Decoupling of Pore Water Chemistry, Bacterial Community Profiles, and Carbonate Mud Diagenesis in a Land-Locked Pool on Aldabra (Seychelles, Indian Ocean)

Comparative pore water-sediment studies are crucial to trace biogeochemical and early diagenetic interactions between mineral and fluid phases. They are commonly conducted in stable environments with long-time diagenetic reactions between sediment and pore water. In contrast, this work presents a comparative study within the Cinq Cases pool system, a shallow and saline water body, with occasional marine influx and short-time diagenetic reactions between sediment and pore water. Cinq Cases is located on the Aldabra atoll in the western Indian Ocean. Sediments span ca. 3800 years and indicate three environmental stages: (i) An initial, at least temporary anoxic, palustrine environment, including meteoric diagenesis (Unit III), (ii) slow marine flooding, with cyanobacteria and sponge blooms (Unit II), and (iii) lagoon flooding, including oxic conditions within the sediment (Unit I). Such frequent changes in diagenetic environments of small water bodies can be retraced by three different proxies representing partially overlapping but different time scales: (i) sediments reflect ancient processes (ii) pore waters are influenced by recent processes, and (iii) bacterial communities reflect an overlay of ancient and recent processes.

孔隙水-沉积物（pore water-sediment）对比研究是示踪矿物相与流体相之间生物地球化学（biogeochemical）与早期成岩作用（early diagenesis）相互作用的关键手段。此类研究多在沉积物（sediment）与孔隙水（pore water）成岩反应持续时间较长的稳定环境中开展。与之不同，本研究针对辛克卡斯池系统（Cinq Cases pool system）展开对比研究——该系统为浅咸水水体，沉积物与孔隙水之间的成岩反应历时较短，且存在偶发的海水注入事件。辛克卡斯池位于印度洋西部的阿尔达布拉环礁（Aldabra atoll）。沉积物沉积年代跨度约3800年，记录了三个环境演化阶段：（1）初始阶段：至少为暂时性缺氧的淡水沼泽（palustrine）环境，伴随大气成岩作用（meteoric diagenesis，第三单元）；（2）缓慢海侵阶段：蓝细菌（cyanobacteria）与海绵繁盛（sponge blooms，第二单元）；（3）泻湖淹没阶段：沉积物内部处于氧化环境（第一单元）。小型水体成岩环境的这类频繁变化，可通过三类代用指标（proxy）进行追溯——这三类指标覆盖的时间尺度部分重叠但各有侧重：（1）沉积物记录古环境过程；（2）孔隙水受现代过程影响；（3）细菌群落（bacterial communities）则同时反映古环境与现代过程的叠加效应。