In the North Atlantic, there is a “circulation pump” for the major ocean currents. Warm surface water from the south plunges into the depth in the north and flows back towards the equator as cold water deep down. This so-called Atlantic Meridional Recirculation Flow (AMOC), thus, serves as a motor of heat exchange and is responsible for the mild climate of Europe.
It is known that this circulation has weakened in recent decades . This is caused by the increasing inflow of meltwater and the dwindling sea ice, both due to climate change. In addition, the location of the sinking areas in the North Atlantic could change.
Camille Lique, University of Brest, France, and Matthew Thomas, Yale University, New Haven, CT, USA, have used a high-resolution climate ocean model to pinpoint the source regions of the recirculation flow more precisely. They added “virtual particles” to the sea at different points and followed their movement along the currents in a simulation. This allowed them to identify the vertical mixing zones and, thus, AMOC’s circulation pumps. The researchers ran these simulations under both preindustrial conditions and at greatly elevated greenhouse gas levels.
They found that the sinking of warm surface water (marine subduction) is currently taking place almost exclusively in the marine regions around Greenland. In a scenario of severe climate change, this contribution of subpolar areas to marine subduction collapses almost completely. Instead, new sea areas at higher and lower latitudes increasingly contribute to the circulation flow: the sinking of warm water is partly shifted to the Arctic Ocean, but partly also to the temperate and even subtropical latitudes. According to the researchers, these changes need to be considered in order to accurately predict the future climate state.
- Latitudinal shift of the Atlantic Meridional Overturning Circulation source regions under a warming climate,
Camille Lique, Matthew D. Thomas,
Nat. Clim. Change 2018.
-  Anomalously weak Labrador Sea convection and Atlantic overturning during the past 150 years,
David J. R. Thornalley, Delia W. Oppo, Pablo Ortega, Jon I. Robson, Chris M. Brierley, Renee Davis, Ian R. Hall, Paola Moffa-Sanchez, Neil L. Rose, Peter T. Spooner, Igor Yashayaev, Lloyd D. Keigwin,
Nature 2018, 556, 227–230.