Pore-water chemistry of ODP Leg 114 holes

Pore-water samples were recovered at five sites from ODP Leg 114 in the subantarctic South Atlantic Ocean and analyzed for pH, alkalinity, chloride, sulfate, fluoride, silica, magnesium, calcium, strontium, potassium, lithium, and barium. At sites in the East Georgia Basin and on the Islas Orcadas Rise, Ca increases and Mg decreases linearly downhole with a DeltaMg/DeltaCa ratio reflecting conservative diffusive exchange and basalt basement reactions. At sites on the west flank of the Mid-Atlantic Ridge and on the Meteor Rise, Ca gradients are nonlinear, and nonconservative DeltaMg/DeltaCa ratios reflect alteration reactions of abundant silicic volcanic ash in the sediment. K decreases linearly downhole at all sites, reflecting uptake by basement and the absence of significant sediment-hosted reactions. SO4 decreases and alkalinity increases downhole are due to a slight sulfate reduction at all sites except at Site 701. Sr increases downhole at all sites except Site 701, with DeltaSr/DeltaCa ratios reflecting diffusive exchange with basement. At Site 704 on the Meteor Rise, there is intense Sr production during carbonate recrystallization in the upper 200 mbsf. Below 200 mbsf at Site 704, the ion concentration product of SrSO4 is constant, suggesting Sr control by celestite solubility. Li and F concentrations display complex behavior related to sedimentary reactions, probably calcite recrystallization (Li uptake and F release).

研究采集了南大西洋亚极地海域大洋钻探计划（Ocean Drilling Program, ODP）第114航次5个站位的孔隙水样品，并对其pH、碱度、氯离子、硫酸根、氟离子、二氧化硅、镁、钙、锶、钾、锂及钡的含量进行了分析。在东乔治亚盆地与奥克达斯群岛海隆站位，钙浓度随钻孔深度线性升高、镁浓度线性降低，其ΔMg/ΔCa比值反映了保守扩散交换与玄武岩基底反应过程。在大西洋中脊西翼与流星海隆站位，钙浓度梯度呈非线性特征，非保守的ΔMg/ΔCa比值则反映了沉积物中大量硅质火山灰的蚀变反应。所有站位的钾浓度均随钻孔深度线性降低，这反映了基底对钾的吸收作用，且未发生显著的沉积物赋存反应。除701站位外，所有站位的硫酸根浓度随钻孔深度降低、碱度升高，这源于各站位发生的轻微硫酸盐还原作用。除701站位外，所有站位的锶浓度随钻孔深度升高，其ΔSr/ΔCa比值反映了与基底之间的扩散交换过程。在流星海隆的704站位，海底以下0~200米（meters below seafloor, mbsf）范围内，碳酸盐重结晶过程伴随强烈的锶生成作用。704站位200米以深海域，SrSO4的离子浓度积保持恒定，表明锶的浓度受天青石溶解度调控。锂与氟的浓度变化呈现复杂特征，与沉积反应密切相关，推测为方解石重结晶过程（锂被吸收、氟被释放）所致。