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SEAS: Student Experiments At Sea

Study site at the East Pacific Rise

The SEAS study site is on the East Pacific Rise mid-ocean ridge. The site contains many hydrothermal vents.

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Part of the mid-ocean ridge system

Map of Pacific showing position of East Pacific Rise study site

The East Pacific Rise forms the boundary of the Pacific and Cocos tectonic plates. At the study site, these plates are separating at a rate of about 11 centimeters a year, one of the fastest spreading rates in the world. The axial trough (valley) along this section of the mid-ocean ridge is as deep as a two-story building and in some places, as wide as an interstate highway.

The study site is located between 9°40' and 10° N latitude and at 104° 17' W longitude on the East Pacific Rise. It is about 500 miles south of Manzanillo, Mexico (the closest shipping port), from where it takes researchers about 2 days to reach the site.

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The Bio-Geo Transect: our long-term study site

Our detailed study site is known as the Biologic-Geologic Transect (or Bio-Geo Transect, for short). The Transect lies between 9°49.61' N and 9°50.36' N and has been the focus of detailed research since 1991. In April of that year, researchers studying this area happened upon a brand new lava flow and what looked like "snow" in the water. It wasn't snow, of course, but turned out to be microbial floc that was floating in the water column. Because of its distinctive look, scientists nicknamed it a "snowblower" event. (See the photos in the right-hand column)

A new biological community forms

Deep-sea mussel bed, also with crabs
Mussels living in diffuse flow
near a hydrothermal vent.

At the time of the 1991 eruption, none of the typical vent animals such as tubeworms, mussels and zoarcid fish were found in the immediate area. Instead, the area was covered with thick, white "bacterial" mats. Recognizing that this might be the opening of a new set of hdyrothermal vents, the scientists decided to mark the area clearly and return to it each year to see if the area was colonized by other living creatures. They devised special markers and placed them all along a line (or transect) in the area of the eruption. Each year following, scientists visited the transect to study changes in the venting and water chemistry as well as in the community of animals that colonized the new habitat.

Studying changes over time

Since scientists placed markers along the Transect in 1991, there have been dramatic changes in the different species of macrofauna (the large animal life including tubeworms, mussels, clams, limpets, crabs, fish, and octopus). Over the years, new species have moved in and crowded out earlier species.

To understand what drives these changes, scientists have used photo-mosaic images to document which species were represented within the community. They also collected temperature, fluid chemistry, and microbial samples from the same area, to correlate data from photographs with changes in environmental parameters. With this information, they have been able to answer a variety of questions about the relationships between organisms and their environments (for example, whether increases in numbers of tubeworms correlate with increases in temperature and vent fluid sulfide levels). By collecting data over several years, we have a long-term, time-series dataset to help us understand factors that control biological community structure.

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Fresh eruption in 2006!

New lava at the East Pacific Rise study site
Fresh lava.

Starting in 2005, seismologists noticed an increase in the number of earthquakes recorded at the study site. Geochemists familiar with long-term patterns in the chemistry of hydrothermal vent fluid also noticed changes indicating different hydrothermal circulation. These observations suggested another eruption was imminent. So when some of the seafloor instruments along the Transect failed to respond in early 2006, scientists felt certain that a new eruption had occurred. Scientists arriving on the scene with a deep-towed camera system and water samplers in May 2006 confirmed these suspicions. The East Pacific Rise study site, including the 15-year old animal community and many of the scientific instruments, was buried in fresh lava!

Although this new eruption seems catastrophic, it is actually a normal occurrence in the deep-sea environment of mid-ocean ridges. And although scientists are disappointed that their experiments are covered with lava, the new eruption affords us the opportunity to continue studying the cycles at vents. The next SEAS cruise, in January 2007, will post updates of what we find and how we continue to study this exciting, extreme environment.

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