Oceanographic processes driving low-oxygen conditions inside Patagonian fjords

• Published in: Biogeosciences Vol. 21; no. 6; pp. 1433 - 1459
• Main Authors: Linford, Pamela, Pérez-Santos, Iván, Montero, Paulina, Díaz, Patricio A., Aracena, Claudia, Pinilla, Elías, Barrera, Facundo, Castillo, Manuel, Alvera-Azcárate, Aida, Alvarado, Mónica, Soto, Gabriel, Pujol, Cécile, Schwerter, Camila, Arenas-Uribe, Sara, Navarro, Pilar, Mancilla-Gutiérrez, Guido, Altamirano, Robinson, San Martín, Javiera, Soto-Riquelme, Camila
• Format: Journal Article Web Resource
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 20.03.2024; Copernicus Publications
• Subjects: Aquaculture; Biogeochemistry; Biological activity; Climate change; Climatic changes; Coastal waters; Coastal zone; Coastal zones; Cruises; Dissolved oxygen; Earth sciences & physical geography; Earth-Surface Processes; Ecology, Evolution, Behavior and Systematics; Environmental sciences & ecology; Estuaries; Eutrophication; Fjords; Hypoxia; Life sciences; Modelling; Multidisciplinary research; Nutrients; Oceanographic processes; Oceans; Oxygen; Oxygen content; Oxygen saturation; Physical, chemical, mathematical & earth Sciences; Physique, chimie, mathématiques & sciences de la terre; Primary production; Reduction; Respiration; Rivers; Salinity; Salmon; Saturation; Sciences de la terre & géographie physique; Sciences de l’environnement & écologie; Sciences du vivant; Sediments; Stratification; Subsurface water; Ventilation; Water masses; Water quality; Water temperature; Water, Underground; Winter; South Pacific; Chile
• ISSN: 1726-4189; 1726-4170; 1726-4189
• DOI: 10.5194/bg-21-1433-2024

The dissolved oxygen (DO) levels of coastal ocean waters have decreased over the last few decades in part because of the increase in surface and subsurface water temperature caused by climate change, the reduction in ocean ventilation, and the increase in stratification and eutrophication. In addition, biological and human activity in coastal zones, bays, and estuaries has contributed to the acceleration of current oxygen loss. The Patagonian fjord and channel system is one world region where low-DO water (LDOW, 30 %–60 % oxygen saturation) and hypoxia conditions (<30 % oxygen saturation, 2 mL L−1 or 89.2 µmol L−1) are observed. An in situ dataset of hydrographic and biogeochemical variables (1507 stations), collected from sporadic oceanographic cruises between 1970 and 2021, was used to evaluate the mechanisms involved in the presence of LDOW and hypoxic conditions in northern Patagonian fjords. Results denoted areas with LDOW and hypoxia coinciding with the accumulation of inorganic nutrients and the presence of salty and oxygen-poor Equatorial Subsurface Water mass. The role of biological activity in oxygen reduction was evident in the dominance of community respiration over gross primary production. This study elucidates the physical and biogeochemical processes contributing to hypoxia and LDOW in the northern Patagonian fjords, highlighting the significance of performing multidisciplinary research and combining observational and modeling work. This approach underscores the importance of a holistic understanding of the subject, encompassing both real-world observations and insights provided by modeling techniques.