Atmospheric Flow Patterns Around the Southern Alps of New Zealand and Implications for Paleoaltimetry

Abstract

The development of relief may generate leeside rain shadows where precipitation δ18O values are lower due to rainout on the windward side. The magnitude of lowering in paleo-δ18O sampled from the leeside of a mountain range should, at least, in principle, be related to the elevation of the mountain range. In order for leeside proxies to record the highest elevations, the majority of air masses need to travel up and over the ridge crest before raining out on the leeside. If atmospheric flow patterns around the mountain range are dominated by flow deflection, air masses that reach the leeside are less likely to record the highest elevations. Using the Weather Research and Forecasting model and Hybrid Single-Particle Lagrangian Integrated Trajectory model, we demonstrate that modern atmospheric flow patterns in the Southern Alps of New Zealand are not dominated by flow deflection. The lack of flow deflection around the Southern Alps and the relatively low relief throughout the uplift history supports the use of leeside isotope records to constrain the timing of uplift, and that uplift likely occurred ~5 Ma based on leeside isotope records. In contrast, orogens that are characterized by high elevations and strong flow deflection, like the Sierra Nevada of California, may not be good candidates for leeside isotope-based paleoaltimetry studies. Ideal candidates for such studies should be characterized by relatively low elevations, low atmospheric flow deflection, and relatively low relief throughout the period of uplift.