ENHANCED SOUTHWESTERLY WIND FLOW AND DISPLACEMENT OF THE POLAR JET STREAM DURING THE LATE PLEISTOCENE IN CALIFORNIA: VENTIFACT AND BEACH RIDGE EVIDENCE AT OWENS LAKE (Invited Presentation)

As climate shifted from late Pleistocene glacial to Holocene interglacial conditions in the western Great Basin, USA, temperature, moisture, and circulation patterns fluctuated. Along the eastern front of the 400-km length Sierra Nevada, which exceeds 4,000 m at the southern end, and the adjacent 200-km long Owens Valley, near-surface winds responded to synoptic flow conditions, topography (high mountains and structural valleys), and the presence of glaciers. Owens Lake lies to the lee of the range at the southernmost extremity of the valley. Temporal changes in the intensity, frequency, extent, and persistence of winds were reconstructed by mapping groove orientations on fossil ventifacts located in proximity to dated Late Pleistocene and early Holocene shorelines, which helped provide age control. In total, 1,254 orientations were mapped. Two principal wind flow directions – northwesterly (~315˚) and southwesterly (~225˚) - were identified. Bidirectional northwesterly and southerly wind regimes (valley winds), parallel to the structural trend, have persisted from the late Pleistocene through to the present. By contrast, high velocity southwesterly (downslope) winds, associated with large-amplitude mountain (lee) waves, are largely absent from today’s record (<3% of winds), but were an important component of late Pleistocene to early Holocene flow. The results support the presence of a strong southern branch of the polar jet stream (PJS) during the Last Glacial Maximum (LGM) and a southward shift in Pacific winter storm tracks during millennial-scale cold intervals of the ensuing deglaciation. High velocity (>30ms^-1) southwesterly downslope winds were enhanced by cold, high-density air at the summit of the glaciated Sierra Nevada. The track of southwesterly winds is approximately perpendicular to the orientation of the range, and is associated with the greatest orographic enhancement of precipitation, the path of atmospheric rivers (AR), and the highest wind velocities. The recognition of enhanced late Pleistocene southwesterly flow sheds light on glaciation in the southern Sierra Nevada, the hydroclimatology of pluvial lakes and rivers, barrier beach development, wind erosion, sand and dust transport and deposition, and seed and pollen dispersal.