Fabian, Jenny; Schulz-Vogt, Heide N: Water column profile data of oxygen, hydrogen sulfide, and nutrients from pump-CTD casts during RV SONNE cruise SO296/2 [dataset]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.983892 (dataset in review)

The water column was profiled for nutrients (nitrate, nitrite, phosphate, ammonium, silicate), gases (hydrogen sulfide, dihydrogen, oxygen), and pH during pump-CTD casts aboard the RV SONNE during cruise SO296/2. The expedition took place from January 21 to February 21, 2023, in the eastern Pacific Ocean, following a route from Talcahuano to San Vicente, Chile. Its primary aim was to investigate the transformation and degradation of organic matter, as well as the effects of water column anoxia on ecosystems, including habitat structure, food webs, and biodiversity. A key focus was also placed on the oceanographic context, particularly microturbulence. Additionally, the expedition examined how postglacial changes in atmospheric and oceanic circulation in the southeastern Pacific have influenced two contrasting fjord systems. The study further assessed the roles of eustatic sea-level rise, regional isostatic uplift, and glacier dynamics in shaping the development of these fjord environments. A pump-CTD (Strady et al., 2008) was deployed at four stations on the Chilean shelf off Concepción and at three stations in the Golfo Almirante Montt (Patagonia). Vertical profiles of temperature, salinity, turbidity, fluorescence, and conductivity were measured in situ using a Sea-Bird Electronics SBE 911plus (SN-0603) conductivity-temperature-depth (CTD) probe, a D&A OBS-3 turbidity sensor, and a WETStar fluorometer, all mounted on a Sea-Bird Electronics SBE 32 rosette. For gas, nutrient, and pH measurements, water was pumped from the CTD to the onboard laboratory via PTFE tubing. In the laboratory, the water flow was split into two continuous lines. One line was connected to an autoanalyzer for automated nutrient analysis (QuAAtro, SEAL Analytics). Prior to autoanalyzer measurements, the water passed through a syringe filter (Whatman GF-075, 0.3 μm pore size) integrated into the tubing. It was then analyzed following the protocols of Hansen & Koroleff (1999) . Measurement precision was 0.3 µM for silicate, 0.01 µM for phosphate, 0.02 µM for nitrate, 0.006 µM for nitrite, and 0.02 µM for ammonium. The other line was directed to a series of sensors integrated into flow-through cells: an optical pH and temperature sensor (PyroScience), several Unisense microelectrodes with different sensitivities for hydrogen sulfide (overall detection limit: 10 nM), a low-range Unisense dihydrogen microelectrode (detection limit: 0.3 µM), and two Unisense oxygen microelectrodes—one standard-range and one STOX (Switchable Trace OXygen) microelectrode for high-sensitivity oxygen detection (detection limit: 13 nM). Due to minimal oxygen contamination through the CTD tubing system, an overall detection limit of 79 nM for oxygen was achieved. All sensors were regularly recalibrated according to the manufacturers' instructions to ensure optimal measurement accuracy. Total sulfide concentrations were calculated from the measured pH, temperature, salinity, and hydrogen sulfide values.