Research Highlight: Cold Storage

Like giant pellets of fertilizer, an ever-growing number of icebergs is changing the ecology of certain areas of the Southern Ocean. These “hotspots” of nutrient infusion are also altering the chemistry of the waters in their immediate vicinity, according to a research team that includes current and former researchers from Scripps Institution of Oceanography at UC San Diego.

Members of the research team said the proliferation of icebergs in the Weddell Sea is another apparent consequence of global climate change, which is causing Antarctic ice shelves to shrink, split apart and calve new icebergs in increasing numbers. The full impact of the icebergs on the processing and sequestering of carbon is a question requiring further study, said Ken Smith of the Monterey Bay Aquarium Research Institute (MBARI), the lead author of the study, which appeared in the June 21 online version of the journal Science.

“While the melting of Antarctic ice shelves is contributing to rising sea levels and other climate change dynamics in complex ways, this additional role of removing carbon from the atmosphere may have implications for global climate models that need to be further studied,” said Smith, a former Scripps Oceanography professor of marine biology.

“Phytoplankton around the icebergs were enriched with large diatom cells, known for their role in productive systems such as upwelling areas of the west coast of the U.S. or ice-edge communities in polar oceans,” said Scripps oceanographer Maria Vernet, another member of the research team. “As diatoms are the preferred food for krill, we expect the changes in phytoplankton community composition to favor grazing as a key biological process involved in carbon sequestration around free-floating icebergs.”

The researchers found that the icebergs — some as much as 12 miles across — are virtually the only way that terrestrial material can escape to the ocean from Antarctica, a continent with no major rivers to transport sediment or biological material. Frozen inside icebergs, nutrients were found to be released far out to sea. The team described “halos” of life around the chunks of ice extending as far as two miles. Those halos contained increased concentrations of phytoplankton, krill, and fishes below the sea surface and of seabirds above it.

To understand the icebergs’ complex impacts, the multidisciplinary team of researchers carried out the most comprehensive study ever done of individual icebergs and their immediate environment, taking a wide array of measurements – physical, biological, and chemical, and using satellite images provided by NASA.

Just getting to the icebergs was a challenge. First the scientists used satellite images to select two icebergs to study in detail. Then they sailed aboard the Antarctic research vessel Laurence M. Gould to reach their targets in the remote Weddell Sea, an arm of the Southern Atlantic Ocean that cuts into the Antarctic continent southeast of Cape Horn. The icebergs in the study were up to a dozen miles long and more than 120 feet high, with one extending nearly 1,000 feet into the depths.

Despite the risks of getting close to these mountains of ice – which can shed huge pieces or overturn without warning – the scientists began their shipboard sampling mere hundreds of feet from the icebergs and continued out to distances of up to 10 to 12 miles, where the icebergs’ influence was no longer detectable.

Based on their new understanding of the impacts of the icebergs and their growing numbers – the researchers counted close to 1,000 of them in a 4,300-square-mile stretch of ocean – the scientists estimate that overall the icebergs are raising biological productivity levels in nearly 40 percent of the Weddell Sea’s area.

--Robert Monroe