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This dataset contains high-quality high-resolution nitrate data collected from a submersible ultraviolet nitrate analyzer (SUNA) mounted on the CTD rosette. Both raw and bias-corrected, quality-controlled data are included. The raw data include the instrument's estimate of nitrate concentration with dark values and light intensity at 256 wavelengths. Our quality-controlled SUNA nitrate data have an accuracy of 0.34-0.78 micromoles per liter, with a precision of 0.08-0.21 micromoles per liter, at a vertical resolution of 1 m. These data are collected from about 21 routinely occupied stations along a cross-shelf transect spanning southward from Martha's Vineyard, MA to just beyond the shelf break onboard the seasonal Northeast U.S. Shelf Long-Term Ecological Research (NES-LTER) survey cruises since February 2019. Data in CSV format.
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Bias‐corrected high‐resolution vertical nitrate profiles from the CTD rosette‐mounted submersible ultraviolet nitrate analyzer
Abstract Measurements by the submersible ultraviolet nitrate analyzer (SUNA) can be used to derive high‐resolution in situ nitrate concentration with reliable accuracy and precision. Here we report our operational practices for SUNA deployment (including pre‐cruise instrument preparation and in‐cruise instrument maintenance) and detailed post‐cruise nitrate quality control procedures for SUNA integrated onto the CTD rosette. This work is based on experiences and findings from over 500 individual SUNA casts collected from 24 cruises (of which 14 cruises have been quality controlled so far) over the past 5 yr. After applying previously published spectral corrections for temperature, salinity, and pressure effects, we found residual biases in SUNA nitrate estimates compared to independently measured discrete samples. We further develop and assess a new two‐step procedure to remove remaining biases: (1) a general temperature‐dependent adjustment at low‐nitrate concentrations; and (2) a cruise‐specific full‐range bias correction. Our final quality‐controlled SUNA nitrate data achieve an accuracy of 0.34–0.78 μM, with a precision of 0.08–0.21 μM, at a vertical resolution of 1 m. Additional comparisons between the nitrate and density data confirm the high quality of the quality‐controlled SUNA data. Although applying spectral correction algorithms increases the accuracy and precision of the instrument‐output nitrate concentration, we emphasize that additional constraints of SUNA measurements against other independent sources (e.g., bottle data, temperature, and density) are irreplaceable to ensure the accuracy of final nitrate data.
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- PAR ID:
- 10559655
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography: Methods
- Volume:
- 22
- Issue:
- 12
- ISSN:
- 1541-5856
- Format(s):
- Medium: X Size: p. 889-902
- Size(s):
- p. 889-902
- Sponsoring Org:
- National Science Foundation
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