Hello Again everyone,
Summer School is not only about attending lectures and learning from the professors, but also about learning from each other. We have all been invited to give talks on our research projects or other topics which are important to us. Yesterday I gave a presentation about some of the tools which we oceanographers use to gather our data. Perhaps you would be interested in these topics as well? Warning: I am a biological oceanographer, and this affects the way I use certain tools and what samples I’m most interested in.
Our first tool is the ship we sail on – this beautiful creation of steel + human ingenuity that allows us to reach the wild regions we have chosen to study.
The next most versatile tool, which is shared between many different disciplines of Oceanography, is known simply as the CTD (Conductivity, Temperature and Depth) profiler. But that is far from all it does. While the simplest version of the CTD can be operated on its own and return just those three variables, the one we have on board is much more exciting. The CTD is deployed as part of the ‘Rosette’ – a cylindrical steel cage with 24 big plastic water bottles bolted to the frame. These 10 liter water bottles are known as “niskins” and they are what allow us to bring water samples back up from different depths. Below and around them, our various instruments are also bolted to the frame:
Conductivity: a sensor which measures the ability of the water to conduct an electrical current, from which we are able to derive the salinity of the water parcel. Salinity is a great natural tracer, and combined with temperature, will give us the density of water. These 3 characteristics can serve as a ‘passport’ and allow us to pinpoint the origin (river, sea, glacier, ocean basin etc) of the water.
Oxygen: a sensor which measures the amount of oxygen in the water – this is useful for biological studies and can also be used as an origin tracer in some special cases.
Temperature: How hot or cold the water is – water has what we call a “high heat capacity,” meaning that it takes a long time to warm it up and a long time to cool it down. This property is what allows us to use temperature as an origin tracer. It is also interesting from a biological standpoint because every critter in the ocean has a range of temperatures in which it will survive better than others. So knowing the temperature of a body of water can help you figure out what lives there.
PAR (Photosynthetically Active Radiation, aka sunlight): Scientists like fancy names and acronyms – but it can get annoying too I know. This little white bulb measures how much light is in the water at any given depth. This can tell us how far down photosynthesis (plants making food from sunlight) can happen, and at what point plants and animals change to different survival methods (that don’t require light).
ADCP: Acoustic Doppler Current profiler – This instrument is for physics mostly. It uses the Doppler effect (like when you hear a fire engine coming from far away and the sound seems to get louder/speed up as it passes you and then slows down as it gets farther away) to measure how fast, and in which direction, the water is moving at each depth. This can help us calculate how much water is moving through a given area, and how currents interact with each other.
Depth (pressure + altimeter): These are a pair of really quite important instruments which work together. The pressure sensor measures how far our instruments are from the surface of the water – we use this to know when we want to take a sample. The Altimeter bounces sound waves off the bottom of the ocean to tell us how close we are to hitting the bottom. With so many expensive instruments on the Rosette, NO ONE wants to hit the bottom and risk breaking anything. In shallow water and calm seas, you can get within 5 meters of the bottom and be safe. Out here in the deep, and without perfect maps, we stay 30 meters off the bottom just to make sure we don’t hit any unexpected rock spires.
Transmissometer: Super awesome, it shoots a beam of light from one end of a tube, and catches it at the other and measures how much of the light beam actually got through. From that we can calculate how much stuff is in the water. Depending on how cool your particular model is, it might be able to tell you if the stuff is sediment particles (dirt) or plankton (cells & other biology) based on the way the light beam scatters.
The key to good science is good record keeping. As we send all these nifty instruments down to the bottom, we write down the latitude and longitude of our station, the time, the date, the weather outside, how deep the bottom is and how deep we’re going, the depth of the first layer of water (which is typically denoted by a rapid change in density known as the pycnocline), the depth of any interesting features in the profile, and the depth where we close each water bottle to get a sample. We also record what further samples (like salinity, nutrients, chlorophyll-a, oxygen isotopes, etc) we will take from which niskin bottle. I could go on, but I think you have enough to process for today. As always, let us know what sparks your curiosity, and we’ll answer you as best and as fast as we can!
