Editor's Note: Woods Hole Oceanographic Institution oceanographer and photographer Chris Linder and science writer Helen Fields are taking part in a six-week cruise of the Bering Sea, a scientific expedition to study the effects of climate change on this polar ecosystem. This is the third blog post. To see all their posts, see "60 Seconds in the Bering Sea."
ON THE ICEBREAKER HEALY IN THE BERING SEA (at latitude 56.3236 N and longitude 171.0294 W), April 23, 2009--Things have changed on the Healy. I can look out my porthole in daylight without being blinded. The seals have disappeared, and the ship is being followed by a couple dozen seagulls and an albatross. People are getting seasick. What changed? We left the ice.
Ice makes for a nice ride – waves don’t travel through a solid as well as they do through a liquid. We spent the first two and a half weeks of the expedition in the ice. The going was smooth, other than the jarring and shaking of icebreaking.
But the point of this expedition isn’t to have a smooth ride. The scientists on the Healy are out here to do science, and that means going into open water, too. The open water is different for the organisms that live here, too – light penetrates much more easily than through the ice and snow, and wind and waves stir things up.
Pat Kelly, an oceanographer at the University of Rhode Island, has been waiting for a chance to put sediment traps into open water. Sediment traps are water-filled plastic tubes that hang in the water, waiting for “marine snow” – mostly zooplankton poop and dead algae – to fall down. Marine snow feeds the organisms that live on the bottom. Over the past few weeks, Kelly has put sediment traps through holes in the ice several times, to catch things drifting down from the ice.
Katrin Iken, a biologist from the University of Alaska-Fairbanks, and University of Rhode Island oceanographer Pat Kelly work with sediment traps on the ice.
Part of the point of this cruise is to contrast ice and open water, so to get a full picture of marine snow in the Bering Sea, Kelly needed to put his sediment traps into the open ocean, too. Getting the traps in the water was quite a production. The traps are on a 125-meter-long rope with buoys at one end and a weight at the other, so it hangs vertically in the water. The traps are mounted in brackets and clipped onto the rope so they sit at different depths.
Kelly puts sediment traps into brackets before they’re lowered into the water.
It took three scientists and two Coast Guard crew members about 40 minutes to get the traps into the water. First a winch lifted the end of the rope with the 135-pound weight. Then the A-frame, a structure at the back of the ship for lowering equipment into the water, tilted back and forth on noisy hydraulics – out to lower the rope, then in so Kelly could clip on the next set of sediment traps. “That was the easy part,” Kelly told me when the last of the buoys went in. “There’ll be more fun than we know what to do with tomorrow.” By “fun” he meant small boats – the usual way to get the sediment traps back – and big waves.
Boatswain’s mate Ray Mendoza prepares ropes that will help the sediment traps get back on board.
But today the waves were too big to launch the Healy’s small boats. Instead the top officers said we’d have to use the ship itself to get the traps back. From the deck, which was going up and down by several feet at a time, boatswain’s mate Trey Huneycutt had to throw a grappling hook to snag a very energetically bobbing buoy. It was a tricky operation. The scientists wore harnesses tied to ropes in case they got tossed off the deck while they were taking the traps off the line.
The orange buoys at the top right mark the top of the sediment traps.
In the end, all went well. Huneycutt caught the buoy, nobody fell in the water, and the sediment traps all got back on board, each with a light brown layer of zooplankton feces at the bottom. “The poop is not going anywhere,” said Kelly. “The poop is in the tubes.” He will analyze the particles from the traps later to see just how much gunk is falling toward the bottom of the ocean.
Kelly said he’s happy with the tiny particles that landed at the bottom of this sediment trap.
Images: Photos by Chris Linder, WHOI