I01 SUNA - Nitrate Observations Corrected

Nitrate SUNA V2 sensors (Sea-Bird Scientific) were deployed on NERACOOS Buoy I (Latitude: 44 deg 6.10'N and Longitude: 68 deg 6.73'W) at 50m from November 6, 2015 to December 3, 2018. This corresponds to University of Maine buoy deployments I0130, I0131, I0132, I0133 and I0134 (http://gyre.umeoce.maine.edu/data/gomoos/buoy/html/I01.html). The sensors were programmed to collect nitrate measurements three times per day (0045, 0845 and 1645 GMT) and more recently, eight times day (0045, 0345, 0645, 0945, 1245, 1545, 1845, and 2145 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 15uM. Whenever possible at the time of buoy deployment and recovery, 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 sensor. 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 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.