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Africa’s fossil fjords hold clues to what the Arctic might look like in the distant future

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Namibia’s ancient dry fjords and modern northern fjords formed under similar conditions, but hundreds of thousands of years apart

Unless you are Namibian, the image above may at first glance appear to be another satellite image of a northern coast cracked by a fjord – possibly Greenland or Norway.

The close similarities in appearance are not just a coincidence; Namibia has a network of fossil fjords that could help climatologists better understand the climate of the past while providing insight into the role modern fjords play in a warmer world, suggest the authors of a recent scientific paper.

A Namibian valley carved out of hard bedrock represents an intact fossil fjord that was carved 300 million years ago, then filled with sediment before being exposed again. Remains of sedimentary rocks (mudstones and sandstone) are visible in the foreground. (Pierre Dietrich)

And they can give us some clues as to how the Arctic fjords might end up in the distant future.

Subtropical Namibia seems an unlikely place to find a glacier-carved landscape, but its climate has not always been so. Some 300 million years ago, during a period known as the Upper Paleozoic Ice House, much of the landmass that is now Africa was near the South Pole, where it was covered with an ice cap measuring 1.7 kilometers (just over 1 mile) thick.

As this ice moved, it carved out long, narrow valleys. As the climate warmed, the ice sheet first shrank to isolated glaciers a hundred meters thick before disappearing altogether. As they narrowed, the valleys served as an outlet for meltwater. When the melting was over, the valleys filled with seawater and formed fjords.

Then as today, the fjords served as major carbon sinks. Modern fjords, which formed about 12,000 years ago, can contain more than 10 percent of the world’s buried carbon, although they make up only 0.1 percent of the world’s oceans. By doing the same, the fjords of the past probably played a key role in regulating the climate, according to the lead author of the article, Pierre Dietrich of the University of Rennes.

Namibia’s fossil fjords would have acted similarly to modern northern fjords. And while fjords in places like Greenland and Norway can be much larger, their appearance is the same as those in Namibia, reflecting similar ways they were formed.

Geologists have long assumed that fjords and other geological features formed by glaciers were transient – that over a relatively short period of time on a geological scale, they would be eroded or collapsed. The fact that Namibia remains standing suggests that the northern fjords could do the same.

The most likely reason Namibia’s fjords did not disappear is that as the waters of the prehistoric fjords receded, sediment began to accumulate. Initially, it protected them. Over time, the sediments eroded, exposing the walls of the now dry fjords.

Thanks to their similarity and relatively pristine condition, Dietrich believes, it is likely that Namibia’s fjords could help modern scientists understand what happened when the Upper Paleozoic Ice Age ended and a warmer climate has set in (ice ages mark the end of a colder period in Earth’s history and, in this case, is its current stage).

This article originally appeared on Arctic Today and is republished with permission.


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