Casting for Clues

In May 2007 and Feely and his colleague, Christopher Sabine, boarded the Research Vessel Wecoma. For the next two months, they sampled ocean waters off the West Coast of North America from Canada to Mexico. They traveled with an international team of scientists—including Debby Ianson from the Institute of Ocean Sciences in Canada and Jose Martin Hernandez-Ayon from the Instituto de Investigaciones Oceanológias in Mexico—conducting the first large-scale carbon survey along the West Coast.

The map shows the path of the Research Vessel Wecoma during the NACP West Coast Survey Cruise. The yellow dots represent station locations, where the crew collected ocean water samples. Map: Cartifact, Inc.

The Wecoma crisscrossed back and forth along transect lines that extend away from the coastline and out past the edge of the continental shelf. At each of the seven or eight stations along the thirteen transects, the scientists deploy a CTD/rosette package. A CTD — an acronym for Conductivity, Temperature, and Depth — is the primary tool for collecting water samples to determine essential physical properties of sea water. It is made up of a set of small probes and bottles that are attached to a large metal rosette wheel. The rosette is lowered on a cable down to the seafloor, and scientists observe the water properties in real time via a conducting cable connecting the CTD to a computer on the ship.

Dr. Feely studying sea conditions for sampling during the 2007 cruise. Photo courtesy of Debby Ianson, IOS, Canada.

At a station near the Oregon-California border, Feely stood on the deck of the Wecoma watching as a winch lowered a large metal rosette assembly of 24 empty water canisters and sensors into the relatively calm ocean. During much of the cruise, frequent 35-knot wind gusts had made the launch of the CTD quite difficult. This day was no different. As the he watched the rosette disappear beneath the surface, Feely voiced his appreciation for the skill of his shipmates, since he knew that the persistent winds they had been battling were precisely the reason why this cruise was scientifically important.

In the early spring, northwesterly winds off the West Coast strengthen in response to seasonal pressure systems in the atmosphere. The winds push warm surface waters away from shore and, in their place, cold, deep waters well up from the depths below. Feely and other scientists aboard the Wecoma suspected that the corrosive waters they detected at deep depths during their first ocean survey might rise toward the surface during such upwelling events. Though no one had ever found “acidified” corrosive waters on the continental shelf off the West Coast of North America before, the team feared that seasonal wind-driven upwelling might bring those waters up from the depths and onto the relatively shallow continental shelf.

During upwelling, displaced surface waters are replaced by cold, nutrient-rich water that wells up from below. NOAA/OER image courtesy of Sanctuary Quest 2002.

The team gathered inside the ship to gaze intently at the computer monitors in the laboratory. Data from the CTD’s sensors streamed across the screens and charted the seawater’s conditions, much like the vital signs on a hospital patient’s monitor. The crew lowered CTD to within 10 meters above the seafloor and then reeled it in again. As the instrument rose toward the surface, the scientists pressed buttons to signal specific water bottles to open and close, allowing them to collect and analyze water samples from different depths. Instantaneous measurements of temperature, salinity, and other physical properties of the samples traveled up the cable, directly to the ship’s computers, allowing the team to preview their findings. The water samples captured in each bottle were eventually brought aboard for further analysis. And so it went at station after station.

(Above) The CTD/Rosette package prior to being deployed from the Wecoma. (Top left) Dr. Debby Ianson from the Institute of Ocean Sciences in Sidney, British Columbia, collecting water samples for biological measurements during the cruise. (Bottom left) Mr. David Wisegarver of PMEL conducting dissolved inorganic carbon measurements. NOAA photos courtesy of Laurie Juranek, PMEL.

After completing their fifth transect, Feely retreated to the quiet of the ship’s lab to collect his thoughts along with the results of the analyses of the water samples gathered to date. Feely double-checked the water’s pH, partial pressure of carbon dioxide (pCO2), and ability to dissolve calcium carbonate at different depths and locations along the coast. (All of these parameters are needed to understand the global ocean uptake of atmospheric carbon dioxide.)

The data from the first five transects confirmed his suspicions. The north winds were causing the upwelling of corrosive waters onto the continental shelf. Feely looked carefully at the results from transect five. There, in an area near the border of Oregon and California, the data showed corrosive waters reaching all the way to the surface of the ocean less than 20 miles away from the shore! Such corrosive waters near the shore meant the problems of ocean acidification could be interfering with marine plants and animals trying to build their shells right then — not 50 or 100 years in the future as scientists had previously thought.

The figure provides a look at the pH of the water sampled at different depths along transect line 5 near the border of Oregon and California. The water upwelling onto the continental shelf recorded lower pH levels than water samples collected farther away from the shelf. The water below the red line was undersaturated with respect to aragonite, a common type of calcium carbonate used in shell-building. Chart: Cartifact, Inc.

His thoughts returned to the oyster crisis back home. Could corrosive waters already be dissolving the fragile shells of oyster larvae on the coast right now? Perhaps Vibrio tubiashii wasn’t only the only suspect in this case. Or, perhaps the bacteria hitched a ride to the hatcheries within the upwelled waters!

When the crew of the Wecoma finished their research cruise in June 2007, the team already had the first draft of a scientific paper describing their findings. That paper appeared in a June 2008 issue of Science. The news was troubling, and not just for the Pacific Coast. 

“Ocean acidification could ultimately threaten a reorganization of the entire marine food chain, which could lead to major changes in the distributions of marine species,” Feely said. “Many valuable marine organisms such as crabs, lobsters, and shrimp are expected to suffer. Many coral reefs, which bring in millions of dollars in revenue for the tourism industry, are expected to be lost. The loss of planktonic species – an important food source for many commercial and recreational fish species — could have significant economic impacts on the multi-billion dollar U.S. seafood industry.”