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 fourth blog post. To see all their posts, see "60 Seconds in the Bering Sea."

ON THE ICEBREAKER HEALY IN THE BERING SEA (at latitude 59.5272 N and longitude 175.2031 W), April 30, 2009—One of the major objectives of this research cruise was to find an ice edge bloom, a spring growth of algae along the edge of the ice. As the ice melts and retreats northward in the Bering Sea, sun hits the water for the first time in months. The algae in the sea can finally burst into action, photosynthesizing and multiplying and feeding the rest of the ecosystem.

Many of the scientists here were on a similar cruise last year, sampling in many of the same places. Last year they never really came across a bloom, says chief scientist Carin Ashjian, a biological oceanographer at Woods Hole Oceanographic Institution in Massachusetts. “We found something, but it wasn’t as dramatic as we wanted last year,” she told me before we got underway. “Perhaps this year we will have better luck.”

Last Saturday, the ship was traveling north through open water.

The ship has instruments that measure temperature, salinity, and other water conditions all the time. At about 8 p.m. on Saturday, on screens around the ship, the chlorophyll line started rising. Chlorophyll is a pigment involved in photosynthesis, so more chlorophyll means more algae in the water.

“I started taking samples,” says Evelyn Lessard, a biological oceanographer from the University of Washington. She ran the water through an imaging flow cytometer, which is basically a microscope that takes  pictures of every cell in samples as the water trickles past it. Flow cytometry was originally developed for medicine – it’s great for photographing cancer cells, but it’s also good for looking at single-celled organisms in sea water.

Evelyn Lessard takes pictures of microorganisms with an imaging flow cytometer, the black box next to her.

She sends an email to the other scientists on board at 10 P.M. to let they know that she's seen a lot of algae: “We have definitely entered an open water bloom," she reports. Biogeochemist Didier Burdloff, from Lamont-Doherty Earth Observatory in New York, says he saw the chlorophyll go up, too. “When we saw something interesting, we quickly picked up the water,” he says. He ran four liters of water through a glass fiber filter; earlier in the trip it would have been difficult to even see anything on the filter but now there’s a visible layer of algae.

Didier Burdloff filtered water – and found algae.

The next morning, we stopped to sample the bloom in depth. Lessard ran samples of the water through her machine again. There were lots of diatoms like she’d seen the night before – they’re a kind of algae that make their own glass shells. She also saw single-celled organisms that eat algae, like predatory ciliates and dinoflagellates.

The scientists on board spent almost a week investigating the bloom as the ship zig-zagged through it, stopping periodically  to sample. Some people measured the amount of chlorophyll in the water and the various nutrients that algae need to grow. Others started experiments with krill and zooplankton, offering them the local water to see what they would choose to eat.

Alexei Pinchuk, a zooplankton researcher from the University of Alaska-Fairbanks, pulled up the tiny animals from several levels of water the other night. His nets give off a faint earthy scent. “The smell is coming from the bloom, from the algae,” he says. “It’s the quickest way to tell there is a bloom.”

Alexei Pinchuk, left, brings his nets on board.

Pinchuk uses a special set of nets that he controls from his laptop, opening and closing them at different depths. He held up a jar full of zooplankton he caught not far below the surface. “Those are the guts,” he says, pointing at the cloud of tiny crustaceans. “They have green guts… they are all stuffed with diatoms.” The zooplankton were enjoying the fruits of the bloom. His data on what animals are found where in the Bering Sea – and all the other measurements of the algae bloom – will help the scientists on this cruise accomplish their goal of figuring out how the Bering Sea ecosystem works.

These jars are filled with zooplankton caught at, from left, 80 to 100 meters (262 to 328 feet), 40 to 60 meters (131 to 197 feet), and 0 to 20 meters (0 to 66 feet) below the water’s surface.

Images: Photos by Chris Linder, WHOI