"News about the USAP, the Ice, and the People"
United States Antarctic Program United States Antarctic Program Logo National Science Foundation Logo

Three people work on sediment core.
Photo Courtesy: Mike McCormick
Scientists Andrew Seraichick, Mike McCormick and Liz Buccerri take samples from a Kasten core taken from the seafloor. The sediment cores contain all sorts of clues about conditions in the Weddell Sea in the past when the Larsen A Ice Shelf waxed and waned.


Drilling for ikaite

Another rare phenomenon in the Southern Ocean proved a little less elusive.

Several shallow sediment cores taken by a device called a Kasten corer from the seafloor contained the rare metastable mineral ikaite, a calcium carbonate that forms under near-freezing conditions that scientists are beginning to use to tease out information about climate and even ice cover in the past as another way to construct a paleoclimate record.

“Our interest in ikaite is related to its very limited geographic occurrence and the interpretation, in the geologic literature, of its pseudomorph, glendonite, as a paleo-indicator of ‘Antarctic-like’ conditions in ancient rock sequences,” Leventer explained.

The exact conditions under which ikaite — looking a bit like Kryptonite — forms and morphs into other minerals are still a mystery to science, according to McCormick.

Green object sticks out of mud.
Photo Credit: Amber Lancaster (PolarTREC 2012), Courtesy of ARCUS
An ikaite crystal in a sediment core from the seafloor.

“There’s quite a bit of interest in learning about how these crystals are formed, so if we have a contemporary model of ikaite formation, then when we find these older ikaites, we have some idea of the actual conditions under which they were made,” he said.

One common denominator, aside from extremely cold waters, is organically rich sediments, Leventer added.

“But these two qualities characterize many more regions of the Antarctic continental margin than sites where ikaite is found,” she said, “so a project goal is to capitalize on the interdisciplinary nature of our research team to study the new cores that contain ikaite, using as many tools as possible.”

McCormick said there are a number of possibilities that may be involved in ikaite formation. For instance, there are high concentrations of ammonium in the cores containing ikaite, along with methane and sulfur.

“[The sediment cores] were actively off-gassing and hissing. You could see the mud squeezing out between the panels. We had to work very quickly to get our samples,” he said. “You could tell when we got one of these cores up. The whole back half of the ship reeked of sulfide.”

The assumption is that the ikaite mineralization process is abiotic, without any biological participation, but microorganisms have been known to play a role in the formation of other minerals, McCormick noted.

“We’re looking at the microbial community right at those levels where the ikaite is being formed,” he said.

Landing biological specimens

Microbes to larger marine fauna are the subject of an altogether different experiment involving a whale carcass that had been purposefully left on the seafloor in the Antarctic Sound back in 2010.

People bring item aboard a ship.
Photo Credit: Amber Lancaster (PolarTREC 2012), Courtesy of ARCUS
The whalebone lander is brought aboard the ship.

Based on a hypothesis first pioneered by Smith about 20 years ago, sunken whale corpses, also known as whale falls, are thought to serve as a catalyst for exotic marine critters capable of existing in extreme environments. In fact, the carcasses can be seen as another sort of proxy — in this case, for the elusive cold-seep communities.

The first LARISSA cruise had left behind a pile of whalebones in a lander, an aluminum frame surrounded by an acoustic release that grips ballast. A coded ping from the ship triggers the acoustic release, bringing the now-buoyant lander to the surface.

The researchers discovered that indeed some of the same suspects known to inhabit cold-seep communities made a home on the whale carcass, including different species of marine worm.

McCormick’s microbes also play an important part in this micro-ecosystem, from the surface to within the core of the bone. The latter appear to thrive in anoxic environments, with the ability to use the fatty lipids in the bones.

“It’s a nice story,” McCormick said. “We’re getting a nice idea of how the microbial communities structure themselves within the whalebone to optimize the retrieval of nutrients and energy out of the components of the bone.”

Even the oceanographers benefitted from recovering the whale lander, which had refused to budge during an earlier attempt to retrieve the experiment during the southbound trip.

“We also recovered a temperature-pressure record from a whalebone lander … yielding a very nice two-year record of bottom temperature in the Sound,” Huber said. “It showed a very dramatic seasonal signal, with the water at the bottom [at 1,000 meters] reaching near-freezing temperatures during the winter months.”

Continuing the adventure

The LARISSA story is not over yet.

The research team has one more expedition planned in 2013 under the current proposal — a trip aboard the new South Korean research vessel Araon, a 109.5-meter-long icebreaker commissioned in 2009.

The scientists will hope the third time is indeed the charm next year.

NSF-funded research for the LARISSA program: Eugene Domack, Hamilton College, Award No. 0732467 External U.S. government site; Maria Vernet, University of California-San Diego Scripps Institution of Oceanography, Award No. 0732983 External U.S. government site; Ted Scambos, University of Colorado at Boulder, Award No. 073292 External U.S. government site; Amy Leventer, Colgate University, Award No. 0732625 External U.S. government site; Michael McCormick, Hamilton College, Award No. 0732917 External U.S. government site; Cindy Van Dover, Duke University, Award No. 0732450 External Non-U.S. government site; Arnold Gordon and Bruce Huber, Columbia University, Award No. 0732651 External U.S. government site; Ellen Mosley-Thompson and Lonnie Thompson, Ohio State University, Award No. 0732655 External U.S. government site; Craig Smith, University of Hawaii, Award No. 0732711 External U.S. government site; Martin Truffer, University of Alaska Fairbanks, Award No. 0732602 External U.S. government site; Erin Pettit, University of Alaska Fairbanks, Award No. 0855265 External U.S. government site; Stefanie Brachfeld, Montclair State University, Award No. 0732605 External U.S. government site; Julia Wellner, University of Houston, Award No. 0732614 External U.S. government site; and Scott Ishman, Southern Illinois University at Carbondale, Award No. 0732554 External U.S. government site.Back   1 2 3