Water samples for total mercury (Hg) and methylmercury (MeHg) were collected in the Southern Ocean between 22 October and 9 November 2022 during the PS133/1 expedition, covering depths from 20 to 7000 m. Sampling was conducted using an ultraclean Titan rosette system (SBE-911Plus, Seabird) equipped with 24 × 12 L Ocean Test Equipment (OTE) bottles and a metal-free winch with a synthetic reinforced Vectran cable. After recovery, the clean CTD rosette was covered with clean plastic caps and transferred by trolley to an ISO Class 5 clean laboratory container. Each bottle was introduced through a clean airlock, rinsed externally with Milli-Q water from the container's integrated water treatment system, and subsampled following GEOTRACES ultraclean protocols. Samples for total Hg were collected unfiltered into pre-cleaned 60 mL glass vials to minimize contamination. Samples for MeHg were collected unfiltered into 250 mL HDPE Nalgene bottles and acidified to 0.4 % v/v with ultrapure trace-metal-grade HCl. Total Hg concentrations were determined using a custom single gold-trap purge and trap system following US EPA Method 1631. Dissolved MeHg concentrations were quantified by gas chromatography coupled to sector field inductively coupled plasma mass spectrometry (GC–SF–ICP–MS) with isotopic dilution calibration.