Thinking about dolphin buoyancy on Chanonry Point

We were back on Chanonry Point near Inverness to watch the dolphins. Marvellous! I got to thinking about floating and sinking. When you get into water, you push water out of the way: we say that the water is displaced. You can catch the displaced water and weigh it. When you get into water, you feel lighter. This is because there is an upwards force on you called "upthrust". That's your buoyancy. Archimedes showed that the upthrust is equal to the weight of the displaced water. By weight, I mean the pull of gravity on that mass of water, measured in Newtons. If the weight of displaced water is more than your own weight, you float. You and the displaced water will occupy the same volume but the displaced water will have more mass and thus you will be less dense than the water. A dolphin can make this happen by filling its lungs with air. I found an excellent article on the various factors that can affect buoyancy in dolphins: http://www.dolphincommunicationproject.org/index.php/2014-10-21-00-13-26/dolphin-science-factoids/item/94360-do-dolphins-float-or-sink