Posted on behalf of Wendee Holtcamp, blogging for Nature aboard the research vessel Thomas G. Thompson.
We’ve had an exciting few days on board the Thompson. The “storm” came and went. For three days, we had gale-force winds kicking up 8-10 foot swells, and some 15-footers. The boat was seriously rocking and rolling. I got to see one of only 2,000 short-tailed albatrosses in the world – a very lucky sighting – and the research continued, day and night, but not without mishap.
The Thompson is traversing back and forth along the Bering Sea shelf (see map below), and a few stations occur off the shelf in deep water. There’s always a question in heavy weather as to whether to sample or not. It costs some $30,000 a day to use the RV Thompson, and every hour is precious during this month of research. But each piece of equipment is also expensive (and for most, there’s only one on board), and people risk their lives recovering it from the sea. The research continued unabated through the weather – deploying the CTD, MOCNESS and other gear. On Monday, chief scientist David Shull sent the Multi-Core down to 2,200 meters – one of the deeper stations sampled. It takes more than an hour to reach the bottom at that depth. By the time the crew raised it back above the surface, the wind picked up and the Multi-Core smacked hard on the boat. First week in, and they’ve damaged an $80,000 piece of equipment. This wasn’t good.
Shull studies how benthic organisms – clams, worms, and other critters living in the sediment – affect nutrient cycling in the Bering Sea. Every time he sends the Multi-Core down, usually once per day, it comes up with tubes full of mud. Shull is interested in what will happen to nutrient cycling and benthic organisms as the climate heats up. “One of the hypotheses we’re testing is how the timing of ice melt affects the fate of organic matter in the food chain,” says Shull. It fits into testing the Oscillating Control Hypothesis, originally proposed by George Hunt, a professor at University of Washington, Seattle, and colleagues. The hypothesis predicts that the Bering Sea ecosystem fluctuates between top-down (pelagic predator) control and bottom-up (nutrient supply) control, and the flip-flop is affected by variations between colder or warmer spring temperatures. I will describe this in more detail in later posts.
By comparing colder sites to warmer ones, and cooler years to warmer years, Shull can make predictions as to how the benthic community may respond to overall warmer temperatures, and how those changes may cascade through the ecosystem.
When the Multi-Core comes up, the mud gets divvied up. Three become “flux cores” processed in the cold lab, kept just above freezing. Technician Greg Brusseau measures oxygen as the benthic organisms in each of these cores deplete it. He measures nitrogen gas, among other things, using a membrane-inlet mass spectrometer. “It tells us how much usable nitrogen is lost by denitrification and annamox [anaerobic ammonia oxidation],” says Shull. Bacteria in the bottom sediment turn usable nitrogen into biologically unusable nitrogen gas through these processes.
Mud from three cores gets sectioned, placed in small tubes, and centrifuged. Then the water from each gets tested for nutrient levels – ammonium, nitrate, nitrite, phosphate, and silicate–using Shull’s Robotic SmartCount. Wineries and medical labs use these but he’s one of the only oceanographers using it to analyze nutrient levels. A fourth tube becomes a “squeeze core”: they squish all the water from the microscopic pores in the sediment and test for nutrients with ‘The Robot’. A final core gets sieved, so they can identify and count the benthic organisms inside.
But if we don’t get the Multi-Core fixed, he may be in a bind.
Previous posts:
Setting sail for climate change research
Photo: Colin Smith
Map: NCAR