Sensitivity of Shelf Sea Marine Ecosystems to Temporal Resolution of Meteorological Forcing

Helen R Powley,Tim Smyth,Jo Hopkins,Jerry Blackford,Jorn Bruggeman

doi:10.1029/2019jc015922

Helen R Powley, Tim Smyth + Show 3 more

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https://doi.org/10.1029/2019jc015922

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Abstract

AbstractPhytoplankton phenology and the length of the growing season have implications that cascade through trophic levels and ultimately impact the global carbon flux to the seafloor. Coupled hydrodynamic‐ecosystem models must accurately predict timing and duration of phytoplankton blooms in order to predict the impact of environmental change on ecosystem dynamics. Meteorological conditions, such as solar irradiance, air temperature, and wind speed are known to strongly impact the timing of phytoplankton blooms. Here, we investigate the impact of degrading the temporal resolution of meteorological forcing (wind, surface pressure, air, and dew point temperatures) from 1–24 hr using a 1‐D coupled hydrodynamic‐ecosystem model at two contrasting shelf‐sea sites: one coastal intermediately stratified site (L4) and one offshore site with constant summer stratification (CCS). Higher temporal resolutions of meteorological forcing resulted in greater wind stress acting on the sea surface increasing water column turbulent kinetic energy. Consequently, the water column was stratified for a smaller proportion of the year, producing a delayed onset of the spring phytoplankton bloom by up to 6 days, often earlier cessation of the autumn bloom, and shortened growing season of up to 23 days. Despite opposing trends in gross primary production between sites, a weakened microbial loop occurred with higher meteorological resolution due to reduced dissolved organic carbon production by phytoplankton caused by differences in resource limitation: light at CCS and nitrate at L4. Caution should be taken when comparing model runs with differing meteorological forcing resolutions. Recalibration of hydrodynamic‐ecosystem models may be required if meteorological resolution is upgraded.

Highlights

Phytoplankton phenology, that is, the timing of phytoplankton blooms, has consequences that cascade through ecological trophic levels, with the potential to change ecosystem structure (Edwards & Richardson, 2004; Platt et al, 2003) and the flux of carbon to the sea floor
The ability of marine ecosystem models to accurately represent and capture changes in phytoplankton phenology, in addition to the magnitude and composition of phytoplankton blooms, is imperative to predict the impacts of environmental change on ecosystem dynamics and the amount of carbon trapped within global shelf seas
This study investigates the response of shelf‐sea ecosystems to the resolution of meteorological forcing in hydrodynamic‐ecosystem models

Summary

Introduction

Phytoplankton phenology, that is, the timing of phytoplankton blooms, has consequences that cascade through ecological trophic levels, with the potential to change ecosystem structure (Edwards & Richardson, 2004; Platt et al, 2003) and the flux of carbon to the sea floor. This is important in shelf seas as they trap a disproportionate amount of carbon from the atmosphere within their sediments compared to the deep global ocean (Bauer et al, 2013; Sharples et al, 2019). On shelves where light rather than nutrient availability limits phytoplankton growth, the spring bloom typically occurs during a period of low grazing pressure when a reduction in turbulent mixing and shoaling of the actively mixing surface layer eases light limitation

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