Scientists 'see' new ocean floor just before and after it is created

Ocean-bottom seismometers, which had been deployed by researchers from the Lamont-Doherty Earth Observatory (LDEO) of Columbia University, detected steadily increasing levels of earthquake activity over several years leading up to 2006. Research teams from WHOI and other institutions then used towed cameras and the submersible Alvin to make a visual confirmation of the seafloor eruptions, which decimated the well-studied communities of tubeworms, mussels, and other unique organisms that had been living at the hydrothermal vents in the area.

A research paper describing the seismic data was authored by Maya Tolstoy of LDEO and includes scientists from WHOI, the University of Hawaii, Brown University, the University of Washington, the University of Florida, and NOAA’s Pacific Marine Environmental Laboratory. The findings will be published in an upcoming issue of Science, with a preliminary analysis being released on 23 November on the Science Express web site.

“We rarely get to observe a deep-ocean eruption just after the fact,” said WHOI geologist Adam Soule, who helped confirm and map the seafloor eruption. “This will add substantially to our understanding of how mid-ocean ridges work.”

Through research expeditions in May and June 2006—as well as another that just departed on 22 November 2006–WHOI researchers have been heavily involved in characterizing the extent of the eruptions and in observing its effects on the communities of unusual species that thrive in the mineral-rich fluids that spew from hydrothermal vents on mid-ocean ridges. More than two-thirds of Earth’s crust is created along seafloor spreading ridges, yet scientists rarely have a chance to observe the process is action.

In 2003, the LDEO team deployed a dozen seismometers on the ocean floor along the East Pacific Rise (EPR), near 9°50’ N latitude, about 400 miles south of Acapulco, Mexico. Each year when they returned to service the instruments, the researchers detected steadily increasing levels of earthquake activity as magma moved beneath the ridge axis. They suspected a major seismic event was imminent. Sometime between May 2005 (the last readout of the seismometers) and April 2006, a series of volcanic eruptions paved over areas of the ocean floor.

A scheduled expedition on the WHOI-operated Research Vessel (R/V) Knorr in April 2006 provided the first hint of an eruption. The LDEO team discovered that most of their instruments could not be recovered and surmised that a seafloor eruption had probably wiped them out.

Securing “rapid response” funding from the National Science Foundation’s Ocean Sciences Division and its Ridge2000 program, a team of researchers led by James Cowen of the University of Hawaii returned to the site in May 2006 on the R/V New Horizon (operated by the Scripps Institution of Oceanography) to survey the ridge axis and to measure and sample the water above the eruption site.

On that May expedition, WHOI marine geologist Dan Fornari and biologist Tim Shank used a towed camera system to make the first visual confirmation of the new eruption along the EPR, observing fresh lava and noting that several seafloor biological communities that had once thrived were now gone.

“The stark contrast between the fresh lava and the older seafloor allowed us to document where the eruption had occurred and how the lava traveled over the seafloor,” said Soule.

Another rapid-response expedition—led by Karen Von Damm of the University of New Hampshire—was launched in June 2006 to use R/V Atlantis and the Alvin submersible (both operated by WHOI) to make more detailed observations and collect geological, chemical, and biological samples from the eruption site. Using observations from the two cruises, Soule compiled and analyzed the data to identify the size of the eruption and map its extent—estimated at nearly 15 square kilometers (9 sq. miles) of the ridge crest.

“The eruptive creation of new hydrothermal vents represents a ‘time-zero’ from which to launch coordinated, interdisciplinary studies to understand how chemical and biological processes govern the initial assembly and development of mid-ocean ridge communities,” said Shank, an associate scientist in the WHOI Department of Biology.

“Because of the background data collected over the past 15 years at the EPR eruption site, as well as the new technologies we have at our disposal, we will be able to tell much more about how seafloor eruptions happen and about how volcanic processes shape and construct the mid-ocean ridge” added Fornari, a senior scientist in the WHOI Department of Geology and Geophysics.

A new research team led by Karen Von Damm of the University of New Hampshire—and including Fornari, and Shank—departed this week on R/V Atlantis to return to the eruption sites. The East Pacific Rise is one of three active seafloor spreading centers targeted by NSF's Ridge2000 program to document the formation of Earth’s crust as it is happening.