BGC-Argo floats reveal nitrite and thiosulfate dynamics in the oceans with high spatiotemporal resolution - Matlab software

This is Matlab software used to calculate nitrite and thiosulfate concentrations from the UV spectra returned by ISUS and SUNA nitrate sensors on Biogeochemical-Argo floats operated by the Monterey Bay Aquarium Research Institute.  There are more than 600 profiling floats distributed around the global ocean with such data available in the MBARI data set. While nitrate sensors are available on floats operated by other programs, the code only works on the intermediate .isus file used at MBARI. If a .isus file is not available, the user would have to adjust the code.

The main loop is the PROCESSNO3NO2S2O3_WEB_2.m Matlab script. The user inputs the WMO (World Meteorological Organization) number of a float with ISUS and SUNA nitrate sensors and it retrieve the .isus files and a .cal  calibration file that enable computation of nitrite and thiosulfate  concentrations. This is primarily useful in oxygen deficient zones, where nitrate is being reduced and nitrite accumulates.

An overview of the code and output is in the PPT file. The algorithm used in the code is described in the manuscript, "BGC-Argo floats reveal nitrite and thiosulfate dynamics in the oceans with high spatiotemporal resolution" by Mariana Bif and Kenneth Johnson. The manuscript has been submitted to Global Biogeochemical Cycles (preprint at DOI: 10.22541/essoar.173532400.05903973/v1). There are some adjustable parameters in the code, as explained in the Bif and Johnson manuscript and code comments. In roughly 80 to 90 per cent of the cases, no adjustment to the default parameters is necessary and the code returns valid data. The remainder of the cases require some adjustment of parameters as outlined in the comments in the code. These cases are apparent if the returned nitrite concentrations are negative.

Note that the nitrite concentrations returned by the script have been validated with shipboard measurements, but there is no direct validation available for thiosulfate. It's presence is consistent with laboratory measurements of UV spectra and the in situ spectra. Those concentrations should be considered provisional.