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Why is the ocean salty? (noaa.gov)
234 points by tosh 39 days ago | hide | past | web | favorite | 90 comments



I like that the article begins with a tl;dr summary of

> Ocean salt primarily comes from rocks on land

Not many articles do that, but it only made reading the rest of the article more appealing to me, not less.


It's called the Inverted Pyramid structure, and it's how articles are supposed to be written. I learned it in junior high [https://en.wikipedia.org/wiki/Inverted_pyramid_(journalism)]. But yeah, it's not how many articles come today:

1. Clickbait headline that tells you nothing. (Unfortunately this article retains that flaw)

2. Introduction by the author of --- the author! He had been thinking about this topic for a long time. He had this conversation with his colleagues about it (reproduced here). Then his editor finally challenged him to have a go at it. So here it is!

3. Encyclopedic history of the topic (question still unanswered).

4. Compendium of assorted controversy and minority opinion (majority opinion still left to be stated).

5. The information.

6. Return to the author, his life, what he's doing afterwards, what he has eaten for breakfast, his favorite color, etc.

7. Request for comments, subscribe, like, share, etc.


>it's how articles are supposed to be written

It's how traditional straight news articles have historically been written in large part for practical reasons. Those reasons were particularly evident for wire service copy where the newspaper using the copy could pretty much cut off the article at any arbitrary point to fit it into whatever hole they had in their layout.

For feature articles and many magazine articles, there's no hard and fast journalism rule to use inverted pyramid and never has been.

You may prefer that everything be written with inverted pyramid and that is certainly your right--and there are often good reasons--but it's not the "right" way to do things.


> for practical reasons

You really think there is no benefit to the reader?

I agree that the Inverted Pyramid is the mainstay of news and would be unfit for a novel and even some long features like you find in New Yorker magazine.

But the problem isn't that there are too many articles written in the Inverse Pyramid that should have been written some other way. The problem is that too many articles that should have been written in the Inverted Pyramid aren't. If you have problems with making judgments and using the word "should," I'm talking about writing in the practical interests of the reader. If the reader comes to the article for information, then the article should get to the point as soon as possible. If the reader comes for entertainment (like a novel) then the writing can follow some other path.

To say that the reason for the Inverted Pyramid was mainly so that syndicates could cut the article at any point to fit the space they had is to ignore all the benefits to the reader. The reader is presented with a large newspaper of various articles, and he is trying to decide which ones to read and which to skip, because he doesn't have time to read a whole newspaper from start to finish every day. Some stories, he just wants the gist, which is why even the headlines are supposed to present the whole story, obviously in outline. A hurried reader can browse just the headlines and know the overall news of the day. A less-hurried reader can read the first paragraph of some of the more interesting stories. And so on.

Even though we don't have paper newspapers as much, we still have readers with short attentions spans. In fact, more so.


It’s been a while since I’ve read Slate but I recall their “Explainer” series always made a point of putting the answer in the first sentence, with the rest of the article serving as amplification. I really liked that, for the same reason you mentioned.


Also helps that the remaining article isn't just filler-text to hide that one actually interesting fact under and instead consists of interesting facts in every sentence.


I wonder why lakes aren't salty?

It's clear why rivers and lakes that eventually empty into the ocean are fresh. Rainwater washes the salt downstream to its ultimate destination.

But many lakes do not have an outlet that leads to the sea. Water flows in and evaporates. Where does the salt go in that case?

Or is it possible that the article doesn't tell the full story, and that salty rocks are confined to a limited number of areas?


Time scale. Lakes are static bodies of water for a few thousand to a million years at a time before some flood or glacier or whatnot flushes them out to the ocean. The ocean stores the accumulated salts of 4.7 billion years of surface rocks.


"Time scale" is actually a wonderful, pithy, accurate explanation for a lot of things!


Salt gets left when oceans get landlocked and die. (Thus the big layers of salt and salt mines). So it isn't really the accumulation of the age of the earth, it's a lot less because much gets redeposited.

But more generally yes, timescale.


> The ocean stores the accumulated salts of 4.7 billion years of surface rocks.

I've always wondered. Were the rocks really there for 4.7 billion years, or did God create the rocks in such a way to trick scientists into believing they've been there for 4.7 billion years?


