Expanding our ability to perform multi-species chemical analyses in-situ in real time would have significant impact in the ocean sciences, chemical oceanography, charting ocean circulation, in understanding the effect of pollutants in the ocean, and the effects of global climate change,

Since their discovery in 1977 at the Galapagos Rift, deep sea hydrothermal vents (HTVs) have been considered a new frontier of planetary exploration…right here on Earth! Ninety-five percent of the species discovered at HTVs are new, thus raising many questions about how they survive in such extreme environments. HTVs are over 4,000 meters in depth with temperatures ranging from 2 to 450°C, and pressures near 400 atm. The study of dynamic biogeochemical processes in the ocean, especially near hydrothermal vents, is a daunting challenge. To undertake such studies requires the ability to monitor a variety of chemical species under extreme conditions in-situ in real time. Our group has investigated the application of new techniques and sensors similar to those we used to analyze the soil on Mars. With support from the NSF, a compact array of real-time sensors using ion selective electrodes (ISE) was developed to measure, under high pressure [1], in-situ, in real-time, inorganic ions present in the vicinity of these thermal vents.

The image above shows the prototype ISE sensor array undergoing in-situ testing in April 2012 on a cruise starting at Franklin Bridge in Philadelphia, down the Delaware River, and then 10 miles off-shore.

In summary, the immediate goal of the proposed work was to develop and demonstrate as a proof-of-concept a sensor array capable of providing simultaneous in-situ real-time nM-mM measurements of ionic species, initially including Na⁺, K⁺, Mg²⁺, Ca²⁺, NO₃^-, NH₄⁺, H⁺, S^2-, F^-, and Cl^-, at extreme depths in seawater. The longer-term objective was to enable follow-on research that, with improved detection limits and selectivity, would provide the ocean sciences community with a new tool for in-situ real-time chemical mapping of a broad range of ionic chemical species in seawater. The proposed effort was divided over two years (2011-2013). During the first year our goal was to design, purchase, fabricate, test, integrate, and field test, a prototype sensor array in easily accessible location traversing fresh and sea water domains. During the second year, building on lessons learned from the first-year evaluation, we made modifications and demonstrated that the sensor array can provide reliable/accurate real-time chemical analyses during cruises in coastal waters (~ 2700m) off of Delaware. We successfully fabricated a subset of the ion selective (ISE) sensors. They have been tested in the lab in a custom-built high-pressure chamber up to 160 bar and in seawater collected during an August cruise from surface to a 2700m depth. In addition, the sensors were also evaluated during a cruise (3/31- 4/3/2012) in Delaware Bay over a 177 km transect starting 26 km south of Franklin Bridge (Philadelphia PA) and ending 20 km offshore from the mouth of Delaware Bay in open ocean. The results show that the prototype ISE sensors are capable of accurately measuring concentrations of the proposed ionic species at pressures up to 160 bar and in real seawater samples. We have shown for the first time the potential ability to use ion selective electrodes (ISE) to obtain in-situ concentrations of several inorganic ionic species, but most importantly shown by comparisons with two other NO₃^- analytical techniques, that we can detect variations of nitrate at ambient concentrations in the micro-molar range in seawater.  

A more detailed report of our results can be found HERE.