Oxygen (O2) is considered an effective indicator of ocean health and climate change. Its level, distribution and variability from sub-seasonal to multidecadal scales provides relevant information on the physical and biogeochemical functioning of the ocean, and often acts to constrain life in the ocean.

Current evidence indicates that the coastal (i.e., most directly influenced by land) and open ocean areas have been losing O2 since the middle of the last century, with consequences for living organisms and biogeochemical cycles that are not yet fully understood. In the open ocean the O2 inventory has decreased by a few percent (i.e., 0.5-3%) and Oxygen Minimum Zones (OMZs) are expanding, which is primarily attributed to global warming although a quantitative understanding is still lacking. The number of hypoxic coastal sites has increased, predominantly in response to worldwide eutrophication; yet trends in deoxygenation in the global coastal zone remain ill-defined.

The development and extension of low O2 concentration areas degrades the living conditions and contracts the metabolically viable habitat for a large number of pelagic, mesopelagic, and benthic organisms. The effects on individuals exposed to low O2 can result in altered foodweb structures.

Deoxygenation affects many aspects of the ecosystem services provided by the ocean and coastal waters. For example, deoxygenation effects on fisheries include low oxygen affecting populations through reduced recruitment and population abundance, and also through altered spatial distributions of the harvested species causing changes in fishing activity. This can lead to changes in the profitability of the fisheries and can affect the interpretation of the monitoring data leading to misinformed management advice.

Model simulations for this century project a decrease in oxygen under both high and low CO2 emission scenarios, while the projections of the coastal ocean at the land-ocean interface indicate that eutrophication will likely continue in many regions of the world. Warming is expected to further amplify deoxygenation in coastal areas influenced by eutrophication by strengthening and extending stratification.

The 53rd Liege colloquium will investigate new developments and insights related to deoxygenation in open and coastal waters.

The colloquium is  organized by the IOC-UNESCO Global Ocean Oxygen Network (GO2NE) and is a contribution to the Global Ocean Oxygen Decade (GOOD) program of the UN Ocean Decade. 

More specifically, the following topics will be considered:

• Deoxygenation: understanding causes and attributing changes.
  Conveners: Ivonne Montes, Andreas Oschlies
• Assessing open ocean and coastal deoxygenation variability and trends.
  Conveners: Hernan Garcia, Francisco Chavez
• Deoxygenation: observing and modelling
  Conveners: Véronique Garçon, Marilaure Grégoire
• Deoxygenation and ocean life
  Conveners: Mike Roman, Denise Breitburg
• Deoxygenation and co-stressors: understanding, monitoring and mitigating deoxygenation in the context of multiple stressors
  Conveners: Grant Pitcher, Minhan Dai
• Ocean Deoxygenation - how the past can inform the future?
  Conveners: Moriaki Yasuhara, Dimitri Guiterez
• Microbial Communities and their controls on biogeochemical feedbacks and interactions
  Conveners: Sean Crowe, Fleur Roland
• Deoxygenation, water quality and the climate system: understanding processes and feedbacks and developing actionable indicators
  Conveners: Caroline Slomp, Nancy Rabalais
• Deoxygenation: ecosystem services, economic and societal consequences.
  Conveners: Karin Limburg, Rashid Sumaila
• Confronting deoxygenation and its impacts: translating science to management and policy
  Conveners: Lisa Levin, Kirsten Isensee, Dorina Seitaj