This last month has been ‘tough’ on our ambassadors. From getting shiny new equipment, having their claws and beaks trimmed up, and enjoying some enclosure upgrades, you’d think they’d be excited about all the nice things we do for them, but they’re creatures of habit. They get a bit salty about change.
As it just so happens, TUI is focusing on oceans this month. So, in honor of those briny waves, and our slightly salty (at the moment) Ambassadors, we decided to dedicate this entire newsletter to the most abundant mineral on Earth: Salt!
What exactly is Salt?
The first thing we need to ask ourselves is: What exactly is the substance we call salt? Our immediate thought is to consider the table salt we may use in our kitchen to season food. It’s small, and looks kind of like a rock or a crystal, right? Scientifically, salt is any substance produced by combining an acid and a base together. This means, the kitchen salt we have on our counter is the product of mixing two other chemicals together. In the case of table salt, those chemicals are Sodium and Chlorine.
By themselves, each of these elements are highly reactive and potentially hazardous to our health, but when they are combined, they create the wonderful and useful substance we call salt.
On its own, sodium is an extremely light and malleable substance known as an alkaline metal. This substance is easily bent, torn or cut, and serves as a good conductor of electricity. But its most notable property is perhaps its reactivity to water. When water comes into contact with sodium, the material will violently burst into flames. The danger of combustion is so high, that even airborne humidity can cause a reaction. (elementalmatter.info)
Chlorine, on the other hand, is a naturally gaseous element of a yellow-green hue. While the gas is toxic, it is not found alone in nature, and is instead combined with other elements to create a chloride or bonded chemical of some sort. In the theme of our topic, it is most often found bonded with sodium to create sodium chloride, or common salt. (rsc.org)
What Makes the Ocean Salty?
So if salt is just Sodium and Chlorine combined, then where does salt come from, and why does it collect in the ocean?
The earth’s oceans actually get their salt from the rocks on land. Whenever it rains on land, the droplets contain some of the carbon dioxide from the air it falls through. This causes the rainwater to become slightly acidic, as some of the water molecules and the carbon dioxide combine to create trace amounts of carbonic acid. This slightly acidic rainfall erodes the rocks, and the carbonic acid breaks down the rocks into salts, which are then swept out to the sea via rivers and streams.
Over 90% of all ions in seawater are sodium and chloride; this makes the ocean “salty.” If all of the salt in the ocean could be removed and spread out over the earth’s land surface, it would be over 500 feet thick. That’s about as tall as 25 giraffes stacked on top of each other! (oceanservice.noaa.gov)
How do Marine Animals Handle this salt?
Most bony fish are like people. They cannot survive with too much salt in their bodies. So there is not a lot of salt mixing with the water and blood inside of a fish. These fish are kind of like the fresh water we talked about in the paragraphs above. But unlike the fresh water above, their skin prevents salt from entering the body to mix with the water inside the fish. Unfortunately, their skin cannot keep water from leaving their body to mix with the more salty solutions around them. So these fish are always losing water to the ocean around them
To combat this, most fish species actually drink a LOT of seawater. Their kidneys are efficient at removing the salt from the water they drink and excreting it in their urine so their bodies can use the new water properly. (amnh.org)
Because they don’t breathe with gills and because their skin is thicker than most fish, marine mammals do not share the same problems that fish do. Instead, they need to find sources of fresh water. To do this, they have adapted a different method of finding drinkable water than simply drinking from the ocean: their food! Most marine mammals obtain their water from their meals, which makes sense since we learned that fish have a higher concentration of drinkable water in their bodies. Marine mammals can also produce water via metabolic breakdown of food. This means they can get fresh water simply by digesting their meals!
To get rid of any excess salt they consume, or any they may drink, marine mammals produce extra salty urine. Since the surrounding seawater is almost 3x saltier than its own blood, the sea lion will collect this excess salt in their urine and excrete it all at once. This means that when they urinate, their urine will be almost 8x saltier than the rest of the water in their bodies, and almost 3x saltier than the surrounding ocean water. (thescientificamerican.com)
Interestingly, unlike other fish species, sharks lose far less water from their skin and gills. This is due to a handy chemical called urea, which helps keep shark’s body in a chemical equilibrium with the ocean water around it. Instead of drinking seawater, sharks absorb some seawater through their gills. Sharks also possess a specialized gland which removes the excess salt and secretes it from the body. This salt gland is found in several species of fish, rays, and even marine reptiles and birds. (amnh.org)
The Amazing Salt Gland
The salt gland is a magnificent natural structure which allows a number of species to survive on little to no fresh water, using the properties of salinity and equilibrium we discussed above. The final product of this process is a solution we call saline.
To work properly, the gland pumps blood with high salt concentrations close to a membrane supplied with fresh water. The salts are attracted to the low salinity of the fresh water, while the membrane keeps the water from mixing back into the blood. This creates a highly concentrated saline solution.
This solution is then excreted from the gland and out of the body, leaving the animal’s blood and body fluids far less salty than their surroundings.
Activities, Videos and More!
The Eyrie is a Patreon based Newsletter dedicated to exploring the intricate and fascinating topics found within the realms of science, nature, education, and conservation. Each month, our team explores a different subject, taking the time to examine the fascinating world around us. With the (mostly) helpful perspectives of our ambassador animals and the insight from our team, this newsletter is chock full of amazing facts, intriguing concepts, and even activities or experiments you can try at home!