Vast differences in polar ocean microbial communities

This new understanding not only sheds light on newly recognized biodiversity patterns but reinforces the importance of study of Earth's polar regions in the face of a changing climate and identifies further need for research on the impacts of sea ice, seasonal shifts, and freshwater input in both regions.

Findings from the most comprehensive comparison of bacterioplankton diversity at both of Earth's polar oceans showed that about 75 percent of the organisms at each pole are different.

"We believe that significant differences in the environmental conditions at each pole and unique selection mechanisms in the Artic and Southern oceans are at play in controlling surface and deep ocean community structure," said Murray, whose participation on this new report resulted from her role as a representative for the U.S. on the Scientific Committee for Antarctic Research (SCAR). Murray, a polar researcher for the past 17 years, has participated in 14 expeditions to the Southern Ocean and Antarctic continent to conduct research and educational activities and worked on the Arctic tundra lake ecosystems in northern Alaska. She also recently authored a policy forum article on major conservation challenges facing the Antarctic region that was published by Science magazine in July, 2012.

Scientists found that the differences between the two poles were most pronounced in the microbial communities sampled from the coastal regions, which is -- "likely a result of the significant differences in freshwater sourcing to the two polar oceans," said Dr. Jean-François Ghiglione, lead author of the report and research professor at the French Microbial Oceanography Laboratory (Observatoire Océanologique) in Banyuls-Sur-Mer.

Dr. Ghiglione adds that in the Southern Ocean, glacial melt-water accounts for most of the freshwater that flows into the system. In contrast, the Arctic Ocean receives much bigger pulses of freshwater from several large river systems with huge continental drainage basins, in addition to glacial melt-water.

While the surface microbial communities appear to be dominated by environmental selection, noted the report's authors, the deep ocean communities are more constrained by historical events and connected through oceanic circulation, providing evidence for biogeographically defined communities in the global ocean.

This unique collaboration was the result of an international effort coordinated by Murray involving scientists from six countries -- Canada, France, New Zealand, Spain, Sweden and the United States. The collaboration was made possible through the International Polar Year, a global research campaign, and the Sloan Foundation's Census of Marine Life Program, which stimulated field efforts at both poles as well as a separate program targeting marine microbes -- International Census of Marine Microbes (ICoMM). Further, the National Polar Research programs from each of the six contributing nations, including the National Science Foundation, supported field expeditions.

"The collective energies required to bring this study to fruition was remarkable," Murray said. "By using similar strategies and technologies in sample collection through next-generation sequencing, we have a highly comparable, unprecedented dataset that for the first time has allowed us to take an in-depth look across a large number of samples into the similarities of the microbial communities between the two polar oceans."

Scientists compared 20 samples from the Southern Ocean against 24 similar samples from the Arctic Ocean taken from both surface and deep waters sites. They also included an additional 48 samples from Earth's lower latitudes to investigate the polar signal in global marine bacterial biogeography.

The researchers specifically compared samples from coastal and open oceans and between winter and summer seasons, to test whether or how environmental conditions and dispersal patterns shape microbial communities in the polar oceans. Samples were processed and analyzed by ICoMM, using an identical approach based on pyrosequencing and involving more than 800,000 sequences from each of the 92 samples.

"Our analyses identified a number of key organisms in both poles in the surface and deep ocean waters that are important in driving the differences between the communities," Murray said. "Still, further research is needed to address the ecological and evolutionary processes that underlie these unique patterns."