Contrasts in turbulent vertical fluxes of nutrients across the permanent Lofoten Basin Eddy in the Nordic Seas

• Main Authors: Bosse, Anthony, Fer, Ilker
• Other Authors: Institut méditerranéen d'océanologie (MIO), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS), University of Bergen (UiB)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2023
• Subjects: [SDU]Sciences of the Universe [physics]; Lofoten; Nordic Seas
• Online Access: https://insu.hal.science/insu-03952247; https://doi.org/10.5194/egusphere-egu22-5808

International audience Mesoscale eddies play an increasingly recognized role on modulating turbulence levels and associated diapycnal fluxes in the ocean, in particular with increased dissipation rates found in anticyclones. In September 2017, the last cruise of the ProVoLo project in the Nordic Seas (https://www.uib.no/en/rg/fysos/97330/provolo) intensively surveyed an energetic mesoscale anticyclone (the permanent Lofoten Basin Eddy) to characterize turbulence of the upper layer and eventually quantify the resulting vertical fluxes nutrients caused by turbulence.The sampling strategy combined ship-borne measurements and autonomous platforms. The vessel carried out a radial transect with stations spaced by 5 km near the center and 10-20 km outside the eddy with measurements of temperature and salinity (CTD), currents (lowered ADCP) and turbulence (Vertical Microstructure Profiler, VMP2000). Water samples were analyzed to estimate the concentration of the main nutrients (nitrate, phosphate and silicate). In addition, two autonomous oceanic gliders were used. A first glider profiling 0-1000 m deep was completing a 6-month mission. A second glider was specifically deployed during the cruise (5 days). This glider was equipped with a dissolved oxygen Aanderaa optode, a WET Labs FLNTU fluorescence and turbidity sensor and a Rockland Scientific Microrider sampling turbulence. It sampled the surface layer (0-300 m) at high temporal (~30 min) and spatial (~500 m) resolution from about 60 km to 5 km of the eddy center.By combining those measurements, we characterized the turbulence dissipation rates, vertical diffusion and its associated fluxes across the different nutriclines from the center to the outside region area of the eddy, revealing significant contrasts. Below the thermocline, turbulent patches were observed within the core with dissipation rates elevated by one order of magnitude relative to the values outside. The higher levels of dissipation rates supported 10-fold stronger vertical diffusion coefficients, ...