(Table 3) Mediterranean core-top d18O values for various planktonic foraminiferal species

A box model is presented to simulate changes in Mediterranean long-term average salinity and d18O over the past 20,000 years. Simulations are validated by comparison with observations. Sensitivity tests illustrate robustness with respect to the main assumptions and uncertainties. The results show that relative humidity over the Mediterranean remained relatively constant around 70%, apparently narrowly constrained to the lower end of the range observed globally over sea surfaces by the basin's land-locked character. Isotopic depletion in run off, relative to the present, is identified as the main potential cause of depletions in the Mediterranean d18O record. Also, slight increases in relative humidity (of the order of 5%) might have caused very pronounced isotopic depletions, such as that in sapropel S5 of the penultimate interglacial maximum. The model shows distinctly non proportional responses of d18O and salinity to environmental change, which argues against the use of isotope residuals in Mediterranean paleosalinity reconstructions.

本文提出了一个箱式模型（box model），用于模拟过去2万年以来地中海长期平均盐度与δ18O（d18O）的变化。通过与实测观测数据的对比，对模拟结果开展了验证。敏感性试验结果表明，该模型对主要假设与不确定性因素均具备良好的鲁棒性。研究结果显示，地中海区域的相对湿度长期维持在70%左右的稳定水平；受该海域的内陆封闭盆地特性影响，其相对湿度范围明显被严格限制在全球海面观测湿度区间的下限附近。相较于现代，径流（run off）的同位素贫化被认为是地中海δ18O记录出现贫化现象的主要潜在诱因。此外，相对湿度小幅提升（幅度约5%）即可引发显著的同位素贫化事件，例如倒数第二次间冰期鼎盛期腐泥层（sapropel）S5中所记录的贫化现象。该模型表明，δ18O与盐度对环境变化的响应显著不成比例，这一结论不支持在地中海古盐度（paleosalinity）重建中采用同位素残差方法。