Atmospheric constraints on δ18O and d-excess in precipitation at the middle latitude in the southwestern Atlantic region

The mid-latitude coastal area at the western South-Atlantic out of the tropics is under the combined effect of different atmospheric circulation patterns at different temporal scales, which can be shown by the isotope composition of precipitation. This pattern effect is more changing and complex than that for the well-studied tropical areas, the isotope studies being an interesting proxy for identifying major processes. This study is focused on the isotope composition of precipitation at a mid-latitude zone, in the western South-Atlantic coastal area of Argentina. δ18O and d-excess were analysed in a data series of 14 years, obtained from the integration of three neighbouring rain collectors at 38°S. A seasonality is observed in both parameters, but with some differences in the extreme months. δ18O showed a seasonality according to the temperature effect, but with a displacement of high values to spring months. Significant linear links between δ18O and Southern Annular Mode (SAM) index and Southern Oscillation Index (SOI) were recognised for the summer and spring seasons, respectively.

南大西洋西部热带外的中纬度沿海区域，受不同时间尺度大气环流模式的共同作用，这一作用可通过降水的同位素组成得以反映。该环流模式效应相较于研究较为充分的热带区域更为多变且复杂，而同位素研究正是识别区域关键过程的有效代用指标。本研究聚焦于阿根廷南大西洋西部沿海中纬度带的降水同位素组成，对位于南纬38°的3台相邻雨量收集器整合得到的14年序列数据中的δ¹⁸O（氧同位素18）与氘盈余（d-excess）进行了分析。两项参数均表现出季节变化特征，但在极端月份存在一定差异。δ¹⁸O的季节变化符合温度效应规律，但高值出现的时间向春季发生了偏移。研究分别在夏季与春季发现，δ¹⁸O与南方环状模（Southern Annular Mode, SAM）指数、南方涛动指数（Southern Oscillation Index, SOI）之间存在显著的线性关联。