This study examines the relationship between the isotopic signature of phytoplankton-derived particulate organic matter (POM) (δ¹³C_POC) and estimates of growth rate and community composition along a north-south gradient in the western Indian shelf waters which possess contrasting biogeochemistry and mixed layers depths. The Eastern Arabian Sea/western Indian shelf turns highly productive due to the SW monsoon induced upwelling at its southern region and experiences drastic seasonal reversal. We have characterized the POM pool by quantifying Chla, particulate organic carbon (POC) and particulate nitrogen (PN), C:N ratios, along with δ¹³C_POC values during the SW Monsoon. The prevailing physicochemical features contrasted between the southern (8°N to 12°N) and northern (13°N to 21°N) stations. Close couplings between POC, PN, and Chla contents indicated the autochthonous nature of POM. Low temperature, shallow mixed layer depths (MLDs), high concentrations of nutrients, POM, and Chla, marked the upwelling signature in the south. Conversely, relatively higher temperatures, salinity, deeper mixed layers (MLs), lower concentrations of nutrients, POM, and Chla were evident at the northern stations. Five times higher POC concentrations were noticed in the south (65.5 ± 22.0 μmol L⁻¹) than in the north (12.8± 5.4 μmol L⁻¹) within the MLs. Phytoplankton community shift (based on marker pigment analysis) and the δ¹³C_POC values were closely coupled. The nutrient replete microphytoplankton (diatoms) dominated southern stations were associated with higher values of δ¹³C_POC (−23.0 ± 2.3‰) which was attributed to faster growth rate_; conversely, the oligotrophic nitrogen-limited waters in the north dominated by pico and nanophytoplankton (haptophytes and cyanobacteria), were characterized by distinctly lower δ¹³C_POC values (−26.6 ± 0.9‰). Phytoplankton growth rates based on a model were consistent with this trend. Our results show that the autochthonous POC is the primary source of organic matter, and the contrasted biogeochemistry induced phytoplankton communities and their growth rates mostly governed the δ¹³C_POC variability in this region. However, the lower values in the subsurface waters at the south were likely to be influenced by light limitation and heterotrophy.

本研究探讨的浮游植物衍生的颗粒有机物同位素特征之间的关系（POM）（δ ¹³ C ^ _POC ），并且具备对比的生物地球化学在印度西部架子水域生长速度和群落组成沿南北梯度的估计和混合层深度。由于西南季风在其南部地区引起的上升流，阿拉伯东部海域/印度西部的陆架变成了高产，并经历了剧烈的季节性逆转。通过量化叶绿素我们已经表征了POM池一个，颗粒有机碳（POC）和颗粒氮（PN），C：N比，随着δ ¹³ C ^ _POC西南季风期间的数值。南部（8°N至12°N）和北部（13°N至21°N）站点的主要物理化学特征形成了鲜明对比。POC，PN，和叶绿素之间的紧密耦合一个内容指示POM的原地性质。低温，浅混合层深度（MLDS），高浓度的营养物质，POM，和叶绿素A，标记在南部的上升流的签名。相反地，相对较高的温度，盐度，更深的混合层（MLS），较低浓度的营养物，聚甲醛，和叶绿素一个在北部站是显而易见的。五倍POC浓度注意到在南部（65.5±22.0微摩尔大号^-1）比北方（12.8±5.4微摩尔大号^-1）内。浮游植物群落移（基于标记色素分析）和δ ¹³ Ç _POC值紧密耦合。所述营养物充分microphytoplankton（硅藻）为主南部站用δ值较高相关联¹³ Ç _POC这归因于更快的生长速率（-23.0±2.3‰）_; 相反地，在北方的贫营养氮限制水域由微微和浮游植物（定鞭藻类和蓝藻）为主，进行表征明显较低δ ¹³ C ^ _POC值（−26.6±0.9‰）。基于模型的浮游植物生长速率与此趋势一致。我们的研究结果表明，原地POC是有机物的主要来源，而对比生物地球化学引起浮游植物群落及其增长率大多是管辖δ ¹³ C ^ _POC在这一地区的变化。但是，南部的地下水域的较低值很可能受到光限制和异养菌的影响。