COSMOGENIC ³⁶CL EXPOSURE AGES OF FULL AND LATE-GLACIAL ICE CAPS ON MAUNA KEA, HAWAI‘I

Glacial landforms and deposits exposed in deep gulches on the south and east flanks of Mauna Kea, Hawai‘i (19.8°N, 155.5°W) indicate that the summit area of the volcano was covered by ice caps at least four different times during the late Pleistocene. The maximum extents of the two latest ice caps (older and younger Makanaka) were essentially the same, reaching ~3400 m above sea level or ~800 m below the summit. These ice caps left behind prominent end moraines, ground moraines, several outwash channels, and at least one boulder-dominated outwash fan. New cosmogenic ³⁶Cl exposure ages for these landforms suggest that the older Makanaka ice cap began retreating 23.3±2.2 ka (2σ - weighted average standard deviation) ago, broadly coincident with the last glacial maximum (LGM), whereas the younger Makanaka ice cap began retreating 13.3±0.7 ka ago, near the onset of the Younger Dryas (YD) chronozone. The ³⁶Cl results for the younger Makanaka deposits may suggest an early YD in the central Pacific (i.e. pre-12.9 ka ago) or surging of the younger Makanaka ice cap early in the YD and retreat shortly thereafter. However, we cannot yet rule out a potential systematic bias associated with spatial and/or temporal production rate scaling functions in our age calculations. Nevertheless, the recognition of the YD in Hawaii implies that late Pleistocene ice caps on Mauna Kea provide a highly responsive record of climatic change in the central Pacific and document a teleconnection with other areas affected by the YD.