X-ray diffraction (XRD) raw data and Rietveld refinement results for precipitates from shipboard ocean alkalinity enhancement (OAE) experiments in the North Atlantic on R/V Atlantic Explorer cruise AE2320 in September 2023

To explore mineral formation due to alkalinity addition, we present results from shipboard experiments in which an aqueous solution of NaOH was added to unfiltered seawater collected from the surface ocean in the Sargasso Sea. Alkalinity addition ranged from 500 to 2000 micromoles per kilogram (µmol/kg) and the carbonate chemistry was monitored through time by measuring total alkalinity (TA) and dissolved inorganic carbon (DIC), which were used to calculate Ω. The amount of precipitate and its minerology were determined throughout the experiments. Mineral precipitation took place in all experiments over a timescale of hours to days. The dominant mineralogy of precipitate is aragonite with trace amounts of calcite and brucite. Aragonite crystallite size increases and its micro-strain decreases with time, consistent with Ostwald ripening. This dataset contains raw XRD data as well as XRD results (mineral abundances, crystallite size, strain, and unit cell parameters) determined via Rietveld refinement. The seawater for the experiments was collected near the Bermuda Atlantic Time Series (31.6667 N, 64.1667 W), which is also the same location where the experiments were conducted and filtered to obtain the precipitates, which were analyzed with XRD.为探究碱度添加诱导的矿物形成机制，本研究报道了一组船基实验的结果。实验中将氢氧化钠水溶液添加至从马尾藻海（Sargasso Sea）表层海域采集的未过滤海水中。实验设置的碱度添加量范围为500至2000微摩尔每千克（µmol/kg），通过测定总碱度（total alkalinity, TA）与溶解无机碳（dissolved inorganic carbon, DIC）实时追踪碳酸盐化学体系的动态演化，并基于这两项参数计算得到饱和指数Ω。实验全程对沉淀生成量及其矿物学特征进行了系统测定。所有实验均在数小时至数天的时间尺度内观测到矿物沉淀现象。沉淀的主要矿物相为文石（aragonite），伴生微量方解石（calcite）与水镁石（brucite）。随反应时间延长，文石的晶粒尺寸逐渐增大，微观应变则逐步降低，这一演化规律符合奥斯特瓦尔德熟化（Ostwald ripening）机制。本数据集包含原始X射线衍射（X-ray diffraction, XRD）数据，以及通过里特维尔德精修（Rietveld refinement）得到的XRD分析结果，具体包括矿物相丰度、晶粒尺寸、微观应变与晶胞参数。实验所用海水采集于百慕大大西洋时间序列观测站（Bermuda Atlantic Time Series, BATS）附近海域（31.6667°N, 64.1667°W），实验场地与海水采样点一致；实验过程中通过过滤采集的未过滤海水获得沉淀，随后采用X射线衍射（XRD）对沉淀进行了矿物学表征。