In:
Earth System Dynamics, Copernicus GmbH, Vol. 10, No. 2 ( 2019-04-26), p. 287-317
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.
Type of Medium:
Online Resource
ISSN:
2190-4987
DOI:
10.5194/esd-10-287-2019
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2019
detail.hit.zdb_id:
2578793-7
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