UC San Diego

The Arctic Ocean, a unique and vulnerable ecosystem, is undergoing profound changes due to climate change, with phytoplankton communities serving as key indicators and influencers of marine health. These communities play a pivotal role in global primary productivity and biogeochemical processes. Despite the Arctic's susceptibility to environmental shifts, there is a scarcity of comprehensive observations regarding how Arctic plankton communities currently respond to seasonal and interannual changes, as well as how they will react to anthropogenic alterations, making modeling crucial for understanding the complex dynamics. This dissertation addresses this critical gap by developing a biodiverse plankton community model, capable of capturing large-scale elemental cycles and the structure of planktonic food webs influencing trophic transfer efficiency (Chapter 1). The Size-based Plankton Ecological Traits model (MARBL-SPECTRA), embedded in a Global Circulation Model, addressing limitations of previous models by incorporating nine phytoplankton and six zooplankton size classes. The model captures large-scale patterns in phytoplankton growth, community structure, and trophic dynamics. Through a hindcast simulation of the Arctic Ocean, the model reveals significant seasonal and interannual variations, highlighting the influence of environmental factors on phytoplankton and subsequent impacts on fish production (Chapter 2). This analysis provides a robust foundation for investigating the broader implications of climate change on Arctic ecosystems. To further illuminate the impacts of anthropogenic climate change on phytoplankton communities, the model is forced under three different Shared Socioeconomic Scenarios, to explore climate-induced shifts in phytoplankton physiology and community structure, unveiling intricate responses in the Arctic ecosystem and emphasizing the profound impact of climate change on marine ecosystems (Chapter 3). These findings bear significance not only for the scientific community but also for policymakers and stakeholders tasked with mitigating and adapting to the profound impacts of climate change in the Arctic. Ultimately, this research provides essential knowledge to address the pressing challenges posed by ongoing environmental transformations in one of the most vulnerable and critical components of the global marine ecosystem.