This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
There's a lot of science lingo I don't know. There's also a lot of nautical lingo I don't know. Combined, I often have no clue what some of the people on the boat are talking about. One term that comes up a lot from the science team is something called the "CTD." As a reader pointed out, the CTD is technically just one sensor on the whole rig pictured below. Everyone on board calls the whole structure "the CTD," probably because saying "the 24 niskin bottles and CTD sensor" doesn't exactly roll off the tongue.
CTD stands for "conductivity, temperature and depth" but it does a lot more than that. As far as I can tell, it's probably the single most important piece of scientific equipment on the boat. It collects water from the ocean, which may sound like an easy thing to do -- we're surrounded by the ocean after all -- but getting the right *kind* of water is key.
Why don't we just throw a bucket overboard to get water? Not all water in the ocean is created equally. You probably know this already. Deep water is cold and dark, while surface water gets more sun. That impacts what can live at different depths. The very surface of the water is often not all that rich - it gets too hot and too rough for most things to live. So in order to get useful samples -- for the crew onboard the Knorr, that means samples with lots of phytoplankton -- scientists have to get water that's a bit deeper. And this is where the CTD comes in.
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Each of those 24 "niskins" -- the grey canisters you see -- collects water. When the CTD is submerged, the canisters are open on both ends and water can flow in and out freely. Someone in the control room decides when to close each bottle (in Knorr speak, whoever's in control is "flying" the CTD). Some people might want water from 50 meters deep, while others might want water from 1000 meters. The flyer simply closes different bottles at these different depths.
Along with the canisters, there are other sensors on the CTD that take readings as it descends -- things like temperature, light and salinity. The more information you have about each sample, the better you can compare them.
When the CTD comes up, everyone on the science team gets to work. Most people need water samples to do their work, whether it's staining for chemicals, looking for viruses, or finding phytoplankton to incubate. So there's actually a water budget: each time the CTD goes down, people can claim a canister or a portion of a canister to analyze.
Lowering the CTD is no small feat. It's really heavy and it's made up of lots of really expensive equipment. (There's a reason they don't let me too close to it.) Moving and dropping the CTD into the water involves a crane, several people, and an equal number of hard hats.
Because the CTD is so important, it will probably be used every day of our cruise. It's the engine of the scientific team, driving the research forward each day.
Have other questions about the cruise? Ask here:
During this trip, I'll be answering your questions about the science, this boat, and life onboard. Want to know how we search for plankton, why we're here, or what the food is like? Just ask me! And if you're wondering how I got here, check out the groups that made this adventure possible: Mind Open Media and COSEE NOW.