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News - May 20, 2002

Dispatch 6, The Straits of Magellan

	Two humpback whales seen in the Grelache Strait. Credit: Kristin Cobb / National Science Foundation   An ice flow in low light. Credit: Kristin Cobb / National Science Foundation   The Nathaniel B. Palmer as seen from an inflatable boat. Credit: Kristin Cobb / National Science Foundation   The National Science Foundation's Palmer Station. Credit: Kristin Cobb / National Science Foundation

May 20, 2002 / The Straits of Magellan -- Scientists on the Nathaniel B. Palmer packed up their equipment this week as the ship headed north toward Punta Arenas, Chile. The ship began to rock as she left the stable ice for open waters, and passengers worked to restore their sea legs for the dreaded Drake Passage, the turbulent stretch of water between Antarctica and South America.

Before they crossed the Drake, however, voyagers had time for a little fun. The Palmer stopped at the National Science Foundation's Palmer Station, where scientists and crew visited elephant seals and penguins on nearby islands, shopped at the station's souvenir store, and hiked a nearby glacier. From the top of the glacier, the constant engine noise of the Palmer faded, leaving the voyagers in an almost overwhelming peace.

Today, as the Palmer reentered the Straits of Magellan -- after a relatively easy crossing through the Drake -- scientists were glad to be finished with their work, but also sad to be leaving their home of the past six weeks.

"I've had a great time and met a lot of interesting people," reflected Phillip Taisey, a student from Northeastern University. "I haven't had a single bad day except for maybe while I was a little seasick at the beginning of the trip going through the Drake."

"The worst rocking we had was on the way out," agreed ship's steward Theresa Wisner, who said the trip was also a success for the cooks. They had the daunting task of feeding 56 people for six weeks without ever restocking the larder.

"If you store things right, they last," Wisner said. "We don't have to think about that when we're home because the supermarket is right down the street."

Though the kiwis and melons ran out early on, there were still plenty of oranges, apples and pears because they were bought unripe and stored in the ship's giant refrigerator. The lettuce lasted almost the whole trip; after it went, Wisner served cabbage for salads.

Wisner made the menu up as she went along, based on what was ripe. "If there was a bunch of celery that was about to go over, I'd make a stir fry because it uses lots of celery. I did a pear breakfast when we had pears that were about to go," she said. Throughout the trip, passengers noticed that yesterday's meat often became today's soup, which helped to minimize waste.

Though the scientists enjoyed the meals on board, they missed food from home. "I can't wait to have a burrito," admitted Wendy Kozlowski of Scripps Institution of Oceanography in La Jolla, Calif.

Scientific Successes

Kozlowski, along with Kristy Aller of Scripps, has been mapping the distribution and abundance of the "primary producers" -- the tiny green phytoplankton at the bottom of the food chain that make food for zooplankton and krill.

"I think the trip went really well," said Kozlowski. "The seas were calmer than during last year's fall cruise." Kozlowski lost only one sampling cast, out of 92, due to bad weather.

Kozlowski and Aller filtered water samples along the Palmer's survey grid, extracting substances like chlorophyll, the green pigment that absorbs the sun's energy for photosynthesis. The amount of chlorophyll in the top layers of water --where the sun can penetrate -- is one indicator of the mass of phytoplankton in the water.

Kozlowski and Aller also measured phaeophytin, a pigment produced when krill break down the chlorophyll of phytoplankton they have eaten. The zooplankton group saw no obvious increases in krill where Kozlowski and Aller saw high phaeophytin. But Kozlowski said the data would need to be analyzed more carefully to look for links between phytoplankton and the ocean physics, nutrients, and biology.

"We did get this chlorophyll plot that matches perfectly with a deep water temperature maximum that John [Klinck] saw," she said, pointing to a plot showing high levels of chlorophyll in the north offshore section of the survey grid. It's possible that deep, warm water intrusions bring nutrients to the continental shelf and feed phytoplankton near the surface, she said.

Another success of the cruise was mapping a new piece of the Southern Ocean floor. The seafloor is rich with volcanoes, deep troughs, and dents where jagged icebergs once scraped across the bottom. These features affect the biology of a region.

For example, SO GLOBEC scientists have slowly been mapping a deep trough that cuts diagonally across the continental shelf of the Western Antarctic Peninsula. Warm water intrusions may enter the continental shelf through this trough, bringing in nutrients and increasing the productivity of the strip. Colder, denser water may also sink deep in the trough, making a habitat for certain types of fish.

Ping Editing" and "Small Footprints

The Palmer maps the depths of the seafloor with a "multibeam" sonar system. "It's essentially just like an echo, when you holler and it bounces back to you --that's how it works," said Suzanne O'Hara of Raytheon Polar Services, Co., NSF's logistics contractor in Antarctica.

Each of the system's multiple beams sends one "ping" each second that bounces back from the ocean floor. "We base our depth on half the time it took the sound to travel," O'Hara explained.

The beams cover a swath of the ocean floor about three times the depth of the water. "If you're only in 400 meters of water, you only get a width of about 1200 meters. And that's a very small footprint on the ocean floor," said O'Hara, who likened it to mowing tiny strips in a large yard.

"If we had wanted to cover the whole shelf slope area, it would take years of just driving back and forth," she said.

SO GLOBEC scientists offset the grid track by about one-half swath width each research trip and then match up the overlapping pieces like a puzzle. The mapped area -- appearing like a boxy maze -- widens with each voyage.

Each evening, the scientists helped remove artifacts from the day's data in a chore called "ping editing." The Palmer was the first NSF Antarctic vessel to acquire a multibeam system in 1994, and any information the scientists collect is new, which motivates every one to help with the task.

Many other scientists -- such as geophysicists, who hope to understand how glaciers once shaped the Antarctic seafloor -- will also use this data.

With only a few hours to go before they reached Punta Arenas -- where the Laurence M. Gould had already arrived -- voyagers gathered for their last dinner in the galley. They marveled at their relative luck with weather and equipment compared to last year's fall and winter cruises.

An enthusiastic Peter Wiebe, chief scientist aboard the Palmer, said, "I have only three words: it went great."