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.
more »
« less
High-resolution vertical nitrate profiles from the CTD rosette-mounted submersible ultraviolet nitrate analyzer over the Northeast U.S. Shelf since February 2019 (NCEI Accession 0297573)
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.
more »
« less
- PAR ID:
- 10592055
- Publisher / Repository:
- NOAA National Centers for Environmental Information
- Date Published:
- Format(s):
- Medium: X
- Location:
- (East Bound Longitude:-70.3366; North Bound Latitude:41.3239; South Bound Latitude:39.7646; West Bound Longitude:-71.3096)
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The Ocean Observatories Initiative (OOI) deployed both the In-Situ Ultraviolet Spectrophotometer (ISUS) and Submersible Underwater Nitrate Sensor (SUNA) for continuous, in-situ measurement of nitrate. At the Pioneer-New England Shelf Array (Pioneer-NES), ISUS/SUNA sensors were deployed at 7-meters depth at the Inshore (ISSM), Central (CNSM), and Offshore (OSSM) Surface Mooring locations. The SUNA sensor replaced the ISUS sensors spring 2018. The SUNA was a major improvement in technology, with significant improvements in accuracy and precision. However, it still suffers from calibration drift due to lamp fatigue and biofouling as well as spectral interference due to bromide and fluorometric CDOM. Drift is corrected by application of post-cruise calibrations to recalculate the temperature-and-salinity corrected nitrate concentration following Sakamoto (2009a) and estimating a linear drift between pre-and-post cruise deployments. Validation is performed by comparison with discrete water samples collected during deployment/recovery of the sensors. These datasets include the nitrate data from the Pioneer-NES ISSM (CP03ISSM-RID26-07-NUTNRB000.nc), CNSM (CP01CNSM-RID26-07-NUTNRB000.nc), and OSSM (CP04OSSM-RID26-07-NUTNRB000.nc) SUNA instruments spanning Spring 2018 through Fall 2022. Each dataset contains the measured nitrate, the temperature-salinity corrected nitrate, the drift-corrected nitrate, and the nitrate following validation with bottle samples.more » « less
-
Particulate organic carbon and nitrogen are measured from discrete bottle samples collected during CTD-rosette casts on Northeast U.S. Shelf Long-Term Ecological Research (NES-LTER) Transect cruises (ongoing since 2017). Sampling frequency is approximately seasonal. Samples were filtered and collected on combusted glass fiber filters, pelletized using ultra clean tin disks, and combusted using a Flash EA1112 CHN analyzer to calculate concentrations of particulate organic carbon and particulate organic nitrogen in micromoles per liter. Values are also reported as concentrations in micrograms per liter and carbon to nitrogen molar ratio.more » « less
-
Particulate organic carbon and nitrogen are measured from discrete bottle samples collected during CTD-rosette casts on Northeast U.S. Shelf Long-Term Ecological Research (NES-LTER) Transect cruises (ongoing since 2017). Sampling frequency is approximately seasonal. Samples were filtered and collected on combusted glass fiber filters, pelletized using ultra clean tin disks, and combusted using a Flash EA1112 CHN analyzer to calculate concentrations of particulate organic carbon and particulate organic nitrogen in micromoles per liter. Values are also reported as concentrations in micrograms per liter and carbon to nitrogen molar ratio.more » « less
-
Dissolved organic carbon and dissolved total nitrogen are measured from discrete bottle samples collected during CTD-rosette casts on Northeast U.S. Shelf Long-Term Ecological Research (NES-LTER) Transect cruises (ongoing since 2022). Sampling frequency is approximately seasonal. Sample collection is paired with particulate organic carbon at surface, subsurface chlorophyll max, and sometimes a third depth. Samples are filtered directly from the CTD rosette and acidified in the field, then analyzed using a Shimadzu TOC-LCPH total organic carbon analyzer coupled to a TNM-L analyzer for total nitrogen. Values are reported in micromoles per liter.more » « less
An official website of the United States government
