| Summary: | The Southern Ocean hosts globally unique and important ecosystems characterized by extreme environmental variability. Superimposed upon this, these systems are now experiencing climate change impacts at rates greater than the global average. Antarctic krill – an ecologically and commercially important species – are highly adapted to their variable polar environment. At annual scales, krill have evolved a life cycle synchronized to seasonal oscillations between productive open-ocean habitats in the summer, and sea ice-dominated habitats in the winter. At interannual scales, krill recruitment is episodic and highly dependent upon highquality habitat, created by optimal environmental conditions occurring every 4-5 years. This project therefore aims to improve understanding of the environmental drivers of krill habitat quality and population success in both open-ocean and sea-ice habitats, in order to better assess their current status and continued survival in a changing Southern Ocean. In the open ocean, krill habitat quality can be influenced by a number of environmental drivers, including temperature and food availability. However, published projections of open-ocean habitat quality have been limited by biases in Earth System Model (ESM) representations of primary production. This thesis minimizes biases in an ESM ensemble using a novel model selection and weighting approach, allowing for projected changes in temperature and primary production to be accounted for. By providing the first circumpolar projections for krill growth potential, this project finds a seasonal shift in habitat quality during the main reproductive season which may have implications for krill population dynamics and interactions with the krill fishery. The environmental drivers of sea-ice habitat quality remain somewhat speculative. Current understanding is limited by challenges in observing the sea-ice environment and so is primarily informed by correlative relationships with relatively simple indicators of sea-ice habitat availability, ...
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