2007-04-27 | SCIENCE
Taking the Ocean's Pulse

By Henry Bortman

Moss Landing, California

The town of Moss Landing, California, lies at the mouth of Monterey Canyon, one of the longest and deepest underwater canyons in continental North America. Virtually unknown, and largely unexplored, the sheer size of Monterey Canyon puts it squarely in league with its celebrated upcountry counterpart, the Grand Canyon. Which explains why the Monterey Bay Aquarium Research Institute MBARIis headquartered here.

So when MBARI's Chris Scholin invited me out for a day on the water, to watch as he performed the a deep-water test of his Environmental Sample Processor (ESP), I eagerly said yes. Then he told me the boat would be departing at 5:30 am.

Scholin has been working on various incarnations of the ESP for nearly 14 years. Back in 2004 he applied to NASA's ASTEP (Astrobiology Science and Technology for Exploring Planets) program for a three-year grant to develop the ESP-II, the generation he's now testing.

The ESP II team aboard the Point Lobos after a successful test at 1,000 meters. From left: Brent roman, software engineer; microbiologist Chris Preston; Chris Scholin, principal investigator; and Doug Pargett, project manager and engineer. Credit: MBARI

ESP-II is designed to slurp up a liter or two of ocean water, filter it to capture any microorganisms that may be present, break open the microbial cells, tag the RNA of pre-selected organisms with a luminescent chemical, and capture a digital image of the resulting glow. It does all this within the confines of a metal cylinder that looks like a downsized oil drum - roughly 16 inches in diameter and 3 feet tall. Its innards are a labyrinth of plastic tubing, valves, a couple of syringes to move liquids from place to place, IV bags filled with various reagents, an Intel ARM processor, 32 megabytes of RAM, a handful of controller boards and a digital imaging device raided from a camera designed for use by amateur astronomy buffs.

Inside this "core unit," sample processing takes place within small pucks, squat metal cylinders the width of a quarter and half an inch tall. Several different types of pucks are used. The first one contains a .22-micron filter that extracts all of the particulate matter, including microbes, from the ocean water. A total of one liter of water is pushed through the filter by a syringe, 25 milliliters at a time.

Another puck houses a DNA probe array on which have been deposited four dozen tiny dots. Each dot, about a millimeter in diameter, is placed on the array by a mechanical pen that is dipped into a well of liquid containing copies of a strand of DNA, one or two dozen oligionucleotides long, that will hybridize with ribosomal RNA from a particular ocean-dwelling organism. For this test, Chris Preston, the microbiologist on the ESP team, is targeting seven different organisms, mostly bacteria, but also some archaea. About a half a dozen dots are used to target each of the organisms; that way, Preston can double-check the accuracy of the test.

ESP lead engineer Scott Jenson and project manager Doug Pargett make final adjustments before sealing up the instrument in its deep-water high-pressure casing. Credit: Henry Bortman

Several additional biochemical reactions then take place, involving first an antigen, then an antibody to the antigen, and finally a chemiluminescent substrate. The process resembles the ELISA test used to detect HIV antibodies. The final result is that the dots on the array glow with varying intensity. If a dot glows brightly, it means the water sample contained a high concentration of the particular organism it was primed to detect (or that the organisms were highly active, or both). If the target organism is absent, the dot will be black. The puck that contains the array has an opening through which the ESP's camera captures an image of the glow.

Last year Scholin's team tested the device in the surface waters of Monterey Bay. That was the first step. The second step was going deep. As we headed out into Monterey Bay, we were embarking on day two of a three-day series of deep-water tests.

To perform in deep water, the ESP needs a front end "sampler" unit, a separate piece of equipment that can collect high-pressure water and depressurize it before sending it to the core. All of the fluids in the core unit are kept at close to one atmosphere, slightly above 15 pounds per square inch. The pressure at 1,000 meters is 15 hundred pounds per square inch. If such highly pressurized water found its way into the ESP, it would break its low-pressure seals, flood the instrument and destroy it. On the first day of testing, the ESP successfully acquired and processed a sample at 500 meters (1,640 feet). On day two, the goal is 1,000 meters, and things aren't going so well.

For deployment in the ocean, the entire ESP - both the core and the sampler - are mounted on a "sled," a four-foot-tall open aluminum frame, which is attached beneath the Ventana, one of MBARI's underwater ROVs (remote operated vehicles). The Ventana is connected via a cable to the ship's power and electronics systems, and in turn the ESP is connected to the Ventana. The entire assemblage, which weighs about 3,200 kilograms (about 7,000 pounds) is lifted over the side of the boat by a massive crane and then released into the water. As the ROV descends, its yellow-clad umbilical cord unwinds slowly from a massive spool.

The ESP, attached to an open aluminum frame below the ROV Ventana, being lowered into Monterey Bay for its first deep-water test at 1,000 meters. Credit: Henry Bortman

Belowdecks is a sophisticated control room - it looks like a compact version of JPL's Mission Control - full of floor-to-ceiling banks of computer and video screens that display various status indicators and underwater images. This is where the team waits for the ESP to send them its picture. On this day, though, the picture never arrives, due to technical difficulties with the sampler.

Later in the week I emailed Scholin to see how the third day had gone. He was thrilled. "We were able to pull a full volume sample at 1,000 meters and the probe array looked great," he wrote back. It was, he said, a "great illustration of doing something for the first time, in the field, not having the benefit of being able to test the integrated system in the lab."

Next year, a ESP unit will be sent into the deepest region of the Monterey Canyon, between 3,000 and 4,000 meters, using an ROV for deployment. Following that, it will be connected to MARS (Monterey Accelerated Research System - no relation to the planet), a network of deep-water monitoring equipment currently being installed at a depth of 860 meters in the Monterey Canyon. It will remain there for a short period of time, sporadically collecting and processing water samples, to see how microbial communities respond to chemical and temperature changes in the deep-sea environment.

Monterey Canyon stretches 95 miles off the coast of central California and descends to an underwater depth of more than 2 miles below sea level.

A similar installation will then take place in the Pacific Northwest, near Axial seamount, an active underwater volcano on the Juan de Fuca Ridge, where the ESP will eventually remain submerged for a full year. Marine researchers in Washington State and Canada are constructing an underwater observation network, NEPTUNE , on the Juan de Fuca tectonic plate, with one of its nodes at Axial. Deploying an ESP unit on the NEPTUNE network will allow scientists to study how fluid flow from the seafloor affects the abundance of different organisms in the deep-sea microbial ecosystem. It may also teach them about organisms that live in the ocean crust, organisms that are usually inaccessible, but that can be ejected into ocean water during an eruption.

The ESP as it exists today is unlikely ever to be used on another planet; none in our solar system is known to have large bodies of liquid water. But Jupiter's moon Europa is believed to harbor a vast ocean beneath its icy crusts, and it is possible that some day a mission to Europa could melt a hole in the moon's surface ice and send a miniaturized derivative of the ESP down to explore the ocean depths for signs of life. The ESP's search strategy would have to be modified a bit. It wouldn't make sense to look for specific terrestrial organisms on Europa; rather, a more generic set of chemical tests would have to be employed. With modification, the ESP could also be used in surface operation, to analyze powdered rock, soil or ice. But imagine the excitement if an ESP-like instrument onboard a Europa deep-sea explorer one day sends back a picture of an array of bright dots. It might not be much to look at, but it could carry a profound message: that we are not alone in the universe, that there is life on another world.

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