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High-Definition Water Data: an interview with Dr. Michael DeGrandpre (Part 1)

Dr. DeGrandpre is a Professor at the University of Montana in Missoula, Montana. His research focuses on the development of autonomous chemical sensors with applications in both marine and freshwater chemistry. He is leading the High Definition Water Data segment of research for The Longest Swim.

The temperature and electrical conductivity (a measurement which is then used to calculate salinity) of seawater relative to its depth might seem like basic information, but these properties can actually help scientists understand large-scale activity in our oceans. For example, researchers use salinity data combined with temperature measurements to calculate seawater density, which is a primary driving force in the movement of major ocean currents. Every day of the expedition, The Longest Swim crew will use a conductivity, temperature, and depth (CTD) device to gather measurements key to several other research projects taking place on-board.

Alongside a CTD device, the crew will be deploying the XPRIZE award-winning i-SAMI Ocean pH Sensor prototype. Scientists can use pH data gathered across the Northern Pacific to track the absorption of anthropogenic, or human-generated, CO2 from the atmosphere. An increased uptake of carbon dioxide gas into the ocean, where it can react with water molecules to release hydrogen ions, results in a decrease in pH known as ocean acidification. This can cause serious damage to coral reefs and other marine organisms whose skeletons may dissolve once their environment’s pH drops too low. The i-SAMI measurements taken during The Longest Swim will help scientists establish a baseline of natural variability in the ocean’s pH, as well as to better track one of the harmful effects of climate change on the marine environment.

How did you get involved with The Longest Swim?

Dr. Ken Buesseler [who oversees the Radiation from Fukushima research segment] is a scientist that I’ve known for a long time and he knew about the in-situ sensor we’ve developed for pH and CO2, which also recently won an XPRIZE for pH sensor development. He contacted me after he got involved with the Swim to see if I’d be interested in adding some measurements to the expedition. We have this instrument called the i-SAMI, which stands for “inexpensive Submersible Autonomous Moored Instrument”, so we offered to allow The Longest Swim to take it and measure pH as they cross the Pacific Ocean.

And how can the i-SAMI help contribute to scientific research?

It’s a highly accurate way of measuring pH spectrophotometrically. [Spectrophotometry is a method which measures the amount of light, in a specific wavelength, that passes through a sample.] The crudest way of measuring pH might be to take a piece of litmus paper, dip it in a solution, and you see a color change. Getting a little more sophisticated, you’d take a glass electrode and do a measurement. But one of the most accurate and precise ways to do it is to use reagent and spectrophotometrically look at the changes within that reagent. This can give us pH values out to the third decimal point, where other methods may only get you to the first or second. When you’re sampling the open ocean you really need that high level of accuracy to understand what’s going on. We’re hoping that it will be in the water much of the time that Ben’s swimming. That particular track that he’s taking probably had not had close monitoring of pH before, so that will be an interesting data set to obtain. There’s a lot of pH data for the Pacific Ocean already but this is going to add many more measurements to that body of data. Along with temperature and salinity measurements, those data will be valuable in helping us understand some of the natural sources of pH variability.

Keep an eye out for the second part of Dr. DeGrandpre’s interview coming soon!

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