Environmental history and tephrostratigraphy at Carp Lake,

Sediment cores from Carp Lake provide a pollen record of the last ca. 125,000 years that helps disclose vegetational and climatic conditions from the present day to the previous interglaciation (120–133 ka). The core also contained 15 tephra layers, which were characterised by electron-microprobe analysis of volcanic glass shards. Identified tephra include Mount St. Helens Ye, 3.69 ka; Mazama ash bed, 7.54 ka; Mount St. Helens layer C, 35–50 ka; an unnamed Mount St. Helens tephra, 75–150 ka; the tephra equivalent of layer E at Pringle Falls, Oregon, <218 ka; and an andesitic tephra layer similar to that at Tulelake, California, 174 ka. Ten calibrated radiocarbon ages and the ages of Mount St. Helens Ye, Mazama ash, and the unnamed Mount St. Helens tephra were used to develop an age–depth model. This model was refined by also incorporating the age of marine oxygen isotope stage (IS) boundary 4=5 (73.9 ka) and the age of IS-5e (125 ka). The justification for this age-model is based on an analysis of the pollen record and lithologic data. The pollen record is divided into 11 assemblage zones that describe alternations between periods of montane conifer forest, pine forest, and steppe. The previous interglacial period (IS-5e) supported temperate xerothermic forests of pine and oak and a northward and westward expansion of steppe and juniper woodland, compared to their present occurrence. The period from 83 to 117 ka contains intervals of pine forest and parkland alternating with pine–spruce forest, suggesting shifts from cold humid to cool temperate conditions. Between 73 and 83 ka, a forest of oak, hemlock, Douglas-fir, and fir was present that has n