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High precision paleosalinity determination from measured porewater density

机译：高精度古色素附近测量的孔水密度测定

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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 x 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 titration 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.
机译：我们开发了一种基于密度的方法，用于确定孔水盐度，可以在小体积样品上进行船上，比目前可用的氯化物滴定技术更高效率和精确。该方法基于最近开发的水柱方法，其通过密度测量和状态的海水热力学方程来确定电导率测量的精度的盐度。成岩作用导致孔水组合物从标准海水值中偏差，影响密度盐度关系，从而通过在将测量的密度转化为氯化物浓度之前通过精确测量每种离子的浓度来校正。我们考虑通过优化扩散模型的成岩作用而随着成岩作用而发生的随着时间的推移而发生的孔水氯化物的扩散变化，作为测量现代孔水的时间，并将最适合盐度转化为时间。我们应用了我们的密度法从从深西北大西洋中收集的邻近的长核中提取的沉降水样，在对理解深水分分布至关重要的区域中确定最后的冰川最大（LGM）底部水容纳。高不确定性与当前的LGM底部水盐度表征及其对LGM推翻循环和气候的影响。密度被确定为2.3×10（ - 6 )g / ml的精度，其转化为LGM盐度的相对不确定度为0.03％。我们比较使用我们的方法测定的高精度氯化物浓度谱，该方法与由平行样品的氯化物滴定确定的曲线谱。当从密度和2.96 +/- 0.12％确定时，我们在预工业和LGM之间的盐度变化为3.07 +/- 0.03％和3.65 +/- 0.06％，当由滴定的Cl-确定时，2.96 +/- 0.21％对于分析的两个共同核心。这与附近的大西洋古病间数据（Adkins等，2002）和全球海平改变确定的盐度变化（Clark和Mix，2002）一致。通过比较这些不确定性，我们证明了与滴定确定的盐度相比，通过密度方案可以确定沉淀物可以更高的精度并且通过密度方案增加再现性。我们的船上方法在进一步的位置应用将提高可用LGM底水盐度重建的分辨率，精度和准确性，从而提高冰川深水块和倾覆循环的表征。

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