I wake on the first day of 2024 to your meditation and scientific observations of salt and learned so much about what I usually measure for recipes or sprinkle on foods. I know someone whose death is held at bay by consuming no salt. Your work as always is both a probe of life on earth and a philosophical way of looking at it.
Walter, your wonderful essays serve as artful meditations that can lead one to further explore the intriguing subjects you present. Today's riff on salt reminded me of the remnants of large rusting iron fire pots we encountered in the marshes of the St. Marks Wildlife Refuge, which you explained were used to evaporate salt as part of the civil war effort. Your essay also prompted me to read about the importance of salt licks as sources of essential minerals for wildlife and farm animals. As a kid visiting the family farm, I was fascinated watching holstein cows in pasture licking out graceful curves in big pink salt blocks, but I don't recall thinking much about the purpose of blocks until I dug into the internet today. As always, thanks for sharing your remarkably wide-ranging and deeply penetrating curiosity. It really is infectious.
I first encountered marshes during a road trip I took between graduation and starting my full-time job. As I drove up the coast from Florida to Georgia, I was stunned by both the beauty and uniqueness of a landscape so affected by daily tides. Thanks for prompting a pleasant trip down memory lane for me!
What a delightful tour de force! Where is sea level affected by the density of the underlying rock? I assume that more dense rock results in higher atmospheric pressure which results in a locally depressed sea level?
Denser rock has more mass and therefore more gravity, depressing sea level above it as a result. It's really a question of the amount of mass underlying the point at which an earth's radius intersects the earth's surface. Sedimentary rocks are generally less dense than igneous rocks such as basalts. Effect of the small differences in sea level on atmospheric pressure is probably very small.
I assume sea water is incompressible. Isn't the depressed sea level a result of increased atmospheric pressure displacing the water above the more dense rock?
Good question. As I understand it, the water is held more strongly over denser rock and less strongly over weaker rock, "pulled tighter" if you please. On a global scale, the surface of equal gravity is not a sphere, but a geoid because mass is not equally distributed in the Earth. Here is a link to how gravity anomolies are measured: https://en.wikipedia.org/wiki/GRACE_and_GRACE-FO. After reading this and other articles, I am not sure that gravity and/or sea level is measured on the scale implied by my claim about relatively local effects of rock density. The gravity measurements clearly show the effects of ocean currents, and can measure the amount (and pressure on the ocean bottom) of water plus atmosphere at any point. Atmospheric pressure is most responsive to heating by the sun and the circulatory pattern thus created. It also affects sea level as anyone near the coast in a hurricane can attest. To refer back to my essay, most of the (static) sea level variation seems to be related to ocean currents. It's a very complex business.
I wake on the first day of 2024 to your meditation and scientific observations of salt and learned so much about what I usually measure for recipes or sprinkle on foods. I know someone whose death is held at bay by consuming no salt. Your work as always is both a probe of life on earth and a philosophical way of looking at it.
Walter, your wonderful essays serve as artful meditations that can lead one to further explore the intriguing subjects you present. Today's riff on salt reminded me of the remnants of large rusting iron fire pots we encountered in the marshes of the St. Marks Wildlife Refuge, which you explained were used to evaporate salt as part of the civil war effort. Your essay also prompted me to read about the importance of salt licks as sources of essential minerals for wildlife and farm animals. As a kid visiting the family farm, I was fascinated watching holstein cows in pasture licking out graceful curves in big pink salt blocks, but I don't recall thinking much about the purpose of blocks until I dug into the internet today. As always, thanks for sharing your remarkably wide-ranging and deeply penetrating curiosity. It really is infectious.
This is an absolutely beautiful meditation on salt. Thank you. I'm so glad Dana Bryan pointed me to your letters.
I first encountered marshes during a road trip I took between graduation and starting my full-time job. As I drove up the coast from Florida to Georgia, I was stunned by both the beauty and uniqueness of a landscape so affected by daily tides. Thanks for prompting a pleasant trip down memory lane for me!
I was once out in the middle of a salt marsh and watched a feral sow and her piglets trot by. I felt I was in the savannas of Africa.
Good heavens! :D
What a delightful tour de force! Where is sea level affected by the density of the underlying rock? I assume that more dense rock results in higher atmospheric pressure which results in a locally depressed sea level?
Denser rock has more mass and therefore more gravity, depressing sea level above it as a result. It's really a question of the amount of mass underlying the point at which an earth's radius intersects the earth's surface. Sedimentary rocks are generally less dense than igneous rocks such as basalts. Effect of the small differences in sea level on atmospheric pressure is probably very small.
I assume sea water is incompressible. Isn't the depressed sea level a result of increased atmospheric pressure displacing the water above the more dense rock?
Good question. As I understand it, the water is held more strongly over denser rock and less strongly over weaker rock, "pulled tighter" if you please. On a global scale, the surface of equal gravity is not a sphere, but a geoid because mass is not equally distributed in the Earth. Here is a link to how gravity anomolies are measured: https://en.wikipedia.org/wiki/GRACE_and_GRACE-FO. After reading this and other articles, I am not sure that gravity and/or sea level is measured on the scale implied by my claim about relatively local effects of rock density. The gravity measurements clearly show the effects of ocean currents, and can measure the amount (and pressure on the ocean bottom) of water plus atmosphere at any point. Atmospheric pressure is most responsive to heating by the sun and the circulatory pattern thus created. It also affects sea level as anyone near the coast in a hurricane can attest. To refer back to my essay, most of the (static) sea level variation seems to be related to ocean currents. It's a very complex business.
Tremendously informative, lyrical, and thought provoking. Like all your writings and I highly recommend your books on Ants to your readers.