黑料视频

Our planet's ocean plays a central role in climate regulation, and the deep ocean 鈥� starting a few hundred meters below the surface - modulates Earth鈥檚 long-term climate evolution. This part of the ocean is largely cut off from the atmosphere, and only flushed when surface water cools and becomes so dense that it can sink to depth. This happens in the North Atlantic and around Antarctica, and these deep-water formation regions thus govern the exchange of heat, greenhouse gases such as CO₂, and oxygen between the large deep ocean reservoir and our thin atmosphere. The continuous formation of the North Atlantic Deep Water (NADW) is a key process in global ocean circulation, comparable to the action of a vast conveyor belt transporting heat, salt, nutrients, and carbon dioxide around the world. This process forms part of the Atlantic Meridional Overturning Circulation (AMOC), which significantly influences the climate in the Northern Hemisphere.

The weakening of those major ocean currents could drastically alter living conditions on the continents, potentially raising or lowering regional temperatures by dozens of degrees Celsius. Understanding and modeling the dynamics of deep water in the oceans is therefore crucial to preparing for such changes.

To understand these shifts in the future, scientists use the past when climate was very different to gain insight into the current and systematic interaction between ocean and climate. At the University of Lausanne (UNIL), a team of scientists has studied the last ice age - which peaked around 20,000 years ago - and retraced the planet's deep ocean currents. Their results have been published in Nature Geoscience.

They demonstrate that, contrary to what was previously thought, the flow path of deep ocean waters remained relatively stable during this period, of extreme cold and massive ice coverage. This discovery challenges earlier hypotheses that ocean circulation had changed dramatically at this point in history.

The findings suggest that deep water formation was more persistent under glacial conditions than previously assumed. "However, we must be careful not to draw simple comparisons with the current situation. The warming we are seeing today, caused by human activity, is indeed much more rapid, and the ice masses much smaller than 20,000 years ago," explains Patrick Blaser, first author of the article and researcher at the University of Lausanne's Faculty of Geosciences and Environment as well as at the 黑料视频 Helmholtz Centre for Ocean Research Kiel (Germany). 鈥淭his study reveals that we still do not fully understand the interaction between ocean and climate system during the ice age. Thus, the Earth system models used for such paleo-reconstructions have significant shortcomings.鈥�

The researcher advocates launching new research based on this breakthrough, to better understand past climate mechanisms, and correct future climate projections. 鈥淭his work is essential if we are to correctly apprehend past, present and future natural phenomena, and meet the challenges that lie ahead.鈥�

To reconstruct ocean currents 20,000 years ago, the researchers combined five different indicators from ocean sediments, including isotope ratios of neodymium, oxygen and carbon, as well as radiocarbon and the chemical composition in the shells of microorganisms. Their approach can be compared to the cross-referencing of several testimonies to observe the same scene. This multi-proxy analysis makes it possible to reconstruct the origin of water masses and their circulation with higher confidence and detail than before (although the rate at which they moved is harder to constrain). This led the authors to challenge the idea that ocean circulation in the North Atlantic came to an abrupt halt during the last ice age.

Publication:

P. Blaser, C. Waelbroeck, D. J. R. Thornalley, J. Lippold, F. P枚ppelmeier, S. Kaboth-Bahr, J. Repschl盲ger & S. L. Jaccard (2025):鈥�Prevalent North Atlantic Deep Water during the Last Glacial Maximum and Heinrich Stadial 1, Nature Geoscience

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