Clay minerals and the stability of organic carbon in suspension along coastal to offshore transects

IF 4.5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta Pub Date : 2025-03-08 DOI:10.1016/j.gca.2025.03.003

Michael Fettweis , Saumya Silori , Rieko Adriaens , Xavier Desmit

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引用次数: 0

Abstract

Particulate (POC) and dissolved organic carbon (DOC) concentration, clay mineral content and composition and the suspended particulate matter (SPM) concentration have been analyzed in water samples taken along transects from the high turbid nearshore to the low turbid offshore on the North Sea shelf. The suspended POC has been classified into a mineral-associated (POC_mineral), a slowly degrading (POC_slow) and a fresh fraction (POC_fresh). The POC_mineral has been estimated based on the clay mineral composition and on literature data of the mineral specific surface area per g and the OC content per specific surface area. It consists of organic molecules adsorbed onto mineral surfaces and is thereby the most refractory fraction. The POC_fresh content (% of POC_fresh in SPM) has been calculated using the semi-empirical POC-SPM model of Fettweis et al. (2022) and is intrinsically labile. The POC_slow content is refractory with variable rates of degradation. The total POC content of the SPM was between 2 and 11%, from which about 0.3–6.6% (0.1–2.1%) was POC_fresh in spring (resp., winter). The POC_mineral content was between 0.4% and 1.1% and decreased towards the offshore, meaning that the POC offshore is less refractory than nearshore. The organic molecules adsorbed onto clay minerals, are dynamically exchanging with the DOC, and thus influencing its fate and concentration. However this process is not sufficient to explain the increasing POC/DOC ratio with increasing SPM concentration, which is further explained by primary production, advection and diffusion, density gradients and seabed erosion. Our results highlight the difficulty and the necessity of estimating the respective sample-POC and DOC concentrations, fluxes and fates along SPM concentration gradients in coastal zones. This is needed as organo-mineral interactions influence the vertical dynamics and horizontal transport of SPM and have an impact on particles and organic carbon fluxes.

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黏土矿物与沿海至近海样带悬浮液中有机碳的稳定性

对北海大陆架从近岸高浑浊到近海低浑浊横断面水样中的颗粒物（POC）和溶解有机碳（DOC）浓度、粘土矿物含量和组成以及悬浮颗粒物（SPM）浓度进行了分析。悬浮的 POC 被分为矿物相关部分（POCmineral）、缓慢降解部分（POCslow）和新鲜部分（POCfresh）。POCmineral 是根据粘土矿物成分以及每克矿物比表面积和每比表面积 OC 含量的文献数据估算得出的。它由吸附在矿物表面的有机分子组成，因此是最难分解的部分。POCfresh 含量（POCfresh 在 SPM 中的百分比）是通过 Fettweis 等人（2022 年）的半经验 POC-SPM 模型计算得出的，具有内在易变性。POCslow 含量是难降解的，降解速度可变。SPM 的总 POC 含量介于 2% 和 11% 之间，其中约 0.3-6.6%（0.1-2.1%）为春季（或冬季）的新鲜 POC。POCmineral 含量在 0.4% 到 1.1% 之间，并向近海方向减少，这意味着近海的 POC 比近海的耐火度要低。吸附在粘土矿物上的有机分子与 DOC 进行动态交换，从而影响 DOC 的去向和浓度。然而，这一过程并不足以解释 POC/DOC 比率随 SPM 浓度增加而增加的现象，而初级生产、平流和扩散、密度梯度和海床侵蚀可进一步解释这一现象。我们的研究结果突出表明，沿岸带 SPM 浓度梯度估算样本-POC 和 DOC 各自的浓度、通量和归宿是困难的，也是必要的。由于有机-矿物相互作用会影响 SPM 的垂直动力学和水平迁移，并对微粒和有机碳通量产生影响，因此有必要进行这种估算。

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来源期刊

Geochimica et Cosmochimica Acta 地学-地球化学与地球物理

CiteScore

9.60

自引率

14.00%

发文量

437

审稿时长

6 months

期刊介绍： Geochimica et Cosmochimica Acta publishes research papers in a wide range of subjects in terrestrial geochemistry, meteoritics, and planetary geochemistry. The scope of the journal includes: 1). Physical chemistry of gases, aqueous solutions, glasses, and crystalline solids 2). Igneous and metamorphic petrology 3). Chemical processes in the atmosphere, hydrosphere, biosphere, and lithosphere of the Earth 4). Organic geochemistry 5). Isotope geochemistry 6). Meteoritics and meteorite impacts 7). Lunar science; and 8). Planetary geochemistry.