Abstract: Despite being an essential physiological component of homeotherm life in polar regions, little is known about the energetic requirements for thermoregulation in either air or water for high- latitude seals. In a joint field and modeling study, the principal investigators will quantify these costs for the Weddell seal under both ambient air and water conditions. The field research will include innovative heat flux, digestive and locomotor cost telemetry on 40 free-ranging seals combined with assessments of animal health (morphometrics, hematology and clinical chemistry panels), quantity (ultrasound) and quality (tissue biopsy) of blubber insulation, and determination of surface skin temperature patterns (infrared thermography). Field-collected data will be combined with an established individual based computational energetics model to define cost-added thresholds in body condition for different body masses. This study will fill a major knowledge gap by providing data essential to modeling all aspects of pinniped life history, in particular for ice seals. Such parameterization of energetic cost components will be essential for the accurate modeling of responses by pinnipeds to environmental variance, including direct and indirect effects driven by climate change. The study also will provide extensive opportunities in polar field work, animal telemetry, biochemical analyses and computational modeling for up to three undergraduate students and one post-doctoral researcher. Integrated education and outreach efforts will educate the public (K-12 through adult) on the importance of quantifying energetic costs of thermoregulation for marine mammals and the need to understand responses of species to environmental variance. This effort will include a custom-built, interactive hands-on mobile exhibit, and development of content for an Ocean Today kiosk.