Reductions in ice cover duration and earlier ice breakup are two of the most prevalent responses to climate warming in lakes in recent decades. In dimictic lakes, the subsequent periods of spring mixing and summer stratification are both likely to change in response to these phenological changes in ice cover. Here, we used a modeling approach to simulate the effect of changes in latitude on long-term trends in duration of ice cover, spring mixing, and summer stratification by “moving” a well-studied lake across a range of latitudes in North America (35.2°N to 65.7°N). We found a changepoint relationship between the timing of ice breakup vs. spring mixing duration on 09 May. When ice breakup occurred before 09 May, which routinely occurred at latitudes < 47°N, spring mixing was longer and more variable; when ice breakup occurred after 09 May at latitudes > 47°N, spring mixing averaged 1 day with low variability. In contrast, the duration of summer stratification showed a relatively slower rate of increase when ice breakup occurred before 09 May (< 47°N) compared to a 109% faster rate of increase when ice breakup was after 09 May (> 47°N). Projected earlier ice breakup can result in important nonlinear changes in the relative duration of spring mixing and summer stratification, which can lead to mixing regime shifts that influence the severity of oxygen depletion differentially across latitudes.

中文翻译：

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较早的冰崩导致双相湖泊春季混合和夏季分层的持续时间和可变性的变化点响应

近几十年来，冰盖持续时间减少和冰层提前破裂是对湖泊气候变暖的两个最普遍的反应。在双相湖中，随后的春季混合和夏季分层都可能随着冰盖的这些物候变化而发生变化。在这里，我们使用一种建模方法来模拟纬度变化对冰盖持续时间、春季混合和夏季分层的长期趋势的影响，方法是在北美的一系列纬度上“移动”一个经过充分研究的湖泊。 35.2°N 至 65.7°N）。我们在 5 月 9 日发现了冰裂时间与春季混合持续时间之间的变化点关系。当冰裂发生在 5 月 9 日之前，通常发生在纬度 < 47°N 的地方，春季混合时间更长，变化更大；当 5 月 9 日之后在纬度 > 47°N 发生冰裂时，春季混合平均为 1 天，变异性较低。相比之下，在 5 月 9 日之前（< 47°N）发生冰裂时，夏季分层的持续时间显示出相对较慢的增长速度，而在 5 月 9 日之后（> 47°N）发生冰裂时，其增长速度加快了 109%。 . 预计较早的冰破裂可能导致春季混合和夏季分层的相对持续时间发生重要的非线性变化，这可能导致混合状态的变化，从而影响不同纬度的氧气消耗严重程度。47°N），而在 5 月 9 日（> 47°N）之后冰裂时，增加的速度加快了 109%。预计较早的冰破裂可能导致春季混合和夏季分层的相对持续时间发生重要的非线性变化，这可能导致混合状态的变化，从而影响不同纬度的氧气消耗严重程度。47°N），而在 5 月 9 日（> 47°N）之后冰裂时，增加的速度加快了 109%。预计较早的冰破裂可能导致春季混合和夏季分层的相对持续时间发生重要的非线性变化，这可能导致混合状态的变化，从而影响不同纬度的氧气消耗严重程度。