Ocean solutions, from landlocked Montana

The world’s oceans are in the midst of a crisis. Rising levels of atmospheric CO2 are driving higher levels of acidity as it dissolves into the seas. The potential biological, ecological and societal impacts are staggering. Studies are finding that the absorption of CO2 emissions is already having a profound influence on ocean chemistry, impacting the health of creatures as small as coccolithophores to as large as giant clams. Coral reefs and other marine ecosystems are threatened and, by extension, so are we. A huge portion of the world’s population depends on the ocean for food and livelihood.

Ocean health is such a global concern that the United Nations proposed as one of its Sustainable Development Goals (#14) to “conserve and sustainably use the oceans, seas and marine resources for sustainable development.”

At Sunburst Sensors, we’ve been working on the problem of ocean acidification for a while — even though we’re based in landlocked Montana. Company founder, Professor Michael DeGrandpre, has been studying ocean-carbonate chemistry for years, and came up with an autonomous pCO2 sensor during post-doctoral studies at the Woods Hole Oceanographic Institution in Massachusetts, more than 20 years ago. Sunburst Sensors was started to sell this sensor to other researchers studying ocean-carbonate chemistry.

Besides carbon dioxide, the carbonate system is determined by pH, alkalinity and total inorganic carbon. In order to understand what’s going on, you need to know at least two of those factors; you can calculate the other two based on the known variables. Having developed a CO2 sensor, we next turned our attention to the development of a pH sensor that could measure long-term pH levels. In cooperation with DeGrandpre’s lab at the University of Montana, we developed the SAMI-pH sensor around 2008, just as ocean acidification was becoming a bigger concern. SAMI stands for “Submersible Autonomous Moored Instrument,” and that sensor — which we’ve improved upon over the years — is the basis of our winning entry’s technology.

When we heard about the Wendy Schmidt Ocean Health XPRIZE, we knew we had to be involved. Rumors of an ocean-pH prize came to us as far back as 2011, but there was nothing official for at least two more years. When we finally saw that it was going to happen, we were all very excited to participate, although also somewhat daunted by the timeline and requirements. We knew we had good technology, but it wasn’t designed to do all the things outlined in the rules.

Our sensor uses a spectrophotometric method. In a lab, someone who wanted to measure the pH of a solution using this method would know roughly the pH range they’re looking at; then they’d select the proper indicator dye, add it to a sample, shine a light through it, and measure its spectral absorbance with a spectrophotometer. Since the absorbance characteristics of the dye are known, pH can then be calculated directly. One of the big advantages this method yields is that you don’t have to calibrate it — you just have to know how your dye works.

Normally, a spectrophotometer is a big machine that sits on your lab bench, but our approach calls for something much more compact that uses far less energy. Our sensor pumps seawater through a tiny flow cell and injects a dye called mCP (meta-Cresol Purple) into the sample stream. As the pH of the solution changes, mCP gains or loses a proton, which changes how it absorbs light. The sensor shines light through the cell at the two wavelengths at which mCP absorbs, depending on what form it’s in. By looking at these absorbance values, we can calculate both the indicator concentration and what we call the “point pH.” Because the reagent “perturbs” the sample (changes its pH) we have to do some math to get the real pH value; basically we draw a line on a plot of “point pH” vs. indicator concentration to the “zero indicator” value. This is the real pH.

We entered two different versions of our SAMI: iSAMI and tSAMI, which stood for “inexpensive” and “titanium” respectively.

The tSAMI is the deep-water version. One of the competition’s requirements was that the devices survive at a depth of 3,000 meters, or almost two miles below the surface. Our production instruments only go to 600 meters (most customers deploy in the first 100 meters), and the deepest a SAMI had ever gone was 900 meters — so this was more than three times that depth. Though we had no good way to test anything at 3,000 meters from our base in Montana, we looked at the requirements and designed a housing that could withstand the pressure. One key was to concentrate on making the point where the fiber optics crossed the pressure bulkhead absolutely leak-proof, because at 4,500 psi, water will find a way.

The iSAMI, our inexpensive model, uses the same technique, but is designed for shallow deployments — only five meters or less. With this minimal-pressure requirement, we could get rid of the fiber optics, put the pump and valve inside the pressure vessel, and integrate the flow cell right into the beam splitter on the circuit board. It works, and it’s affordable — but if you were to take it any deeper than five meters, it would stop working altogether.

XPRIZE is doing a great thing here, calling attention to a real problem and getting people to think about how to solve it. Even though we ended up winning, I think a lot of the technology that was entered into the contest will keep moving forward in the next couple of years, so we can’t rest on our laurels and say we’re the best. Second place Team ANB has a very interesting approach, and I’m curious to see what they do with it going forward. And Team Durafet has some of the smartest people in the field, with lots of resources. They will certainly continue to improve.

I think we have a responsibility to put the attention and money we won to work delivering products that continue to further this important research. Part of what we’re going to do is get iSAMI into production. What we entered was more or less a prototype; now it’s time to turn it into a real product that we can get into the hands of the scientific community.

We’re also investigating getting our pH and possibly CO2 sensors into the Global Drifter Program, an array of surface-drifting buoys that record things like temperature and position; other instruments could be added, and we’re trying to make something to support that platform. These drifters are basically disposable, so people aren’t too psyched to throw a $15,000 instrument on them; they want something that’s reasonably inexpensive but still provides good data. And with our help, that’s what they’ll get.

James Beck, The Huffington Post, 21 September 2015. Article.

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