8 Million Years Of Climate History Found Beneath The South-East Pacific

Scientists have found new information about Earth's climate over the last 8 million years by studying a long sediment core taken from the South-East Pacific Ocean. The research was conducted by scientists from the Leibniz Institute for Baltic Sea Research Warnemünde (IOW) and was published in the journal Nature Communications. The core, collected near the Drake Passage close to Antarctica, shows how ocean currents and temperatures have changed, and how these changes have affected the level of carbon dioxide in the atmosphere.

Antarctic Circumpolar Current

The Antarctic Circumpolar Current (ACC) is the strongest ocean current in the world, and it is still sensitive to temperature changes. It flows around Antarctica and connects the Pacific, Atlantic, and Indian Oceans. It plays a major role in Earth's climate by helping move heat, salt, nutrients, and carbon dioxide between these oceans.

The Drake Passage, where the sediment was collected from a depth of 3800 metres, is the narrowest part of this current. The team examined layers of mud and particles that have settled on the seafloor over the millions of years. They were able to look at changes in ocean temperature and current strength over a long period.

What Did the Researchers Find

Alkenone paleothermometry is a method which involves studying chemical compounds known as alkenones. These compounds are left behind when certain single-celled algae die and are produced in different forms depending on the water temperature at the time.

By examining 300 samples from a 380-metre-long sediment core, researchers created a detailed timeline of sea surface temperatures, with each data point separated by about 25,000 years.

One surprising discovery was that between 2.2 and 5.3 million years ago, the ACC actually became stronger during long cold periods that lasted about 400,000 years.

Previously, experts believed that in the past million years, the ACC strengthened during short warm periods that lasted around 10,000 years. The finding suggests that the way the ocean and atmosphere interact can vary depending on the timescale being studied. The study also challenges the idea that the Earth experienced widespread cooling around 2.7 million years ago, when large ice sheets started forming in the Northern Hemisphere.

Interestingly, scientists found that the Southern Ocean, particularly the South-East Pacific, actually warmed by about 5°C during that time, a warming that lasted 700,000 years.

Why It Matters

Scientists believe that this warming event likely weakened the ACC, allowing more CO2 to build up in deep ocean waters. Eventually, this CO2 was released into the atmosphere, followed by a gradual drop in CO2 levels, which may have contributed to the cooling that came later. This could have disrupted the circulation of deep ocean waters in the Atlantic, triggering the formation of large ice sheets in the north.

Understanding how Earth's climate behaved in the past is essential for predicting how it might change in the future. The research team plans to continue their studies in this region with even greater detail in future projects. They hope to improve the accuracy of modern climate models and more accurately predict the future of our planet's climate as global warming continues.

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