29 August 2016
Less ice, more food?
Posted by larryohanlon
This is the latest in a series of dispatches from scientists and education officers aboard the National Science Foundation’s R/V Sikuliaq. Read more posts here. Track the Sikuliaq’s progress here.
By Kim Kenny
An introduction to the research
Two teams will do separate but related scientific work aboard the Sikuliaq over the next month. The following is an overview of their proposed research and what they expect to find:
Dr. Laurie Juranek leads a team of 11 from Oregon State University’s College of Earth, Ocean, and Atmospheric Sciences (CEOAS). Juranek and her colleagues are investigating how Arctic sea ice change is affecting the region’s chemistry and ecology.
Arctic ice loss due to climate change is no scientific secret. The plight of polar bears and higher surface temperatures from lower albedo – an indication of how well a surface reflects solar energy – are relatively well known consequences. (Reminder: we’re talking about sea ice loss here, which doesn’t cause sea level rise, because the ice displaces the same amount of water as the corresponding melt. The loss of ice on land in the Arctic is part of what makes low-lying nations like the Marshall Islands vulnerable).
But what isn’t as well known is that less sea ice means more food. Food in the form of phytoplankton, the tiny marine plants upon which all other life in the ocean depends. And not just more food, but more of it later in the Arctic season.
Maybe. We don’t really know for sure. That’s why there are research cruises.
Phytoplankton are like any other plants in that they need two things to survive: sunlight and nutrients. With markedly less sea ice, more sunlight is getting through to the newly exposed water and the phytoplankton beneath the surface. More sunlight – more phytoplankton.
The other half of the equation – nutrients – come from more frequent and more intense storms. This increased storm activity has been going on in the Arctic for decades. Storms mix everything up, bringing nitrogen, carbon dioxide, and the other energy sources phytoplankton need to the surface. The decrease in ice plays a role here too – with less ice, storms are able to have more of a mixing effect since they’re not as encumbered by physical boundaries. So, generally, more storms – more phytoplankton.
(Storms actually reduce the amount of sunlight getting through to the water and the phytoplankton, temporarily making it harder for plants to grow. But when things have settled down after storms, the effect is net positive for marine plant growth.)
The fact that sunlight and nutrients create more productive conditions for phytoplankton alone isn’t novel. But the idea that it may be happening later in the season is. This timing is crucial because over the course of millennia, ecology has become well attuned to the changing of seasons and all that comes with it.
Juranek describes it like a grocery store. Normally, by the late summer most of the phytoplankton are gone. But now that there’s much more open water, sunlight, and storms in the late season, the grocery store of phytoplankton is open longer. The shoppers include everything that eats phytoplankton, from zooplankton (tiny marine animals) to mollusks (think oysters, clams, and mussels) to whales. But since the amount and location of phytoplankton isn’t consistent throughout the Arctic, not all shoppers get the same access to food. And that can have disastrous or life-saving consequences depending on your place in the food web.
Not every animal in the Arctic eats phytoplankton, but if they don’t eat it, they depend on another animal that does. Walruses, for example, don’t have phytoplankton for breakfast, lunch, or dinner, but they do depend on shellfish for all of the above. Filter feeders like oysters and clams need phytoplankton, and so the walrus needs phytoplankton.
It isn’t enough to know that phytoplankton are there, where they are, or how many of them exist; we need to know how they’re living. This is done by measuring rates of primary productivity, essentially how much food the phytoplankton grocers are putting on the shelves.
Phytoplankton can be likened to the trees that help us breathe – both create carbohydrates and oxygen as a result of photosynthesis. But unlike massive and long-living trees, phytoplankton are microscopic and have a lifespan of days. There’s much more turnover.
How much turnover is there? How much nitrogen, carbon, silica and other nutrients are they using to grow? And how does the rest of the community respond – what is the net production when the whole community has eaten its fill? This is what the OSU team is trying to find out.
How to do this? One way is to measure oxygen. The oxygen phytoplankton produce has a unique chemical signature of isotopes (the same element but different sized nucleuses). The team will look at how much of these isotopes are in the water, and so infer how much phytoplankton are producing.
This is somewhat of a novel technique. Many studies of primary productivity focus on the presence of chlorophyll, the distinguishing green pigment of algae and plants. But although chlorophyll can give a great picture of phytoplankton activity, it doesn’t tell the whole story. Chlorophyll means plants are present, but more chlorophyll doesn’t necessarily mean more activity. More oxygen does.
Oxygen isn’t the only thing being used to determine primary productivity. The OSU team can also measure the amount of nitrogen and carbon in the water to get a better picture of what the phytoplankton and rest of the community are doing.
Juranek has good reason to think there’s more phytoplankton activity because this won’t be the first time she’s seen it. The prediction is based on prior data from an Arctic research cruise she took in 2011 and 2012. But that data is only one of the few that can help scientists get a picture of what’s happening in the late season. The dataset collected on this cruise will be the biggest and most detailed yet, thanks in large part to a little sled (which I’ve not yet had the honor of meeting but have decided to name Rosebud). The sled will be towed along the back of the ship and take continuous measurements of nutrients, carbon, and optical properties of the water that will be sent back to the ship’s lab – via cable – for analysis.
These measurements are done in just a few seconds. This is unlike what’s usually done: the “bottle” technique, where bottles of water are essentially pulled up from different depths and analyzed on the ship before being sent down again. With that method, you can get a few hundred measurements in a month. On this trip, the team will probably get 20,000 measurements in the same amount of time.
This improved database will help confirm or contradict the team’s prediction: There are substantial pockets of primary productivity later in the Arctic season than previously thought.
If we did one of those word maps that show which words were used most in the preceding paragraphs, “phytoplankton” would probably loom large above the rest. This research isn’t just about phytoplankton. But it is a big, central part, so we’ll start here. Carbon cycling, your time will come soon enough.
As of today, some of the team is aboard the Sikuliaq and making their way through the Unimak Pass from Seward to Nome, Alaska. The rest of the team will join them in Nome on August 31. Then, after a couple more days of set-up, the Sikuliaq will set off in the direction of Barrow and the scientific adventure begins.
It really began a while ago. Months – and years, if you count the previous cruises that established baseline data – of preparation has gone into making this research expedition a reality. The writing of proposals, completing the NSF review process, collaborating with local communities and organizations like the Alaska Eskimo Whaling Commission, purchasing and prepping gear, assembling a team, and spending lots of money and time in the process. Ship time is valuable, and scientists tend to work long hours to make sure they can get the most out of it. Because you can’t have the same kind of discovery back home in the lab under controlled conditions as you do out at sea. It makes all the prep work worthwhile – no matter what we find, it’ll be a step toward better understanding the rapidly changing Arctic.
Coming soon: a brief introduction to the work of the team from the College of William & Mary’s Virginia Institute of Marine Science (VIMS), led by Dr. Rachel Sipler, and more about where we’re going. Stay tuned!
Kim Kenny is a freelance journalist who specializes in science writing and multimedia. This post was originally published on thedynamicarctic.wordpress.com