The abrupt transition from the last ice age (glacial) into the warm Holocene interglacial was associated with major changes in Earth's biota. In Arctic regions, species went through large-scale shifts in distribution and several groups became extinct, leading to rearrangements in ecological communities. However, it is unclear to what extent these changes were unique to the transition into the Holocene, or if such major turnovers have been recurrent during previous glacial-interglacial transitions, of which there have been 14 during the past million years. This PhD project will apply cutting-edge ancient DNA techniques to sediments from northwestern North America to test the magnitude of ecological changes across multiple glacial-interglacial transitions over the past 450,000 years. This project will test whether ecological changes across glacial-interglacial transitions are comparable and can therefore serve as a model for predicting changes associated with ongoing climate warming.