Abstract
We analyzed 28-year-long monthly oxygen isotope composition of precipitation (δ18Op) data from Punta Arenas (Chile) on the leeward side of the Andes to understand how different synoptic weather types and moisture transport pathways influence δ18Op variability in this region. Combining weather station 6 h precipitation data and atmospheric back trajectories, we found that in such a region where the atmospheric circulation pattern is dominated by very strong westerlies, an increased monthly proportion of easterly-delivered precipitation—with the air-mass trajectory path evading the influence of Andean “isotopic rain shadow” and having less rainout en route—would increase δ18Op. These synoptic easterlies are a result of quasi-stationary blocking-like flow that are an important but underappreciated part of regional circulation patterns and climate. In addition, synoptic easterlies are more often associated with heavy precipitation events as shown by weather station data and higher deuterium excess that indicates weaker post-condensation raindrop re-evaporation. Therefore, our analysis demonstrated the process link between the frequency of synoptic weather types characterized by blocking-like flow and temporal variations in δ18Op in Southern Patagonia. We conclude that isotope proxy paleo-records in this region could provide unique insights into the behaviors and dynamics of the large-scale Southern Hemisphere Westerly Winds over long timescales.
Highlights
Stable isotopes in water (δ18 O and δ2 H) have been widely used as geochemical tracers for the hydrological cycle
Mean monthly proportions of precipitation derived from the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) framework (Table 1) and precipitation-producing trajectory frequency contour plots (Figure 4) are consistent with empirical observations that the strong Southern Hemisphere Westerly Winds (SHWWs) belt dominates over Punta Arenas all year long
Weather station precipitation data and back-trajectory modeling are combined to quantify the proportions of precipitation delivered from different trajectory clusters that are characterized by different synoptic weather types on monthly basis
Summary
Stable isotopes in water (δ18 O and δ2 H) have been widely used as geochemical tracers for the hydrological cycle. The Rayleigh distillation model that depicts isotopic fractionations in air mass rainout processes could explain much of δ18 Op variability at various temporal and spatial scales in both observations and models [3,4,5]. These well-established relationships between δ18 Op and climatic variables led to applying stable isotope proxies in terrestrial climate archives to reconstruct past hydrological
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