FT-ICR MS peak lists of dissolved organic matter along a seasonal oxygen-recovery gradient in a coastal bay of the North Yellow Sea

Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) peak lists for solid-phase-extracted dissolved organic matter (SPE-DOM) from bottom waters of a seasonally low-oxygen, mariculture-influenced bay around Yangma Island, North Yellow Sea, China. Water was sampled at four stations (S1-S4) on four cruises between August and October 2019 (10 August, 18 August, 29 September and 20 October), spanning a bottom-water dissolved oxygen recovery gradient of 2.5-7.2 mg/L generated by the breakdown of summer thermal stratification. All samples are bottom water collected about 1 m above the seafloor, so the layer is not coded in the sample names. Spectra meeting the quality criteria were obtained for 14 of the 16 station-cruise combinations: S3 on 18 August and S1 on 20 October are absent. The dataset comprises one CSV file with 6,588 assigned molecular formulae, one per row. For each formula it reports elemental composition (C, H, O, N, S), heteroatom class (CHO, CHON, CHOS, CHONS), theoretical neutral monoisotopic mass, H/C and O/C ratios, double bond equivalent (DBE), modified aromaticity index (AImod) and nominal oxidation state of carbon (NOSC), followed by the relative peak intensity in each of the 14 samples, normalized to the total assigned signal intensity of that sample so that each sample column sums to 1. A value of 0 means the formula was not detected in that sample. Sample columns are named MP<yymmdd>_<station>, for example MP190810_S1. An accompanying README file documents every column, the sample naming scheme and the acquisition parameters. These data support the research article "Selective reorganization of DOM and lifestyle-dependent microbe-DOM coupling along a coastal seasonal oxygen gradient" (Marine Pollution Bulletin, Manuscript No. MPB-D-26-02329), in which the station positions are shown in Figure 1a.