519 / 2024-09-18 09:40:47

Frontal Subduction and its Influences on the Phytoplankton Distributions on the Norwegian Sea Slope

subduction,frontogenesis,Norwegian Sea slope front

The slope and shelf regions of the Norwegian Sea are characterized by high biological productivity that supports elevated biomasses of high-trophic-level predators and fisheries. The main currents in the Norwegian Sea Slope are the Norwegian Atlantic Slope Current carrying warm and saline water from the Atlantic and the Norwegian Coastal Current carrying cold and fresh water, which yield a salinity-controlled density front influencing the distributions of plankton. In spring 2019, a cruise was conducted in the Norwegian Sea slope and shelf regions for resolving mesoscale physical and biological processes by employing a Moving Vessel Profiler (MVP) equipped with coupled physical-biological sensors. Observations from the MVP showed that chlorophyll maxima occurred at the surface offshore of the slope front and at the subsurface inshore of the front, reaching depths of up to 150 m, suggesting a significant frontal subduction. Dynamic diagnosis based on the cruise data revealed strong relative vorticity and convergence at the place where the signal of chlorophyll maxima descended, indicating prevailing frontogenetic processes. Satellite image of surface chlorophyll concentrations suggested that the front exhibited a meandering structure with a wavelength of about 35 km, and the surface front observed during the cruise was near the meander. An idealized numerical model which can resolve submesocale processes was developed to explore the mechanisms of frontal subduction. Preliminary results indicate that subduction occurs at the wave trough, a region typically associated with frontogenesis. Furthermore, frontogenesis appears to be linked to the curvature of the meander.