Dr Mirjam Glessmer, currently working at the Geophysical Institute, University of Bergen, invited me to watch her demonstrating the interaction of sea water and fresh water when subjected to centrifugal forces.
So... we have salt water dyed magenta held in an upside down flask in the centre of a tank filled with fresh tap water.
When the revolving tank is stopped magenta-dyed salt water billows out evenly across the tank, slowly mixing with the freshwater.
Density of seawater is higher than fresh water. Viscosity (i.e., internal resistance to flow) of seawater is also higher than that of fresh water.
Thank you Mirjam!
(Dr Mirjam Gleßmer is a Postdoctoral Fellow in Physical Oceanography/Climate Dynamics at the Geophysical Institute, University of Bergen).
Staying at Ann Karin's house, overlooking the sea at the entrance to Bergen between the Askøy and Sotra suspension bridges, I spent a lot of time watching the sea traffic - small speed boats, sail boats, vast cruise ships, tug boats, containers and reefers, even the occasional rowboat - passing by, and the ever-changing surface of the sea flowing back and forth, waves and ripples spreading out from the boats. But even when vessels were not passing there were times when we could see areas where the surface of the water was disturbed - a sort of agitated flurry on the surface, and flow lines - and these were probably caused by fresh water flowing off the land into the sea and the interaction between them.