Atmospheric constraints on δ¹⁸O and <i>d</i>-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.南大西洋西部非热带中纬度沿海区域，受不同时间尺度下多种大气环流模式的共同影响，该影响特征可通过降水中的同位素组成得以体现。相较于研究较为充分的热带区域，此类环流模式的影响更为多变且复杂，而同位素研究是识别区域主要水文气象过程的有效代用指标。本研究聚焦阿根廷南大西洋西部沿海中纬度地带的降水中同位素组成，对38°S处三台相邻雨量收集器整合得到的14年降水时间序列数据中的δ¹⁸O（氧-18同位素比值）与氘盈余（d-excess）开展了分析。两类参数均呈现季节变化特征，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，但其高值出现的时段偏移至春季。研究发现，δ¹⁸O与南极环状模（Southern Annular Mode, SAM）指数的显著线性关联出现在夏季，与南方涛动指数（Southern Oscillation Index, SOI）的显著线性关联则出现于春季。