A flow cytometric analysis of picoplankton (Prochlorococcus (Pro), Synechococcus (Syn), picoeukaryotes (Peuk) and heterotrophic bacteria (Hbac) was performed along a meridional transect (88°E, 10°S – 4°N) in the eastern equatorial Indian Ocean (EEIO) during the boreal fall intermonsoon period. The transect spanned contrasting physical and chemical conditions, allowing investigation of the effects of environmental gradients on picoplankton distributions. Hbac accounted for more than 80% of the total picoplankton abundance. Among picophytoplankton, Pro was numerically dominant, with abundances at least one order of magnitude greater than those of Syn and Peuk. Vertically, Pro was mainly distributed in the upper mixed layer while the subsurface Peuk abundance maxima usually coincided with the subsurface chlorophyll a maxima. Physical processes controlled the picoplankton distribution patterns. The maximum prokaryotic picoplankton (Pro, Syn and Hbac) abundances occurred at the center of a cyclonic eddy at 2°N. The depth-integrated picoplankton abundances increased northwards along the transect and were inversely related to the stratification strength. This gradient probably resulted from a combination of physical processes, such as the intrusions of the Bay of Bengal runoff and Indonesia throughflow, advection by the Wyrtki jets and strong stratification south of the equator. This study highlighted the dynamic response of picoplankton to complex physico-chemical conditions in the EEIO.

流式细胞仪分析微微浮游生物（Prochlorococcus（Pro），Synechococcus）（Syn），皮真核生物（Peuk）和异养细菌（Hbac）在北半球秋季季风期间沿赤道东印度洋（EEIO）的子午线（88°E，10°S – 4°N）进行。该横断面跨越了相反的物理和化学条件，可以研究环境梯度对微微浮游生物分布的影响。Hbac占浮游生物总丰度的80％以上。在浮游植物中，Pro在数量上占主导地位，其丰度比Syn和Peuk的丰度至少高一个数量级。在垂直方向上，Pro主要分布在上部混合层中，而地下Peuk丰度最大值通常与地下叶绿素a重合。最大值。物理过程控制了微微浮游生物的分布模式。最大的原核微微浮游生物（Pro，Syn和Hbac）丰度出现在2°N的旋风涡旋中心。深度整合的微微浮游生物的丰度沿着该断面向北增加，并且与分层强度成反比。这种梯度可能是由于物理过程的结合而产生的，例如孟加拉湾径流的入侵和印度尼西亚的通流，Wyrtki射流的平流作用以及赤道以南的强烈分层。这项研究强调了微型浮游生物对EEIO中复杂的物理化学条件的动态响应。