Oxygen deficit rose more than a fixed 138:16 nitrate ratio predicted at 200 m in matched CalCOFI samples from 1984-2020

We tested whether nitrate change accounts for oxygen-deficit change at a fixed oxygen-to-nitrogen ratio. We used observed CalCOFI bottles at 200 m and matched 224 station-quarter groups in 1984-2002 and 2003-2020. Oxygen deficit rose by 15.86 micromol/L. Nitrate rose by 1.09 micromol/L. At a ratio of 138:16, the residual deficit increase was 6.47 micromol/L, with a conditional 95% three-year block interval of 4.84 to 8.14. This result does not fit a fixed-ratio-only accounting model with unchanged initial properties. It does not identify a physical cause. The residual stayed positive with a 170:16 ratio and in a shorter 1994-2020 check. The 100 m interval included zero; the 300 m residual was positive. Fixed-depth water movement, source-water change, variable biological ratios, sampling changes and measurement error limit the test. Code, selected source data, hashes, joint block draws and an independent arithmetic audit are included.

CalCOFI · oxygen deficit · nitrate · stoichiometry · matched sampling · ocean deoxygenation · block bootstrap