Sarcasm like this doesn't typically go well here. This isn't Slashdot or /r/atheism. Believe it or not, there are religious people of various faiths on here, both in and out of the tech community. Statements like this don't add to the discussion, are frivolous and sorta mock peoples' believes.


I wasn't being sarcastic, or mocking anyone's beliefs, scientific or religious. Nor am I an atheist or got lost and think I'm on Slashdot. I was merely putting forth a question I've always thought was intellectually interesting, something that's supposed to be encouraged here. [1]

[1] https://news.ycombinator.com/newsfaq.html


In that case, the answer to your question is that there is no answer, that there can never be an answer (unless God tells us) and that there does not need to be an answer.

If God really made it so that it's impossible to tell that they are not 4.7 billion years old, then it is simply impossible to tell so, hence there can be no answer.

And there does not need to be an answer, because if there really is no way to tell that they are not 4.7 billion years old, then by definition there cannot be any situation where it would make a difference. So, it's perfectly valid to just state that they are 4.7 billion years old.

I am in fact atheist, this is the viewpoint that I have from the discussion whether maybe our entire universe is just a computer simulation ran by some alien race or such.

If we talk about it with the religious tangent, there's of course further questions: Some people interpret the Bible to contain an age of the universe. So, is that interpretation of the Bible wrong or not? And if it's not, why would God want to trick us with those rocks? Did he create the universe some few thousand years ago, but thought it'd be a more interesting world, if there was some backstory to it? So, does he want us to explore this backstory? Or is it a test of your faith in the Bible? ...which to my knowledge really doesn't state a concrete date for creation, so at least to me that'd be strange.


Some lakes are salty. The Dead Sea and the Caspian, for example.

But many lakes do not have an outlet that leads to the sea. Water flows in and evaporates. Where does the salt go in that case?

It sticks around. The terminal lakes which aren't salty are generally ones which only formed recently (e.g., after the most recent glaciation) or ones which are not fed by rivers (e.g., Oregon's Crater Lake).


FWIW, the Dead and Caspian seas are actually dismembered bits of ocean. They're salty because their water was originally salty. The only salty lake I can think of that didn't begin with ocean water is the Great Salt Lake, which is an evaporated basin from a much larger lake that just happened to sit on salty bedrock.


https://en.wikipedia.org/wiki/Salt_lake lists a number of salt lakes.

One is https://en.wikipedia.org/wiki/Mono_Lake , which did not begin with ocean water.

Another one is https://en.wikipedia.org/wiki/Don_Juan_Pond , which is a shallow Antarctic hypersaline lake that almost never freezes.

https://en.wikipedia.org/wiki/Little_Manitou_Lake_(Saskatche... is a terminal lake which formed after the Ice Age.

I'll also add a non-endorheic salt lake, https://en.wikipedia.org/wiki/Great_Salt_Plains_State_Park , made salty from the dried salts from an ancient inland sea. (I think it's the Western Interior Seaway, but I could be wrong.) In any case, it began with ocean water, which dried up, and that salt is dissolving again.


> Normally, water that has accrued in a drainage basin eventually flows out through rivers or streams on the Earth's surface or by underground diffusion through permeable rock, ultimately ending up in the oceans. However, in an endorheic basin, rain (or other precipitation) that falls within it does not flow out but may only leave the drainage system by evaporation and seepage. The bottom of such a basin is typically occupied by a salt lake or salt pan.

https://en.wikipedia.org/wiki/Endorheic_basin

It turns out that they are salty. They are often not as salty as the ocean though because oceans have been getting saltier for millions of years.


Most lakes have an outlet. The US great lakes for example all share a river that's also the source of Niagara Falls.

On top of that, some lakes do get salty. Such as the 'salt lake' near Salt Lake City.


...which is named the Great Salt Lake, by the way.


The situation you describe is rare, so you don’t see it often. But the Dead Sea, and Great Salt Lake are examples of what you describe.

Plus, as another commenter says, it takes time and lakes are typically transient structures on a geological timescale.


Most lakes actually do have an outlet to the sea.

Because they normally fill up whatever basin they're in and pour over some edge.


Love any science article that provides a clear, scientifically accurate answer to any question my 6 year old asks me.

That's a lot of salt, though: "if the salt in the ocean could be removed and spread evenly over the Earth’s land surface it would form a layer more than 500 feet thick."


