The first of its kind

Today’s guest blogger is Josh Sokol, science-journalist-in-training at the MIT Graduate Program for Science Writing. Josh is traveling with the Cohen lab in Palau to report on their research.

It’s about two in the afternoon, raindrops from a sun shower are splashing into the cotton candy-turquoise water of a Palauan reef flat, and Bill Martin is visibly relieved. His instrument for measuring carbonate chemistry is safe, sound, and talkative on the sandy bottom eight feet below a gently rocking boat. The RATS has been deployed.

Bill packs the tools he will need to deploy RATS out on the
reef. In the background, RATS is ready for launch.

“RATS” is one of those forced acronyms; the kind scientists are fond of torturing into recognizable phonetic shape. It stands for the Robotic Analyzer (for) Total (CO2 system in) Seawater. Encased in a yellow-painted aluminum frame, two intake valves pull seawater through a set of tubes and chambers to determine water pH and the concentration of dissolved inorganic carbon. And the RATS does this autonomously, in place, for as long as you tell it to…all of which is a huge advancement over earlier devices that fill a limited number of bags with water, samples which then must get picked up periodically to be analyzed back in the lab.

Why total CO2 system? Because of the four quantities of carbon chemistry you can poke and prod seawater to measure – pH, alkalinity, the partial pressure of carbon dioxide, and the concentration of dissolved inorganic carbon – at least two are needed to understand the whole system. The RATS probes pH and dissolved inorganic carbon, the two measurable attributes that, when paired, yield the most precise estimate of what’s going on in terms of carbonate chemistry. With them you can calculate the aragonite saturation state, a key measure of how predisposed seawater is to letting animals like corals and clams pull calcium carbonate out of the ocean and into their hard skeletons. 

Lifting RATS off the boat and onto the scaffolding tower
before lowering it into the water.

RATS is useful, clearly. But the deployment of about 250 pounds of homemade water-resistant parts and electronics, initially developed by emeritus WHOI scientist Fred Sayles and shepherded for the last six years by Bill, was far from easy.

About an hour before the cool rain, before Bill Martin’s sigh of relief, the RATS had to be moved into position from the Palau International Coral Reef Center (PICRC). With the smell of gasoline fumes wafting from the waiting boat, technical lead Pat Lohmann, Cohen lab grad student (and Palau Expedition 2015 blog author) Tom DeCarlo, and PICRC staff use a stocky, squat red crane to lift the frame and deposit it on board.

After loading up dive equipment for Pat and Tom and a cooler that serves as a dry box for Bill’s computer and notebook, the small boat is crowded. Floor space is at a premium. The driver, Mars, takes the boat roaring out across the deeper, darker blue waters of the lagoon as the wind whips back. Up ahead, barely visible, are thin white tufts of fur: the waves breaking on the crest of the barrier reef itself, a vivid reminder of the service the reef does to Palau by sheltering the islands from the open ocean's energy.

Carefully transferring RATS from the dock to the small boat
that will transport it out to the reef.

As the boat approaches the reef flat, still behind the line of crashing waves, the water turns to iridescent blue-green when the depth drops dramatically. A rickety scaffolding tower of ugly, faded scrap metal, erected by Pat and Tom to lower instruments into the water, is visible first as a faint line on the horizon. Three platforms at different heights emerge into focus, looming out of the water like the bare girders of a tiny, absurd city skyline. Two birds sitting on it fly off as the boat draws near.

Using a pulley mounted on the tower, Tom, Pat, and Mars lift the RATS up and off the boat and lower it into the water. Tom free dives to grab the cable and hands it back into the boat, allowing Bill to talk to the instrument from the command line; to test it while hunched over his computer. Under the boat’s canopy it’s still too bright to see the screen, so Bill covers himself and the laptop with a jacket as if he’s an old-timey camera operator. Prompted from a checklist on laminated pages, Bill records pHs and temperatures as the RATS’ sensors equilibrate. After a sweaty half an hour, he’s taken a sample measurement and confirmed that the instrument works. Then Bill disconnects, his part done.

Pat and Tom walk RATS from the scaffolding tower to its
new home in an array of other instruments.

The command testing over and that light rain falling, Pat and Tom don SCUBA gear and splash into the water. Patches of coral are few and far in between on the sandy bottom, but small fish dart around clumps of algae. Pat and Tom harness the RATS, inflate a balloon to make it weightless, and walk the instrument over to set it down next to a row of other Cohen lab equipment – including the exact device the RATS (in theory) replaces, with its 48 bottles that fill with seawater one by one and then have to be retrieved.

The RATS touches down, the wide circles on its base sinking a little into the sand. A triggerfish, all dramatic curves and orange and black markings, loiters over a clump of nearby coral as Pat and Tom swim back over to the scaffolding, climb up, and clamber into the boat. RATS is home.