OURS IS A BRINY WORLD
Aristotle (350 BC) was the first to cogently describe what we call the water or hydrologic cycle, stating in his “ Meteorology”(@340BC) “by the sun the finest sweetest water is everyday carried up …into vapor..where it condenses into clouds by the cold…and so returns to earth”… as rain.
The hydrologic cycle states that water circulates through the atmosphere, oceans and on and within continents and into rivers all driven by solar radiation. Evaporation produces water vapor which condenses into clouds and which eventually produce precipitation in the form of liquid rain, or ice in diverse forms. Rain falls to earth, flows over the surface or seeps underground on its eventual way to the world ocean. On this course, fresh water tends to dissolve minerals such as salts and carry them to the sea. Thus the seas become salty.
Did you know that the Earth is the only “watery planet” in our solar system? Blue water covers more than 70% of the planet’s surface. Almost all of it ( 97%) is of the briny type, undrinkable, useless for washing clothes, cooking or cleaning. The “fresh” or “sweet” water we so crave on a hot summer day makes up only 3% of the total. But of that three percent (3%) about 2% is still tied up as solid glacial ice (We are still recovering and warming up from the last Ice Age) Only 1% of the total is “fresh” liquid water! Of this liquid fresh water most is underground as “ground water” filing the tiny voids between sand or mineral grains. Only a tiny portion perhaps only 0.3% of the total is the sparkling surface waters in rivers, streams, ponds, lakes, and not so sparkling swamp and marsh water. Naturally some small percent of this total (perhaps 0.001%) is always in the atmosphere as solid liquid or gas.
As a youngster living close to the rock-strewn North Shore of Long Island, one learned early on just how “briny” sea water was. Long Island Sound water tasted salty, and was more dense than fresh water, so it pleasantly buoyed up a skinny, boney kid who struggled to learn how to swim. For kids, swimming and floating was easier in the Sound than in the fresh water in near-by fresh water Deep Pond.
Then too Long Island Sound water left a film of dried salt all over one’s body. If your clothes were soaked at the beach, or while boating, and dried by the time you reached home, salt crystals formed in the fabric and remained there to keep a kid’s sweaters damp and clammy permanently. That is, until Mom put them through the clothes washer.
But it was the huge, rough-surfaced erratic boulders scattered along our beach which provided absolute visual proof. On any hot summer day during ebb tide (low water) one could always find clumps of little, grayish-white salt crystals in the small depressions on the tops of those big boulders. On flood tide, sea water collected in the hollows and evaporated away in the sun on the ebb tide, leaving behind a scant teaspoon-cluster of grayish crystals. My friends and I tasted this “sea salt”. The crystals were salty, and a bit more bitter than regular table salt. Sea salt is—just like table salt—mostly sodium chloride, but it has other “chlorides” as well, such as potassium and magnesium chloride. Coming from a depression in a sea-side boulder it also had, bits of seaweed, barnacles and brown algae too.
Oceans are salty. The average salt content of the world ocean is about 35 parts of salt to one thousand parts water (or 35ppt). That is equal to about 35 grams of “salt” in each kilogram (1000g, or 1 liter) of sea water. In “Mom’s kitchen” terms that is about 1.2oz of salt (in “weight” oz) in about two pounds of sea water (or about one really full one-quart bottle of water). Another way to say this is that sea water is about 3.5% salt.
Some oceans are saltier than others. The Mediterranean and Red Sea are more “salty” than other bodies of sea water. The salinity of the Red Sea and near-by Persian Gulf are in the 40g per liter or 40 ppt, or 4% range. The eastern Mediterranean has a similar high salinity. Both bodies of water are located on parts of the Earth surrounded by global desert zones (the desert latitudes (30N and 30 S) and for this reason have few fresh water rivers flowing into them. These oceans are in latitudes where they also experience high levels of sea water evaporation but little replenishment of fresh water by rain or river inflow.
While marine bodies such as Long Island Sound, partly enclosed by land, in the temperate and rainy Mid Latitudes where rainfall is high and where major fresh water rivers and streams empty into it result in lower salinity levels. Long Island Sound water averages about 2.7% salt while, across Long Island, in the Atlantic Ocean near Smith’s Point Beach, sea water is about 3.5% and even tastes considerably saltier. Saltiness is not confined to marine environments.
