N01 SUNA - Nitrate Observations Corrected

One SUNA V2 and two ISUS (Sea-Bird Scientific) were deployed on NERACOOS Buoy N (Latitude: 42 deg 19.48'N and Longitude: 65 deg 54.55'W) at 50m, 100m and 180m, respectively, from July 26, 2016 to July 15, 2017. This corresponds to University of Maine buoy deployment N0120 (http://gyre.umeoce.maine.edu/data/gomoos/buoy/html/N01.html). The sensors were programmed to collect nitrate measurements three times per day (0045, 0845 and 1645 GMT) over a fixed sampling window of 30 seconds at approximately 1.4 readings per second. Five measurements recorded in the middle of the 30 second data stream were transmitted back to the University of Maine Physical Oceanography Group via cell phone. The mean concentration and standard deviation were calculated for each specific sampling time. If the standard deviation for a mean was greater than 2uM, the values were eliminated. Surviving data were then quality controlled (QCed) by removing outliers assessed as values less than -0.5uM and greater than 30uM. At the time of buoy deployment, a standard CTD cast was conducted with a carrousel water sampler equipped with Niskin bottles. Ground truth water samples were collected at the same depth as the nitrate sensors. These samples were analyzed for nitrate concentrations at the University of Maine using a Bran Luebbe AA3 Autoanalyzer and standard techniques. Ground truth corrections were added or subtracted as an offset only if the difference between the nitrate concentration of the water sample collected and the mean nitrate sensor reading at approximately the same time was greater than 2 uM. Upon recovery of the instruments, the data was processed using the software provided by Sea-Bird (UCI and ISUS.com) and compared with the real-time measurements as a check for accuracy. In the event that the sensor was not able to transmit in real-time, the processed data was QCed. Please contact David Townsend, University of Maine, School of Marine Sciences if you have any questions.