Auckland, New Zealand – When it comes to the world’s oceans, the South Pacific gyre is about as remote – and lifeless – as it gets. Expeditions to visit comparable sites around the globe – in the Atlantic and Indian oceans, for example – have turned up rich microbial ecosystems at or below the seafloor. Yet similar inquiries at the South Pacific gyre have not uncovered any such biological wealth. The mystery behind this particular ocean anomaly continues to elude scientists, but recent data gathered by Integrated Ocean Drilling Program (IODP) researchers may shed light on the darkest part of the seafloor, and the little bit of life it sustains.
In late fall 2010, an international team of scientists participating in the IODP South Pacific Gyre Subseafloor Life Expedition cored seven sites off the coast of Auckland, New Zealand in an area called the South Pacific gyre – one of the largest, most remote, and least explored areas of the world’s oceans. Their preliminary report (now available online at http://publications.iodp.org/preliminary_report/329/) offers a glimpse into one of the most fascinating ocean phenomenon yet to be studied.
Ocean gyres – sometimes called vortexes – consist of massive, rotating systems of ocean currents. Five major gyres exist worldwide: one each in the Indian, North Atlantic, South Atlantic, North Pacific, and South Pacific oceans. The IODP research team, working aboard the scientific research vessel JOIDES Resolution, retrieved cores of sediment and rock beneath the South Pacific gyre, hoping to find evidence of microbial life.
Asking questions about life beneath the seafloor is routine for Steven D’Hondt, professor at University of Rhode Island, who led the expedition along with fellow co-chief scientist Fumio Inagaki of the Japan Agency for Marine-Earth Science and Technology.
“We were exploring a place [the South Pacific gyre] that’s twice the size of North America, and has scarcely been explored before,” D’Hondt said. “So instead of Lewis & Clark setting out in search of the long-extinct American Elephant, we were looking for the microbes beneath the sea.”
Wanting to know more about microbial communities at or beneath the seafloor isn’t just a matter of curiosity – understanding these tiny lifeforms could teach us about the way water flows into and out of a gyre, the ways in which wind patterns affect these kinds of anomalous ocean currents, and the relationship between ocean currents and the development of sea life worldwide. Knowing more about subseafloor life could also help scientists answer some fundamental biochemical questions: how, for example, do organisms living in million-year-old rock and buried thousands of feet below the seafloor, acquire energy?
Seeking an answer to these questions and more, scientists on the South Pacific Gyre expedition set off with two major goals: 1) to document the nature of microbial communities and test the limits of life in the most food-poor deepsea sediment and 2) to explore the influence of crust age and sediment thickness on microbial communities, determine the availability of microbe energy sources, and better understand the evolution of crust rock.
Similar research into other, less remote ocean gyres has yielded rich information about subseafloor microbial communities, including establishing the existence of life as deep as 1.6 kilometers (1 mile) below the seafloor, and revising long-held beliefs about the limits of life in our organic world. Scientists once thought that information gleaned from one gyre could translate across to all such systems, but the results from IODP Expedition 329 may call that assumption into question.
“The South Pacific gyre is unlike any other place – or gyre – on Earth,” explained Inagaki. “When compared to other ocean systems, this gyre is remarkably organic-poor. Surface chlorophyll concentrations and primary productivity (measures of energy production by tiny plants and microbes) reach lower values here than in any other region of the ocean. At the same time, samples scraped from the seafloor here exhibit the lowest seafloor cell concentrations ever found.”
So why does the South Pacific gyre harbor so little life while other gyres and ocean regions support so much? D’Hondt and Inagaki theorize that the answer may lie in the way microbes use oxygen, carbon and nitrogen at the seafloor.
Using data collected from the expedition, D’Hondt and Inagaki’s team has determined that net rates of organic oxidation and nitrogen reduction – the means by which microbes produce energy – are extremely low at the South Pacific gyre. In fact, organic oxidation at this ocean vortex occurs at rates thousands of times below the net respiration rates seen at other sites in the Pacific Ocean, such as the Peru Margin and the Pacific upwelling zone. In addition to this, organic carbon content – critical for sustaining life – decreases so rapidly with depth at the South Pacific gyre that it drops below detectable levels after just the first few centimeters below the seafloor.
Despite the shallow nature of the South Pacific gyre’s microbial community, life does appear to sustain itself in the region. D’Hondt and his colleagues estimate the age of some of the microbial processes in those few centimeters at tens of millions of years – raising many more questions that IODP scientists may soon explore.
The Integrated Ocean Drilling Program (IODP) is an international research program dedicated to advancing scientific understanding of the Earth through drilling, coring, and monitoring the subseafloor. The JOIDES Resolution is a scientific research vessel managed by the U.S. Implementing Organization of IODP (USIO). Together, Texas A&M University, Lamont-Doherty Earth Observatory of Columbia University, and the Consortium for Ocean Leadership comprise the USIO. IODP is supported by two lead agencies: the U.S. National Science Foundation (NSF) and Japan’s Ministry of Education, Culture, Sports, Science, and Technology. Additional program support comes from the European Consortium for Ocean Research Drilling (ECORD), the Australian-New Zealand IODP Consortium (ANZIC), India’s Ministry of Earth Sciences, the People’s Republic of China (Ministry of Science and Technology), and the Korea Institute of Geoscience and Mineral Resources.
For more information about IODP Expedition 329 – South Pacific Gyre Subseafloor Life, visit http://iodp.tamu.edu/scienceops/expeditions/south_pacific_gyre_microbio.html.
For more information about the JOIDES Resolution, visit www.joidesresolution.org.
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For more information about the Integrated Ocean Drilling Program, visit www.iodp.org.
Matthew E. Wright
Communications Manager, Scientific Ocean Drilling Programs
Consortium for Ocean Leadership
Integrated Ocean Drilling Program Management International, Inc. (IODP-MI), Tokyo, Japan