Sources of oceanic freshwater content along the western Antarctic Peninsula (PAL-LTER Study Region) determined by the stable isotope composition (d18O) of seawater.

The oceanic distribution of d18O is determined largely by the same processes that control salinity. Surface d18O reflects the magnitude and spatial distribution of freshwater inputs, and it is a conservative tracer in the ocean interior. The great benefit of d18O is obtained from the circumstances under which it exhibits behavior different to that of salinity. One such circumstance derives from the salinity and d18O values in precipitation, with salinity being constant with latitude (typically zero), while in general d18O in precipitation becomes progressively isotopically lighter toward the poles. This results in glacial ice (which derives from high-latitude precipitation) being very isotopically light, enabling d18O to be a useful tracer of glacial discharge to the ocean (e.g., Schlosser et al. 1990; Weiss et al. 1979). Another difference occurs in regions influenced by sea ice, which greatly affects salinity during its formation/melt cycle but has only minimal impact on d18O. This decoupling of the two tracers allows them to be used in tandem to quantitatively separate freshwater inputs from sea ice melt and those from meteoric sources (precipitation plus glacial discharge). For this, a simple three-endmember mass balance can be used. For details please see Meredith, M. P., H. J. Venables, A. Clarke, H. W. Ducklow, M. Erickson, M. J. Leng, J. T. M. Lenaerts, and M. R. van den Broeke. 2013. The freshwater system west of the Antarctic Peninsula: Spatial and temporal changes. Journal of Climate 26:1669-1684.δ¹⁸O（d18O）在海洋中的分布主要由控制海水盐度的相同过程决定。表层海水δ¹⁸O可反映淡水输入的规模与空间分布特征，且在海洋内部属于保守性示踪剂。δ¹⁸O的显著优势体现在其行为与盐度出现差异的场景中。其中一类场景源自降水的盐度与δ¹⁸O值特征：降水盐度随纬度基本保持恒定（通常为0），而总体而言，降水中的δ¹⁸O值随纬度向极地逐渐降低，同位素组成愈发偏轻。这使得源自高纬度降水的冰川冰具有极轻的同位素组成，从而令δ¹⁸O成为示踪海洋冰川融水输入的有效示踪剂（例如Schlosser等，1990年；Weiss等，1979年）。另一类差异出现在受海冰影响的海域：海冰在形成与融化周期中会极大地改变海水盐度，但对δ¹⁸O的影响微乎其微。这两种示踪剂的解耦特性使得二者可协同使用，以定量区分海冰融化与大气成因淡水来源（降水叠加冰川融水）的淡水输入。对此可采用简单的三端元质量平衡模型进行计算。详细细节可参见Meredith, M. P.、H. J. Venables、A. Clarke、H. W. Ducklow、M. Erickson、M. J. Leng、J. T. M. Lenaerts及M. R. van den Broeke于2013年发表的研究：《南极半岛西侧的淡水系统：时空变化》，刊载于《Journal of Climate》第26卷，页码1669-1684。