ABSTRACT Comparing two different techniques applied for the extraction of marine pore water samples from sediments, the well-established whole round (WR) method and the more recent Rhizon method, in terms of their effects on stable calcium isotope ratios in extracted pore waters, we recognize a systematic offset between the two sampling methods. Higher δ44/40Ca values are associated with lower Ca concentrations for the Rhizon sampling technique and lower δ44/40Ca values are associated with higher Ca concentrations for the corresponding WR-derived pore water samples. Models involving Rayleigh fractionation and mixing calculation suggest that the observed offset is most likely caused by a combined process of CaCO3 precipitation and ion exchange taking place during Rhizon sampling-induced CO2 degassing. Changing pressure, extraction time or extraction yield during WR pressing does not lead to a variation in δ44/40Ca, indicating that no Ca isotope fractionation takes place during the sampling of pore water. On the basis of analytical and modelling results, WR samples appear to provide δ44/40Ca values that are more representative of the ‘true’ pore water isotopic composition. While the difference between the sampling techniques is close to the present-day analytical precision of Ca isotope analysis, it may become more relevant with increasing analytical precision in the future.

中文翻译：

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提取技术对海洋孔隙水钙浓度和同位素比的影响

摘要 比较从沉积物中提取海洋孔隙水样品的两种不同技术，成熟的整轮 (WR) 方法和最近的 Rhizon 方法，就它们对提取的孔隙水中稳定钙同位素比率的影响而言，我们识别两种采样方法之间的系统偏移。对于 Rhizon 采样技术，较高的 δ44/40Ca 值与较低的 Ca 浓度相关，较低的 δ44/40Ca 值与较高的 WR 衍生孔隙水样品的 Ca 浓度相关。涉及瑞利分馏和混合计算的模型表明，观察到的偏移最有可能是由在 Rhizon 采样引起的 CO2 脱气过程中发生的 CaCO3 沉淀和离子交换的联合过程引起的。压力变化，WR 压榨过程中的提取时间或提取率不会导致 δ44/40Ca 的变化，表明在孔隙水采样过程中没有发生 Ca 同位素分馏。根据分析和建模结果，WR 样品似乎提供了更能代表“真实”孔隙水同位素组成的 δ44/40Ca 值。虽然采样技术之间的差异接近当前 Ca 同位素分析的分析精度，但随着未来分析精度的提高，它可能会变得更加相关。WR 样品似乎提供了更能代表“真实”孔隙水同位素组成的 δ44/40Ca 值。虽然采样技术之间的差异接近当前 Ca 同位素分析的分析精度，但随着未来分析精度的提高，它可能会变得更加相关。WR 样品似乎提供了更能代表“真实”孔隙水同位素组成的 δ44/40Ca 值。虽然采样技术之间的差异接近当前 Ca 同位素分析的分析精度，但随着未来分析精度的提高，它可能会变得更加相关。