Experimental data on enhanced benthic weathering in organic rich Baltic Sea sediments

Enhanced mineral dissolution in the benthic environment is currently discussed as a potential technique for ocean alkalinity enhancement (OAE) to reduce atmospheric carbon dioxide (CO2) levels. This study explores how biogeochemical processes affect the dissolution of alkaline minerals in surface sediments during laboratory incubation experiments (January - May 2022). These involved introducing dunite and calcite to organic-rich sediments from the Baltic Sea under controlled conditions in an oxic environment. The sediment cores were incubated with Baltic Sea bottom water. Eight sediment cores were placed in a rack in an upright position. The bottom water was carefully removed via suction and replaced with a known volume (1.5 l – 2.0 l) of filtered (0.2 µm) Baltic Sea bottom water in order to remove pelagic auto- and heterotrophs and suspended particles. The volume of water added depended on the height of sediment in each core which varied slightly due to the recovery method. After this procedure, a gaseous headspace of ca. 10 cm was left in each core. Furthermore, the cores were equipped with adjustable stirring heads that contained ports for inserting optodes to continuously record pH and oxygen (O2) concentrations in the overlying water. In order to prevent anoxic conditions developing, ambient air was bubbled into the water column. The water column in each core was slowly and continuously flushed with a constant throughflow of 40 µl min-1 from a single reservoir of bottom water. The residence time of the water inside the cores was thus about 4 to 5 weeks. Bottom water samples were taken from the outflow of each core over a time period of several hours. Thus, samples represent the average outflow over the respective time period. Sampling intervals increased from daily during the first two weeks to every three to four days and weekly towards the end of the experiment. All samples were filtered through a 0.2 µm cellulose membrane filter and refrigerated in 25 ml ZinsserTM scintillation vials. A 5 ml aliquot was frozen directly after the sampling procedure for later nutrient analysis. Nutrient measurements were performed either via manual photometric measurement (NH4) or using a Seal – AnalyticalTM QuAAtro autoanalyzer (PO43-). Samples for total alkalinity (TA) were analyzed directly after sampling by titration of 1 ml of bottom/pore water with 0.02N HCl. Titration was ended when a stable purple color appeared. […]

底栖环境中的矿物强化溶解，目前被视为一种可用于海洋碱度增强（Ocean Alkalinity Enhancement, OAE）以降低大气二氧化碳（CO₂）水平的潜在技术。本研究针对2022年1月至5月开展的室内培养实验，探讨生物地球化学过程对表层沉积物中碱性矿物溶解过程的影响。实验在可控有氧环境下开展，将纯橄榄岩与方解石添加至取自波罗的海的富含有机质沉积物中。沉积物柱样采用波罗的海底层水进行培养：将8根沉积物柱样直立放置于样品架上，通过抽吸方式小心移除原有底层水，再注入已知体积（1.5 L~2.0 L）经过0.2 µm滤膜过滤的波罗的海底层水，以去除浮游自养生物、异养生物及悬浮颗粒物。注水量取决于每根柱样内的沉积物高度，而沉积物高度因采样回收方式存在小幅差异。完成上述步骤后，每根柱样顶部保留约10 cm的气体顶空空间。此外，柱样配备可调式搅拌头，搅拌头带有插孔，可插入光极探头以连续记录上覆水体的pH与氧气（O₂）浓度。为避免出现缺氧环境，向水柱中通入环境空气进行曝气。通过单一底层水储液罐，以40 µl·min⁻¹的恒定流速缓慢持续冲洗每根柱样内的水柱，因此柱样内水体的停留时间约为4至5周。从每根柱样的出水口采集底层水水样，采样时长为数小时，因此所采集的水样代表对应时段内的平均流出液。采样间隔从实验前两周的每日一次，逐步延长至每3至4天一次，实验末期改为每周一次。所有水样均通过0.2 µm纤维素膜滤器过滤后，置于25 ml Zinsser™闪烁瓶中冷藏保存。每份水样取5 ml子样品，在采样完成后立即冷冻保存，用于后续营养盐分析。营养盐测定采用两种方法：氨氮（NH₄⁺）采用手工光度法测定，正磷酸盐（PO₄³⁻）则采用Seal Analytical™ QuAAtro全自动化学分析仪进行检测。总碱度（Total Alkalinity, TA）水样在采集后立即进行分析：取1 ml底层/孔隙水样，用0.02N盐酸进行滴定，直至出现稳定的紫色时终止滴定。[…]