Sunken islands discovered in the Caribbean

Coral reefs on lava plinths still reached the water surface 40 million years ago

Map of the Caribbean: On nautical charts, the islands that have now been discovered have not yet been recorded. © USGS
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In the depths of the Caribbean there are sunken islands, which are not yet recorded in any nautical chart. Now, scientists found evidence during a six-week expedition with the German research vessel Meteor. They discovered undersea surveys that were still on the surface about 40 to 50 million years ago. They were once created by lava outcrops and coral.

The central Caribbean was the destination of an expedition of scientists of various disciplines with the German research ship Meteor. Among other things, it was intended to shed light on the geology of the subsoil in this troubled area, where earthquakes occur again and again, most recently in Haiti in January 2010. Among other things, the researchers mapped the topography of the Caribbean seabed with the help of the fan-echo sounder - and experienced some surprises.

Because it quickly became apparent that the existing nautical charts for this area, which are mostly based on satellite data, are anything but accurate. Some undersea mountains, which were registered on the nautical charts, did not exist in reality. In other cases, the maps showed flat areas that were actually mountainous. Measurements with the fan echo sounder revealed elevations of more than 1, 000 meters above the ocean floor.

Coral islands drowned in the sea

However, the biggest surprise - and the decisive clue - brought samples that brought the so-called dredge from the flanks of the newly discovered submarine mountains to light. These large steel baskets are lowered on a steel cable several kilometers long and dragged across the seabed to collect samples of rock and organisms. In the samples from the subsea hills, the researchers discovered structures that were not allowed to exist on the deep sea hills. The corals, snails and red algae tubers typically only emerge in the light-flooded waters of the shallow ocean depths.

Scientists examine soil samples from the island flank University of Greifswald

For the researchers, it was clear: the submarine mountains, whose peaks are now in water depths of 800 to 1, 000 meters, must have once been islands in the Caribbean Sea. The samples and forms of the hills determined by means of a forest echo sounder indicate that the newly mapped seamounts were once coral reefs protruding from the water. The exact age of the reefs still needs to be clarified in detail, but it can already be said that they originated about 40 to 50 million years ago. The growth of the coral reefs could apparently initially keep up with a steady sinking of the underground. Then they died and disappeared with time in the depths. display

Lava towers formed island bases

In further echosounders, the scientists found that the reefs were sitting on a second, much larger platform that is now lying in water depths of about 1, 600 to 1, 800 meters. These platforms, which are also found under other sunken islands, clearly rise above the deep-sea level at about 4, 000 meters of water depth and are the result of a large submarine basalt outflow.

This lava spill occurred in the Middle Cretaceous, approximately 80 to 90 million years ago, and covered much of what was then the Caribbean Sea with a powerful layer of lava. The determination and dating of rock samples from the trawl nets and from the dives with the diving robot ROV Kiel 6000 proves this. The basalt platforms were apparently initially close to or possibly above the water level, indicating rounded basalt scaffolds. Such Ger lle can only arise in highly agitated water, as it occurs in rivers or in the sea surf.

(University Greifswald, 10.05.2010 - NPO)