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Rising Temps Lower Polar Bear Mercury Intake 气候变暖为北极熊健康带来福音

As climate change warms the Arctic, sea ice there is disappearing at record rates—sea ice that polar bears prefer to prowl. As a result, some bears are spending more time on solid land. And are thus switching up their diets, too. Instead of the ringed seals they ate out on the ice, the bears are foraging¹ on bowhead whale carcasses, cast up on the beach.

随着气候变化使北极变暖，北极的海上浮冰（海冰）正在以创纪录的速度消失。然而，北极熊非常喜欢在海冰上徘徊。这一现象导致一些北极熊花费更多时间在陆地上逗留，也因此改变了它们的饮食习惯。与此前在冰上捕食环斑海豹不同，它们现在以觅食被冲到沙滩上的北极露脊鲸的尸体为生。

So what does this mean for them?

那么，这对它们来说意味着什么呢？

\"It's sort of good news/bad news." Melissa McKinney, an ecotoxicologist at the University of Connecticut. The bad news is that the bears are losing vital habitat. But the silver lining³ is that bears decamping to land have lower levels of toxic² mercury due to their changes in diet.

“这既是一个好消息，也是一个坏消息。”康涅狄格大学的生态毒理学家梅丽莎·麦金尼（Melissa McKinney）说道。坏消息是，北极熊正在失去对它们至关重要的栖息地。但不幸中的万幸是，由于北极熊撤到陆地上生存导致其饮食发生变化，它们接触的有毒汞也随之减少。

McKinney and her team studied hair samples from one polar bear population in Alaska, from 2004 to 2011. In that time they saw a 65 percent drop in the bears' mercury levels—to concentrations below the known threshold for negative biological effects. And it looks like the different diet may be the reason.

2004年至2011年，麦金尼和她的团队研究了阿拉斯加某个北极熊种群的毛发样本。在此期间，她们发现北极熊身上的汞含量下降了65%——浓度达到了已知负面生物学效应的阈值以下。饮食的变化可能是其原因。

Bowhead whales feed on plankton⁴, while ringed seals eat fish and other animals in which mercury has had the chance to accumulate. "So if polar bears are feeding on prey⁵ items that are lower in the food chain, then they're likely experiencing a less mercury-contaminated food source than they would be otherwise."

露脊鲸以浮游生物为食，而环斑海豹则以鱼和其它体内会积聚汞的动物为食。“因此，如果北极熊捕食的是食物链中较低层的猎物，那么它们的食物来源可能会遭受较少的汞污染。反之则不然。”

The bears that feed on whales are also in better condition—higher body-mass index. And being well fed means their bodies don't need to break down fat and muscle energy stores, where a lot of whatever mercury they have consumed is locked up. The study is in the journal Environmental Science and Technology.

以鲸鱼为食的北极熊体质也似乎变得更好了——身体质量指数更高了。吃得好就意味着它们的身体不需要分解脂肪和肌肉能量储备，因而大量它们消费的汞均被冻结。这项研究发表在《环境科学与技术》杂志上。

“We see polar bears as a sentinel of climate change. And I think it's really important for us to remember that, either positively⁶ or negatively, climate change can shape the risks that are posed by other environmental stressors—in this case toxic pollutants⁷." Of course, it would be better to stop the warming and have less mercury in the environment. But the takeaway here is that climate change has multiple effects that go beyond disappearing ice.

“我们将北极熊视为气候变化的哨兵。我认为对我们来说谨记这一点非常重要，不管是积极的还是消极的，气候变化会影响其他环境压力因素造成的风险——这种情况下，是对有毒污染物的影响。”当然，最好的还是阻止气候变暖，减少环境中的汞含量。但此处得出的结论是，气候变化带来的影响不只是海冰消融，它还有多种影响。