Ecosystem structuring by pulses of internal wave breaking

Informations

Funding country

Norway

Acronym

-

URL

-

Start date

1/1/2020

End date

12/31/2023

Budget

979,572 EUR

Fundings

Abstract

Vertical mixing in the ocean is an essential mechanism controlling how marine ecosystems work. All marine life builds on primary production that mostly occurs in the upper ocean, where sunlight is available for growth of phytoplankton. Besides sunlight, primary production also requires nutrients originating from the deep ocean. Strong phytoplankton bloom can occur when nutrients from the deep ocean are mixed upwards to meet sunlight near the surface. This requirement is foremost met during spring time, as winter is generally too dark and nutrients that were brought upward during winter storms are quickly consumed before the summer. However, another mechanism that can mix nutrients vertically are breaking internal waves in the ocean. Internal waves are disturbances at the interface between heavy bottom water and lighter surface water. In the Norwegian Sea such waves are generated when tidal flow is forced over subsea mountain ridges. During wave breaking, strong vertical mixing can occur throughout the entire depth of the ocean providing vast amounts of nutrients to the upper ocean. Primary production can thereby be sustained throughout the entire spring and summer, with tides as a periodic and predictable trigger. Surface signatures of internal waves are frequently observed in satellite images in the Norwegian Sea off Lofoten and Vesterålen, a spot with a remarkable abundance of marine life. This location even hosts rare colonies of cold water coral, a species requiring rather large and steady supply of nutrients. In the EcoPulse project, mathematical models are beeing used to investigate criteria for breaking of internal waves. Along with field observations of ocean currents, tides and nutrient transport, the research group is investigating the role of internal wave breaking for the local ecosystem and cold water coral in particular. Update autumn 2021: - To understand and quantify the exact mechanisms of internal waves that contribute to vertical mixing, idealized numerical experiments have been carried out. The simulations tell us under which criteria internal waves at Hola are expected to break, and which part of the water column is succeptible to enhanced vertical transport, transferring nutrient between benthic and palagic layers. - Case studies on synergy between satellite imagery, wave theory and regional ocean circulation models is beeing conducted, looking at historic wave breaking events at Hola. - Field work to collect data of hydrography, ocean currents, turbulence and nutrient transport near the Hola reef is completed. - Localisation of coral reef sites are analysed in context with ocean circulation patterns on the Norwegian Shelf. Update autumn 2022: - Field work at Hola has been repeated with additional measurements - The numerical experiments in Basilisk are completed