This collaborative study between the Polar Oceans Research Group, Old Dominion University, and the University of Wisconsin-Madison will identify and investigate the causal mechanisms through which changes in sea ice and variability in the western Antarctic Peninsula marine ecosystem affect recruitment in Adelie penguin populations. The approach combines data collection, extensive data analyses, and the development of a bioenergetics model of penguin chick growth that provides a framework for investigating the physical and ecological factors that determine chick fledging weight, which is linked to recruitment success. The available data base spans 30 years at Palmer Station, and four major research programs, including the Southern Ocean experiment of the Global Ocean Ecosystems Dynamics program (SO-Globec). SO-Globec is a multidisciplinary effort focused on understanding the physical and biological factors that influence growth, reproduction, recruitment and survival of Antarctic krill (Euphausia superba). The program uses a multi-trophic level approach that includes the predators and competitors of Antarctic krill, represented by other zooplankton, fish, penguins, seals, and cetaceans. It is currently in a synthesis and modeling phase. This collaborative project is concerned with specifically with the sea ice dynamics that constrain ecological processes, and will be integrated with other synthesis and modeling studies that deal with primary producers, grazers, predators, and other higher trophic levels.