Miocene orographic uplift forces rapid hydrological change in the southern central Andes

Abstract

Rainfall in the central Andes associated with the South American Monsoon and the South American Low-Level Jet results from orographic effects on atmospheric circulation exerted by the Andean Plateau and the Eastern Cordillera. However, despite its importance for South American climate, no reliable records exist that allow decoding the evolution of thresholds and interactions between Andean topography and atmospheric circulation, especially regarding the onset of humid conditions in the inherently dry southern central Andes. Here, we employ multi-proxy isotope data of lipid biomarkers, pedogenic carbonates and volcanic glass from the Eastern Cordillera of NW Argentina and present the first long-term evapotranspiration record. We find that regional eco-hydrology and vegetation changes are associated with initiation of moisture transport via the South American Low-Level Jet at 7.6 Ma, and subsequent lateral growth of the orogen at 6.5 Ma. Our results highlight that topographically induced changes in atmospheric circulation patterns, not global climate change, were responsible for late Miocene environmental change in this part of the southern hemisphere. This suggests that mountain building over time fundamentally controlled habitat evolution along the central Andes.

Mio-Pliocene aridity in the south-central Andes associated with Southern Hemisphere cold periods

“…Likewise, δD isotopic measurements in volcanic glass suggest a period of aridity in the Angastaco basin (∼25.5°S) from ∼6.3-5.1 Ma (Fig. 2G) (28,35). Inferred aridity is broadly synchronous with carbon isotope excursions thought to record the (49,54,76).…”

“…It thus remains unclear whether the timing and extent of latest Miocene landscape ecologic changes in the south-central Andes were primarily controlled by tectonic-orographic effects or by globalscale changes in climate (e.g., refs. [33][34][35].…”

Why mountains matter for biodiversity

“…They can be used to reconstruct past elevations and thus to trace the evolution of both mountains and taxa over time. The results of these analyses can be directly applied to historical biogeographical studies in mountain regions (Lagomarsino et al, 2016;Mulch, 2016;Rohrmann et al, 2016;Spicer, 2017).…”

Controls on Deuterium Excess across Asia

“…In addition, d-excess is not normally obtained from proxy material, as minerals are analyzed for either δ 18 O or δD, whereas both are needed to calculate d-excess. There is a potential to combine proxies, such as δ 18 O from carbonate and δD from volcanic glass, to estimate ancient d-excess for a region (e.g., [53]), although considerable uncertainty is introduced by using different sample types for each element, as the number of variables that could affect results increases. That said, because d-excess is highly sensitive to mountain climatology, a multi-proxy approach may hold potential as a way of constraining the initiation of paleo-rain shadow development in and around the Tarim Basin, with implications for the timing of mountain formation and related geodynamic forcing mechanisms.…”