Mean annual air temperatures in the High Arctic are rising rapidly, with extreme warming events becoming increasingly common. Little is known, however, about the consequences of such events on the ice‐capped lakes that occur abundantly across this region. Here, we compared 2 years of high‐frequency monitoring data in Ward Hunt Lake in the Canadian High Arctic. One of the years included a period of anomalously warm conditions that allowed us to address the question of how loss of multi‐year ice cover affects the limnological properties of polar lakes. A mooring installed at the deepest point of the lake (9.7 m) recorded temperature, oxygen, chlorophyll a (Chl a ) fluorescence, and underwater irradiance from July 2016 to July 2018, and an automated camera documented changes in ice cover. The complete loss of ice cover in summer 2016 resulted in full wind exposure and complete mixing of the water column. This mixing caused ventilation of lake water heat to the atmosphere and 4°C lower water temperatures than under ice‐covered conditions. There were also high values of Chl a fluorescence, elevated turbidity levels and large oxygen fluctuations throughout fall and winter. During the subsequent summer, the lake retained its ice cover and the water column remained stratified, with lower Chl a fluorescence and anoxic bottom waters. Extreme warming events are likely to shift polar lakes that were formerly capped by continuous thick ice to a regime of irregular ice loss and unstable limnological conditions that vary greatly from year to year.

中文翻译：

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北部偏远湖泊的极端变暖和政权转向扩大的变异性

高北极地区的年平均气温迅速上升，极端变暖事件变得越来越普遍。然而，关于此类事件对整个地区大量发生的冰湖的后果知之甚少。在这里，我们比较了加拿大高北极地区Ward Hunt Lake中2年的高频监测数据。其中的一年包括一段异常温暖的天气，使我们得以解决多年冰盖的丧失如何影响极地湖泊的湖泊学性质的问题。安装在湖泊最深处（9.7 m）的系泊设备记录了温度，氧气，叶绿素a（Chl a），2016年7月至2018年7月的水下辐照度，以及自动摄像头记录的冰盖变化。2016年夏季，冰层完全丧失，导致风完全暴露，水柱完全混合。这种混合导致湖水热量排到大气中，并且水温比冰雪覆盖的情况低4°C。在整个秋季和冬季，Chl a荧光值也很高，浊度升高，氧气波动较大。在随后的夏季，湖保留了它的冰盖和水柱仍然分层，具有较低叶绿素一个荧光和缺氧的底水。极端变暖事件很可能使以前被连续厚冰覆盖的极地湖转变为不规则的冰流失和不稳定的气候条件，这种情况每年都在变化很大。