Modeling the Impact of Fine Temporal and Spatial Scale Processes on Large-scale Ecosystem Dynamics and Carbon Cycling.

Fine temporal (days) and spatial scale (1-10 km) physical dynamics can impact primary production and carbon cycling in the ocean through changes in mixed layer depths and nutrient cycling. However, the large-scale implications of these bio-physical interactions on ecosystem composition and carbon cycling remain uncertain as they are difficult to observe and challenging to model. We introduce a new modeling approach, the Spatially Heterogeneous Dynamic Plankton (SHiP) model, which allows for the incorporation of sub-grid cell dynamics into coarse resolution models through the probabilistic representation of episodic events. The model was applied to the Hawaiian Ocean Time-series site to explore the importance of fine-scale spatial and temporal heterogeneity on ecosystem composition and carbon dynamics at the site. Significant differences were seen between nutrient concentrations, biomass values, and carbon cycling dynamics when the model was run in a temporally and spatially heterogeneous mode relative to the traditional homogeneous approach. Specifically, increased coexistence between phytoplankton groups, higher predator to prey ratios, increased resilience to perturbations, and increased export ratios were observed in the SHiP simulations relative to a homogenous grid cell simulation. These findings suggest that the incorporation of fine-scale bio-physical interactions is important for the accurate representation of marine ecosystems dynamics.