(单词翻译:单击)
听力文本
This is Scientific American's 60-second Science, I'm Christopher Intagliata.
Ten thousand years ago, the Sahara had extensive grasslands and was dotted with lakes and trees. But some 5,000 years ago, that "Green Sahara" dried up to become the enormous desert we know today. And scientists now think that this climate shift had effects far away—including causing a megadrought in Southeast Asia.
Kathleen R. Johnson, a paleoclimatologist and geochemist at the University of California, Irvine, says the key to that discovery were stalagmites collected in a cave in northern Laos.
"Stalagmites are really amazing archives of past climate variability. People are more familiar with things like tree rings and ice cores or ocean sediment cores. Well, stalagmites work in a similar way, in that they're deposited over time."
Johnson's team analyzed trace elements and carbon and oxygen isotopes in the hardened cave drippings. That information enables researchers to determine rainfall patterns over the millennia. And Johnson and colleagues discovered signs of a 1,000-year-long drought in Laos, which began around the same time the Sahara dried up—about 5,000 years ago.
As for why the two events might be connected? The researchers simulated the drying out of the Sahara using climate models—and they included a couple things we know happened, including the subsequent disappearance of vegetation and a connected increase in airborne dust—and found those variables would have been capable of cooling down the Indian Ocean.
"And so those cooler ocean temperatures led to less moisture being brought by monsoon circulation in the summertime, when that region gets most of its rainfall."
The details are in the journal Nature Communications.
One of Johnson's co-authors is Joyce White, a consulting scholar at the Penn Museum. She studies the human history of Southeast Asia. And her reaction when she first heard about the drought:
"I said, 'Oh my God, that's the missing millennia.'"
The "missing millennia" because she says archaeological data is scant in that part of Southeast Asia, from 4,000 to 6,000 years ago. White says it's a critical period in which hunter-gatherers gave way to farmers.
"And there are a lot of debates about how the two periods related to each other, but we lacked the evidence in the area I'm most interested in, which is the Mekong Valley."
White says this study doesn't answer that question directly—but the megadrought is a tantalizing new clue for archaeologists as they continue to investigate those "missing millennia."
Thanks for listening for Scientific American's 60-second Science. I'm Christopher Intagliata.
参考译文
这里是科学美国人——60秒科学系列，我是克里斯托弗·因塔格里塔。
一万年前，撒哈拉拥有广阔的草原，遍布湖泊和树木。但大约5000年前，“绿色撒哈拉”干涸成我们今天所知的巨大沙漠。科学家现在认为，这种气候变化产生了深远的影响，包括在东南亚造成特大干旱。
凯瑟琳·R·约翰逊是加州大学欧文分校的古气候学家和地球化学家，他表示，这一发现的关键是在老挝北部洞穴中收集的石笋。
“石笋非常神奇，它保留着过去气候变化的记录。人们更熟悉树木年轮、冰核或海洋沉积物核等东西。石笋也以类似的方式工作，即随时间的推移而沉积。”
约翰逊的团队分析了硬化洞穴水滴中的微量元素和碳氧同位素。这些信息使研究人员能够确定几千年来的降雨模式。约翰逊和同事发现了老挝长达1000的干旱迹象，这场干旱大约始于5000年前，与撒哈拉沙漠干涸的时间差不多。
至于为何这两个事件可能有关联？研究人员用气候模型模拟了撒哈拉干旱的过程，他们纳入了我们知道已经发生的两件事情，随后植被的消失和与之相关的空气中灰尘的增加，他们发现这些变量能使印度洋降温。
“因此，海洋温度降低导致夏季季风环流带来的水分减少，而夏季正是该地区降雨量最多的时候。”
研究详细信息发布在《自然通讯》期刊上。
约翰逊的合著者之一是宾夕法尼亚博物馆的咨询学者乔伊斯·怀特。她研究东南亚人类史。她第一次听说这场干旱时的反应是：
“我说，‘哦，我的天哪，这是缺失的千年。'”
她称之为“缺失的千年”是因为，东南亚该地区4000至6000年前的考古资料缺失。怀特表示，那是狩猎-采集者让位给农民的关键时期。
“关于这两个时期相互关联的方式存在很多争论，但在我最感兴趣的地区，即湄公河流域，我们缺乏证据。”
怀特表示，这项研究并没有直接回答这个问题，但对于考古学家来说，在他们继续调查“缺失的千年”时，这场特大干旱是诱人的新线索。
谢谢大家收听科学美国人——60秒科学。我是克里斯托弗·因塔利亚塔。
译文为可可英语翻译，未经授权请勿转载！
重点讲解
重点讲解：
1. dry up (使)枯萎；(使)干透；
The fountain is reputed never to dry up.
这口泉号称从不干涸。
2. be familiar with 熟悉的；熟知的；
Everyone is familiar with the TV screen's hypnotic power.
大家都很熟悉电视屏幕的吸引力。
3. cool down (使)变凉；(使)冷却；(使)降温；
The other main way the body cools itself down is by panting.
喘气是身体自身降温的另一个主要方式。
4. give way to 向…让步；向…妥协；
He should give way to a younger, more decisive leader.
他应该让位于更年轻、更有决断力的领导者。
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