We have done over 60 CTD casts on this expedition! It’s truly amazing. For new readers, CTD stand for conductivity, temperature, and depth, and is an instrument that we lower down into the water – way down, sometimes to a couple thousand meters – to take water samples at many different depths. And “cast” refers to the process of lowering it into the water for measurements and then bringing it back out again to get the water samples. I’ve told you about some of the activities in the hydrochemistry lab – studying the oxygen, nitrates, and salt content levels, temperatures, and phytoplankton growth in water samples taken by the CTD – and here are some of the people that make it happen!
- Anna Nesterovich is measuring the silica content of water from different depths. Photo from Anna Nikulina
Hey Lindsay,
I was wondering once you collect the information from the water samples, what do you do with that information? Do you model the information, or does it just go into a database? Very curious, let me know!
Hi Sabrina, you are on the right track with your ideas about what scientists do with the water samples! Some measurements are done “on the spot” like temperature, salinity, depth, oxygen levels. These are even done when the instrument is still in the water and before they even have the samples in the lab! Once the water samples are collected when the instrument comes back on the ship, some procedures are done right away, like some of the oxygen experiments (because you have to be so careful not to contaminate them with oxygen from the air). But the samples will all go back with the scientists to their respective institutions, where a lot of the analysis will be done long after we’re off the ship. But they will all still be collaborating with each other, and sharing the data and what they learned (because as I said, what each of them are doing is part of the big picture of climate)!
Dear Lindsay, how does the CTD get the water in the grey bottles? the exact amount that each bottle needs?
Hi Daniella, that’s a question that I had to ask at first too! On the way down, the bottles on the CTD rosette are open, and the instruments take measurements of water temperature, salt content, and pressure. On the way back up, scientists electronically send a signal down the cable to each bottle, to snap closed at a certain depth. So each bottle takes a sample at a different depth. And the bottles are bigger than the amount of water that the scientists need for their experiments, so they always have enough, and even some left over if they need it.
Hi Lindsay. When the CTD is cast into the water, how long do you have to for it to come out of the water ?
Dear Rochae, it depends a lot on how deep we’re sending it down – sometimes it is “only” several hundred feet (which is still far), and sometimes we send it down almost to the bottom – almost 2.5 MILES down. When we send it down, we take measurements on the way down (like temperature, oxygen, and salt content), and then take water samples on the way up! For a 1000meters cast, it takes about an hour on the way down, and an hour and a half on the way up (because we let it sit still for a minute every time we stop to take a measurement at each depth).
Hi Lindsay. Has there ever been a case where the CTD was placed into the water and it got stuck so you werent able to retrieve it? If so, what do you do in case like this ?
Hi Rochae, it has happened that the CTD or the related instruments might get temporarily stuck, but we would never leave it behind – it is expensive, amazing equipment. One time on the ship, the winch (which is the wheel/gear on the ship that the cable attached to the CTD wraps around) got stuck, but they fixed it pretty quickly and got the CTD back up again.
Hi Lindsay,
I am happy to see chemists at work in the chemistry lab on board. I am a chemist by training (though my career has taken me away from the labs for more than 20 years).
Is there anything that really differentiates the arctic odean from other oceans around the globe (different trace amounts of elements, usual concentration of specific solutes …?). I’d be curious to know if any of the chemists on board could comment.
Thank you!
Pierre
Hi Pierre, I talked with some of the chemists here for you, and here’s a little more information about Arctic chemistry. It is a really unique system, and Arctic waters can actually be tracked as currents head into the Atlantic and elsewhere. Oxygen levels are one example of unique conditions: in general, you’d expect higher oxygen levels in fresher, colder waters, and lower oxygen levels in more saline warm waters. But in the Arctic, the presence of sea ice suppresses surface mixing with atmospheric oxygen, which leads to decreased oxygen levels in the water (as opposed to in the tropics, where events like algal blooms would tend to increase oxygen levels). I’m told by the chemistry team that this question has a lot of possible details in the answer (as you might expect, being a chemist yourself), so let me know if you want to know more!
Hello Lindsay,
I hope all is well. I just wanted to ask if the oxygen levels are lower in such freezing waters like those, as opposed to other warmer waters.
Hi Camila, great question, I spoke with one of the chemists onboard for you. There can be a really long answer explaining the factors involved in your question, but to sum it up, you would expect the oxygen levels in fresher, colder waters to be higher, and the oxygen levels in warmer, saltier waters to be lower. In the Arctic, the presence of sea ice can suppress the mixing of atmospheric oxygen at the surface, which leads to decreased oxygen levels in the water. In the tropics, algal blooms would tend to increase oxygen levels. And as a whole, oxygen levels decrease with depth in the oceans.
hello i wanted to know what was the hardest part of the 60 CTD casts on your expidition ?
Dear Kayla, I asked the scientists your question on your behalf, and they said that at the beginning, the most challenging thing was to figure out the most efficient process for organizing how they work with the samples when the CTD rosette comes out of the water. Some of the experiments are sensitive to gases in the atmosphere (like the oxygen experiments), so those samples need to be processed first, and there are a lot of experiments and a lot of scientists with different goals and needs. But they have the process “down to a science” now.