FULL REVIEW PAPER
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What is already happening?
- The aragonitic calcium carbonate saturation horizon has become shallower by 10–15m per year in the subpolar North-east Atlantic.
- Laboratory experiments have shown that cold-water corals exposed to undersaturated aragonite conditions are unable to maintain the calcification of their skeletons. Lowered pH has been found to depress feeding activity in deep-sea demosponges and increase foraging times of deep-sea echinoids.
- Changes in the mean state of the North Atlantic Oscillation (NAO) has led to changes in water current strength and circulation in the North Atlantic, which has a negative impact on dispersal and settlement of the larvae of the cold-water coral Desmophyllum pertusum.
CONFIDENCE LEVEL
LOW
Low evidence, medium agreement
There is a medium level of agreement and low amount of evidence concerning how deep-sea habitats are currently being affected by climate change. A general lack of long-term continuous sampling limits understanding. There is good agreement (but with low evidence) for decreasing pH in UK deep-sea waters.
What could happen in the future?
- Under a high-emissions scenario, models predict that the amount of Particulate Organic Carbon (POC) reaching the Atlantic seafloor will decrease by ≤15%, resulting in a ≤7% reduction in benthic biomass.
- Under a high-emissions scenario, models predict a substantial decrease in seafloor habitat suitability for cold-water corals in the North Atlantic (~30° to 60° N), with ~85% of existing features predicted to be exposed to increasingly acidic waters by 2060.
CONFIDENCE LEVEL
LOW
Low evidence, medium agreement
There is good consensus on the direction of change, but not on the magnitude of climate change effects on deep-sea habitats. Amount of evidence is low because few studies provide regional or local predictions, and models incorporating deep-sea habitats are relatively recent.
Key Challenges and Emerging Issues
- Building knowledge of the physical environment influencing UK deep-sea communities, including hydrography and POC flux, as well as collecting time-series data on community change.
- Building knowledge of deep-sea biological communities and ecosystem functioning, as this is still lacking for large areas of the UK deep-sea, including pelagic habitats.
- Developing more regional, rather than ocean-scale predictions to understand how UK deep-sea habitats will respond to future climate change. Models must consider impacts of multiple stressors on both benthic and pelagic habitats.