ONSET AND CULMINATION OF NEOGLACIATION IN THE SIERRA NEVADA, CALIFORNIA

Multiple sediment cores from two paternoster lakes (First and Second lakes) in North Fork Big Pine Creek, Sierra Nevada, preserve the most detailed and complete record of Holocene glaciation yet recovered in the range. The lakes are fed by outwash from the Palisade Glacier, the largest (~1.3 km²) and presumably longest-lived glacier in the Sierra Nevada, and capture essentially all of the rock flour produced by the glacier. Distinct late-Holocene (Matthes) and late-Pleistocene (Recess Peak) moraines lie between the modern glacier and the lakes. The lakes have therefore received continuous sedimentation since the retreat of the Tioga glacier (Last Glacial Maximum) and capture rock flour related to all post-LGM advances.

We collected a total of 6 long cores and 1 detailed short core from the lakes. The deepest cores bottomed in pre-Holocene outwash or slopewash at ~5.5 m sediment depth. Equipment limitations prevented penetration to refusal in the sediments. An age model based on 13 calibrated radiocarbon-dated macrofossils from the longest core indicates Neoglaciation began 3200-3300 cal. yr B.P., followed by glacier maxima at ~2800, ~1600, ~700 and ~100 cal. yr. B.P., the most recent peak being the largest. The cores also record a possible glacier advance during the earliest Holocene. Rock flour flux is lowest between ca. 11,200-3200 cal. yr B.P., suggesting glaciers were absent from the range during that period. Analyses of particle-size, organic content, tephras and pollen, to be presented at the meeting, will further constrain the character of the environmental fluctuations related to the rock-flour variations. We will also present results of high-resolution (last ~1000 yr) sediment sampling conducted this summer using a Glew minicorer. These data should improve our resolution of the most recent events, including the Little Ice Age and proposed mega-droughts in the region.