The biological pump (BP) in oceans refers to the fraction of phytoplankton organic matter sinking out of the euphotic zone (surface layer) into below the pycnocline layer (bottom layer) in the water column. Currently, sediment traps are commonly used to estimate organic settlement and carbon sequestration in open oceans, but the installation of the sediment traps in the ocean requires special efforts, let alone the temporal and spatial discordance of particle sinking trajectory from the surface to the bottom. Net community production is used only for the euphotic zone. Thus, there has been a lack of a simple method to estimate the export flux of organic carbon from the surface to bottom layer and to quantify BP efficiency in the coastal areas. In this study, we develop a conceptual model to illustrate carbon sequestration processes from the surface to the pycnocline layer and the bottom layer. The idea is to examine an increase (the release) in dissolved inorganic carbon (DIC) and organic carbon (DOC) in the bottom layer. Based on this model, a new method was developed to estimate carbon sequestration (CS) and carbon sequestration efficiency (CSE). Two cruises in May and August in 2016 were conducted to establish a three-end-member mixing model of θ-S which is used to estimate biologically mediated DIC (ΔDIC = DIC-DIC) in relation to the conservative mixing of DIC. Based on the density gradient threshold of 0.03 kg mm, the water column is separated into the surface mixed layer, the pycnocline layer and bottom layer and integrated ΔDIC (IntΔDIC) in the three layers are estimated. The same approach is applied to dissolved organic carbon (DOC) data which are used to make the same calculation with the mixing model to obtain the sequestrated DOC mass in the bottom layer. Carbon uptake and carbon sequestration (CS) can be calculated as the integrated ΔDIC in the surface mixed layer and bottom layers, respectively. Carbon sequestration efficiency (CSE), which is defined as sum of bottom layer Int ΔDIC + Int ΔDOC divided by the whole water column integrated ΔDIC can also be calculated. The results showed that during algal blooms driven by abundant nutrients from the Pearl River Estuarine water in May, little sinking carbon was observed due to the absence of the bottom layer, resulting in low CSE. In contrast, in August, even no significant algal bloom occurred, the strengthened water stratification, lead to a substantial increase in the CS(449.49 ± 366.14 mmol C m), leading to an increased CSE to a range of 0 ∼ 92.79 % (average 60.55 ± 25.07 %). The carbon sequestration rate was 55.61 ± 45.30 mg C m d. The new method, based on vertical changes of DIC and DOC due to biological uptake or release in relation to the conservative mixing of water masses, provides an easy and direct tool to estimate carbon sequestration and carbon sequestration efficiency in the stratified water column in coastal waters.

中文翻译：

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估算沿海水域碳汇及其效率的新方法


海洋中的生物泵（BP）是指浮游植物有机物从富光带（表层）沉入水体密斜层（底层）以下的部分。目前，沉积物捕集器通常用于估算公海的有机沉降和碳封存，但在海洋中安装沉积物捕集器需要特殊的努力，更不用说颗粒从表面到底部的下沉轨迹的时空不一致。净群落生产仅用于亮光带。因此，一直缺乏一种简单的方法来估计有机碳从地表到底层的输出通量并量化沿海地区的BP效率。在本研究中，我们开发了一个概念模型来说明从表面到密斜层和底层的碳封存过程。这个想法是检查底层溶解的无机碳（DIC）和有机碳（DOC）的增加（释放）。基于该模型，开发了一种估算碳封存（CS）和碳封存效率（CSE）的新方法。 2016年5月和8月的两次航行旨在建立θ-S的三端元混合模型，用于估计与DIC保守混合相关的生物介导的DIC（ΔDIC = DIC-DIC）。基于0.03 kg·mm的密度梯度阈值，将水柱分为表层混合层、密斜层和底层，并估算三层的积分ΔDIC（IntΔDIC）。同样的方法也适用于溶解有机碳（DOC）数据，这些数据用于与混合模型进行相同的计算，以获得底层中封存的 DOC 质量。 碳吸收和碳封存（CS）可以分别计算为表面混合层和底层的积分ΔDIC。碳封存效率（CSE）定义为底层Int ΔDIC + Int ΔDOC之和除以整个水体积分ΔDIC。结果表明，5月份珠江口水体在丰富的营养物质驱动下藻华爆发期间，由于缺乏底层，下沉碳很少，导致CSE较低。相比之下，8月份，即使没有发生明显的藻华，水层化的加强，导致CS（449.49±366.14 mmol C m）大幅增加，导致CSE增加到0 ∼ 92.79 %（平均）范围。 60.55±25.07%）。固碳率为55.61±45.30 mg C·m·d。该新方法基于与水团保守混合有关的生物吸收或释放引起的DIC和DOC的垂直变化，为估算沿海水域分层水体的碳封存和碳封存效率提供了一种简单直接的工具。