If we somehow collected up all of the accessible concentrated deposits of salt in and on the land, and put it in the sea, how much more salty would the sea be.
Of course this question probably can’t be answered with precise certainty as some estimates and outright guesses will need to be in the mix, but for the purposes of the question:
‘Accessible concentrated deposits’ includes things like:
any solid ‘rock salt’ deposits that could theoretically be mined
salt lakes, coastal pans and landlocked seas, either dry, or where the salinity is greater than that of typical seawater
salt deposits that are not necessarily mostly sodium chloride, but are readily soluble in water
all of the unused salt that has already been extracted and is sitting in stockpiles, sacks, supermarket and salt cellars (I imagine this will be a proportionally tiny amount)
some reasonable estimate of yet-undiscovered salt deposits that meet the above criteria
It probably needs to exclude things like ‘salty soil’ where the proportion of salts is some smallish percentage.
Budget is irrelevant. Ecological impact is irrelevant. We’re going to dig up all the salt we can find and distribute quite evenly into the oceans (‘oceans’ being defined by any commonly accepted metric).
We might have to do some very loose back of the envelope calculations here, since a source like the USGS just states “World continental resources of salt are vast, and the salt content in the oceans is nearly unlimited.” in their summary of the state of salt production and reserves.
The volume of the oceans is 1.35 \times 10^9\ km^3 or 1.35 \times 10^{21}\ litres. Salt concentration is about 35 grams per litre. So 4.7 \times 10^{13}\ tons of salt.
Salt isn’t all that dense, only 2.16.
So the fractional volume of salt in seawater is about 0.016.
The area of the Earth is 5.1 \times 10^8\ km So if the Earth was perfectly smooth, the oceans would be 2.6km deep. Dried out the height of the salt in the oceans spread evenly over the Earth would be 42 metres deep.
There are buried salt deposits that are kilometres deep. Say in the Gulf of Mexico. They probably don’t meet the OP’s criteria. So,
I’m going to bet that the available salt deposits are a literal drop in the ocean compared to the salt already there.
I recall one argument about the Gaia hypothesis was that that the total amount of salt in the world, if it all went into the oceans at the same time, would be saline enough to kill all the salt water wildlife. Current geological trends seem to be making more salt reserves as the current ones find their way back into the oceans - almost like it was on purpose.
This article claims, “…suggest that for the first 500 million years of Earth’s existence, its oceans may have contained a salt level as high as 7.5%. Today’s oceans, by comparison, are about 2.5% salt.” So about triple today’s salinity.
What I found astounding from a time in petroleum exploration geophysics was just how much salt there is in deep strata. Geologists talk of evaporates. Huge multi kilometre thick layers of salt deposited from evaporating ancient seas that were subsequently covered by sedimentary or volcanic processes. These are of interest as they can form a useful seal over economically feasible oil and gas. Moreover the salt is mobile, moving like a lava lamp, potentially trapping and concentrating viable deposits under the edges of mushroom shaped diapires.
The above cite seems to suggest that at least some of these deposits would be subject to recycling in subduction zones, taking salt away from the crust again. Which seems reasonable.
Still not an answer to the OP.
Interesting question, here is what I can tell from experience: many cities in Europe are called after the salt deposits below: Salzburg (Salt-Burg), Hallstadt (Hals is Greek for salt), Halle, Hallein, Reichenhall… I visited some of those places as a kid and was told that when 1 km of sea evaporates it leaves 15 m of salt. They are tourist attraction now, I loved to visit them. The salt deposits being up to 1 km thick means there must have been a repeated cycle of evaporation and re-filling of the basins that formed the sediments, lots of salt was taken from the oceans for that. And when the whole Mediterranean Sea evaporated (see Messinian Salinity Crisis)
The amount of Messinian salts has been estimated as around 4×1018 kg (but this estimate may be reduced by 50 to 75% when more information becomes available and more than 1 million cubic kilometres, 50 times the amount of salt normally in the Mediterranean waters. This suggests either a succession of desiccations or a long period of hypersalinity during which incoming water from the Atlantic Ocean was evaporated with the level of the Mediterranean brine being similar to that of the Atlantic. The nature of the strata points strongly to several cycles of the Mediterranean Sea completely drying and being refilled.
Such salt depositis are fairly common, they exist not only in Europe, but in North America, Russia, India, China, Iran, Kazachstan, the Arabian Peninsula… Which suggests that a lot of salt has been taken from the seas by this mechanism. Not a drop in the ocean, as has been suggested. But how much, really? I am ready to believe 7.5%, but I wonder how you would prove that all the salt that exists was dissolved in the oceans at some point and when that point was: pre-cambrian? Perhaps the Cambrian explosion took place because the salt concentration was low enough for multi-cellular beings for the first time? Wildly speculating here, but as I wrote: very interesting question.
Assuming accessible concentrated deposits = Salt in Sedimentary rocks on Earth’s crust (roughly 10 mile deep)
With that assumption, Oceanic and Sedimentary rock salts → both come from teh decomposition of igneous rocks. The estimates are: From the leached igneous rocks; 68% of the sodium is oceanic and 32% remains in sedimentary rocks.
So if all the salt from the sedimentary rocks (this will include all salt domes, and salt formations, salt deposits, etc) was added to the ocean, the salt concentration will go up from 35 grams per liter to 35*100/68 ~ 52 grams per liter
Cite : This percentage is about 32 per cent of the total sodium in the igneous rocks, so that the oceanic sodium, which represents the quantity removed from the rocks by leaching, amounts to 68 per cent of the total sodium originally in the rocks.
(See page marked 30 on the top left hand corner of this report. Or Page 35 of 122 of the pdf file : https://pubs.usgs.gov/pp/0127/report.pdf)
Now if you included the salt in the igneous rocks of the crust too, then the salinity will go up about 35 times.
(doublechecking with a logical test: multiplying pretty much nothing with something nearly unlimited - the result will be vast - so, sounds about right)
I’m curious about the mechanism of salt “capture”. I can see, if the Straits of Gibraltar became blocked, the whole of the mediterranean might essentially dry up and create a salt pan, then get covered with dust and mud. But how do whole swaths of Texas to Alberta get this treatment? Did the inland Sea in North America close from the outside edges first? You would think that otherwise, most salt would be “swept out to sea” into the rest of the ocean. Yet even Louisiana seems to have a deeper layer of salt covering the oil in the delta.