Phytoplankton play a major role on Earth, impacting the global distribution and cycles of carbon, oxygen, nitrogen, sulfur, and other elements, and structuring marine food webs. One fundamental trait of phytoplankton with direct biogeochemical implications is their size, as it governs metabolic and sinking rates as well as prey–predator interactions. Phytoplankton size spans approximately 3.5 orders of magnitude (when expressed as an equivalent spherical diameter), and thus measuring the full range in size distribution of phytoplankton is challenging and rarely attempted. Here, we constructed phytoplankton size spectra by merging state-of-the-art cytometry and imaging cytometry measurements that were collected in the western North Atlantic Ocean, along a latitudinal gradient (36°N to 55°N) and during different phases of the annual cycle of phytoplankton. The derived spectra show a seasonal pattern that parallels changes in phytoplankton biomass, and do not always follow a commonly assumed power-law model. Shifts in size spectra were more pronounced in the sub-Arctic and temperate subregions, compared to the subtropical region of the study area. We evaluated the relationships between different size groups and environmental parameters to derive ecologically meaningful size groups. Finally, to simulate Ocean Color remote-sensing algorithms of phytoplankton size, we compared temporal variations in descriptors of the size spectra (median particle size, phytoplankton size distribution exponent) with optical size proxies derived from light absorption and attenuation; good agreement was observed in the northern sections of the study area where temporal changes in community size structure were more pronounced.

中文翻译：

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北大西洋西部的浮游植物大小分布及其季节变化

浮游植物在地球上发挥着重要作用，影响碳、氧、氮、硫和其他元素的全球分布和循环，并构建海洋食物网。具有直接生物地球化学意义的浮游植物的一个基本特征是它们的大小，因为它控制着代谢和下沉速率以及猎物 - 捕食者的相互作用。浮游植物的大小跨越大约 3.5 个数量级（当以等效球直径表示时），因此测量浮游植物大小分布的全范围具有挑战性且很少尝试。在这里，我们通过合并在北大西洋西部收集的最先进的细胞术和成像细胞术测量结果构建了浮游植物大小光谱，沿纬度梯度（36°N 至 55°N）和浮游植物年度循环的不同阶段。派生的光谱显示出与浮游植物生物量变化平行的季节性模式，并不总是遵循通常假设的幂律模型。与研究区的亚热带地区相比，亚北极和温带亚地区的尺寸光谱变化更为明显。我们评估了不同大小组和环境参数之间的关系，以得出具有生态意义的大小组。最后，为了模拟浮游植物大小的 Ocean Color 遥感算法，我们将大小光谱描述符（中值粒度、浮游植物大小分布指数）的时间变化与源自光吸收和衰减的光学大小代理进行了比较；