhere else than planned.

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On the bridge, discussing the scientific plan for the next day. Picture courtesy of Angus Munro.

The cruise ended up being great learning experiences for me. For the first time, I got to decide how to allocate ship time to best investigate the question that I thought was most interesting, a topic that I had never had (the chance) to deal with previously.

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Getting the small boat ready to recover a mooring. Photo courtesy of Angus Munro.

At the same time, I had the opportunity to learn from – and work with – the best. One of the practical highlights: A mooring release had not been working reliably in the past, but it was the one that we had with us on this cruise. So what to do?

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Recovering a mooring. Photo courtesy of Angus Munro.

Easy! Just tie a rope from the mooring to a tree! (Ok, so maybe this isn’t generally helpful, but if you are in Lokksund, this is genius)

And then I got to spend a lot of my time on watch (and a lot of my time off watch) discussing what we were seeing in the new data, what we could learn from that, where we should go next to prove or disprove our new theories.

And I got to watch a great teacher interact with his students (other than me). I saw how he challenged, how he encouraged, how he helped, how he guided, how he inspired.

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Bringing the mooring back on deck. Photo courtesy of Angus Munro.

Thank you so much, Tor, for being the role model you are and for having given me all of this, which I have since been striving to give to my own students.

All photos in this post were taken by Angus Munro (thanks!) on the 2012 GEOF332 student cruise.

Student cruising

Why student cruises always end up being on the most beautiful days of the year, or: why student cruises are an important part of the education.

Remember the picture I showed in the last post, that was worthy of being on an Advent calendar or postcard? The one below?

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FS Håkon Mosby arriving back in Bergen in November 2013.

That was taken on this year’s GEOF130 student cruise.

And remember the ice-on-Hardangerfjorden picture I shared a while back? This one?

Oh, taken on this year’s GEOF332 student cruise.

And the student cruise before, GEOF130 in 2012, looked like this:

See a pattern here?

So how come we always end up being out on the perfect day? Well, firstly, clearly I am that good. Or that lucky. But then, the perfect day only becomes the perfect day when you give it the chance.

What I mean is that on student cruises, it is easy for a day to become perfect. Because it is exciting to be on a research ship for the first time, to figure out how to measure oceanographic data, to develop a feeling for how much the ship is actually supposed to be rolling before you have any reason to become concerned, to see how your oceanography classes apply to the real world, to put on an orange one-fits-all survival suit, to gauge how you can influence the quality of the data by paying attention (or not), to get a break from your everyday life, to eat all the awesome food all the time, to visit the captain on the bridge, to see the familiar city from the water, to see a whole new world opening up to you, to experience what it could be like to be an oceanographer.

Especially in the “introduction to oceanography” lecture GEOF130, the student cruise is so much more than just knowledge transfer – it is an incredibly important part of building a professional identity that helps students to find motivation to sit through boring lectures and to fight through difficult exams because in the end they will then get to do this again: to go an another cruise and have more perfect days at sea.

 

Ice in the ocean – my historical photos

Ice formation in the ocean – using my own photos to tell the story.

Recently I talked about using my own photo to explain the generation of wind-generated waves to students. And then I realized that there is another set of photos that I have been using for teaching purposes for years that I could share here, too. Those are photos that I took on my very first “real” (as in “not a student, but participating in real research”) cruise back in 2003. In a time when pictures were still analog and you could take 36 pictures and then you had to change to a new film if you had planned ahead and brought one. I think I brought 6 films on the one-month cruise. It seemed excessive at the time, and today I easily take that amount of pictures in a day, especially when at sea and in the ice.

Anyway, let’s talk about the ice.

Newly forming  ice in the front, older ice in the back.

In the picture above you see several different kinds of ice: Older ice that looks like what you would imagine ice to look like in the back towards the horizon, and newly forming ice between the old ice and the ship. The ice has only just started freezing and forms a slush at the ocean’s surface that dampens out wave movement. In places, pancake ice is starting to form.

Pancake ice.

Pancake ice are almost round pieces of ice that are formed when slush freezes together. Since there is still some wave action in the water, the little ice plates bump into each other, forming a little puffy rim. Pancakes typically have a sizes ranging from the palm of your hand to maybe half a meter.

Several of the pancakes frozen together to form larger ice floes.

If the sea state isn’t too rough and the cooling continues, several of the pancakes freeze together to form larger ice floes.

Pancakes frozen together to form a closed surface.

Eventually, pancakes freeze together to form a closed surface.

Sea ice cover, additionally covered in snow.

If cooling persists, the sea ice cover thickens gradually, and snow falls on the surface.

I was so lucky to see all of these different stages of ice on my very first research cruise! And I was even luckier – in this year’s GEOF332 “field course in oceanography”, I got to show pancake ice to my students, in Hardanger fjord in February! Granted, the pancakes were really thin and we never got to see a closed sea ice cover, but what an awesome first day for a student cruise!

The Hardanger fjord covered in pancake ice on February 1st, 2013.