Read The Rime of the Modern Mariner—a blog from the 2008 Antarctic iceberg expedition.
30 May 2008
Chasing icebergs—Part II
Why would anyone want to go to Antarctica in the middle of winter? Well, for one thing, it's a good place to study icebergs. In December 2005, marine ecologist Ken Smith led a team that spent a month in Antarctica's Weddell Sea, and came away with a new perspective on icebergs. Instead of just immense chunks of sterile ice, they found that some Antarctic icebergs are floating oases of life. In June 2008, Smith and his colleagues will be heading south again, this time to find out more precisely why icebergs attract so much marine life.
|In 2005, MBARI researcher Ken Smith (at right) led an expedition to study life around Antarctic icebergs using a variety of tools, including this small remotely operated vehicle (ROV). Smith will be returning to Antarctica in June 2008 with an improved ROV and a host of other high-tech oceanographic instruments. Image: (c) 2005 Rob Sherlock|
The cruise will take place in the Weddell Sea—a huge embayment in the Antarctic coastline, located more or less due south of the Atlantic Ocean. On its western side, the Weddell Sea is bounded by the 2,000-kilometer-long Antarctic Peninsula, which protects the sea from the full force of the Southern Ocean. Most of the Peninsula's coastline is covered with glaciers. Where these glaciers flow into the sea, they form shelves of ice that can be dozens of kilometers wide and up to several hundred meters thick.
Over the last 50 years, however, the Antarctic Peninsula has warmed dramatically. In part because of this warming, the ice shelves along its shoreline have begun to break apart, releasing huge numbers of flat-topped, "tabular" icebergs into the Weddell Sea.
Smith's research group is sailing into this iceberg breeding ground to study the marine life that thrives around the floating islands of ice. In addition to studying the animals that live on and around the icebergs, the team will also survey the icebergs themselves, using radio-controlled planes, a robotic submarine, and ship-mounted radar and sonar systems.
|This composite satellite image shows Antarctica, the Antarctic Peninsula, and the Weddell Sea. At its widest, the Weddell sea is about 2,000 kilometers (1,250 miles) across. Image courtesy of NASA|
During their 2008 cruise, Smith's research team hopes to estimate the amounts of nutrients being released by different icebergs into the surrounding ocean. They will also study how rapidly algae take up these nutrients and use them (along with carbon dioxide from the surrounding seawater) for photosynthesis. The next step is to understand how much organic matter from the algae is being consumed by different types of marine animals. Finally, the researchers will try to measure how much of this organic matter (which is mostly carbon) is sinking to the seafloor. This is an important question because when organic carbon (in the form of dead algae and animals) sinks to the deep seafloor, it helps remove carbon dioxide from the Earth's atmosphere, and thus could help mitigate global warming.
|During their 2005 cruise to the Weddell Sea, Smith's team studied this very large iceberg, which was about five kilometers (three miles) wide and 21 kilometers (13 miles) long. Smith and his fellow researchers found zones of abundant marine life around both large icebergs such as this one, and around smaller bergs that were only a few kilometers across. Image: (c) 2005 Rob Sherlock
To achieve these ambitious goals, Smith and his collaborators have developed a variety of new, high-tech research tools. For example, they are taking two radio-controlled airplanes. MBARI researchers Steve Etchemendy and Kim Reisenbichler will use tiny cameras on these planes to photograph the tops of the icebergs, looking for crevasses, melt-water lakes, and bird life. The planes will also drop small Global Positioning System (GPS) beacons on individual icebergs so that the researchers can track the icebergs as they drift across the Weddell Sea.
To study how much sediment the icebergs are releasing, MBARI researchers and engineers built a small fleet of robotic "sediment traps." As their name implies, sediment traps are large funnels that oceanographers place in the ocean to catch sediment and particles of organic material drifting down from the surface waters. Unlike most sediment traps, which are attached to the seafloor, Smith's "Lagrangian" sediment traps are programmed to sink to a particular depth, drift underneath an iceberg, then rise to the surface after a specified period of time (which must be long enough that the sediment trap will have drifted out from underneath the iceberg by the time it surfaces). Designing and programming these sediment traps was a tricky process, which required months of work by MBARI engineers Brett Hobson, Alana Sherman, and Paul McGill.
|MBARI engineer Brett Hobson works on one of the "lagrangian sediment traps" that will released into the ocean to drift underneath Antarctic icebergs. The white funnels will collect sediment and organic matter that is released as the icebergs melt. Image: Todd Walsh (c) 2007 MBARI|
Working with engineers Hobson, Sherman, and McGill, mechanical engineering technicians Larry Bird and John Ferreira added a host of ingenious new instruments, which greatly expand the ROV's usefulness. The Phantom now carries three different sampling devices: a syringe sampler to collect small water samples, a suction sampler (which works like an underwater vacuum cleaner), and a "gulper" for large (2 liter) water samples.
The "hot-rodded" ROV also sports two additional thrusters (propellers) and a longer (670-meter) control cable, so it can travel farther under the ice. Instead of a front "grill," the ROV has a plankton net for collecting tiny algae and animals. MBARI technicians also added a scraper for collecting algae directly off the ice itself. Because they could not add additional channels to the ROV's remote control system, the MBARI team had to find ways to activate many of their new tools using specific movements of existing systems such as its mechanical arm and camera pan-and-tilt mount.
In addition to bringing a wide variety of research tools, Smith and his colleagues have assembled a large, multi-disciplinary research team for this expedition. Physical oceanographers and ocean engineers will study the movement and evolution of the icebergs and map the undersides of the icebergs using sonar. Marine chemists will measure nutrients and various trace elements in the water around the icebergs. Some marine biologists will study microscopic algae and organic material in the water around the icebergs. Other marine biologists will study microscopic animals and larger organisms, such as fish and birds, that cluster around the icebergs. Additional researchers, such as MBARI's Jacob Ellena, will be making sure that the expedition's field data are carefully organized and archived for easy access at the end of the cruise.
|This photograph shows the Phantom DS2 remotely operated vehicle, with some of the new tools that were added for the 2008 expedition (compare with 2005 photo above). This photograph was taken while the vehicle was being tested in MBARI's Test Tank. Image: Kim Reisenbichler (c) 2008 MBARI|
Smith and his team depart for their Antarctic expedition from Punta Arenas, Chile, on May 31, 2008, and return about one month later, on June 30. In scheduling this ambitious project, Smith did not actually choose the depths of Antarctic winter. In fact, this was the only time period during 2008 when the 300-foot research icebreaker Nathaniel B. Palmer was available. However, as Smith points out, it is important to know how iceberg ecosystems work in winter as well as in summer.
With such a creative and dedicated team, Smith will no doubt come back with plenty of scientific data and fascinating observations. As a sequel to Smith's 2005 expedition, this cruise will not only give scientists new perspectives on Antarctic icebergs, but could also shed light on larger issues, such as global climate change.
- Expedition blog by Nancy Etchemendy
- Fiction-based blog by Nancy Etchemendy
- Press Release and fact sheet on cruise by Nancy Etchemendy (2-Mbyte PDF file)
- MBARI Expeditions web page on this expedition
- Melting Antarctica — a scientist's blog from the Antarctic expedition by Maria Vernet
- Antarctic Icebergs: hotspots of ocean life (MBARI News Release on findings from 2005 cruise)
- Photographs of icebergs from Smith's 2005 cruise.
- Information on the formation and breakup of Antarctic ice shelves.
- Detailed Map of Antarctica (PDF file)
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