Abstract

Coastal dune areas (n=14) in the central west coast of North America are evaluated by bare earth lidar hill-shaded images for preserved dune migration directions (orientations) to establish seasonal ranges and means of paleo wind-stress directions (bearings ° TN) in the field region (~3,000 km distance, generally north-south). Three periods are targeted for measured parabolic and transverse dune form orientations, including historic time, late-Holocene time (5–1 ka), and latest-Pleistocene time (30–17 ka). These periods correspond to dated intervals (¹⁴C, TL, OSL or historic aerial photos) of transgressive dune mobility in the field region, prior to hiatuses of dune sand supply and prolonged vegetative stabilization. The 14 representative study sections were profiled for topsoil chronosequences (n=69) to confirm dune feature relative ages of emplacement and preservation. The measured dune feature orientations (° TN) from latest-Pleistocene time (n=44), late-Holocene time (n=48), and historic time (n=52) demonstrate increasing dune migration orientations or bearings from northeast to southeast with decreasing latitude for all three dune age groups. Conversion from dune migration direction to wind-stress direction (180° rotation) yields westerly wind-stress directions (means) at ~37.0° N, ~43.0° N, and ~44.5° N latitudes, respectively, during the latest-Pleistocene, late-Holocene, and historic periods. The westerly mean wind-stress latitudes (above) represent spatial/temporal balances between opposing seasonal wind-stress directions and little or no net-littoral (alongshore) transport. The changes in westerly wind-stress localities (latitudes) from latest-Pleistocene time (~37.0° N) to late-Holocene time (~43.0° N) are interpreted to represent a northward shift of northwest summer diurnal coastal winds and mean winter storm track landfalls of ~6.0° N latitude or a south to north distance of ~600 km. The empirically established changes in paleo wind-stress directions are consistent with modeled paleoclimate trends and could serve as analogs for future climate change impacts in the study region.

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