Human body fluids are salty too. Blood, urine, tears and sweat all have salt concentrations on a weight to volume basis of about 0.9% or 9g of salt per liter of fluid. (Or @ 0.4-0.5% on weight to weight ratio) While sea water has about 35g per liter or is 3.5% salt. Thus sea water is almost four times “saltier” than our body fluids. See below. Except for those regions above, the World Ocean is very well mixed, and all off shore marine water has the average of about 35 grams of salts in every liter of sea water. That is a lot of salt!
To understand how much salt that represents, one might imagine a circumstance in which all the ocean water were to evaporate away. (Keep in mind, that when sea water evaporates only water (H2O) leaves the ocean. Salt is trapped in the remaining water and remains behind permanently.) With its present salinity and assuming the planet was a perfect sphere, some investigators have calculated that the evaporation process would leave a thick layer of salt crystals about 131meters thick ( @ 430 ft) all across the Earth’s sea bottom ( Oceans represent @ 70% of the earth surface) . Obviously that amount of salt is a huge unimaginable amount of salt. But where does it come from?
Sodium Chloride (NaCl) is most common “sea salt” because the element sodium is one of the more common elements in the Earth’s crust (It is about the sixth most common). But the element chlorine is rare as a crustal element. So one wonders where did all this chlorine come from to combine with sodium to produce the vast quantities of sodium chloride (and the other chloride salts) we find in the world ocean
Salts are formed as the rocks and minerals of the earth’s crust (the rocky continents) are chemically altered by contact with water and gases of the atmosphere. The Earth’s crust is generally divided into lighter less dense rocks which form the higher standing continents and the denser rocks which form the crust of the ocean basins. The crust is primarily composed of the elements oxygen and silicon along with aluminum and other metallic elements which make up the bulk of the solid earth’s rocky crust.
A very common rock forming mineral, plagioclase feldspar, is a sodium rich feldspar (It is chemically a sodium-calcium aluminosilicate). Plagioclase feldspar is one of the most abundant mineral type since it is a major constituent of Earth’s mantle rocks (which make up 80% of earth volume). As a result of volcanic processes these deep earth minerals are released violently or extruded quietly onto the earth’s surface and exposed to its atmosphere. When this occurs they are chemically and physically altered in a process called “weathering”. The weathering process of plagioclase feldspars is a main source of the sodium ions.
Whereas, chlorine is a much less common element. However, chlorine is found in volcanic gases in the form of gaseous HCL. Volcanic eruptions from the deep earth produce great quantities of water vapor, carbon dioxide and sulfur dioxide which make up 99% of volcanic gas volume. The remaining 1% are gases such as hydrogen sulfide, carbon monoxide, and hydrogen chloride, and other even more rare gases. (The water vapor from volcanic eruptions no doubt is the source of the Earth’s oceans.)
Thus in the Earth’s ancient history the ions necessary to produce sodium chloride seem likely to have been derived from the elemental geological process of weathering of sodium bearing plagioclase-rich rocks and the explosive exhalations of chlorine bearing gases from volcanic eruptions. The latter produced chloride ions while the former produced sodium ions.
Thus the massive sea salt amounts in the present day ocean, are the result of the long slow process of weathering of rocks (Na or sodium ions) combined with the continual intermittent gaseous volcanic exhalations ( HCL) of the chloride ions from the earth’s interior.
It must have taken billions of years for these processes of salt formation to reach the present state of ocean salinity. The world ocean salinity must have been much less in the distant past. Perhaps when the simplest eucaryote cells formed in a rocky ocean pool billions of years ago ocean salinity was much lower. This may explain why present day ocean salinity is about four times that of human body fluids.
(Incidentally, about 6 million years ago (6 MYA) the entire Mediterranean Sea actually did evaporate away and it left behind thick layers of salt! This occurred when the Mediterranean’s only connection to the Atlantic Ocean closed up as a result of the African continental plate moving north to press into Europe. No Atlantic water could flow in to the sea basin to replace the water constantly evaporating away. The result left thick layers of salt and other evaporites on the sea floor. The dry land connection from Africa to Europe also permitted plants and animals from Europe and Africa to mix as they moved across the dry landscape. (That is another story).
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