白令海峡是俄罗斯与美国阿拉斯加之间宽约80公里的海域，研究人员计算后发现，它能影响整个北半球的气候。这个发现回答了困扰了科学家十几年的问题，说明某些因素看似不起眼的变化将如何改变全球的气候。

The Bering Strait, the 80-kilometer-wide stretch of ocean between Russia and Alaska, can strongly influence the climate of the entire Northern Hemisphere, researchers have calculated. The findings answer a question that has dogged scientists for the past decade, and they demonstrate how seemingly slight changes in certain factors can impact global climate.

在过去的几百万年里，地球总处于冰川循环中，冰河期有规律地来来去去，持续10万年左右，再停个1-1.5万年。最近的一次冰河期大约在1.1万年前结束。每到冰河期，地球表面大都被厚达几公里的冰原覆盖。冰原也呈周期变化，增厚了又变薄、前进了又后退，每个阶段能延续数千年。但之前一直没有找到这种周期变化的原因。

For the past several million years, Earth has been locked in a glacial cycle. Ice ages come and go with remarkable regularity, lasting 100,000 years or so and then letting up for 10,000 to 15,000 years. The last such ice age ended about 11,000 years ago. Within each ice age, the kilometer-thick ice sheets that cover much of the top of the world also go through cycles, thickening and thinning, extending and receding, over periods lasting a few thousand years. But until now, no one has been able to pinpoint the cause of these oscillations.

现在这个亟待解决的问题已经由美国国家大气研究中心（位于科罗拉多州博尔德市）的海洋学家胡爱学和同事作出了回答，他们研究了白令海峡对冰川振荡变化可能造成的影响。他们知道在过去的冰河期里，有时海平面下降会使海峡中出现大陆桥。胡爱学的团队分析了海洋的沉淀物，发现大陆桥出现的时间似乎与冰原的振荡变化有关。所以研究人员将海洋沉淀物的数据与已知会引起或终结冰河期的地球轨道和旋转变化数据一起输入新的超级计算机模型。本周他们在《自然-地球科学》网络版上进行了报告，模型显示白令海峡的状况是造成冰原振荡的直接原因。

This pressing question has now been tackled by Aixue Hu, an oceanographer at the U.S. National Center for Atmospheric Research in Boulder, Colorado, and colleagues. They studied the Bering Strait’s potential impact on glacial oscillations. They knew that every so often during past ice ages, drops in sea level created a land bridge across the strait. By analyzing data from ocean sediments, Hu’s team found that the timing of the bridge’s appearance seemed to be linked to the oscillations of the ice sheets. So the researchers combined the ocean sediment data with calculations of Earth’s orbital and rotational variations–which are known to trigger or end the ice ages–into a new supercomputer model. As they report online this week in Nature Geoscience, the model shows that the Bering Strait’s status was directly responsible for the ice-sheet oscillations.

根据这个模型，事情的发展如下。在冰河期开始时，巨大的冰原逐渐扩张，蔓延至北美、格林兰、欧洲和亚洲北部。冰原消耗了大量的水分，海平面迅速下降，横跨白令海峡的大陆桥浮出水面。海峡封闭后，水流不能从太平洋进入大西洋，由于缺少了这部分水流，大西洋变得更咸、更温暖，所以更容易进入北冰洋。温暖的海水沿着边缘渐渐融化了冰原，使北冰洋和大西洋的淡水增多，海平面随之提高，北半球的气候趋于温和。一旦海面达到足够的高度，白令海峡再次开通，寒冷的太平洋海水又进入了北冰洋，气候变冷，冰原再次向外蔓延。整个过程循环往复。

Based on the model, this is what happens. At the beginning of an ice age, massive sheets of ice build up and advance across North America, Greenland, Europe, and northern Asia. These sheets sequester a great deal of water, causing sea levels to plunge and exposing the land bridge across the Bering Strait. When the strait closes, water cannot flow from the Pacific Ocean into the Arctic Ocean. The loss of that inflow means saltier–and warmer–water from the Atlantic Ocean has an easier path into the Arctic. The warmer water melts the ice sheets around their edges, which in turn floods the Arctic and Atlantic oceans with fresh water, raising sea levels again and moderating the northern climate. Once the seas are high enough, the Bering Strait reopens, cold Pacific water reenters the Arctic, the climate cools enough for the ice sheets to advance, and the whole process repeats.

胡爱学说，现在还不能确定温暖的海水和冰原在哪里交汇，如何相互作用。要找出这个答案，就需要全新的模型，他补充道。

Still undetermined, Hu says, is exactly where and how the warming waters interact with the ice sheets. Finding that out is going to require a new generation of models, he adds.

国家海洋和大气管理局（新泽西州普林斯顿）的流体动力学家罗纳德·斯托弗同意这个看法。他表示如果要完全理解文章所描述的过程，就要先建立起一个与之适应的冰原模型。不过，这项研究确实让我们对过去的气候变化有了更多了解，“并让我们对未来的预测也更有信心。”

Fluid dynamicist Ronald Stouffer of the National Oceanic and Atmospheric Administration in Princeton, New Jersey, agrees. A full understanding of the process described in the paper will have to wait until a comparable ice-sheet model can be developed, he says. Nevertheless, the research improves our understanding of past climate variations “and therefore gives us more confidence in future projections.”

本文由Crux译自ScienceNOW Daily News，英语作者Phil Berardelli
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