Data_Sheet_1_Alkaline mineral addition to anoxic to hypoxic Baltic Sea sediments as a potentially efficient CO2-removal technique.pdf

Recent studies have begun to explore the potential of enhanced benthic weathering (EBW) in the Baltic Sea as a measure for climate change mitigation. To augment the understanding of EBW under seasonally changing conditions, this study aims to investigate weathering processes under anoxia to hypoxia in corrosive bottom waters, which reflect late summer conditions in the Baltic Sea. Dunite and calcite were added to sediment cores retrieved from Eckernförde Bay (Western Baltic Sea) with a constant flow-through of deoxygenated, CO2-enriched Baltic Sea bottom water. The addition of both materials increased benthic alkalinity release by 2.94 μmol cm−2 d−1 (calcite) and 1.12 μmol cm−2 d−1 (dunite), compared to the unamended control experiment. These excess fluxes are significantly higher than those obtained under winter conditions. The comparison with bottom water oxygen concentrations emphasizes that highest fluxes of alkalinity were associated with anoxic phases of the experiment. An increase in Ca and Si fluxes showed that the enhanced alkalinity fluxes could be attributed to calcite and dunite weathering. First order rate constants calculated based on these data were close to rates published in previous studies conducted under different conditions. This highlights the suitability of these proxies for mineral dissolution and justifies the use of these rate constants in modeling studies investigating EBW in the Baltic Sea and areas with similar chemical conditions. Generally stable pH profiles over the course of the experiment, together with the fact that the added minerals remained on the sediment surface, suggest that corrosive bottom waters were the main driving factor for the dissolution of the added minerals. These factors have important implications for the choice of mineral and timing for EBW as a possible marine carbon dioxide removal method in seasonally hypoxic to anoxic regions of the Baltic Sea.

近期已有研究开始探索波罗的海强化底栖风化（enhanced benthic weathering, EBW）作为气候变化减缓手段的潜力。为加深对季节变化条件下EBW的认知，本研究旨在探究腐蚀性底层水体中从缺氧到低氧环境下的风化过程，该环境对应波罗的海夏末的水文条件。研究人员将纯橄榄岩与方解石添加至从埃克恩弗尔德湾（波罗的海西部）采集的沉积岩芯中，并以恒定流速通入脱氧且富二氧化碳的波罗的海底层水体。与未添加矿物的对照实验相比，两种矿物的添加分别使底栖碱度释放量提升了2.94 μmol·cm⁻²·d⁻¹（方解石组）与1.12 μmol·cm⁻²·d⁻¹（纯橄榄岩组）。该超额通量显著高于冬季条件下测得的通量值。与底层水体氧浓度的对比分析表明，碱度通量峰值出现在实验的缺氧阶段。钙与硅通量的升高表明，碱度通量的提升可归因于方解石与纯橄榄岩的风化作用。基于本实验数据计算得到的一级反应速率常数，与此前不同条件下相关研究报道的速率值较为接近。这证实了这些通量作为矿物溶解替代指标的适用性，同时证明了在波罗的海及其他化学条件相似区域开展EBW相关模拟研究时，可采用本次得到的速率常数。实验过程中pH剖面整体保持稳定，且添加的矿物始终留存于沉积物表面，上述结果表明腐蚀性底层水体是驱动添加矿物溶解的主要因素。上述结论对于将EBW作为波罗的海季节低氧-缺氧海域的海洋二氧化碳移除手段时，矿物种类与施用时机的选择具有重要指导意义。