Testing the Refugia Hypothesis in Southeast Alaska Using Paleogenetics and Glacial Chronology

Vast ice sheets covered northern North America during the last Ice Age. These ice sheets blocked movements of plants and animals between Asia and the Americas for many thousands of years. Many species died out and others were forced into isolated, ice-free areas (refugia) north and south of the ice sheets. Today?s plants and animals carry the genetic legacy of the Ice Age and this refugial isolation, but it is not completely known how it impacted and shaped the past trajectory of many species and their movements following the retreat of the ice sheets. Yet, such knowledge is important for understanding how plants and animals may respond in the future due to environmental changes. The exact extent and timing of ice coverage is also poorly known, and islands along the northwestern coast of North America are hypothesized to have escaped Ice Age glaciation. This means they could have acted as a unique bottleneck for the passage of plants and animals in the geologic past, and even perhaps that they were an early gateway for the peopling of the Americas. This research is aimed at improving knowledge of a critical region for plant, animal, and even human migration: Southeast Alaska. We are testing the hypothesis that coastal areas in Southeast Alaska escaped ice cover by collecting rock samples that will tell us whether or not landscapes were covered by ice and when they became ice-free. We are studying the DNA preserved in fossil bones from mammals that died thousands of years ago. This research project is providing much needed insights into the history of iconic mammals and their environmental conditions in Southeast Alaska. The westernmost extent and timing of ice cover along the North Pacific Coast during the Last Glacial Maximum is poorly known, leaving unanswered fundamental questions about the impact of climatic change on biotic diversification and postglacial colonization of the Americas. Various lines of evidence point to the existence of a viable, ice-free coastal corridor that may have played an important role for biotic exchange between the Old and New Worlds during the last Ice Age. This project is designed to be the definitive test of the hypothesis in support of coastal refugia. We are taking advantage of cutting-edge technologies in cosmogenic nuclide exposure dating and paleogenetic analyses of an unparalleled fossil collection from caves in SE Alaska to achieve two key objectives: (1) directly determine if SE Alaska provided ice-free refugia for terrestrial mammals during the LGM, and (2) constrain the extent and history of the western Cordilleran Ice Sheet during the LGM. Whether the hypothesis is supported or not, this highly interdisciplinary project will deliver results with high impact and have important implications for many different disciplines spanning the geological, biological, paleontological, and archeological sciences. The results will answer a broad range of key questions about the dynamic glacial conditions of SE Alaska during the Ice Age, biogeographic history of mammal island populations, and the configuration and timing of an available migration corridor for the postglacial peopling of the Americas. This research will (a) provide training opportunities for graduate and undergraduate students, (b) broadly disseminate results and links to associated relevant topics, such as environmental change and human migration, through a website, and (c) organize a workshop in SE Alaska with public and K-12 outreach components to synthesize past and current research and focus on the intersection between research, natural resource management, and the impact of future climate projections on biotic systems across the archipelago. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.