10.1594/PANGAEA.983110Utsumi, Giovanna S AGiovanna S AUtsumi0009-0002-4581-246XUniversity of GeorgiaMedeiros, Patricia MPatricia MMedeiros0000-0001-6818-2603University of GeorgiaPANGAEA2026CaliforniaDissolved Organic MatterEndorheic saline lakesFT-ICR MSMono LakeSample code/labelDATE/TIMELATITUDELONGITUDEDEPTH, waterMass-to-charge ratioPeak intensityCTD/RosetteFourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), Bruker; coupled with 21 Tesla (T) magnet2017-05-23T00:00:00/2018-10-09T00:00:00Dataset10.1007/s00027-026-01283-610.1111/gbi.124373206154 data pointstext/tab-separated-valuesCreative Commons Attribution 4.0 InternationalWe investigated the composition of dissolved organic matter (DOM) in the hypersaline Mono Lake in California (USA), providing a detailed molecular characterization of DOM in this extreme ecosystem during a shift in limnological conditions (2017–2018). This dataset contains DOM molecular data (mass-to-charge ratios and peak intensities) obtained using ultrahigh-resolution mass spectrometry (21T Fourier transform ion cyclotron resonance mass spectrometry, FT-ICR MS; Bruker). Water samples were collected seasonally at depths ranging from 0.5 m to 35 m, using a CTD rosette as described in Phillips et al. (2021). Additionally, the dataset includes DOM molecular data from two main creeks - Lee Vining Creek and Rush Creek - as well as from a dominant phytoplankton species, Picocystis sp.-119.0314999978115437.95729999989599Mono Lake, California, United States of AmericaNational Science Foundationhttps://doi.org/10.13039/100000001DMR-1644779National High Magnetic Field Laboratory Renewal 2018-2022University of Georgia Research Foundationhttps://doi.org/10.13039/10001248319250PM1UGARF IDC