A Modeler’s First Cruise

By Daan Reijnders

“Well, I’m somewhat of a stowaway here…” This is how I’ve been introducing myself to some crew members in the messroom during dinner or when fetching some late-night cereal. I had never been to the open sea before this cruise. I usually study the ocean from my desk, using models. Some are idealized, capturing just the essence of a particular process, while others aim to represent the ocean as well as possible. Still, we will never be able to simulate the entire ocean, with all its diverse structures, in the finest details. This is why sea-going oceanographers embark on research cruises – to try to observe how the ocean truly behaves.

Although ocean observations are not directly part of my Ph.D. research at Utrecht University, I consider myself a physical oceanographer-in-training. Of course, part of that training is to get out there and see the thing I’ve been studying from my desk for the past years. With some asking around, I was lucky to get a spot in Femke de Jong’s science party from the Royal Netherlands Institute for Sea Research (NIOZ) on this cruise aboard the R/V Neil Armstrong. Our goal is to recover and deploy moorings that are part of OSNAP (Overturning in the Subpolar North Atlantic Program), together with scientists from the University of Miami. Last week, we steamed off from Reykjavik, and we will return there again in two weeks.

Daan and Emma sampling salts from the Niskin bottles
Daan and Emma sitting at the CTD station

While we’re working on the mooring array, we’re ‘doing CTDs’ along the way, measuring conductivity, temperature and depth at specific locations. This helps us understand the water’s profile and properties at the locations between the moorings. CTDs are the “bread and butter of observational oceanography”, as Bill Johns, chief scientist of this cruise, phrased it during the science briefing. So, what better way to immerse myself in observational oceanography than to immerse the CTD into the water every day? By the way, CTD refers to the measurements, the activity of taking those measurements and the instrument set we use for it. As a ‘CTD watch’, I take care of the measurements by dropping a set of instruments into the water, or rather, communicating with the bridge and the winch operator to carefully lower the CTD to specific depths. The CTD’s casing is lined with a ‘rosette’ of so-called Niskin bottles, that can be closed at specific depths to sample water, which is used for calibration of the instruments. Every time the CTD gets back on deck after we sent it off to 20 meters from the ocean floor (making sure not to hit it!), we take the samples from the Niskin bottles. We literally get in touch with the water’s profile as the sampled water that streams over our hands get colder with the depth at which the bottles were closed. If I’d ask for more immersion, I’d have to jump off the ship and swim away with the pilot whales.

I’ve now grown accustomed to my bread and butter and hopefully, it’s smooth steam from here on out. With approximately one week done and two ahead, I’m looking forward to helping out with the recovery of the NIOZ moorings, but also to continued fun with everyone on board. The major takeaway from my participation on this cruise is an obvious one: it takes a tremendous amount of effort in terms of time, planning, resources and most of all people power to deploy a mooring or to go out on a CTD transit, from the scientists and engineers to the mates, oilers or cooks that form the ship’s crew. It’s something I knew, but also something I will forever appreciate, whether I’ll be looking at observations or models. What is the latter without the former anyway? In any case, after this experience (and earning my sea legs) I’ll never again have to introduce myself as a mere stowaway modeler.

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