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Dispatch 22: Carbon dioxide (CO2) measurements on Ice-Tethered Profilers

Mike DeGrandpre

September 30, 2020

Today, we recovered an ITP with a sensor installed that measures the seawater’s carbon dioxide content.  Earlier in the program we deployed a similar looking ITP, also with one of these carbon dioxide sensors.  Mike DeGrandpre, although not onboard, has sent in a special dispatch describing this sensor and his work:

Ice-Tethered Profilers (ITPs) were developed at Woods Hole Oceanographic Institution to measure temperature and salinity from below Arctic ice to ~800 m depth. The profiler climbs up and down a cable attached to a surface buoy that transmits the data back to Woods Hole via satellite.  The ITPs, deployed in the Arctic Ocean since 2005, have also measured dissolved O2, currents, and bio-optical parameters during some missions and in 2012 our group at the University of Montana added CO2 measurements to their capabilities. In this case we clamped a Submersible Autonomous Moored Instrument for CO2 (SAMI-CO2) to the cable directly below the ice. Our instrument is too large for the profiler, but is small enough to fit through the ice-fishing-sized hole through which the ITPs are deployed. We ran into some technical problems early on thereby proving "Murphy’s Law of autonomous sensors” - that the likelihood of something not working is directly proportional to your confidence that nothing will go wrong. We’ve overcome those challenges (knock on wood, autonomous sensor folks can be quite superstitious) and have now collected numerous full year CO2 data sets in the surface of the Arctic Ocean.  These data are highly valuable - most Arctic Ocean CO2 measurements have been made in late summer when sea ice is reduced and sunlight is abundant. With year-long CO2 data sets, we can better quantify the exchange of CO2 with the atmosphere, how CO2 is controlled by biological production and how ice formation and melting are changing the carbon cycle. We look forward to continuing deployment of our SAMI-CO2 sensors on the ITPs and examining the exciting data that they produce!

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