The Story at the Bottom of the South China Sea

by | 2.10.2014 at 11:17am
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Sediments drilled from beneath the South China Sea are a window into the region’s past geology and climate. (Bill Crawford/IODP)

We have drilled 2,600 feet below the sea floor and in another 500 feet, will reach the crystalline igneous basalt of the ocean crust. Though finding the age of the basalt is our main aim, the thick sediments that overly the crust also have a story to tell. As the sediments build up over time, they record the geological and climate history of the region.

There are the muds, silts, and sands, shaken loose from shallower depths and transported by gravity down-slope to the deep basin, where our first drill site is located. Ultimately, these sediments come from erosion of the surrounding land, and in this tectonically active part of the world, there is a lot of erosion going on. The island of Taiwan, for example, is being tectonically uplifted at a rate of about 0.2 inches per year, and is being eroded at about the same rate. This may not sound like much uplift, but imagine a world without erosion, Taiwan would stand 12 miles high after 4 million years. All that eroded rock ends up on the seabed, and some of it may find its way to our site.

There are the tiny shells of foraminifera and coccolithophores (familiar to us as chalk, in their pure rock form). They form a continual rain from the sea surface, and build up slowly but steadily on the seabed. The overturn of marker species shows us the age of the sediments, and their chemistry carries a record of ocean temperatures in the past.

Finally, there are volcanic sediments – from thin ash layers from distant volcanoes, to thick beds containing coarse chunks of rock exploded from nearby volcanoes. The close volcanoes are no longer active, and some have sunk beneath the sea to become seamounts. We will know from the depth of these beds in the sediment succession when the volcanoes erupted and for how long they were active.

This diversity means there is always something new and interesting to see in each 33-foot-long core that comes up from the sea bed, each another chapter in the geological history of the South China Sea. Among the 32 scientists on board, we have specialists in sedimentology, micropaleontology, volcanology and other fields. We are an international group; about half of us hail from China, a quarter from the U.S, and the rest from Australia, Brazil, France, Switzerland, Japan, Taiwan, and the Philippines (so there’s a good mix of music in the core laboratory – very nice). And that’s just the science party – the ship’s crew is almost as diverse.

 

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