That sounds huge until you ponder that the water that salt is dissolved in is a layer many hundreds of feet thick covering 70% of the surface. :)


What if you took all the water out of the oceans and layered it over the land? how thick would that water be?


Just a guess, but around 14000 feet.

If 3.5% of the water is salt and that would create 500 feet of salt if staked on land, then the remaining 96.5% would make 13785.7 feet of water assuming salt and water has the same density.


Right order of magnitude. There's 1.33×10^9 km^3 water in the ocean. .510×10^9 km^2 surface area on the earth. .292 of the surface is land. If I did the math right that's about 29,000 feet.


So Waterworld got something right.


If your numbers are right, the quotient is about 2.7km which is 8555 feet.


1.33/.51/.292 is about 8.9km. You're spreading the ocean over the surface of the entire earth instead of just the continents. Average ocean depth is 12,000 feet, and there's less land than ocean, so the answer must be greater than 12,000 feet.


As high as Mt. Everest. Crazy!!


It's actually 2.7km, approximately 8600 feet.


Hang on, I’m not a chemist, but I imagine we’re missing a couple things. One of which being electrostriction — the process through which the volume of water actually condenses with salt.

So it could be greater than you’ve estimated.


Not trying to be pedantic.

The presence of water bodies itself is what defines the current borders of "the land". If you take the water out, aren't you just creating more land surface?

Which you then have to cover with the water you're taking out. Until it all evens out.


I came here too just to remark how well-written it is.

Simple writing isn't easy. It doesn't just flow out. Garbage flows out. Well-chosen words in just the right order lie in the tenth rewrite, by the person who has studied writing for ten years.


"We don't have a water problem, we have a salt problem." - Joe Rogan


The US Geological Survey gives a slightly more nuanced answer (https://water.usgs.gov/edu/whyoceansalty.html), based (as I understand it) on comparatively recent progress in understanding this question.

It turns out that in addition to the "standard" explanation that the oceans' salt comes from rain dissolving rocks on land, another quite important contributing factor is the activity of hydrothermal vents on the ocean floor. As I understand it, the high temperature of the water emerging there helps it to carry very large amounts of dissolved minerals from deep in the crust back into the sea (and that our models of ocean salinity wouldn't work without this contribution).


What I find fascinating is how in fact we are dependent on Natrium (https://www.youtube.com/watch?v=J3HivpHP-5I), presumably because our organisms originated from oceans to begin with.

Yet still, if dominating salt were Lithium or Potassium, we'd still probably happen to evolve, yet with slightly different cellular features.


Life is even more strange, because plants use very little sodium, so the relation is not straightforward ...

From https://en.wikipedia.org/wiki/Sodium_in_biology

> In C4 plants, sodium is a micronutrient that aids in metabolism, specifically in regeneration of phosphoenolpyruvate (...) and synthesis of chlorophyll. In others, it substitutes for potassium in several roles, such as maintaining turgor pressure and aiding in the opening and closing of stomata. [Note: most plants are C3] [...]

> Since only some plants need sodium and those in small quantities, a completely plant-based diet will generally be very low in sodium. This requires some herbivores to obtain their sodium from salt licks and other mineral sources.


Interesting that you say Natrium (as opposed to Sodium), but Potassium, not Kalium. I thought use of the two variant names for those elements was 100% correlated. Are there regions of the world where that is not the case?


I just screwed up at being smartass :)

It is Kalium here too, but I did heard Potash before when referring to a mineral or fertiliser.


Supposing a terraforming species (like humans) never arose, will the ocean get saltier and saltier over the eons and eventually be inhospitable to all but the hardiest of microbes?


IANAG, but you're not accounting for processes that remove salt from the ocean. All of our salt mines come from somewhere -- crust that's been elevated to make an inland sea, that gradually evaporates and leaves a salt deposit. This can then get buried.

Possibly when the tectonic processes stop on Earth, the oceans will continue to get salty from weathering of rocks. And you won't have much addition of water from volcanism, only a little bit from space. But life gets generally hard without active tectonics anyway.


Salinity levels will vary, but there is no trend to increasing salinity globally. Remember that water is still being “added” to the surface through volcanic activity, and the water cycle dominates, while the current rate of loss to space is quite low. I’m not sure whether volcanic activity is likely to slow before Sol starts to seriously cook off our water, but one of those would eventually lead to a reduction of surface water. That in turn, as with the Dead Sea, will lead to a higher concentration of dissolved solids in seawater.

