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Published today in听Nature Geoscience,听the team found that the Gulf Stream鈥檚 slowdown in the 20th century is unprecedented听and is likely linked to human-induced climate change.听听

A major mechanism for heat redistribution听and crucial to the world鈥檚 climate, an abrupt slowdown of the AMOC could trigger disruptions around the听globe听- including a sudden rise in regional sea levels, changes in the position of major rainfall and arid climate zones.听听

The听international听research听team听made up of scientists from Ireland, Britain and Germany听were able to reconstruct the flow history of the AMOC听over the last 1600 years听by听using听a听range听of听several different and largely independent proxy indicators听including听data from听tree rings, ice cores, ocean sediments, and corals, as well as from historical data,听such as ship logs.听

Analysis of the collated听data indicates听that whilst AMOC has been relatively stable until the 19th century, the system of ocean currents began to decline by the end of the Little Ice Age听after听around 1850, with a second, more drastic decline following since the mid-20th century.听

The study findings build upon,听and are consistent with,听previous research led by study co-author Dr David Thornalley (乱伦秀 Geography). A听2018听Nature听study by Dr Thornalley听used the size of sediment grains in marine听cores听to reconstruct the strength of important听deep sea听currents, and alongside data听used to听reconstruct听past听surface ocean temperatures,听it听provided the first ocean evidence听for听the unprecedented nature of recent changes in the AMOC. Further work听by Dr听Thornalley鈥檚听team,听in听a听2020听Geophysical Research Letters听study, went further and revealed how the extreme state of Atlantic circulation caused听20th听century听warming of听the surface ocean in the Northeast Atlantic听that was unprecedented听in the last 10,000 years.听听

Dr听Thornalley听said: 鈥淲hilst climate modelling has long predicted a slowdown of the AMOC as a result of human-induced warming, this study听shows听the听increasing evidence听in support of the听modern听Atlantic Ocean听undergoing unprecedented changes听in comparison听to the last millennium, and in some cases longer.听Alongside other human pressures on the marine environment, the changes we are observing in ocean circulation听are听impacting听marine ecosystems in both the surface and deep ocean. We听will听need to take account of these ongoing changes in our efforts to conserve and manage marine resources.听听

鈥淥verall,听this new study听highlights听that major changes are听occurring, but听it also draws attention to how听in听future work听we听must听aim to resolve which components and pathways of the AMOC have changed, how, and for what reason听鈥� there is a lot we still need to learn.鈥澨�

AMOC is a key control on both regional and global climate.听Whilst a slowdown of the AMOC could imply more extreme and intense winter weather events in Europe, the consequences could be manifold for people living on both sides of the Atlantic听鈥� with the east coast of the US vulnerable to flooding.听

Dr Levke Caesar, lead author (ICARUS Climate Research Centre, Maynooth University, and guest scientist at听Potsdam Institute for Climate Impact Research听(PIK))听said: 鈥淭he northward surface flow of the AMOC leads to a deflection of water masses to the right, away from the US east coast. This is due to Earth鈥檚 rotation that听diverts moving objects such as currents to the right in the northern hemisphere and to the left in the southern hemisphere.听As the听current slows down, this effect weakens and more water can pile up at the US east coast, leading to an enhanced sea level rise.鈥澨�

Study initiator Professor听Stefan听Rahmstorf听(PIK)) said:听鈥淚f we continue to drive global warming, the Gulf Stream System will weaken further - by 34 to 45 percent by 2100 according to the latest generation of climate models.听This could bring us dangerously close to the tipping point at which the flow becomes unstable.鈥澨�

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Caption:听鈥淣ew synthesis of evidence suggests the Gulf Stream System is at its weakest in over a millennium.听Credit: Natalie听Renier/Woods Hole Oceanographic Institution鈥澨�

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