Seawater samples were retrieved from depth using standard oceanographic sampling equipment and then collected by vacuum filtration onto 0.2 µm pore size Durapore membrane filters; these were frozen immediately at -80°C. Extraction was performed using a modified Bligh and Dyer (Bligh and Dyer, 1959; https://doi.org/10.1139/o59-099) method described in Popendorf et al. (2013; https://doi.org/10.1007/s11745-012-3748-0). Lipid extracts were analyzed by HPLC-ESI-MS with data dependent-MS2 acquisition on a high-resolution, accurate mass Thermo Q Exactive Hybrid Quadrupole-Orbitrap mass spectrometer (ThermoFisher Scientific, Waltham, MA, USA) coupled to an Agilent 1200 HPLC system (Agilent, Santa Clara, CA, USA). The HPLC-ESI-MS method is described in Collins et al., 2016 (https://doi.org/10.1021/acs.analchem.6b01260). The LOBSTAHS lipidomics discovery software (Collins et al., 2016; https://doi.org/10.1021/acs.analchem.6b01260) was used to putatively identify HPLC-MS features in the data. We confirmed each LOBSTAHS identification using two additional means: (1) via comparison of data-dependent MS2 spectra with those from authentic standards or published reference spectra and (2) by requiring the presence of the same compound identity in data acquired in the opposite HPLC-ESI-MS ionization mode. We confirmed all LOBSTAHS identities at the lipid class level (e.g., PC versus PE, or MGDG versus TAG) using a new, experimental LOBSTAHS feature which automatically detects diagnostic product ion fragments and constant neutral losses (as given in Popendorf et al., 2013; https://doi.org/10.1007/s11745-012-3748-0) in the available data-dependent MS2 spectra for each sample. After identification, quantification of analytes was performed using a series of standard curves, followed by normalization to concentration of an internal standard.Lipid identities are resolved only to the level of bulk fatty acid composition (i.e., the sum of the properties of the substituents at both the sn-1 and sn-2 positions). As a result, in some cases (e.g., DGTS_DGTA 32:1), several different molecules having the same bulk fatty acid composition have been identified. These can be distinguished by retention time, which is given in the "Comment" field for each entry.