Tidal impacts on primary production in the North Sea

Abstract

Abstract. This study highlights the importance of tides in controlling the spatial and temporal distributions of phytoplankton and other factors related to growth, such as nutrients and light availability. To quantify the responses of net primary production (NPP) to tidal forcing, we conducted scenario model simulations considering M2 and S2 tidal constituents using the physical–biogeochemical coupled model ECOSMO (ECOSystem MOdel). The results were analyzed with respect to a reference simulation without tidal forcing, with particular focus on the spatial scale of the tidally induced changes. Tidal forcing regulates the mixing–stratification processes in shelf seas such as the North Sea and hence also influences ecosystem dynamics. In principle, the results suggest three different response types with respect to primary production: (i) in southern shallow areas with strong tidal energy dissipation, tidal mixing dilutes phytoplankton concentrations in the upper water layers and thereby decreases NPP. Additionally, tides increase turbidity in near-coastal shallow areas, which has the potential to further hamper NPP. (ii) In the frontal region of the southern North Sea, which is a transition zone between stratified and mixed areas, tidal mixing infuses nutrients into the surface mixed layer and resolves summer nutrient depletion, thus sustaining the NPP during the summer season after spring bloom nutrient depletion. (iii) In the northern North Sea, the NPP response to tidal forcing is limited. Additionally, our simulations indicate that spring bloom phenology is impacted by tidal forcing, leading to a later onset of the spring bloom in large parts of the North Sea and to generally higher spring bloom peak phytoplankton biomasses. By testing the related changes in stratification, light conditions and grazing pressure, we found that all three factors potentially contribute to the change in spring bloom phenology with clear local differences. Finally, we also analyzed the impact of the spring–neap tidal cycle on NPP. The annual mean impact of spring–neap tidal forcing on NPP is limited. However, locally, we found substantial differences in NPP either in phase or anti-phase with the spring–neap tidal cycle. These differences could be attributed to locally different dominant factors such as light or nutrient availability during spring tides. In general, we conclude that in shallow shelf seas such as the North Sea, intensified vertical mixing induced by tidal forcing could either promote NPP by counteracting nutrient depletion or hinder NPP by deteriorating the light environment because of the resuspension and mixing of suspended matter into the euphotic zone.

Understanding the Role of Organic Matter Cycling for the Spatio-Temporal Structure of PCBs in the North Sea

“…Figure 5) demonstrated that during summer, a subsurface maximum of BIO was formed as a result of stratification and near surface nutrients depletion. Subsurface production occurs in a depth interval between 10 and 25 m, as has been described earlier in, e.g., [56], and which is in accordance to observations [57].…”

“…To estimate POP export to the deeper ocean beyond the shelf edge, we combined transport fields from the high resolution prognostic model setup for the coupled North Sea and Baltic Sea (lateral boundary at 60 • N) [23] with results from an exterior diagnostic shelf sea model [34]. The horizontal resolution of the advection model was ∆ϕ = 6 and ∆λ = 10 , and in the vertical, the water column was resolved by 20 z-levels with the lower boundaries at 5,10,15,20,25,30,35,40,48,56,64,72,80,88,100,125,150,200, 400 and 3500 m. The hydrodynamic model setup has previously underwent extensive validations [35], and it has been shown to well-replicate the interannual variations in the hydrodynamic conditions in the North Sea and Baltic Sea system [36]. From a long term ECOSMO model simulation [28] that was forced by atmospheric boundary conditions from the NCEP/NCAR re-analysis [37], we selected the years 2004-2008, for which we had atmospheric inputs and high resolution river load data available.…”

Tidally Induced Temporal Variations in Growth of Young‐of‐the‐Year Pacific Cod in the Yellow Sea

“…Like many previous studies of temporal zooplankton variations from echo observations (Ibáñez-Tejero et al, 2018;Petrusevich et al, 2020;Sharples et al, 2007;Zhao et al, 2019), this result suggests that the vertical distribution of zooplankton was relatively dispersed in summer with a stronger tidal current during spring tides, while DVM was more regular and the vertical zooplankton distribution was relatively concentrated above the YSCWM.…”

The Budget of Macrobenthic Reworked Organic Carbon: A Modeling Case Study of the North Sea

“…In the latest simulation, an updated set of river runoff and nutrient loads with a more complete spatial and temporal coverage has been applied. A detailed description of the data sources is given in Zhao et al ().…”