The Influence of Phytoplankton Productivity and Molecular Physiology on Biogeochemical Dynamics of Two Contrasting Ocean Environments

Understanding the controls on oceanic primary production is crucial to elucidating it’s influence on global biogeochemical cycling, ocean health, and climate regulation under current and future climate scenarios. The NASA EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) program aims to investigate and constrain the mechanisms controlling oceanic primary production and the proportion of this fixed carbon that is exported from the surface to the deep ocean (i.e., sequestered on the human time scale). Field campaigns were conducted in summer of 2018 to Ocean Station PAPA in the Subarctic North Pacific and in spring of 2021 to the Porcupine Abyssal Plain in the North Atlantic. These two systems are case studies, representing end members for the lows and highs of open ocean primary production, foodweb dynamics, and carbon export in the open ocean. Through a combination of field-based measurements for environmental parameters, phytoplankton biomass, production, physiology, and gene expression, as well as targeted culture-based studies, I have been able to elucidate some of the key differences between these representative systems. Out of my analysis one continuous theme emerges: phytoplankton size, used as a proxy for differing taxonomic groups, plays a central role in (1) the strength of control environmental parameters have on phytoplankton, (2) the ability of a system to buffer and/or capitalize upon changes to a system, and (3) the efficiency of a system in nutrient cycling and carbon export. As anthropogenic climate change continues to alter the natural world, additional work is needed in exploring the relationships of in situ, size-fractionated measurements and molecular-level analyses in order to groundtruth remote sensing and ecosystem models moving forward.