The current (meaning billion+ years) homeostasis goes like this: https://science.nasa.gov/earth-science/oceanography/physical...


It’s completely breathtaking how massive our planet is in every measure that matters. And then we find out how big Jupiter is, VY Canis Majoris... The universe is a wonderful place!


I've often wondered what living on a earth-like planet as large as Jupiter would be like. People on the other side of this "planet" would be aliens to you.


Nice thought but earth like planets can never get that big because of gravity.


A rocky planet the size of jupiter is not physically impossible. It is almost certainly incompatible with life, but there is nothing in the laws of physics that would cause such a sized planet to explode or collapse.


It would not explode or collapse, but it would almost certainly be molten liquid and/or gaseous rock for a very, very long time


Yes that is why I said it is unlikely to be compatible with life.

It would almost certainly be molten at the surface with no water no matter the distance from the star due to radioactive decay.


I had to check if this was true. So, Jupiter is about 10x the diameter of Earth, which means it has 100x the surface area. So while it would still be possible to travel anywhere by jet, it would be impossible to travel everywhere in one human lifetime (e.g. there would be 100x the number of cities, nations, etc, and it's already unlikely that any human has visited every major city). So yeah, tentatively I think it's true.


By that argument, people on the other side of the earth from you are already aliens to you. Why would it matter if you personally visit everywhere "of significance"?


You may enjoy reading Ringworld - it involves life on the inside of a Dyson ring totalling 3*10^6 the surface area of Earth.


Or the Majipoor series (Lord Valentine's Castle, etc.) https://en.wikipedia.org/wiki/Majipoor_series

> Majipoor is a planet much larger, though far less dense, than the Earth. It has been settled by humans, Ghayrogs, Skandars, Vroons, Liimen, Hjorts and other alien races for many thousands of years. These races live in an unstable truce with the shape-changing aboriginal inhabitants of the planet, the Piurivar.

I don't remember the size but TVTropes says it's "ten times the size of Earth". http://tvtropes.org/pmwiki/pmwiki.php/Literature/MajipoorSer...


At the same time, on average the universe contains nothing. It is so vast, that even if all stars were VY Canis Majoris, it would be still pretty much devoid of anything.


And also at the same time, even the occasional mass concentrations in between are, in all likelihood, mostly rather bland and boring compared to earth, with its magnificent abundance of self-organizing and self-replicating patterns. Even the more interesting aspects of geology tend to be direct or indirect traces of life.

Or maybe not, and there actually is every imaginable wonder out there, including a planet where mattresses naturally occur, but my money would be on earth being pretty much as amazing as it gets.


Dark matter would like to have a word with you.

If there is one thing we have learned through the history of science, it's to be careful about statements like "X contains nothing".


IIRC dark matter is believed to exists because some equations predict a single digit multiple of accounted mass in the Universe. That's not so much to change the mostly-void perception.


that's relative. the further your frame of reference expands, the older the image of earth observable at the border of the frame of reference is, so a few billion light years out, even earth would look boring. And even if that still implied 'mostly-void', I will take it compared to 'pretty much devoid'.



This made me wonder towards if the ocean is therefore becoming saltier & if so, at what pace? Found: https://www.seeker.com/are-the-oceans-getting-saltier-176509...


Interesting historical fact: The salinity of the Earth's oceans was proposed as a clock for measuring the Earth's age by Halley in 1715. This method ultimately arrived at ages around 50 million years (it didn't account for salt losses due to tectonic activity) and was one of the major stepping stones towards establishing public confidence in the idea of an "old" Earth.


But Earth is about 4.54 billion years old [1].

[1] https://www.space.com/24854-how-old-is-earth.html


50 million years is an improvement over textual Bible belief of five thousand.


Hence my comment about how they didn't account for salt being lost due to tectonic activity. Lose salt, and you get an underestimate of the age of the oceans.


The oceans are not saturated with salt, and there aren't many processes that extract salt from the ocean, but the process that made the oceans salty to begin with continues.

Also, the Earth is slowly losing its atmosphere, and with it -presumably- some water.

