Buoyant

Salt water is more buoyant than fresh water.

How can ships be buoyant when not even rocks are?

Unsurprisingly, ducks are buoyant.

She was in a buoyant mood.

Audubon was blessed with good health, length of years, a devoted and self-sacrificing wife, and a buoyant, sanguine, and elastic disposition. He had the heavenly gift of enthusiasm—a passionate love for the work he set out to do. He was a natural hunter, roamer, woodsman; as unworldly as a child, and as simple and transparent. We have had better trained and more scientific ornithologists since his day, but none with his abandon and poetic fervour in the study of our birds.

And of course, in order to understand the Earth's past and how it got to where it now is, it is important to have a basic knowledge of plate tectonics, which explains how the planet's continental and oceanic crusts are part of the lithospheric plates that are buoyant and ride upon the highly viscous asthenosphere.

I’m in a buoyant mood.

There was no delirium when he awoke in the morning. Instead, there was only a feeling of buoyant health. In fact, Dave Hanson had never felt that good in his life—or his former life. He reconsidered his belief that there was no delirium, wondering if the feeling were not itself a form of hallucination.

[...] the accelerated, high-frequency East Coast express timetable, operating this year in a buoyant economic environment, is beginning to attract more business travel to rail (although there is still a long way to go before the potential is fully realised); [...].

It[China] had a buoyant economy outperforming forecasts. Its unemployment rate was among the lowest in years. While consolidating his power for a second term, Mr Xi proudly pointed to China's "flourishing" growth model as something other countries could emulate.