Marine picophytoplankton are abundant in many oligotrophic oceans, but the known geographical patterns of picophytoplankton are primarily based on small-scale cruises or timeseries observations. Here, we conducted a wider survey (5 cruises) in the Bay of Bengal (BOB), South China Sea (SCS) and Western Pacific Ocean (WPO) to better understand the biogeographic variations of picophytoplankton. Prochlorococcus (Pro) were the most abundant picophytoplankton (averaging [1.9−3.6] × 104 cells ml−1) across the 3 seas, while average abundances of Synechococcus (Syn) and picoeukaryotes (PEuks) were generally 1−2 orders of magnitude lower than Pro. Average abundances of total picophytoplankton were similar between the BOB and SCS (4.7 × 104 cells ml−1), but were close to 2-fold less abundant in the WPO (2.5 × 104 cells ml−1). Pro and Syn accounted for a substantial fraction of total picophytoplankton biomass (70−83%) in the 3 contrasting seas, indicating the ecological importance of Pro and Syn as primary producers. Pro were generally abundant in oligotrophic open waters; however, the exceptional presence of Pro near the SCS coast was potentially associated with the Kuroshio intrusion. Syn and PEuk abundances were higher near freshwater-dominated areas, which was likely due to dilution waters. Water temperature and cold eddies were also major drivers responsible for the biogeographic distributions of picophytoplankton. Although Pro, Syn and PEuks showed negative correlations with nutrient concentrations, their maximal abundances in vertical distribution showed positive correlations with the nutricline depth, indicating that nutrient availability plays a 2-faceted role in regulating the biogeographic variation in picophytoplankton.

中文翻译：

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三个对比鲜明的海洋中微型浮游植物的生物地理变化：孟加拉湾、南海和西太平洋

海洋微型浮游植物在许多贫营养海洋中非常丰富，但已知的微型浮游植物地理模式主要基于小规模航行或时间序列观测。在这里，我们在孟加拉湾 (BOB)、南海 (SCS) 和西太平洋 (WPO) 进行了更广泛的调查（5 次航行），以更好地了解微型浮游植物的生物地理变化。原绿球藻 (Pro) 是 3 大洋中最丰富的微型浮游植物（平均 [1.9−3.6] × 104 个细胞 ml−1），而聚球藻 (Syn) 和微型核生物 (PEuks) 的平均丰度通常低 1−2 个数量级比亲。BOB 和 SCS 之间的总微型浮游植物的平均丰度相似（4.7 × 104 个细胞 ml-1），但在 WPO 中的丰度接近 2 倍（2.5 × 104 个细胞 ml-1）。Pro 和 Syn 在 3 个对比鲜明的海洋中占总微型浮游植物生物量 (70-83%) 的很大一部分，表明 Pro 和 Syn 作为初级生产者的生态重要性。Pro 在贫营养开放水域中普遍丰富；然而，南海沿岸附近 Pro 的特殊存在可能与黑潮入侵有关。Syn 和 PEuk 丰度在以淡水为主的地区附近较高，这可能是由于稀释水所致。水温和冷涡流也是导致微型浮游植物生物地理分布的主要驱动因素。尽管 Pro、Syn 和 PEuks 与养分浓度呈负相关，但它们在垂直分布上的最大丰度与营养线深度呈正相关，