When glaciers covered this now arid region of the world

If the word “fjord” immediately makes us think of Norway, a team of geologists have just found traces of these great valleys carved by glaciers in an entirely different region of the world: Namibia. These ancient fjords allow us to learn more about the penultimate glaciation the Earth experienced, but also about the role sea fjords play in the carbon cycle and in climate regulation.

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[EN VIDÉO] The evolution of the Earth’s ice mass between 2003 and 2010
Globe glaciers and ice caps (in yellow) masses were measured over an eight-year period as part of the GRACE programme. Blue and red are used respectively to determine how much ice is lost or gained. © NASA

The straits are generally characterized by narrow valleys with high slopes that cut the coast and invaded by the sea, and they represent the coastal landscapes of the countries located in the highlands. latitudes, like Norway, bears witness to the last ice age it went through tr. These great valleys are the result of laborEat Glaciers at the continental base. They therefore represent valuable sites for understanding glacier dynamics during major ice ages. but that is not all. The fjords are also centers of very important sedimentary deposits. Therefore, they play a major role in organic carbon storage Thus it has the potential to influence the climate. Therefore, their study is essential to understanding the evolution of Earth’s climate over geological time. However, there are a few examples of fjords dating back to before the Cenozoic Era, which would allow us to study glaciers before the last Neolithic glaciation. quadrilateral After the formation of the Norwegian Straits. The rarity of ancient fjords must be associated with Morphology, which makes them particularly susceptible to corrosion.

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Monuments of the ancient fjords of Namibia

However, a team of researchers led by Pierre Dietrich from the University of ren Discover a whole network of ancient fjords on the northwest coast of Namibia. These fjords formed during the penultimate glacier episode dating to the end ancient life. This period lasted from -360 to -260 million years ago, making it a particularly long glacial period in Earth’s history. At that time, Namibia was part of Gondwana subcontinent. “This is the first example of a fjord fossils fully preserved”, Explains Pierre Dietrich. “The desert landscape of northern Namibia is actually an ancient ice landscape!”

The ancient network of fjords in Namibia today is characterized by valleys that cut a series of plateaus. These valleys, which are now occupied by rivers, are from 1 to 5 kilometers in width and 80 to 130 kilometers in length. Their icy past is not in doubt for geologists Its bottom as well as its sides are marked by traces of the passage of ancient glaciers. Streaks and dents, as well as various marks of friction and wear of the ice, characterize the basement rocks. These effects make it possible to create The direction of the flow of the previous glacier. The researchers also found sediment An glacier dating back about 300 million years, and consisting of many rock debris. Thanks to these witnesses to the glaciation as well as to the post-glacial deposits above them, geologists She was able to reconstruct the dynamics of the ice sheet at that time.

Ice cover about two kilometers thick

The depth of the cracks, with the depth of the fjords reaching 1.7 kilometers, as well as the presence of many irregular rocks, indicates the presence of an ice cover that completely covered the valleys during the first stage of the glaciation. Thus, the thickness of the ice has exceeded 1.7 km. ice cream Flowing in these valleys is fed by a large ice cap located in the far east. This phase of the maximum was followed by a decrease in ice thickness. It is not excluded that this ice age was marked by several cycles of lower extremities, ending with source Total invasion of ice and sea in fjords. “Straits also have a very strong control over the stability of the caps because they dry the ice from the caps into areas where the ice is melting and disintegrating. As the ice flows more, the fjords widen under the influence of erosion, which increases the impact of erosion. Drainage Fjords. Over time, hats have become more sensitive to climate changes ”, Adds Pierre Dietrich.

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Studying the ancient sea fjords of Namibia also provides a better understanding of the fjord climate change The drastic event that occurred between the glaciation at the end of the Paleozoic and the continuous warming that followed. These ancient fjords, as well as those of today in South America and South Africa, may have facilitated the deposit and long-term storage Carbon organic. The burial of large amounts of organic matter in glacial valleys may have contributed significantly to the decrease in carbon dioxide2 Atmosphere at the beginning Permin. This case would have made it possible to regulate the warming associated with the weakening of large carbon reservoirs in Carbonated.

The results of this study published in the journal geology, shows the importance of geomorphology and sedimentology in reconstructing past climates and glacial dynamics.

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