{"id":598391,"date":"2026-04-10T18:22:11","date_gmt":"2026-04-10T18:22:11","guid":{"rendered":"https:\/\/www.newsbeep.com\/au\/598391\/"},"modified":"2026-04-10T18:22:11","modified_gmt":"2026-04-10T18:22:11","slug":"this-massive-ocean-current-needed-one-missing-piece-to-begin","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/au\/598391\/","title":{"rendered":"This Massive Ocean Current Needed One Missing Piece to Begin"},"content":{"rendered":"

The Antarctic Circumpolar Current, or ACC, is the most powerful ocean current on Earth. It circles Antarctica and links the Atlantic, Pacific, and Indian oceans, shaping the movement of heat, nutrients, and water through the global ocean system.<\/p>\n

Its origin matters because the current is tied to one of the biggest climate reorganizations in Earth\u2019s history. Around 34 million years ago, the planet shifted from a warmer greenhouse state to a cooler icehouse world, with large and lasting polar ice sheets beginning to take hold.<\/p>\n

The simulations show gateway opening was not enough<\/p>\n

For years, scientists have associated the birth of the ACC with the widening and deepening of ocean passages as Australia and South America moved away from Antarctica. The new research does not reject that idea, though it narrows it. According to lead author Hanna Knahl <\/a>of the Alfred Wegener Institute, the gateways alone were not sufficient to establish a complete circumpolar flow.<\/p>\n

The team reconstructed Earth as it was about 33.5 million years ago and ran high-resolution coupled simulations that included ocean circulation, the atmosphere, land surfaces, and the Antarctic ice sheet. These simulations were then compared with geological reconstructions from the same period. The study found that an early \u201cproto-ACC\u201d formed in the Atlantic and Indian sectors, yet it did not complete a full circuit around Antarctica.<\/p>\n

\"EogmEOGM Southern Ocean circulation showing proto-ACC, coastal currents, and gateway flows \u00a9PNAS<\/p>\n

Instead, after reaching the Tasman Gateway between Antarctica and Australia, the eastward-flowing current turned north and weakened along the coasts of Australia and Zealandia. The Pacific sector remained comparatively calm. The paper <\/a>says the main limitation was the position of the winds. In the Early Oligocene setup, the strongest westerlies were not aligned with the deepest parts of the Tasman Gateway, which reduced the wind forcing needed to sustain a full circumpolar current.<\/p>\n

Knahl said there had already been signs that wind in the Tasman Gateway played a major role. The new simulations, she said, clearly show that only when Australia had shifted farther north and the strong westerly winds blew directly through the gateway could the current fully develop. In the model, catabatic winds descending from the East Antarctic Ice Sheet also weakened the westerlies in that key region, which further disrupted the flow.<\/p>\n

A weaker early current changed Antarctica\u2019s climate in a different way<\/p>\n

The study also shows that the Southern Ocean around 34 million years ago did not behave like the one seen today. Rather than a strong, continuous ring current isolating Antarctica from warmer waters, the model produced a more uneven circulation pattern, including a strong Antarctic Coastal Current and an expanded Weddell Gyre.<\/p>\n

That distinction matters because the fully developed ACC now helps keep warmer waters away from Antarctica, which supports the long-term stability of the ice sheet. In the Early Oligocene simulation, by contrast, warm surface waters <\/a>could still approach parts of the continent. According to the paper, this helped create a very different pattern of ocean heat transport, with stronger thermal connectivity in the Weddell Sea and Australian basin, while the Pacific sector stayed cooler and fresher.<\/p>\n

\"EogmEOGM ocean model mesh with highest resolution in the Southern Ocean \u00a9PNAS<\/p>\n

The researchers also link this circulation pattern to the development of the Antarctic ice sheet. Their results support earlier work showing that East Antarctic glaciation began before a fully developed ACC was in place. The study says ice formation was more closely tied to falling carbon dioxide levels, regional topography, and precipitation patterns than to immediate thermal isolation by a strong circumpolar current.<\/p>\n

The broader climate setting was already shifting rapidly. During the Eocene\u2013Oligocene transition, atmospheric CO2 fell from roughly 1,000 parts per million in the late Eocene to about 600 ppm in the Early Oligocene Glacial Maximum. The authors write that mountain building, carbon dioxide drawdown, and the opening of Southern Ocean gateways all contributed to the climate transition, though none of those changes on their own produced the ACC in its modern form.<\/p>\n

The researchers also stress that the ancient climate is not a direct template for the future. Knahl said past warm, CO2-rich climates can help scientists understand Earth system behavior, though the climate of the past cannot be projected one-to-one onto the future. In this case, the study\u2019s central point is straightforward: Earth\u2019s most powerful ocean current did not simply switch on when the seaways opened. It formed through a more specific alignment of geography, winds, ocean circulation, and ice.<\/p>\n","protected":false},"excerpt":{"rendered":"The Antarctic Circumpolar Current, or ACC, is the most powerful ocean current on Earth. It circles Antarctica and…\n","protected":false},"author":2,"featured_media":598392,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[22],"tags":[64,63,75,128],"class_list":{"0":"post-598391","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-environment","8":"tag-au","9":"tag-australia","10":"tag-environment","11":"tag-science"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts\/598391","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/comments?post=598391"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts\/598391\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/media\/598392"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/media?parent=598391"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/categories?post=598391"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/tags?post=598391"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}