Plasticity of marine ecosystem dynamics as a condition for its stability: modeling seasonal and vertical dynamics of the Arctic shelf ecosystem

Ecosystem stability is a central concept in systems ecology, yet its manifestation in marine ecosystems, particularly in low-productivity Arctic shelf ecosystems under climate-driven variability, remains insufficiently understood. These systems face heightened vulnerability from anthropogenic impacts and have scarce field observations. The restructuring of functional regimes in sensitive Arctic ecosystems and community reorganization necessitates modeling studies to identify stability boundaries. Here, we apply a calibrated hierarchical model to investigate the seasonal and vertical dynamics of phytoplankton, zooplankton, nitrates, and organic matter in a low-productivity Arctic shelf ecosystem. The model accounts for matter transfer along the food chain in accordance with conservation laws. For phytoplankton, it incorporates nitrate consumption, zooplankton grazing, photoinhibition, and organotrophy. The equations include phytoplankton consumption by zooplankton and zooplankton consumption by fish. External forcings comprise surface heat fluxes, seasonal variation, and vertically nonuniform temperature and illumination. Numerical experiments varying key parameters, such as maximum growth rates and half-saturation constants, reveal stable dynamical regimes and the restructuring boundaries of the dynamics. Nonlinear transitions from single-peak low-productivity dynamics (Kara Sea-like) to dual-peak high-productivity regimes (Barents Sea-like) occur without loss of stability. Zooplankton responses lag behind of phytoplankton but remain stable across trophic cascades. Spatially resolved simulations reproduce realistic surface and subsurface phytoplankton maxima (SMPs), with their timing and depth governed by physiological traits and hydrophysical conditions. The wide-range parameter variations explored in the model simulations support the hypothesis that under-ice phytoplankton blooms may occur in low-productivity Arctic seas - events that remain beyond the reach of both field surveys and satellite monitoring. The model's results are consistent with available Arctic shelf observations. These results demonstrate robust ecosystem plasticity amid parameter shifts that mirror Arctic warming, linking microscale physiological traits to macroscale functional stability and thereby informing projections for climate-stressed shelves.