深海隐士，高深莫测（有声）
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Ocean plants buried in sediment can help reveal Earth’s temperature thousands of years ago. That’s according to Daniel Sigman of Princeton, winner of a 2009 MacArthur“genius grant”. Dr. Sigman has been trying to piece together how efficiently tiny ocean plants – algae – were using nitrogen about 20,000 years ago.
Daniel Sigman: Algae require nitrogen to grow, and their bodies, in turn, fuel the rest of the ocean food web.
Sigman explained that by measuring algae’s use of nitrogen, he can gauge how much these ancient organisms used another important element – carbon dioxide, or CO2. All earthly plants use CO2 for photosynthesis. CO2 is also a major greenhouse gas in Earth’s atmosphere. Excess CO2 warms the Earth.
Daniel Sigman: The ocean is responsible for lowering carbon dioxide in the atmosphere as much as the forests on land are.
That’s because algae take CO2 out of surface water. And, when the algae die, Sigman said, they sink.
Daniel Sigman: And transfer it into the deep sea where it cannot escape back to the atmosphere.
That's cooling the planet. Dr. Sigman is currently working to determine the role the ocean played in the global cooling that caused the last ice age. His early research indicates that algae in polar oceans might have played a role.
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