Temperature Sensitivity of Size-fractionated Phytoplankton Growth and Net Primary Production Rates on the Northeast US Shelf

Understanding the spatiotemporal variations of phytoplankton growth and identifying its primary drivers is critical for assessing ocean biogeochemical cycles, productivity, and food web dynamics. In this study, we developed a data-driven, size-fractionated model to estimate phytoplankton growth rates on the Northeast US Shelf (NES). By utilizing comprehensive data collected during the NES Long-Term Ecological Research cruises, we applied both sequential model-based Bayesian optimization algorithm and Random Forest machine learning method to identify the primary stressor modulating phytoplankton growth. Our findings suggested temperature as the predominant limiting factor across the entire shelf, resulting in high/low growth rates in warm/cold season, respectively. Additionally, we conducted an attribution assessment using Taylor expansion to quantify the relative contribution of environmental drivers to growth rate variability. Our analysis revealed that the projected warming on the NES could impact the growth rates of small- and large-sized phytoplankton differently. Within the small-sized phytoplankton, biomass concentrations were relatively insensitive to environmental changes while growth rates were enhanced by higher water temperature, indicating these cells are likely to experience increased growth and net primary production rates as temperature rises. In contrast, the impacts of stratification-induced nutrient depletion on the growth and net primary production rates of large-sized phytoplankton were more dominant. This size-dependent phytoplankton seasonal dynamics provides valuable insights into the response of shelf ecosystem primary production in the context of global warming.

Presentation Preference: Oral

Primary Presenter: Zhengchen Zang, LUMCON (zzang@lsu.edu)

Authors:

Rubao Ji, Woods Hole Oceanographic Institution  (rji@whoi.edu)

Diana Fontaine, University of Rhode Island  (fontained@uri.edu)

Pierre Marrec, University of Rhode Island  (pmarrec@uri.edu)

Susanne Menden-Deuer, University of Rhode Island  (smenden@uri.edu)

Tatiana Rynearson, University of Rhode Island  (rynearson@uri.edu)

Rachel Stanley, Wellesley College  (rstanle2@wellesley.edu)

heidi sosik, Woods Hole Oceanographic Institution  (hsosik@whoi.edu)