Ocean phytoplankton play a critical role in the global carbon cycle, contributing ∼50% of global photosynthesis. As planktonic organisms, phytoplankton encounter significant environmental variability as they are advected throughout the ocean. How this variability impacts phytoplankton growth rates and population dynamics remains unclear. Here, we systematically investigated the impact of different rates and magnitudes of sea surface temperature (SST) variability on phytoplankton community growth rates using surface drifter observations from the Southern Ocean (>30°S) and a phenotype-based ecosystem model. Short-term SST variability (<7 days) had a minimal impact on phytoplankton community growth rates. Moderate SST changes of 3–4°C over 7–45 days produced a large time lag between the temperature change and the biological response. The impact of SST variability on community growth rates was nonlinear and a function of the rate and magnitude of change. Additionally, the nature of variability generated in a Lagrangian reference frame (following trajectories of surface water parcels) was larger than that within an Eulerian reference frame (fixed point), which initiated different phytoplankton responses between the two reference frames. Finally, we found that these dynamics were not captured by the Eppley growth model commonly used in global biogeochemical models and resulted in an overestimation of community growth rates, particularly in dynamic, strong frontal regions of the Southern Ocean. This work demonstrates that the timescale for environmental selection (community replacement) is a critical factor in determining community composition and takes a first step towards including the impact of variability and biological response times into biogeochemical models.

中文翻译：

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拉格朗日海面温度变化对南大洋浮游植物群落增长率的影响

海洋浮游植物在全球碳循环中起着至关重要的作用，占全球光合作用的约 50%。作为浮游生物，浮游植物在整个海洋中平流时会遇到显着的环境变化。这种可变性如何影响浮游植物增长率和种群动态仍不清楚。在这里，我们使用来自南大洋 (>30°S) 的表面漂移观测和基于表型的生态系统模型系统地研究了海面温度 (SST) 变异的不同速率和幅度对浮游植物群落生长速率的影响。短期海温变化（<7 天）对浮游植物群落增长率的影响很小。7-45 天内 3-4°C 的适度海温变化在温度变化和生物反应之间产生了很大的时间滞后。SST 变化对社区增长率的影响是非线性的，是变化速度和幅度的函数。此外，拉格朗日参考系（遵循地表水块的轨迹）中产生的可变性的性质大于欧拉参考系（固定点）内的可变性，这在两个参考系之间引发了不同的浮游植物响应。最后，我们发现这些动态并没有被全球生物地球化学模型中常用的 Eppley 增长模型捕捉到，并导致对群落增长率的高估，特别是在南大洋的动态、强大的锋区。