October 1, 2017

A Small Ocean Acidification Sensor Could Serve a Large Need

By Bayley Connors, BURECS

How do you improve an advanced sensor already holding the potential to affect the narrative of climate change? For starters, shrink it. Dr. Aleck Wang, a MIT Sea Grant funded scientist at the Woods Hole Oceanographic Institution, hopes to do just that.

It began in 2013 when Dr. Wang first designed the Channelized Optical System, CHANOS for short. The sensor was able to record measurements in seawater that are crucial to marine scientists, including a measure of acidity, or pH and a measure of total amount of CO2 dissolved in water known as DIC. While the instrument was able to provide precise and accurate measurements in situ, because of its size and power consumption, it could only be deployed on large observing platforms, such as buoys.

Now, years later, funding from MIT Sea Grant will help remove this limitation through the design of CHANOS II, a new sensor featuring the latest innovation from Dr. Wang’s lab in Woods Hole. A newly engineered manifold component and a miniature pumping system will allow the device to be drastically smaller and power friendly than its predecessor. This will prove critical in expanding its applications from large platforms to small mobile underwater vehicles.

“The significant advancement of this development is that CHANOS II will be fast and small enough to achieve both high resolution spatial mapping on mobile platforms and high-frequency time-series measurements at fixed locations,” says Dr. Wang. Its design allows near-continuous (~1 Hz) in-situ measurements, assessing DIC and pCO2 of seawater simultaneously. As such, the seawater CO2 system at a location can be fully characterized by a single sensor.

Measuring pH in coastal waters can be challenging because changes in salinity or water clarity can make measurement less accurate. In that case, Wang’s sensor can measure pCO2 rather than pH alongside DIC. Both DIC and pCO2 are largely unaffected by salinity and changes in water quality. The development of a sensor that allows for accurate carbonate measurements in the coastal ocean enables researchers to ask more difficult and nuanced questions.

Researchers who study ocean acidification in coastal or other highly dynamic systems will especially benefit from the sensor’s ability to perform near-continuous measurements. Currently, DIC and related variables are typically analyzed by taking a single bottle sample, forcing scientists to assume uniform concentrations across coastal areas. Dr. Wang emphasizes, “Nobody has done this kind of resolution yet – we don’t know what the variability is across relatively small space.” The CHANOS II will be the first DIC sensor that can make near-continuous measurements, allowing researchers a picture into how these variables change over spatial scales as small as a centimeter. This sensor’s capability has the potential to change how coastal ocean acidification is thought about, to reveal new phenomena, and to give researchers a baseline to form new hypotheses never considered before.

For now, Dr. Wang and his team are working on the hardware’s testing and development. He, and many researchers alike, is looking forward to its initial deployment in the coming year. The potential implications held by the device have certainly left many within the scientific community eager to see what it brings.

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