Observed trends in marine ecosystems (coral bleaching, disruptions of food web due to differential responses of species to warming) are expected to continue and accelerate during coming decades. A particular concern is the rapid loss of sea ice, affecting krill, fish, seals, and polar bears negatively to an extent that makes polar bears a species threatened with extinction. The melting of ice sheets and changes in ocean circulation both reduce salinity in high-latitude oceans, which affects plankton communities and threatens polar species such as the narwhal and migratory whales. Sea-level rise is expected to put a third of sea turtle nesting beaches at risk.
Increased atmospheric CO2 concentrations affect ocean pH negatively, a trend which is expected to continue by 0.3-0.4 units until 2100. This trend is expected to impact almost all life in the ocean, but particularly benthic calcifying organisms. Particularly, organisms using aragonite for their shells will be at risk of extinction (these are widespread and important for the food web in Arctic and Southern Oceans).
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