Learning the Water Sampling Routine

Foggy weather as the rosette sits just below the surface. Photo by Monica Nelson.

By Monica Nelson

Many of us on the CTD watches are physical oceanographers but we were charged with collecting biogeochemical data to complement the OSNAP mission. In addition to the usual water sampling to calibrate the salinity sensors on the rosette, we’ve been collecting water samples to calibrate oxygen sensors and samples to measure ocean carbon, nutrients, and oxygen isotopes (which indicate glacial melt) in the lab once we’re back on land.

For several of our CTD watch brigade, it’s their first time on a research vessel, and for most of us, we’ve never collected samples like these before – let alone been in charge of coordinating it. Trying to figure out how it’s all going to work was daunting and definitely a little nerve wracking. We’re the only science party doing an Irminger Sea section this year, so there’s pressure to do it right.

I was nervous for our test cast, the dress rehearsal before we started the real science, but the mechanical arm that lifts the rosette didn’t work properly. The anxiety of doing the rosette dance well is replaced by the anxiety that we won’t be able to use the rosette at all. Modifications made by the crew while we were in Reykjavik to make it safer restricted its motion. Science at sea is always a matter of overcoming the unexpected. After a few hours delay, now well past bedtime for the midnight-to-noon shift, we all scurried back out on deck for a second attempt. This time the rosette deployment went smoothly, our precious package of sensors and water sampling bottles was swallowed by the sea and dove towards the sea floor. The cable lowering the rosette transmits data back to the boat, allowing us to see the measurements real-time. We sat in the cozy lab, eyes fixed on the squiggly lines worming their way down the computer screen – a different coloured line for each variable we’re measuring. Together, based on the data we were getting back, we chose the water depths we want to sample and sent messages down the wire to close the water sampling “Niskin” bottles.  With five different types of water samples needed, it took some figuring to make sure everyone got the water they want. With each person voicing their sampling needs, Bobby, at the helm of the CTD, was getting inundated with requests.

Computer screen with colorful squiggly lines – aka CTD downcast data. Photo by Monica Nelson.

With all the bottles fired we got the rosette back on deck and a flurry of activity ensued: start downloading the lowered ADCP data, turn the secondary CTD off, and start collecting water samples!

Both watches were doing the test cast together so there was twice as many people out on deck as there normally would be. Meg was overseeing me (Monica) and Hiroki taking water samples for oxygen and carbon. I was overseeing Arthur and Matt taking water samples for nutrients and oxygen isotopes. And Aaron was overseeing Arthur and Matt taking water samples for salinity. Aurora and Nicole were learning how to run the lowered ADCP while also trying to shepherd the rest of us around the rosette in the right order. Too many people needing to be in too many places at once without getting in each other’s way. We’d talked through the sampling strategy and practiced at the sink, but that was our first time doing the dance around the rosette. With heightened stress levels, and so much to try and keep straight, we stumbled through the motions in a state of mild chaos.

Our dress rehearsal on the test cast did not leave me resting assured that we were ready for the real show. I went to bed uneasy about how the first few Irminger Sea stations would go the next day. But when the sampling starts in earnest, there was only four people to communicate between and only one person responsible for any given type of sample – a much better recipe for avoiding tripping each other up. All went well and the vials of sea water start stacking up.

Chaos on the test cast cleared the way for calm on the casts that mattered.

Sunny skies and calm seas for rosette deployment. Photo by Monica Nelson.

By night and by day we repeated this dance while watching the waves, the clouds, and the growing number of sea birds following the boat. By the time we got to the tightly-spaced casts on the Greenland coast we were dancing elegantly and efficiently around the rosette. We’d found our rhythm as a team and our muscle memory guided us through the routine as one.

After 51 CTD casts we’d sampled our way across the entire Irminger Sea from south of Iceland to Greenland and completed our first pass of the Kangerlussuatsiaq/Lindenow trough on the southeast Greenland shelf. We’ve learned to bring a speaker out to the rosette and we’re sampling and shaking bottles to tunes under the ship’s spotlight.

Matt and Nicole of team “Nicebergs”, midnight to noon watch. Hiroki and Aaron not featured. Photo by Aaron Mau.
Bobby, Aurora, Arthur and Monica of team Niisa, noon to midnight watch. Photo by Margaret Lindeman.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.