Photo: S-E. Arntdt/Azote
Understanding of regime shifts is important, because along with their potential impacts on economies, societies and human well-being, they are often difficult to anticipate and costly or impossible to reverse. The detailed regime shift descriptions upon which this analysis was based were collected and compared using a standardized template that is available on the website regimeshifts.org.
Arctic sea ice loss
A regime shift from ice-covered oceans to summer ice-free oceans is occurring as the Arctic warms.
Greenland ice sheet collapse
The great ice sheet of Greenland is melting, however the shift to an ice free Greenland is expected to take centuries
Thermohaline circulation is the global movement of ocean water from the surface to the deep ocean, which has a major role in regulating global climate. This movement has been halted in the past due to large inflows of freshwater.
Marine food webs: Community change and trophic level decline
A shift from a marine ecosystem with high numbers of larger predatory fish to one dominated by smaller fish, which often leads to trophic webs more vulnerable to climate change, disease, or fishing.
A shift from oxygen rich water which supports a diverse marine ecosystem, to nutrient rich water which supports a limited population of low oxygen tolerant species - which are also known as 'dead zones.'
The crash of high value commercial fish species to persistent low population levels. These crashes can reshape marine food webs when species with similar functional responses have already been diminished (e.g. top predators or herbivores).
Primary production in the Arctic Ocean
An ongoing shift of polar marine ecosystems from low to higher primary productivity due to warmer temperatures and nutrient enrichment. It is uncertain whether energy and nutrients will cascade up to higher trophic levels (e.g. fish) or trapped in lower trophic levels such as plankton and jellyfish.
A special case of fisheries collapse, because salmon migrate from inland waters to marine ecosystem and back. Salmon response to climate variability can be affected by fishing and erosion of genetic diversity due to hatcheries. The potential collapse of salmon populations greatly weakens the flow of energy and nutrients from marine to terrestrial ecosystems near rivers.
Shift of flora and fauna on and in marine sediments from algae and filter feeders to seaweed (macroalgae).
Shift from highly structured kelp forests to urchin barrens, which are dominated by high populations of sea urchins.
Coastal marine eutrophication
Shift from clear, low-nutrient water to turbid, nutrient-rich water in coastal areas.
Peatland systems can shift from bogs, sphagnum-dominated peatlands with long-term carbon storage in peat and fens, to peatlands that include shrubs and trees. Peatlands can be more biologically productive, but store less carbon in the permafrost.
Thermokarst lake to terrestrial ecosystem
Thermokast lakes form atop melting permafrost, such lakes can quickly drain and become terrestial ecosystems, often tundra.
River channel position
In freshwater lake and river systems, a river channel position regime shift occurs when the main channel of a river abruptly changes its course to a new river channel.
Salt marshes to tidal flats
Coastal ecosystems of the intertidal zone, can shift between vegetated salt marshes and vegetation free tidal flats.
The ability of Arctic people move across the landscape to trade, hunt and gather is being restricted by changing arctic landscapes. This restrict may result in a loss of the social capacity to move leading to a social-ecological regime shift.
Tundra to boreal forest
Shrubs from boreal forest can spread into tundra, which promotes the spread of further vegetation, converting tundra to forest. This change is slow.
Steppe to tundra
The transition from steppe (a grassland) to tundra (mosses and shrubs growing in waterlogged soils), or vice versa, is a regime shift that can occur in cold terrestrial ecosystems.
Coniferous to deciduous boreal forests
Coniferous trees thrive and create cold, moist soil conditions, while deciduous forests thrive in and help create nutrient-rich, dry and warm soils. The balance between these alternative regime can be shifted by changes in precipitation, temperature and fire.
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