Ice sheet expansion may have started 2,000 years ago, but we canceled that

本文为原文前 6,000 字符的节选翻译，完整内容请查看原文。

Barnes Ice Cap sits on the central plateau of Baffin Island, in the Canadian Arctic. It is the last surviving fragment of the Laurentide Ice Sheet, the largest of the Pleistocene ice sheets, which at its peak buried most of Canada under two miles of ice and locked away around 80 meters of sea level. That remnant has now yielded direct physical evidence that ice sheets might have reversed their retreat and started to grow again thousands of years ago.

巴恩斯冰盖位于加拿大北极地区巴芬岛的中央高原上。它是劳伦泰德冰盖最后幸存的碎片，也是更新世最大的冰盖。在其鼎盛时期，它将加拿大大部分地区埋在两英里厚的冰层之下，并锁住了约80米的海平面高度。这一残余物现在提供了直接的物理证据，表明冰盖可能在数千年前就已经停止了退缩并开始重新增长。

In a recent Science study, researchers show that the Laurentide reached its smallest size about 3,600 years ago, then started re-expanding roughly 2,000 years ago, which the team interprets as the opening move of the next glaciation. Apparently, this brand-new ice age was on its way until about 1960, when human-caused climate warming reversed it.

在最近发表于《科学》杂志的一项研究中，研究人员表明，劳伦泰德冰盖在约3600年前达到最小规模，随后在约2000年前开始重新扩张，研究团队将其解读为下一次冰期的开端。显然，这场全新的冰河时代一直在酝酿之中，直到1960年左右，人类引起的气候变暖才将其逆转。

“Barnes is the last remaining piece of one of the domes of the Laurentide Ice Sheet,” says Nicolás Young, a geologist at Columbia University’s Lamont-Doherty Earth Observatory and lead author of the study. As that enormous dome thinned through the Holocene, its margin withdrew up onto Baffin Island, and what’s left today is the deflated core of something that was once two miles thick.

“巴恩斯是劳伦泰德冰盖圆顶之一最后剩下的部分，”哥伦比亚大学拉蒙特-多尔蒂地球观测站的地质学家、该研究的主要作者尼古拉斯·杨（Nicolás Young）说。随着那个巨大的圆顶在全新世期间变薄，其边缘退缩到了巴芬岛上，今天留下的只是曾经两英里厚冰层的萎缩核心。

The reason Barnes can testify about its own history, Young explains, comes down to the temperature at its base. Most glaciers are warm-based, meaning meltwater at the bed lets them slide, and sliding ice grinds up everything beneath it, erasing the record. Barnes is cold-based, and thus frozen directly onto the bedrock beneath it, which prevents it from sliding.

杨解释说，巴恩斯冰盖之所以能证明其自身的历史，归结于其底部的温度。大多数冰川是暖底的，这意味着底部的融水使其能够滑动，而滑动的冰层会磨碎其下方的所有东西，从而抹去记录。巴恩斯冰盖是冷底的，因此直接冻结在下方的基岩上，这防止了它的滑动。

“If there is an ice event where you live and you have to go and scrape off your windshield, that ice that’s plastered to the windshield of your car, that’s a good example of how cold-based ice operates. It’s sort of just stuck to what it’s on,” Young says. This stuck ice preserves what’s beneath instead of eroding it. As the Laurentide retreated across the plateau, tundra plants colonized the newly bare ground. When the ice came back later, it simply smothered them in place and held them there, intact, for two millennia.

“如果你住的地方发生了结冰事件，你不得不去刮挡风玻璃，那么粘在车窗上的冰就是冷底冰运作方式的一个很好的例子。它就像是粘在它所覆盖的东西上一样，”杨说。这种粘附的冰保护了下方的东西，而不是侵蚀它。当劳伦泰德冰盖穿过高原退缩时，苔原植物在裸露的地面上定居。后来当冰层回来时，它只是将它们原地覆盖，并让它们在那里保持了完整两千年。