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A team analyzing sediment cores off the coast of Chile has now found the evidence. <\/p>\n
Chemical signals locked inside shells smaller than a grain of sand show that the predicted response unfolded rapidly 39,400 years ago.<\/p>\n
Clues from old shells<\/p>\n
Pushpak Martin John Nadar, a paleoclimate researcher at the University of Bergen (UiB<\/a>) in Norway, led the team. <\/p>\n They read chemical fingerprints locked into tiny shells of seafloor microorganisms called foraminifera, built from the water around them.<\/p>\n Carbon and oxygen isotopes are slightly different chemical forms of each element. <\/p>\n Those isotopes remain locked within the shells and let researchers trace deep water from tens of thousands of years ago. <\/p>\n Their core sits off the coast of Chile, where Southern Ocean flows push north into the Pacific.<\/p>\n The window they zoomed in on falls around 39,400 years ago. Greenland ice cores show that the North Atlantic had grown unusually cold during that period and had likely weakened.<\/p>\n How the Atlantic stalls<\/p>\n Scientists call this loop the Atlantic<\/a> Meridional Overturning Circulation (AMOC). <\/p>\n Warm, salty surface water moves north, releases heat into the atmosphere, sinks, and then returns south at depth. Without it, the planet\u2019s heat budget would look different.<\/p>\n A slowing loop affects more than the North Atlantic. Models predict that a weaker AMOC pushes heat and nutrients around the global ocean in unexpected ways. <\/p>\n Recent observations confirm a decline<\/a> is already underway. Nadar\u2019s team wanted to know if old sediments<\/a> hold physical traces of that change reaching far from the Atlantic. <\/p>\n If they do, today\u2019s slowing AMOC could already be reshaping ocean chemistry far beyond the Atlantic.<\/p>\n A signal in the Pacific<\/p>\n Inside the cores was a remarkable story. Around 39,400 years ago, bottom waters off Chile warmed quickly, oxygen levels climbed sharply, and carbon isotopes rose. <\/p>\n All three changes lined up at once. Such alignment is rare in paleoclimate records, where changes usually unfold gradually. <\/p>\n Together those signals describe water that had recently been present at the surface. <\/p>\n Ocean researchers call this enhanced ventilation, meaning the water had recently contacted the atmosphere, picking up oxygen<\/a> and shedding nutrients.<\/p>\n The water<\/a> mass is the Antarctic Intermediate Water, which forms near Antarctica and spreads toward the tropics about half a mile below the surface. <\/p>\n Until this study, no one had tied its response to an Atlantic slowdown so precisely.<\/p>\n The chemical response<\/p>\n A sharp oxygen jump stood out. That kind of rise happens when recently surfaced water arrives at depth. <\/p>\n Carbon isotopes confirmed it. The chemical signature matched freshly circulated water rather than the depleted signal left by stagnant deep water.<\/p>\n The slight bottom-water warming matched what climate models predict when AMOC slows. <\/p>\n Heat that would normally travel north may instead have accumulated in the Southern Hemisphere, nudging warmth into the intermediate layer.<\/p>\n Nutrients<\/a> in this layer also dropped. That decline likely signals a wider redistribution of biological fuel through middle waters, feeding surface ecosystems far away.<\/p>\n That interpretation fits earlier work<\/a> describing the Southern Ocean as the deep ocean\u2019s largest oxygen source.<\/p>\n Deeper, warmer layers<\/p>\n In model after model, a weaker AMOC pushes the thermocline, the boundary between warm surface water and cold depths, downward in the Pacific. <\/p>\n Northward heat transport stalls and warmth accumulates south of the equator instead. Nadar\u2019s results match that prediction with real-world evidence.<\/p>\n The chemical signals in the Chilean cores look exactly like what would happen if the thermocline deepened and the layer just below the surface pulled in younger, surface-influenced water.<\/p>\n Such corroboration is rare in paleoclimate work. Models predict one outcome, but real sediment records rarely confirm it. <\/p>\n Matching the models against the sediment record clarifies how the global ocean responds when part of its circulation weakens.<\/p>\n Carbon\u2019s missing piece<\/p>\n Ice cores show that carbon dioxide rose during these old Atlantic slowdowns, and scientists have argued for decades about why. <\/p>\n Some proposals lean on deep Pacific waters, and others focus on a Southern Ocean upwelling near Antarctica.<\/p>\n The new findings narrow the field. If the intermediate water was venting more vigorously then, stored carbon<\/a> could have escaped to shallower layers, where it exchanges with the atmosphere. <\/p>\n Earlier research<\/a> on Antarctic bottom waters suggests a related role. That doesn\u2019t settle the CO2 puzzle on its own. <\/p>\n But it removes some candidate explanations and leaves a smaller set that future studies can test against more sediment records and more climate simulations.<\/p>\n The implications ahead<\/p>\n The AMOC is weakening now, and the same physical levers from 39,400 years ago are at work again.<\/p>\n If Antarctic intermediate waters react today as they did then, oxygen, carbon, and nutrient patterns across much of the ocean could shift substantially.<\/p>\n For fisheries, those shifts could affect productive zones off South America and Africa, where intermediate-layer nutrients feed surface life.<\/p>\n For forecasting, models that ignore the Southern Hemisphere\u2019s response to Atlantic changes will miss part of the picture.<\/p>\n The Bergen team has shown the linkage is real, rapid, and chemically detectable. Researchers no longer need to assume the Antarctic-to-Atlantic feedback exists from models alone.<\/p>\n The sediment record confirms that the process occurred before, and that it could occur again.<\/p>\n The study is published in Communications Earth & Environment<\/a>.<\/p>\n \u2014\u2013<\/p>\n Like what you read? Subscribe to our newsletter<\/a> for engaging articles, exclusive content, and the latest updates.<\/p>\n Check us out on EarthSnap<\/a>, a free app brought to you by Eric Ralls<\/a> and Earth.com.<\/p>\n \u2014\u2013<\/p>\n","protected":false},"excerpt":{"rendered":"Climate scientists have modeled a weakening Atlantic current for years, and the results have repeatedly pointed in the…\n","protected":false},"author":2,"featured_media":475430,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[61,60,82],"class_list":["post-475429","post","type-post","status-publish","format-standard","has-post-thumbnail","category-science","tag-ie","tag-ireland","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/posts\/475429","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/comments?post=475429"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/posts\/475429\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/media\/475430"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/media?parent=475429"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/categories?post=475429"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/tags?post=475429"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}