Abstract Several cyclonic (CE) and anticyclonic (ACE) eddies form in the Bay of Bengal (BoB) and they expect to contain different proportion of nutrients due to divergence and convergence of waters respectively and may have impact on phytoplankton composition. In order to test this hypothesis, one CE and two ACE (north ACE (ACEN) and south ACE (ACES)) were sampled in the BoB during spring intermonsoon. Higher concentration of dissolved inorganic nitrate and lower dissolved inorganic phosphorus was observed in the upper 25 m of water column in the CE and contrasting to that was observed in the ACE regions. Silicate concentrations were above the limiting levels for diatoms growth in the study region. High dissolved organic nitrogen (DON) and phosphorus (DOP) were observed in the upper 10 m in the CE and 80 m in the ACEs. Due to lack of nitrate in the study region DON seems to support phytoplankton growth in the BoB. The phytoplankton groups were estimated using marker pigment composition and dominant groups were evaluated using pigment ratios. Occurrence of autotrophic dinoflagellates were observed only in the ACES, which was formed in the central eastern BoB. Premnesiophytes, chrysophytes were found only in ACEN which was formed in the northeastern shelf region. In addition to this, prochlorophytes and chlorophytes were also found in both ACEN and ACES. The concentration of fucoxanthin, marker pigment for diatoms, was low and confined to the subsurface waters in the CE and ACEN regions due to unavailability of nitrate and their inability to uptake DON. This study suggested that eddies bring different composition of phytoplankton from the region of their origin to the open sea resulting in variations in their diversity. This may have impact on food web dynamics in the BoB. More than 50 eddies form each year in the BoB and their impact on the taxonomic and size composition of phytoplankton and fluxes of carbon to depth needs further studies.

中文翻译：

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涡流对孟加拉湾浮游植物组成的影响

摘要 孟加拉湾 (BoB) 形成了多个气旋 (CE) 和反气旋 (ACE) 涡流，它们预计会因水域的发散和汇合而分别含有不同比例的营养物质，并可能对浮游植物的组成产生影响。为了验证这一假设，在春季季候风期间在 BoB 中采样了一个 CE 和两个 ACE（北 ACE (ACEN) 和南 ACE (ACES)）。在 CE 的上部 25 m 水柱中观察到较高浓度的溶解无机硝酸盐和较低的溶解无机磷，与在 ACE 区域观察到的情况相反。硅酸盐浓度高于研究区域硅藻生长的极限水平。在 CE 的上部 10 m 和 ACE 的 80 m 处观察到高溶解有机氮 (DON) 和磷 (DOP)。由于研究区域缺乏硝酸盐，DON 似乎支持 BoB 中浮游植物的生长。浮游植物群使用标记色素组成进行估计，优势群使用色素比率进行评估。仅在 ACES 中观察到自养鞭毛藻的发生，其形成于 BoB 中东部。Premnesiophytes, chrysophytes 仅在形成于东北陆架区的 ACEN 中发现。除此之外，在 ACEN 和 ACES 中也发现了原叶绿素和叶绿素。由于无法获得硝酸盐且无法吸收 DON，岩藻黄质（硅藻的标记色素）的浓度很低，并且仅限于 CE 和 ACEN 地区的地下水。这项研究表明，涡流将不同的浮游植物组成从它们的起源地区带到公海，导致它们的多样性发生变化。这可能会对 BoB 中的食物网动态产生影响。每年在 BoB 中形成 50 多个涡流，它们对浮游植物的分类和大小组成以及碳向深度的通量的影响需要进一步研究。