Oceans cover about 70 percent of the Earth's surface and about 97 percent of all water on and in the Earth is saline —there's a lot of salty water on our planet. But, where did all this salt come from? Salt in the ocean comes from rocks on land.
Here's how it works:. The rain that falls on the land contains some dissolved carbon dioxide from the surrounding air. This causes the rainwater to be slightly acidic due to carbonic acid. The rain physically erodes the rock and the acids chemically break down the rocks and carries salts and minerals along in a dissolved state as ions.
The ions in the runoff are carried to the streams and rivers and then to the ocean. Many of the dissolved ions are used by organisms in the ocean and are removed from the water. Others are not used up and are left for long periods of time where their concentrations increase over time. The two ions that are present most often in seawater are chloride and sodium. The concentration of salt in seawater its salinity is about 35 parts per thousand; in other words, about 3. In a cubic mile of seawater, the weight of the salt as sodium chloride would be about million tons.
A cubic mile of seawater can also contain up to 25 pounds of gold and up to 45 pounds of silver! But before you go out and try alchemy on seawater, just think about how big a cubic mile is: 1 cubic mile contains 1,,,, gallons of water! Saltwater intrusion threatens the water supplies of many coastal communities. Management of these water supplies requires well-designed and properly maintained and operated salinity monitoring networks.
Long-standing deficiencies identified in a salinity monitoring network in southwest Florida during a study Prinos, help to illustrate All water, even rain water, contains dissolved chemicals which scientists call "salts.
Water is fresh or salty according to individual judgment, and in making this decision man is more convinced by his sense of taste than by a laboratory test. It is one's taste buds that accept one water and reject another. The rain physically erodes the rock and the acids chemically break down the rocks and carries salts and minerals along in a dissolved state as ions.
The ions in the runoff are carried to the streams and rivers and then to the ocean. Many of the dissolved ions are used by organisms in the ocean and are removed from the water. Others are not used up and are left for long periods of time where their concentrations increase over time. The two ions that are present most often in seawater are chloride and sodium.
By the way, the concentration of salt in seawater salinity is about 35 parts per thousand. In other words, about 35 of 1, 3.
And, just so you don't think seawater is worthless, a cubic mile of it also can contain up to 25 pounds of gold at a concentration of 0. Before you go out and try alchemy on seawater, though, just think about how big a cubic mile is 1 cubic mile contains 1,,,, gallons!
In , scientists exploring the NW Eifuku volcano near the Mariana Islands reported seeing small white chimneys emitting a cloudy white fluid near the volcano's summit, as well as masses of bubbles rising from the sediment around the chimneys. In this picture you can see masses of minerals and carbon dioxide escaping from the earth's crust into the ocean.
These vents contribute dissolved minerals to the oceans, which is one reason the oceans are salty. Credit: NOAA. Rivers and surface runoff are not the only source of dissolved salts.
Hydrothermal vents are recently-discovered features on the crest of oceanic ridges that contribute dissolved minerals to the oceans. These vents are the exit point on the ocean floor from which sea water that has seeped into the rocks of the oceanic crust has become hotter, has dissolved some of the minerals from the crust, and then flows back into the ocean.
With the hot water comes large amounts of dissolved minerals. Estimates of the amount of hydrothermal fluids now flowing from these vents indicate that the entire volume of the oceans could seep through the oceanic crust in about 10 million years.
The amount of salt in sea water also determines the temperature at which sea water freezes. Adding salt to water lowers the freezing temperature. Yet, despite the saltiness of the ocean, sea ice contains very little salt, about a tenth of the amount of salt that sea water has. This is because ice will not incorporate sea salt into its crystal structure.
Therefore, sea ice is actually drinkable. The temperature and salinity of the sea water also help determine its density. As the temperature of sea water decreases the density also increases. Also, as the salt content of sea water increases , so does its density. This makes the density of sea water, unlike fresh water, below the freezing point. So, in situations of sea ice formation, the salinity, and therefore the density of the underlying water continues to increase well after an area is iced over.
The salinity sensor detects the microwave emissivity of the top 1 to 2 centimeters about an inch of ocean water — a physical property that varies depending on temperature and saltiness. The instrument collects data in kilometer-wide mile swaths in an orbit designed to obtain a complete survey of global salinity of ice-free oceans every seven days. Data from Aquarius has unveiled a world of varying salinity patterns. The Arabian Sea, nestled up against the dry Middle East, appears much saltier than the neighboring Bay of Bengal, which gets showered by intense monsoon rains and receives freshwater discharges from the Ganges and other large rivers.
Another mighty river, the Amazon, releases a large freshwater plume that heads east toward Africa or bends up north to the Caribbean, depending on the prevailing seasonal currents. One of the features that stand out most clearly is a large patch of highly saline water across the North Atlantic. This area, the saltiest anywhere in the open ocean, is analogous to deserts on land, where little rainfall and a lot of evaporation occur.
In future years, one of the main goals is to fine-tune the readings and retrieve data closer to the coasts and the poles. Land and ice emit very bright microwave emissions that swamp the signal read by the satellite. Another factor that affects salinity readings is intense rainfall. Heavy rain can affect salinity readings by attenuating the microwave signal Aquarius reads off the ocean surface as it travels through the soaked atmosphere. Rainfall can also create roughness and shallow pools of fresh water on the ocean surface.
An ultimate goal is combining the Aquarius measurements to those of its European counterpart, the Soil Moisture and Ocean Salinity satellite SMOS to produce more accurate and finer maps of ocean salinity. In addition, the Aquarius team, in collaboration with researchers at the U. Learn More About This Image. Salinity Although everyone knows that seawater is salty, few know that even small variations in ocean surface salinity i.
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