General Description and Scientific Significance

The R/V SONNE SO296/2 – MAPUCHE expedition was conducted between January 21 and February 21, 2023, aboard the German research vessel R/V SONNE, departing from and returning to Talcahuano, Chile. The expedition was led by the Leibniz Institute for Baltic Sea Research Warnemünde (IOW) in collaboration with the University of Concepción, the Millennium Institute of Oceanography (IMO), and other national and international institutions.

The primary objective was to investigate the effects of extreme oxygen depletion and anoxic conditions within the water column on biogeochemical processes, marine ecosystems, and food webs in the coastal upwelling system off Concepción, a highly productive region associated with the Southeastern Pacific Oxygen Minimum Zone (OMZ).

The expedition focused on two contrasting environments:

1. The coastal upwelling system off Concepción, characterized by low-oxygen waters and high biological productivity. 
2. Patagonian fjord systems with naturally anoxic and permanently stratified waters, used as comparative environments for studying extreme carbon and nutrient cycling processes. 

During the expedition, high-resolution measurements of dissolved oxygen, hydrogen sulfide, nutrients, pH, temperature, and salinity were carried out, together with biological and geochemical sampling aimed at evaluating organic matter transformation and degradation, microbial community responses, and the structure of ecosystems exposed to oxygen-deficient conditions.

The expedition also marked a milestone for deep-ocean research in Chile through the deployment of the first FETCH AZA bottom pressure sensors in the Atacama Trench, initiating the Integrated Deep-Ocean Observing System (IDOOS). These instruments were installed to continuously record pressure variations associated with oceanographic and geodynamic processes, establishing the first permanent deep-ocean monitoring infrastructure promoted by IMO in the trench.

The campaign also included oceanographic stations off the coast of Concepción, as well as fieldwork in the Almirante Montt Gulf and Patagonian fjord systems, enabling comparisons between oceanic oxygen minimum zones and naturally anoxic fjord environments.

For IMO, this expedition represented a strategic opportunity to investigate the processes regulating productivity, biodiversity, and carbon transfer in one of the most important oceanographic systems of the Southeastern Pacific. It also marked the beginning of the IDOOS observational program.

 

Scientific Objectives

• Characterize the biogeochemical processes associated with oxygen-deficient waters off Concepción.
• Evaluate the transformation, degradation, and export of organic matter under low-oxygen conditions.
• Analyze the effects of anoxia on microbial communities, benthic fauna, and marine food webs.
• Determine the vertical distribution of dissolved oxygen, hydrogen sulfide, nutrients, and other chemical variables throughout the water column.
• Investigate the relationship between surface productivity, organic matter transport, and deep-water oxygen consumption.
• Compare biogeochemical processes in the Southeastern Pacific Oxygen Minimum Zone with those occurring in naturally anoxic Patagonian fjords.
• Generate high-resolution oceanographic observations to better understand ecosystem dynamics under extreme oxygen-deficient conditions.
• Deploy the first FETCH AZA bottom pressure sensors to initiate a continuous deep-ocean observation system in the Atacama Trench as part of the IDOOS program.

Onboard Technology

• R/V SONNE research vessel.
• CTD-Rosette system with Niskin bottles for hydrographic profiling and water sampling.
• Pump-CTD for high-resolution measurements of dissolved oxygen, nutrients, hydrogen sulfide, and other chemical properties of the water column.
• High-sensitivity oxygen sensors for detecting extremely low oxygen concentrations.
• Nutrient and dissolved gas analysis systems.
• FETCH AZA bottom pressure sensors, deployed in the Atacama Trench for continuous monitoring of oceanographic and geodynamic processes.
• Plankton nets for characterizing pelagic communities.
• MOCNESS (Multiple Opening/Closing Net and Environmental Sensing System) for stratified sampling of zooplankton and vertically migrating organisms. During the expedition, MOCNESS deployments were conducted at deep stations, including one at approximately 1,600 m depth. 
• Multibeam acoustic systems for water-column and seafloor characterization.
• Benthic sampling equipment and instrumentation for analyses of seafloor communities.

Participating Institutions

• Millennium Institute of Oceanography (IMO)
• University of Concepción (UdeC).
• Leibniz Institute for Baltic Sea Research Warnemünde (IOW), Alemania. 
• Institute for Chemistry and Biology of the Marine Environment (ICBM), University of Oldenburg, Germany.
• University of Colorado Boulder, United States.