Fröhberg, Nico; Schmidt, Katja; Bardenhagen, Mirja; Poehle, Sandra; Anagnostou, Eirini; Pedre, Ignacio; Koschinsky, Andrea: Major, minor and trace element composition including REY of water column samples from the plume of the Kairei hydrothermal vent field acquired during cruise SO301 (KABA) [dataset]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.989559 (dataset in review)

This dataset presents major, minor, and trace element including rare earth element and yttrium (REY) concentrations from the Kairei Hydrothermal Field (KHF) plume in the Central Indian Ridge (Indian Ocean), collected during RV Sonne expedition SO301 from November 2023 to January 2024. The purpose of the study was to map the hydrothermal plume distribution and characterize trace metal behavior in the water column to understand geochemical cycling as well as microbial trace metal interactions at this active vent site. Hydrographic measurements were obtained using a SBE11Plus Conductivity-Temperature-Depth (CTD) system equipped with sensors for conductivity, temperature, pressure, and oxygen concentration. Hydrothermal plume detection was accomplished using miniature autonomous plume recorders (MAPR) measuring turbidity via boosted-gain backscatter sensors and oxidation reduction potential (ORP) using platinum electrodes against silver/silver chloride reference potentials. A total of 13 CTD tow-yo stations and two 12.5-hour yo-yo time series stations were conducted at the vent site. Water samples were acquired using both the vessel's CTD-rosette system (modified with latex springs to minimize contamination) and an autonomous trace metal rosette (TMR) constructed with a titanium frame and equipped with contamination-free O.T.E. Model 114 and Model 110 samplers. The TMR was deployed at 10 hydrocast stations to obtain contamination-free samples from the non-buoyant plume and background waters. Samples were processed onboard under filtered air using a class 1000 laminar-flow bench and acidified with ultrapure hydrochloric acid for storage. Dissolved trace metal concentrations (including cadmium, cobalt, copper, iron, manganese, nickel, lead, vanadium, zinc, and rare earth elements and yttrium) were determined using tandem inductively coupled plasma mass spectrometry (ICP-MS/MS; Thermo Fisher iCAP-TQ) with automated online pre-concentration via SeaFAST SP2. Additionally, direct ICP-MS (Perkin Elmer NEXion 350x) analysis was performed for cesium, molybdenum, and uranium after sample dilution. Major element compositions (including boron, calcium, potassium, magnesium, sodium, sulphur, silicon, and strontium) were measured by ICP OES (Spectro Ciros Vision). Sequential filtration through 0.8, 0.2, and 0.015 µm pore sizes was applied at selected depths to investigate particle size fractionation effects.