Abstract In order to examine the role of eddies on total and size-fractionated primary production, two cyclonic (CE), one anticyclonic (ACE) and no-eddy (NE) regions were sampled in the BoB during pre-summer monsoon (June 2019). The upper ocean is strongly stratified due to freshwater discharge from major rivers. Low (high) nutrients concentrations were noticed in the ACE (CE) regions due to convergence (divergence). Prominent existence of deep Chlorophyll-a maximum (DCM) was observed and its depth is governed by mixing associated with eddies. High concentration of zeaxanthin and fucoxanthin was observed in the upper 50 m and DCM respectively. The dominant contribution of picoplankton biomass (40–80%) to total phytoplankton biomass was observed in the photic zone whereas micro and nanoplankton contributed between 10 and 30%. The photic zone integrated total primary production was higher in the CE and NE than ACE regions associating with higher nutrients in the former than latter region. The primary production by microphytoplankton was higher in the CE and NE than ACE regions. Higher picophytoplankton production was observed at depth below 10 m from surface (10–80%) than nano and microphytoplankton (1–30%). The microphytoplankton production was higher in the CE (164 ± 16 mgC m−2 d−1) than ACE (60 ± 26 mgC m−2 d−1) due to availability of nutrients in the former region resulted from upwelling of subsurface waters. The photic zone integrated total and microphytoplankton primary production displayed linear relation with nutrients (nitrate and phosphate) and inverse relation was observed with picophytoplankton suggesting that the availability of nutrients due to eddy-driven mixing determined the contribution of primary production by different size classes. This study suggests that eddy-driven nutrients increased contribution of primary production by microphytoplankton leading to enhanced export production under CE in the BoB and therefore, these regions can be considered as an efficient regions of carbon sequestration for the atmospheric CO2. More than 30 eddies form every year with life time of 3–6 months and its impact on sinking carbon fluxes and atmospheric CO2 sequestration in the BoB needs evaluation using numerical modelling.

中文翻译：

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涡流在控制孟加拉湾总初级生产和分级初级生产中的作用

摘要 为了检验涡流对总初级生产和分级初级生产的作用，在夏前季风期间（2019 年 6 月）在 BoB 中采样了两个气旋 (CE)、一个反气旋 (ACE) 和无涡 (NE) 区域。 ）。由于主要河流的淡水排放，上层海洋具有强烈分层。由于收敛（发散），在 ACE (CE) 区域注意到低（高）营养物质浓度。观察到深叶绿素 a 最大值 (DCM) 的突出存在，其深度由与涡流相关的混合控制。分别在上部 50 m 和 DCM 中观察到高浓度的玉米黄质和岩藻黄质。在透光区观察到微型浮游生物生物量（40-80%）对总浮游植物生物量的主要贡献，而微型和纳米浮游生物贡献了 10% 到 30%。CE 和 NE 的透光区综合总初级产量高于 ACE 区域，与前者的养分高于后者的区域相关。CE 和 NE 的微型浮游植物初级产量高于 ACE 地区。在距地表 10 m 以下深度观察到的微型浮游植物产量 (10-80%) 高于纳米和微型浮游植物 (1-30%)。CE (164 ± 16 mgC m-2 d-1) 的微型浮游植物产量高于 ACE (60 ± 26 mgC m-2 d-1)，这是由于前一个区域的营养物质的可用性是由地下水上升造成的。综合浮游植物总产量和微型浮游植物初级生产的光带显示出与养分（硝酸盐和磷酸盐）的线性关系，而在微型浮游植物中观察到反比关系，表明由于涡流驱动的混合，养分的可用性决定了不同大小等级初级生产的贡献。这项研究表明，涡流驱动的养分增加了浮游微型植物对初级生产的贡献，导致 BoB 在 CE 下的出口产量增加，因此，这些区域可以被认为是大气 CO2 固碳的有效区域。每年形成 30 多个涡流，寿命为 3-6 个月，其对 BoB 中下沉碳通量和大气 CO2 封存的影响需要使用数值模型进行评估。