Why is the dead sea so much saltier than the ocean?
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Water flows in, carying minerals from the ground like salt. Water doesn’t flow out from the sea, it only evaporates. But salt doesn’t evaporate, so salt concentrates in the water.
Tl;Dr – no outflow, just evaporation.
Evaporation. The dead sea used to be part of the ocean, however it cot cut off and became landlocked. Positioned in the desert, the water slowly evaporated over time, slowly raising the salt concentration.
You know how sauce becomes more salty when you cook it (“reducing” is the cooking term), that’s what the earth did with that body of water
The Dead Sea experiences a higher ratio of evaporation-to-volume than the ocean does, and has less fresh water relative to its volume flowing into it.
The Dead Sea is what is called “endorheic”, which means that it is a lake or other body of water that has no outputs – water flows into it, but no water flows out of it to the oceans.
When water first rains, starting the water cycle, it has no minerals or other substances (*generally* speaking) dissolved in it, because it condensed from water vapor which is pure H2O. Then, as that water hits the ground and flows along, it slowly picks up minerals and other substances from the ground around it. For instance, if you live in an area with a lot of limestone, the water you might get from a well is “freshwater” technically, but it has a lot of calcium dissolved in it, and thus it’s “hard water” which causes scaling, etc.
Salt is something that dissolves very easily in water, and it’s all over the place on Earth, so the water that flows out to the ocean slowly picks up salt, making it the salt water we know of. It took this water a very long time – billions of years, to get as salty as it is now, and in a few more billion years, it would be even more salty. This is because, as the water evaporates from the ocean – the second half of the water cycle – it leaves that salt behind, forming that pure H2O that condensed back into rain. The entirety of earth is a closed loop, so the salt just stays in the ocean over time, but there is a *lot* of water in the ocean, so the fraction of salt is relatively stable except over very long (geological) timescales.
The Dead Sea, because it is endorheic, has this happen on a much much faster timescale. Water flows in with salt in it, the water in the lake gets saltier, water evaporates leaving the salt behind, and the cycle repeats. But because the lake is so much smaller than the ocean, this happens much quicker, leaving a much saltier lake than the oceans where all that salt has more water to dilute it in.
This has also accelerated in recent (last few hundred) years, as more water is taken from the Jordan river, the main source of the Dead Sea, for irrigation purposes. So the water level of the Dead Sea keeps dropping as more water evaporates and less water comes in, but the same amount of salt is still there, so the amount of salt in any given amount of water is increasing even faster than it would naturally.
If the Dead Sea were to suddenly have a river sprout out of it and go to the ocean (ignoring for a moment that it’s ~430 meters below sea level, so the ocean would flow in not the Dead Sea flow out), the salt would gradually be diluted in the billions and billions of litres of ocean water, and the overall salt content there would be, effectively, unchanged. But in the tiny lake, it’s proportionally a lot of salt.
The ocean’s salinity doesn’t change because, for the most part, it’s a closed system: any water that *leaves* the ocean eventually makes it *back* to the ocean, aside from very small amounts.
That isn’t true of the Dead Sea. The water that leaves the Dead Sea mostly does not ever return to it, but the salt it had dissolved sticks around. Like most lakes without an outlet, that means the Dead Sea steadily accumulates salt that has no good way to leave, making it extremely salty.
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