We have developed a density-based method for determining porewater salinity that can be performed shipboard on small volume samples with greater efficiency and precision than the currently available shore-based chloride titration technique. This approach is based on a recently developed water column method that determines salinity at the precision of a conductivity measurement through density measurements and the seawater thermodynamic equation of state. Diagenesis causes deviations in porewater composition from standard seawater values, affecting the density salinity relationship, that we correct for through precise measurements of each ion's concentration before converting measured density to chloride concentration. We account for the diffusive change in porewater chloride that occurs over time independent of diagenesis by optimizing diffusion modeled, sea-level determined bottom water chloride as a function of time to measured modern porewater and converting the best fit to salinity.

We applied our density method to porewater samples extracted from adjacent long cores collected from the deep western North Atlantic, determining Last Glacial Maximum (LGM) bottom water paleosalinity in a region critical to understanding deep water mass distribution. High uncertainty is associated with current LGM bottom water salinity characterizations and their implications for LGM overturning circulation and climate. Density was determined to a precision of 2.3 × 10⁻⁶ g/mL, which translates to a relative uncertainty of 0.03% for LGM salinity. We compare the high precision chloride concentration profiles determined using our method to profiles determined from chloride titrations of parallel samples. Salinity change at our site between the pre-industrial and LGM is 3.07 ± 0.03% and 3.65 ± 0.06% when determined from density and 2.96 ± 0.12% and 1.96 ± 0.21% when determined from titrated Cl⁻ for the two co-located cores analyzed. This is consistent with nearby deep Atlantic paleosalinity data (Adkins et al., 2002) and global sea-level-change determined salinity change (Clark and Mix, 2002). By comparing these uncertainties we demonstrate that porewater salinity can be determined to a higher precision and with increased reproducibility through our density protocol compared to titration-determined salinity. Application of our shipboard method at further locations will increase the resolution, precision, and accuracy of available LGM bottom water salinity reconstruction, improving the characterization of glacial deep water masses and overturning circulation.

我们已经开发出一种基于密度的确定孔隙水盐度的方法，该方法可以在船上对少量样品进行处理，其效率和精度要高于目前基于岸边的氯化物滴定技术。该方法基于最近开发的水柱法，该方法通过密度测量和海水热力学状态方程以电导率测量的精度确定盐度。成岩作用会导致孔隙水成分与标准海水值发生偏差，从而影响密度盐度关系，在将测得的密度转换为氯离子浓度之前，我们需要通过精确测量每个离子的浓度来进行校正。

我们将密度方法应用于从北大西洋西部深部采集的相邻长岩心提取的孔隙水样品中，确定了对了解深水质量分布至关重要的区域的最后冰川最大（LGM）底水古碱度。当前LGM底水盐度特征及其对LGM倾覆环流和气候的影响具有高度的不确定性。确定密度的精度为2.3×10 ^-6g / mL，这意味着LGM盐度的相对不确定度为0.03％。我们将使用我们的方法测定的高精度氯化物浓度曲线与平行样品的氯化物滴定测定的曲线进行比较。在我们的工业化前和LGM之间站点盐度变化是3.07±0.03％和3.65±0.06％从密度测定和2.96±0.12％和1.96±0.21％时从滴定氯确定时^-对于两个位于同一地点的核心进行了分析。这与附近的深大西洋古盐度数据（Adkins等，2002）和全球海平面变化确定的盐度变化（Clark and Mix，2002）是一致的。通过比较这些不确定性，我们证明与滴定法测定的盐度相比，通过我们的密度方案可以更高精度地测定孔隙水的盐度，并具有更高的重现性。在更远的地方应用我们的船载方法将提高可用的LGM底水盐度重建的分辨率，精度和准确性，从而改善冰川深水团块的特征和倾覆环流。