MBARI Team Earns XPRIZE to Measure Ocean Acidity

Jul 24, 2015

MBARI scientist Ken Johnson displays the sensor-equipped buoy that earned a second place X-Prize for accurately measuring ocean acidity.
Credit Rex Sanders

Burning fossil fuels dumps excess carbon dioxide into the atmosphere, causing global warming and increasing acid levels in the ocean. Scientists call ocean acidification "the other CO2 problem." Teams from around the world competed for the Wendy Schmidt Ocean Health XPRIZE to build the best sensor to measure acid levels, also known as pH.

On July 20, a team including scientists from the Monterey Bay Aquarium Research Institute (MBARI), won prizes in the contest.

"Getting involved in the XPRIZE is a way to compare my sensor versus everybody else's," says Ken Johnson, a member of the team.

Predicting Changes Requires Data

The competition started with 18 teams. After several rounds of testing, five teams made it to the finals offshore of Hawaii, which just finished. Johnson is a member of Team Durafet, one of the finalists in the contest to assess ocean acidification. "Some of the biggest names did not make it," he says.

Scientists already understand the basic principles of ocean acidification. Humanity has dumped more than 500 billion tons of carbon dioxide into the atmosphere. The ocean soaked up about one third of that CO2, turning it into acid. That increased acidity can dissolve the shells of tiny ocean plankton, mussels, clams, and other shellfish.

"The oyster spat, the little baby oysters can't survive in this water that is acidic enough to dissolve their shell," Johnson says.

Ocean acidification could harm coral reefs, salmon, and anything that eats shellfish. Computer models say that ocean acid levels could increase 150 percent by the end of the century. Scientists hope to predict changes in different parts of ocean by gathering detailed pH data. Johnson's been working on this problem since 1975, when he wrote his first paper about monitoring ocean acidification using a glass electrode.

"There are very few places where we actually measure over time, make a time series measurement of pH," says Johnson, "especially in the open ocean, because it's so expensive to put ships out there."

Eight years ago, Johnson and his team started working on their latest pH sensor, based on Honeywell's "Durafet" chip developed for factories. Johnson wanted to measure the acid levels of the Southern Ocean that surrounds Antarctica, which is especially sensitive to pH changes due to the colder water. His sensor is built into a buoy that drifts through the ocean, which also measures oxygen, nitrate, chlorophyll, temperature, and salinity.

Gathering Accurate Data Over Years

Every five to ten days, the buoy automatically dives over a mile deep and then floats back up, taking measurements along the way. When it reaches the surface, the buoy sends a burst of data via satellite to the Internet for everyone to use.

"One of our big contributions has been to adapt [the pH sensor] to run at the high pressure of the deep ocean," says Johnson.

One problem Johnson had to solve was making sure pH measurements stay accurate over the eight year life of the buoy. Each sensor needs special preparation before it goes to sea.

"We calibrate the pH in sea water where we can know from colorimetric techniques in the laboratory exactly what the pH is," says Hans Jannasch, a research specialist at MBARI. "Then we enter our last calibration coefficients into the floats before they get deployed."

Ken Johnson and Team Durafet were awarded a second place prize for the accuracy of their sensor. The prize includes $250,000. Meanwhile, Johnson's group at MBARI is busy building and deploying more sensors. They aren't waiting to measure big changes in the ocean caused by humans burning fossil fuels.