Dynamic Flux Balance Analysis Reveals Climate-Driven Shifts in Arctic Diatom Succession and Bloom Dynamics

There is a critical need to understand the impact of climate change on marine microorganisms, especially phytoplankton, which are responsible for as much as half of atmospheric oxygen and are critical for the global carbon cycle. Climate change is causing drastic alterations in marine ecosystems, with the Arctic Ocean experiencing unprecedented environmental changes such as sea ice retreat and rising temperatures. These changes threaten to have severe consequences on the global carbon cycle, specifically on processes mediated by marine phytoplankton communities. Diatoms are one of the primary carbon-fixing phytoplankton in the Arctic Ocean and represent a critical sink within the global carbon cycle and are especially vulnerable to these changes. Spring blooms of diatoms in the Arctic account for approximately 20% of annual carbon fixation, but climate change effects will fundamentally change the environmental conditions that govern these blooms' dynamics. The succession pattern of diatom communities, from early blooming Thalassiosira to later-blooming Chaetoceros, is a critical driver of carbon sequestration, yet our understanding of how these patterns will respond to climate change remains limited. To address this knowledge gap, we developed dynamic flux balance analysis models incorporating complex empirical environmental parameters to simulate the annual life cycle of Thalassiosira and Chaetoceros. Model validation against historical data successfully recreated known diatom succession patterns, predicted post-bloom diatom biomass and nutrient concentrations independently, and recreated the known diatom succession pattern. Our models predicted that climate change will cause earlier, shorter, and more intense phytoplankton blooms, which are less effective at sequestering carbon. However, we found the succession pattern including diatom-cyanobacterial symbiosis may provide resilience because blooms including both symbiotic Chaetoceros and non-symbiotic Thalassiosira did not suffer losses in carbon sequestration.