Low oxygen conditions have already been reported for various aquatic systems, from lakes, estuaries and coastal areas to off-shore regions of the World Ocean, where water ventilation is not able to renew the oxygen consumed by degradation of organic matter.
In the coastal ocean, dead zones have spread exponentially since the 1960s and have been reported for more than 400 systems (e.g. Baltic, Black, Kattegat Sea, Gulf of Mexico, East China Sea) with 39 % of them along the coast of Europe. In shallow areas, where the bottom is occupied by ecologically and economically valuable benthic communities, hypoxic/anoxic conditions may lead to and have already resulted in catastrophic losses.
Eastern boundary upwelling systems (EBUSs) are characterized by high biological activity and heterotrophy that, in combination with weak ventilation, results in oxygen minimum zones (OMZs) in sub-surface waters. Suboxic waters extend from shallow depths over several hundred meters of the water column and support major perturbation of marine biogeochemical cycles. Furthermore the OMZs play a critical role on atmospheric chemistry through emission of climate reactive trace gases. These regions are also the siege of complex air-sea-land interactions that the current generation global models cannot properly resolve, which has put a stringent limitation on our predictive capabilities at a wide range of timescales.
Inland waters are hotspots of biogeochemical cycling in the terrestrial biosphere. Holomictic lakes usually present seasonally bottom anoxic waters while meromictic lakes are among the systems having a permanently anoxic deep waters, in which anaerobic processes generate reduced compounds (CH4, H2S, NH4+...). The seasonal or permanent oxic-anoxic interface presents a redox gradient, in which various biogeochemical processes take place (some unique), mediated by a diverse community of microorganisms.
In the coming decades and centuries, it is foreseen that deoxygenation will increasingly stress aquatic ecosystems in a way that is currently ignored on the global scale, but admitted as only local problems. The expansion of O2 minimum zones and resulting biogeochemical and ecological changes will make impossible the Good Environmental Status of marine and freshwater ecosystems, as well as their functioning and ability to underpin the delivery of services. These themes are in the focus of several international initiatives (SOLAS, IMBER, GEOTRACES, CLIVAR, etc.) and projects (PERSEUS, HYPOX, EMODNET, etc.).
The 46th Liege colloquium will investigate new developments and insights related to the critical problem of ocean deoxygenation, low oxygen zones in marine and freshwater systems.
For additional information please visit the conference webpage...