长江口−东海内陆架早期成岩过程及影响因素

Early diagenetic processes and influencing factors of the Changjiang River Estuary and East China Sea inner-shelf

边缘海沉积物中的早期成岩作用是影响碳循环和埋藏的重要过程,目前对早期成岩过程及其影响因素的了解还不够深入。于2018年8月在长江口-东海内陆架采集了短柱状沉积物,对间隙水中溶解无机碳(DIC)、溶解无机氮(DIN)、二价铁(Fe ^(2+))、二价锰(Mn^(2+))和硫酸根(SO_(4)^(2-))离子等参数进行了分析,并结合表层沉积物中粒度、比表面积、有机碳及稳定碳同位素组成和底层水环境参数,研究了不同沉积环境下沉积物中的早期成岩过程及其影响因素。结果表明,长江口-东海内陆架泥质区沉积物间隙水中DIC和NH_(4)^(+)的浓度随着深度的增加逐渐增大,且在其中心站位有较高的DIC、NH_(4)^(+)产生通量(分别为4.03 mmol/(m^(2)·d)和0.57 mmol/(m^(2)·d))和SO_(4)^(2-)消耗通量(-4.56 mmol/(m^(2)·d)),沉积物扰动深度为20~40 cm,自长江口向浙闽沿岸逐渐降低;而在砂质区,各溶质在剖面上均无明显变化,且通量较小(DIC:0.60 mmol/(m^(2)·d);NH_(4)^(+):-0.03 mmol/(m^(2)·d);SO_(4)^(2-):-1.05 mmol/(m^(2)·d)),沉积物不存在扰动。扰动层厚度与沉积物间隙水中DIC和NH_(4)^(+)等溶质通量呈正相关,表明沉积物的物理扰动是影响泥质区沉积有机碳再矿化的重要因素。综合上述结果,发现沉积有机碳在泥质区扰动层的降解方式以铁锰还原作用为主,扰动层以下以硫酸盐还原作用为主,而在砂质区的降解主要靠耗氧呼吸作用。本研究丰富了长江口及邻近海域沉积动力过程对早期成岩作用影响的认识,有助于深入理解大河河口及邻近海域有机碳的循环和埋藏。

Early diagenesis in marginal sea sediments is an important process that affects carbon cycling and burial.Early diagenetic processes and influencing factors,however,remains poorly constrained.Dissolved inorganic car-bon(DIC),dissolved inorganic nitrogen(DIN),Fe^(2+),Mn^(2+),sulfate and other parameters in sediment porewaters of five short cores collected in August 2018 from the Changjiang River Estuary and East China Sea inner-shelf were analyzed.In combination with grain size composition,specific surface area,organic carbon concentrations and stable carbon isotopic composition in surface sediments and bottom water parameters,the early diagenetic pro-cesses and influencing factors in sediments under different sedimentary regimes were studied.Concentrations of NH+4DIC and in sediment porewaters in the mud area gradually increase with depth,and relatively high production NH_(4)^(+)SO_(2)-4fluxes of DIC and(4.03 mmol/(m^(2)·d)and 0.57 mmol/(m^(2)·d),respectively)and consumption fluxes of(-4.56 mmol/(m^(2)·d))are observed at the center of the mud area,while in the sandy area,there are no obvious vari-ations of these solutes,and the fluxes are lower compared with those in muddy sediments.According to the vertical distributions of these solutes in the sediment porewaters,the sediment disturbance depth in the mud area varies at 20-40 cm,and gradually decreases from the Changjiang River Estuary mud area to the Zhe-Min coast mud area,whereas in the sandy area,no sediment disturbance is found.The thickness of sediment disturbed layer is positively NH+4correlated with solute fluxes(e.g.,DIC and)in sediment porewaters,indicating that the physical reworking of sediments is an important factor affecting the remineralization of sedimentary organic carbon in the mud area.In general,the main decomposition pathway of the sedimentary organic carbon in the disturbed layer of the mud area is iron/manganese reduction,and below the disturbed layer the main pathway is the sulfate reduction,while in the sandy area,the main degradation pathway is aerobic respiration.This study enriches the understanding of the im-pact of sedimentary dynamic processes on early diagenesis in the Changjiang River Estuary and adjacent sea areas,and contributes to better understand the cycling and burial of organic carbon in the large-river estuary and adjacent sea areas.