This is version 3.0 of MARHYS (MARine HYdrothermal Solutions) database. The database is a global compilation of marine hydrothermal vent fluid compositions. The database includes data presented in journal publications, book chapters and monographs and includes compositions of hydrothermal fluids, end members and background seawater. Detailed sample information (metadata) is provided along with the chemical composition, which enables the unique identification of discrete vent fluid samples. The database contains concentrations of major-, minor- and trace elements, as well as, reduced carbon compounds and isotope compositions. All concentrations are converted into units per kg of vent fluid and chemical data of unique samples reported in different publications are merged into unique sample entries.In brief, the following changes have been applied in the compilation of MARHYS database version 3.0 compared to version 2.0: Data of 126 new references have been added to the database. A large number of new hydrothermal vent sites is now incorporated: Daxi Vent Field, Explorer Vent Site, Kasuga Vent Sites, Kemp Caldera, La Scala Vent Field, Maka Hydrothermal Field, Minami-Ensei, Sea Cliff Hydrothermal Field, Tarama Knoll Vent Sites (and some more). The size of the database has nearly doubled compared to Version 2.0 and now contains 6003 merged sample entries with 86738 single parameters determined (compared to 3394 merged entries in Version 2.0). The complete sample information section for a large number of entries was again overhauled and harmonized with the help of the new data. The sample information section for some vent sites has majorly improved (eg. EPR 9°N, Lucky Strike, Lost City). Some new parameters are now included in the database: ∑REE, DOC, δ41K, δ53Cr, δ56Fe, δ57Fe, δ88Sr, 222Rn, 226Ra (to mention some of them). A small number of faulty concentrations was detected and corrected. The reference list was updated.

The main file containing the final product is:MARHYS_DB_3_0.xlsxThe remaining files are provided to be able to track the processing of the data:MARHYS_DB_3_0_Rawdata.xlsx provides a one-by-one copy of the single datasets as provided in the original source.MARHYS_DB_3_0_RawdataConverted.xlsx provides a one-by-one copy of the single datasets with converted units.MARHYS_DB_3_0_Unmerged.xlsx provides the data in the format of MARHYS Database without sample entries being merged.MARHYS_DB_3_0_MergeHistory.xlsx provides a list of all sample entries that were merged.MARHYS_DB_3_0_ReferenceList.docx provides all references included.Please note: Please always cite the base publication (Diehl & Bach, 2020; doi:10.1029/2020GC009385) along with this dataset. We encourage users of the database to also cite the original literature whenever possible. If you want to address any inquiries about the database, do not hesitate to contact the support centre (marhys@uni-bremen.de). The MARHYS database is an ongoing project and will be updated once a year.