Thermohaline circulation
[3] The water in these circuits transport both energy (in the form of heat) and mass (dissolved solids and gases) around the globe.
Both of them also appear to be slowing down due to climate change, as the melting of the ice sheets dilutes salty flows such as the Antarctic bottom water.
In the Northern Hemisphere, AMOC's collapse would also substantially lower the temperatures in many European countries, while the east coast of North America would experience accelerated sea level rise.
The collapse of either circulation is generally believed to be more than a century away and may only occur under high warming, but there is a lot of uncertainty about these projections.
In 1908, Johan Sandström performed a series of experiments at a Bornö Marine Research Station which proved that the currents driven by thermal energy transfer can exist, but require that "heating occurs at a greater depth than cooling".
Thus, this water sinks downward in the Norwegian Sea, fills the Arctic Ocean Basin and spills southwards through the Greenland-Scotland-Ridge – crevasses in the submarine sills that connect Greenland, Iceland and Great Britain.
[18] In the Southern Ocean, strong katabatic winds blowing from the Antarctic continent onto the ice shelves will blow the newly formed sea ice away, opening polynyas in locations such as Weddell and Ross Seas, off the Adélie Coast and by Cape Darnley.
Increasing salinity lowers the freezing point of seawater, so cold liquid brine is formed in inclusions within a honeycomb of ice.
In the Pacific Ocean, the rest of the cold and salty water from the Atlantic undergoes haline forcing, and becomes warmer and fresher more quickly.
Deep waters have their own chemical signature, formed from the breakdown of particulate matter falling into them over the course of their long journey at depth.
Wallace Broecker, using box models, has asserted that the bulk of deep upwelling occurs in the North Pacific, using as evidence the high values of silicon found in these waters.
[28] Direct estimates of the strength of the thermohaline circulation have also been made at 26.5°N in the North Atlantic, by the UK-US RAPID programme.
Large influxes of low-density meltwater from Lake Agassiz and deglaciation in North America are thought to have led to a shifting of deep water formation and subsidence in the extreme North Atlantic and caused the climate period in Europe known as the Younger Dryas.
This reduction in confidence was likely influenced by several review studies that draw attention to the circulation stability bias within general circulation models,[33][34] and simplified ocean-modelling studies suggesting the AMOC may be more vulnerable to abrupt change than larger-scale models suggest.
[38] and result in atmospheric trends similar to those that likely occurred during the Younger Dryas,[39] such as a southward displacement of Intertropical Convergence Zone.
[44][45]: 1240 Climate models currently disagree on whether the Southern Ocean circulation would continue to respond to changes in SAM the way it does now, or if it will eventually adjust to them.
[45] A key reason for the uncertainty is the poor and inconsistent representation of ocean stratification in even the CMIP6 models – the most advanced generation available as of early 2020s.
