![]() For example, nutrients produced during the re-mineralization of organic matter at the deep seafloor are ultimately used by phytoplankton to produce organic matter that fuels secondary production. Deep-sea ecological processes and characteristics, such as nutrient cycling, carbon sequestration, productivity, habitat provision, and trophic support, underlie the healthy functioning of ocean ecosystems and provide valuable ecosystem services to mankind ( Thurber et al., 2014). Oceans thus help to buffer multiple aspects of global climate change and their effects on marine and terrestrial ecosystems ( Reid et al., 2009). The oceans are a major sink for CO 2 produced by the burning of fossil fuels ( Pauchauri et al., 2014) as well as for the heat produced by the greenhouse effect ( Glecker et al., 2016). ![]() We also consider how these changes may combine with other anthropogenic stressors (e.g., fishing, mineral mining, oil and gas extraction) to further impact deep-seafloor ecosystems and discuss the possible societal implications. In this paper, we provide a detailed overview of the impacts of these changing environmental parameters on deep-seafloor ecosystems that will most likely be seen by 2100 in continental margin, abyssal and polar settings. Unfortunately, how these major changes will affect deep-seafloor ecosystems is, in some cases, very poorly understood. Another important environmental parameter, the flux of particulate organic matter to the seafloor, is likely to decline significantly in most oceans, most notably in the abyssal and bathyal Indian Ocean where it is predicted to decrease by 40–55% by the end of the century. O 2 concentrations will also decline in the bathyal NE Pacific and Southern Oceans, with losses up to 3.7% or more, especially at intermediate depths. Bathyal depths (200–3000 m) worldwide will undergo the most significant reductions in pH in all oceans by the year 2100 (0.29 to 0.37 pH units). Projections suggest that abyssal (3000–6000 m) ocean temperatures could increase by 1☌ over the next 84 years, while abyssal seafloor habitats under areas of deep-water formation may experience reductions in water column oxygen concentrations by as much as 0.03 mL L –1 by 2100. Rising atmospheric greenhouse gases are bringing about significant changes in the environmental properties of the ocean realm in terms of water column oxygenation, temperature, pH and food supply, with concomitant impacts on deep-sea ecosystems. ![]() Although poorly known, deep seafloor ecosystems provide services that are vitally important to the entire ocean and biosphere. The deep sea encompasses the largest ecosystems on Earth. ![]()
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