Most of the time when oceanographers talk about nutrients, they’re referring to nitrate and phosphate, which, along with carbon, make up the building blocks of life. But in addition to these major nutrients, phytoplankton need tiny amounts of certain metals to grow and survive — just like humans need our daily vitamins in addition to carbohydrates, protein, and fats. Scientists call these elements “trace metals” because they are very scarce throughout most of the ocean. For every million molecules of salt in the ocean, there’s usually only a single iron atom (or less, in some places!).
Measuring such low concentrations of metals is difficult and costly, but most of what makes trace-metal work complicated is just keeping everything free of contaminants. Because metal is everywhere on the ship, the trace metal team has special tools they use to collect their water with as little influence from the ship as possible. They also do all of their filtering and other work in special labs on board that are designated as trace-metal-clean. All of their analysis will have to wait until we’re back on land — the delicate instruments that can be used to detect tiny amounts of elements are definitely not built for going to sea!
The trace metal team collects water in two ways, depending on what they’re using it for. The first is using special, metal-free versions of the bottles the rest of us use to collect water on the CTD rosette. But since the rosette is also made of metal, they have to attach each of their nine bottles to a Teflon cable by hand as they lower them down into the ocean. The water collected in the bottles is filtered and, once we’re back on land, will be analyzed for both dissolved and particulate trace metals such as iron and cobalt.
When the team wants more than a few liters of water from a certain area, they have to break out the big guns — in this case, a funny, sled-shaped contraption affectionately known as Big Jon. Big Jon goes over the side of the ship and pumps water from the surface into the trace-metal lab. Because it stays several yards away from the ship, it minimizes the influence of the ship’s metals on the water we’re collecting.
The trace metal team uses Big Jon to get the water for the experiments we’re running on board (more on those soon). For each experiment, we have to collect almost 600 liters of water — that’s enough to fill close to 4 standard bathtubs! (In comparison, the trace-metal-clean bottles I mentioned above only hold 5 liters of water each).
Our journey has taken us back south over the past week, into stormier seas and colder waters. One benefit of this is that it gave us a second chance at seeing icebergs — and boy, did the ocean deliver! On Sunday night, the bridge spotted a giant iceberg on the radar screen. Although the light was fading, we were able to get a pretty good view of it. Yesterday afternoon we were treated to an even closer berg drifting by. Now that we’ve all crossed “iceberg” off our bucket lists, it really is time to head north!
Giuliana Viglione is a journalist and science communicator who has joined Senior Research Scientist Barney Balch’s research cruise to study the impact of coccolithophores in the Southern Ocean. On board the ship, she’ll be helping the team carry out experiments, document the research cruise, and conduct educational outreach with students across the country. She can be reached at email@example.com.