– Florence van Tulder
Hi Lindsay, its Chris from LEOMHS. Do you apply any knowledge of Physics towards the work that you do in the Arctic?
Hi Chris, absolutely, physics is everywhere! You should look at the blog this Friday morning 9/13, because I wrote a post especially for you and the other students who have been asking me about all the ways physics is “onboard” with us. Everything, from how the ship moves, to how we run experiments, to how we lower things in the ocean, to how we graph and analyze our data, to the colors in the ice, is all physics!
What would you classify as the greatest challenge for you when trying to experiment and research about the Earth’s climate meanwhile you are in this expedition?
Hi Vilanea, the thing that is most challenging is the huge variety of things to learn onboard. Trying to understand how the experiments work, what the processes are that the scientists go through in their experiments, how the ship works and navigates through the ice, and even how the ice is formed and what it means for the whole Arctic climate, is pretty challenging, but pretty awesome.
Did you experience any complications when using the tool?
Hi Stephanie, there was a time when the gear (called a winch) that the CTD cable is wrapped around on the ship got stuck, so they had to fix that to get the cable unstuck and the CTD back to the surface again. But we have done over 90 CTD casts by this point, and it runs smoothly nearly all the time!
Hello Lindsay,
I believe that just the term “Biological Oceanographer” sounds completely astonishing and complex. I really liked the whole idea of the CTD and its functions. I’m not sure if studying the samples you get back from underwater is part of your tasks or obligations. However, I’d like to know if it is and whether you’ve discovered or spotted anything different or new in your samples?
Dear Yohandra, here is your answer, straight from Florence, who wrote about all these cool careers!: On this cruise, I am a student before being a researcher. However, on previous cruises (mostly in the Bering Sea), I have been in charge of filtering our water samples looking for chlorophyll. When you filter water, depending on how much stuff is there, there will be more or less color on your filter, and this changes from station to station. Sometimes, you could catch something a little larger than anticipated – like a pteropod (marine snail) or ctenophore (like a little jelly-fish, but not quite).
Also, using the PAR instrument how far below water have you guys gone? Did you not any odd plants growing underwater even without sunshine/light?
Hi Yohandra, I checked with Florence (who wrote about the PAR), and here is the answer, direct from her!: The PAR sensor goes as far down as the CTD rosette. As for how far light penetrates, that depends on what’s happening in that particular location. If we are near a river, sediment outflow might make the water really cloudy. If there is a phytoplankton bloom, the concentration of plankton might block out light to the lower levels of the water. As soon as you get below the light level, there are quite a few different survival strategies for plants. My favorite is chemosynthesis – instead of using light for energy, the plants and animals that live at hydrothermal vents (underwater volcanoes) use the heat and nutrients released from the vent to make their food. If you want to try this at home, you can take a white bucket lid, for example, attach a string, and lower it into the water (pond, ocean , etc), and mark the rope when you can’t see the lid anymore. If you measure the length of the rope that was underwater, you have your own “light depth.”
hi Lindsay its Oscar from leomh, whats the deepest dive you have done ?
what type of animals do u see under the water ?
Hi Oscar, the deepest we have gone is 3,800meters (almost 2.5 miles)! Of course when I say “we,” I mean that we have sent instruments down to the ocean floor on cables, in order to take measurements of the water between the bottom and the surface. We do not physically go in the water ourselves. So we don’t see firsthand any animals in the water, although when we bring water samples up from the ocean, they might contain microscopic organisms called phytoplankton, which are the base of the ocean food chain and very important for the environment.
Hi Lindsay,
How long do you keep the CTD in the water for the data collection?
Dear Marlene, the CTD always goes down to nearly the ocean floor, so how long it is down depends on the depth of the water at the time. I think the shortest one has been around 250meters deep, and the deepest has been 3,800meters deep (almost 2.5miles)! To give you an idea, for a depth of about 1000meters,, it takes about an hour for the CTD to go down (taking measurements as it goes), and then it takes about an hour and a half to come back up, because that is when it stops at several different depths to take water samples.