Geofizički seminar: Jasen Jacobsen

Sadržaj

On diel time scales, baroclinic motions of internal density surfaces can affect marine primary production by altering the availability of light and nutrients to phytoplankton. Two examples of this process are the generation of internal tides and island trapped waves. When the barotropic surface tide encounters variable bathymetry, flow along the slope generates baroclinic internal tides. Near the generation region, internal tides propagate with a fixed angle to the horizontal in a coherent structure known as an internal tide beam. Idealized simulations of the generation of internal tide beams with the Regional Ocean Modeling System (ROMS) coupled with a simple Nutrient, Phytoplankton, Zooplankton, Detritus (NPZD) model reveal that primary production is enhanced within the tidal beam ray path. The sensitivity of the primary production response to the energy content of the tidal beam is obtained by adjusting the height and slope of the generating feature. Across the range of bathymetries tested, this work shows that primary production responds to vertical parcel displacement through the light field (light effect) and an advective flux divergence of the nutrient field (nutrient effect). By comparing these drivers, we find that the nutrient effect explains more variance in primary production and is an order of magnitude larger than the light effect. In comparison, island trapped waves, such as those observed around the Island of Lastovo in the Adriatic Sea, may also affect light availability and nutrients for primary production. These waves become trapped around islands by a resonant interaction between diurnal forcing and seasonal stratification. Preliminary results of idealized simulations configured in ROMS coupled with a simple NPZD model show that the nonlinear structure of island trapped waves cause the primary negative phase wave-front to be preceded by gradual upwelling. The upwelling signature of island trapped waves enhances both nutrient and light availability for primary production, stimulating increases in both phytoplankton and zooplankton biomass. This talk will present idealized numerical modeling results and compare the biological response to these two baroclinic waves.