Size-fractionated particulate total mercury and monomethylmercury concentrations in the Southern Ocean during the PS133/1 expedition (22 October – 9 November 2022)

Concentrations of particulate total mercury (Hg) and monomethylmercury (MMHg) were determined in size-fractionated suspended particles collected in the Southern Ocean between 22 October and 9 November 2022 during the PS133/1 expedition. Particles were collected using battery-powered in situ large-volume pumps (McLane Research Laboratories, Inc. and Challenger Oceanic's Stand-Alone Pumping System, SAPS) equipped with 142 mm diameter filter holders (MULVFS style; Bishop et al., 2012). Pumps were deployed at depths ranging from 25 to 350 m. Each filter holder contained two filters for size fractionation: a 51 μm Sefar Petex screen (SEFAR GmbH)—acid-leached prior to the cruise—mounted above a pre-combusted QMA filter (nominal pore size ~2.2 μm), separating particle size classes of 2.2–51 μm and >51 μm. Particulate total mercury was quantified by thermal decomposition, amalgamation, and atomic absorption spectrophotometry (TDA–AAS) using a DMA-EVO Direct Mercury Analyzer (Milestone). MMHg concentrations were determined by gas chromatography–cold vapor atomic fluorescence spectrometry (GC–CVAFS) using a Brooks Rand methylmercury analysis system following acid digestion. Data are reported both as mass-specific concentrations (ng g⁻¹ of suspended particulate matter) and as volume-normalized concentrations (pmol L⁻¹), corrected for the volume of water filtered.