Of course, there's still a lot of water in rocks, so it's possible that the oceans could gain water and thus less salty.

But my guess is it's getting saltier.


Any idea about this line from the seeker article above?

> "Salt ions themselves aren't added or removed from the ocean, but water molecules are freely gained or lost through the processes of evaporation and precipitation, or freezing and melting of ice," said Ruth Curry, a senior research specialist at the Woods Hole Oceanographic Institution.

"Salt ions aren't added". That doesn't seem right...


Woods Hole is a fine research institution. I think you can assume they were trying to make the concept accessible to layman.

And I think they are trying to not get into all the complexities (yes, Na+ and Cl- ions are added/removed in some natural processes, but many times less readily than water). One could easily point tectonic processes and salt loss via evaporite layer deposition, but you don't lose a lot by not going into the weeds.


O2 and H2O are both too heavy to escape earth.

Earth loses few kilograms of hydrogen and tens of grams helium per second to space.


How come the H and He don't just form a layer on top of our Nitrogen atmosphere? Why do they achieve escape velocity when they go into space?


Thermal loss. The molecules in a gas have certain kinetic energy distribution. Highest energy H and He atoms reach escape velocity in the upper part of the atmosphere.

Earth's magnetic field protects it from solar winds so Earth is not losing significant amount of any heavier atoms or molecules.


Solar wind must play a big part.


> By some estimates, if the salt in the ocean could be removed and spread evenly over the Earth’s land surface it would form a layer more than 500 feet thick, about the height of a 40-story office building.

Needless to say [almost] every land plant and creature on Earth would die in such an event. I just wonder (out of pure bizarre curiosity) what would happen if the salt in the ocean could be removed and put somewhere in the outer space - what part of the ocean life would survive and how much impact would it have on the land life.


I’d be curious to know how much energy would be required to separate all that salt from that water, especially in terms of the total solar energy Earth receives. If, hypothetically, all that solar energy were devoted to desalinization, how long would it take?


> how much impact would it have on the land life.

Sounds like oceans would be significantly lower, for one!


What I'm wondering is why humans can't drink the water from the most ubuquitous reservoir on earth.


Because we come from the middle of Africa


That was hundereds of thousands of years ago and we (well, many of us) have adapted to drinking milk (as adults) during that time.

So even though much of the planet is covered with sea water very few mammals have developed the ability to use sea water for hydration. I just find that surprising.


Processing milk is a digestive change, and one that mammals are all able to do at some point. It’s not a very far leap. Processing water with the sea’s salinity would require changes to how our cells are constructed, or at least would require massive changes to our kidneys. There’s simply no (or not enough) selection advantage for it to have happened.


The vast majority of humans don’t live within walking distance of the ocean, it probably wasn’t a big evolutionary pressure to be able to drink seawater.


Actually, the vast majority of the humans live on the land within a very short distance of the oceans.

The thing is that we need a fairly careful balance between salt and fluid in our bodies, too much salt and our nervous system gets upset.


>The thing is that we need a fairly careful balance between salt and fluid in our bodies

True, but we ingest all sorts of substances in amounts that we don't need. The rest is usually excreted unless having a store of it is useful (like with fat).


We excrete a lot of salt already, kidneys do hard work. Ingesting salt water would quickly overwhelm their capability to shed the salt. Incidentally, this kind of over-concentration+some kernel to start crystallization around can cause kidneystones.


That's all true, but you're merely describing the status quo. I'm asking why our kidneys (and those of most other mammals) have not evolved to process sea water.

Apparently there was not enough evolutionary pressure and that is what I find very surprising.


The subjects to study would be Cetacea, there should be at least a partial answer there:

https://en.wikipedia.org/wiki/Cetacea

There is this bit:

"The kidneys are long and flattened. The salt concentration in cetacean blood is lower than that in seawater, requiring kidneys to excrete salt. This allows the animals to drink seawater."

So for those animals that returned to the sea from the land that pressure was there and they seem to have adapted in that sense.

Humans - and most other mammals - being land dwellers we always had access to rivers and rainfall both of which are fresh.


Posing this question to a young earth, christian, literal bible believer will generate interesting conversations.


I strongly suspect that it won't.


Is ocean salt equilibrium?


I'd be salty too if I had such a rocky interaction with the world.


[flagged]


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