Diapycnal mixing across the photic zone of the NE-Atlantic

• Main Authors: Haren, Hans, Brussaard, Corina P. D., Gerringa, Loes J. A., Manen, Mathijs H., Middag, Rob, Groenewegen, Ruud
• Format: Text
• Language: English
• Published: 2020
• Subjects: Yoyo; Northeast Atlantic
• Online Access: https://doi.org/10.5194/os-2020-73; https://os.copernicus.org/preprints/os-2020-73/

Variable physical conditions such as vertical turbulent exchange, internal wave and mesoscale eddy action, affect the availability of light and nutrients for phytoplankton (unicellular algae) growth. It is hypothesized that changes in ocean temperature may affect ocean vertical density stratification, which may hamper vertical exchange. In order to quantify variations in physical conditions in the Northeast Atlantic Ocean, we sampled a latitudinal transect along 17 ± 5° W between 30 and 62° N in summer. A shipborne Conductivity-Temperature-Depth CTD-instrumented package was used with a custom-made modification of the pump-inlet to minimize detrimental effects of ship motions on its data. Thorpe-scale analysis was used to establish turbulence values for the upper 500 m near the surface from 3 to 6 profiles obtained in a short CTD-yoyo, 3 to 5 h after local sunrise. From south to north, temperature decreased together with stratification while turbulence values weakly increased or remained constant. Vertical turbulent nutrient fluxes across the stratification did not vary with latitude. This lack of correspondence between turbulent mixing and temperature is suggested to be due to internal waves breaking and acting as a potential feed-back mechanism. Our findings suggest that nutrient availability for phytoplankton in the euphotic surface waters may not be affected by the physical process of global warming.