Rocks Beneath the South China Sea Will Help Explain How Oceans Form

New Scientist
Stories from New Scientist.
Feb. 8 2014 7:30 AM

How Do You Make an Ocean?

Why I’m drilling for rocks beneath the South China Sea.

Jian Lin on the JOIDES Resolution drill ship in the South China Sea.
Jian Lin on the JOIDES Resolution drill ship in the South China Sea.

Photos courtesy of Jian Lin/Woods Hole Oceanographic Institution

Jian Lin is a geophysicist at the Woods Hole Oceanographic Institution in Massachusetts. He is co-chief scientist on the International Ocean Discovery Program, which will begin drilling in the South China Sea this month.

Jon White: You are co-lead of an international project to drill for rock samples in the South China Sea. Why is that sea bed of such interest?
Jian Lin: We want to answer questions about when it was formed, in part because it is a great analogue for the Atlantic and Indian Oceans. In the Atlantic, for example, Europe and Africa are moving away from the Americas. With the South China Sea, the southern part moved away from the northern.

JW: Why not drill in the Indian or Atlantic Oceans?
JL: The South China Sea is smaller, so easier to study. You don't need as many samples to understand its geological history. Also, while the Atlantic is still getting bigger because the sea floor is still spreading, that process has ended in the South China Sea. So we can study it from start to finish.

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JW: What key questions do you hope to answer?
JL: There are two. First, when did the southern part of the sea start to move away from the northern? Second, when did this stop? Some geologists argue that movement started about 42 million years ago; others say 32 million. For the end point, some say 35 million years ago, and others argue it was 16 million. Our purpose is to use state-of-the-art tools to try to nail down the answer.

JW: How will you gather the samples?
JL: We will be at sea for 60 days, which gives us time to drill at three sites—one in the northern part of the sea, where we will drill to 2 kilometers, and two in the eastern basin, where we will drill to 1 kilometer.

Map of the South China Sea, with inset of the drilling ship JOIDES Resolution.

Image courtesy Jian Lin/Woods Hole Oceanographic Institution

JW: What kind of rock do you expect to find?
JL: For all three sites, we expect to see layers and layers of sediment until we reach the bottom 100 meters or so, where we will find the original volcanic rocks that formed in the sea. Both types of rock are very important.

JW: How will you determine how old they are?
JL: The sediment layers contain fossils of very tiny ocean creatures. We can determine how old these are and use this to date the sedimentary rocks at different depths. For the volcanic rocks, we use chemical methods to determine when they formed. Using these two techniques, we can identify the age at various depths to work out what happened when.

We hope that if everything comes out OK, we will be the first to precisely determine the sea's age and start to answer the key questions.

JW: What other things might this project help us to understand?
JL: We also plan to study the microbiology in the ocean crust, to see if there are new microbes at these great depths.

But principally, knowing the timing of the South China Sea's formation will let us better understand the interaction of the many tectonic microplates in Southeast Asia. And it will give us insights into climate change. The sediments contain extremely rich information about the climate over millions of years—including sea surface temperature. We expect to see a beautiful record of climate change in our cores.

This article originally appeared in New Scientist.

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