Posted on behalf of Wendee Holtcamp, blogging for Nature aboard the research vessel Thomas G. Thompson
We’re nearing the end of our voyage, but not before a couple of exciting projects started, and finished. Over 27 days, we zigzagged across the eastern Bering Sea, mostly staying on the continental shelf. The four times we crossed the shelf slope into deeper waters, scientists deployed a contraption to catch “marine snow” – dead phytoplankton, organic matter, and the poop of organisms that slowly drifts down to the seafloor. The purpose? To study how a warming climate will affect the carbon cycle here.
The team includes Pat Kelly, Matt Baumann, and Jonathan Whitefield; Kelly and Baumann work under S. Bradley Moran at the University of Rhode Island, as technician and graduate student, respectively, and Whitefield works for Michael Lomas from Bermuda Institute of Ocean Science. These chemical oceanographers are interested in how the timing of sea ice melt and associated phytoplankton blooms affect benthic-pelagic coupling; in other words, how much marine snow reaches the ocean floor (benthic) versus being consumed in the water column (pelagic).
When sea ice melts late, the more typical condition here, phytoplankton blooms are diatom-rich. Because diatoms are large and also create massive blooms, more grows than gets consumed – and that means more sinks to the seafloor, feeding benthos. In warmer years, flagellates outnumber diatoms, and they get consumed more in the water column. Bloom types differ between spring and summer as well, and that’s also part of their research. Baumann and Kelly focus on the carbon export – or sinking particles – end of the equation, and Whitefield measures phytoplankton productivity, or as he puts it, “how fast the grass grows”.
They deploy the sediment traps where the shelf slope breaks, between 100-200m (the shelf is too shallow for the device), and then extrapolate their data to the rest of the shelf using radionuclide tracers. The device includes five steel frames, separated by 10 to 40 meters, and each holding four upright plexiglass tubes. Buoys at the surface allow the device to float with currents.
How do they find this ‘needle in the haystack’ after 24 hours, when they retrieve it? Every hour, an ARGOS satellite transmitter emails the coordinates to the scientists. As the ship nears the last known location, the team gazes through binoculars for orange buoys from the pilothouse. Once spotted, the ship edges closer until the traps can be slowly pulled up on the main deck.
After getting the traps on board, the team runs the contents from each of the tubes through a filtration rig. This takes up to three days, depending on the amount of plankton – or, as Kelly says, how much “filter schlop” slows it down. One time on the trip, the water had a lot of Phaeocystis, a flagellate phytoplankton that grows profusely, slowing the filtering rate. It will take months to complete everything back at their respective labs, but they have now officially collected their last Bering Sea water sample.
At the end of last week, we reached the northernmost point on our journey, which chief scientist David Shull dubbed Benthic Nirvana. Shull wanted to core sediment at the St. Lawrence Island polynya, an area that remains unfrozen throughout winter even though it’s surrounded by ice. They’re very important for marine mammals, and, for Shull’s interest, polynyas have sediment with high levels of organic matter and high biological productivity.
Since then, we’ve made a beeline towards Dutch Harbor. With only a few more days on board, scientists have started packing up. And to top off the end of the journey, we’ve seen sunshine and blue skies, plus breathtaking 1am sunsets, a welcome relief after so many grey days at sea. I spent some time just marvelling at the open ocean. It can be a rough, foreboding place. Although impacted by whaling and marine mammal harvesting, bottom trawling and heavy fishing efforts, the Bering Sea’s 2 million square kilometres still support an abundance of marine life. That includes the Marine Stewardship Council sustainable-certified Alaska pollock fishery, which drives a large portion of this Bering Sea Project research. The question is, can science keep the fishery sustainable as the region warms, while maintaining a healthy and productive marine ecosystem?
Images: Wendee Holtcamp
Previous posts:
The importance of zooplankton, alien-like and otherwise
Phytoplankton, micropoop, and the bottom of the food chain
Wild Weather, Damaged Equipment & the Oscillating Control Hypothesis