Hawaii Ocean Time-series (HOT)
in the School of Ocean and Earth Science and Technology at the University of Hawai'i
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Real-time nitrate concentrations were measured with a Satlantic ISUS V3 (#097). The ISUS is a chemical-free, solid-state sensor that uses ultraviolet absorption spectroscopy to measure continuous nitrate concentrations. Data was collected from as many 1000m casts as possible. Instrument drift was corrected via calibration with bottle inorganic [nitrate+nitrite] analyzed using a six-channel Bran Luebbe Autoanalyzer III. Only samples below 200m were used in the calibration where nitrite values at Station ALOHA are considered negligable. A linear relationship of the form, Vnitrate = b*VISUS + a, was used.
Data was logged internally and also collected using the Sea-Bird CTD system. Internally recorded profiles were latter downloaded after the cruise. CTD values were preferencially reported unless the data was considered bad. A common reason for bad data was a poor seal when connecting the Analog output cable to the CTD. Internally recorded data was then substituted.
Stack plots of CTD nitrate and bottle inorganic [nitrate+nitrite] for 2015
are shown in the figures below. The offset is 5 µmol/kg.