Why is sea water salty?

[diverdan214]

"There are three main sources of the sea's saltiness: weathering of rocks on land, volcanic gases, and circulation at deep-sea hydrothermal vents. When water combines with carbon dioxide it becomes acidic. Consequently, water vapor condensing to form rain in Earth's atmosphere, which contains carbon dioxide, tends to be slightly acidic. Rain that falls on land, even if only slightly acidic, effectively dissolves rocks and sediments in a slow process we call weathering...Runoff and rivers carry the products of weathering , dissolved minerals, from the land to the sea...if we compare the composition of river water to seawater, we notice several distinct differentces...Volcanic eruptions that spew gas rich in cholrine and sulfate from the Earth's interior account for some of the missing constituents, but until recently, scientists were pussled by the oceans abundance of calcim and lack of magnesium...The mystery was solved with the discovery and study of circulation at deep-sea vents...chemical interaction with the underlying molten material causes circulating seawater to lose magnesium and gain calcium."- Ellen J. Prager with Sylvia A. Earle "The Oceans" McGraw-Hill 2000 Pgs. 74-75

Good book.

I'd go with because little kids pee in it...which is why you shouldn't. That way you combine two lessons.

 

[eponym]

Griff - clear and cogent! Thanks for posting that--It'll be fun to use this question in open water classes.

Bryan

 

[fire_diver]

My 9 years old asked me the question this week end, and I could not recall of a satisfactory answer. Who has one?

millions of years of fish pee

FD

 

[gangrel441]

heya guys,
just saw this one and thought i'd give the simple explenation. mineral ions such as potassium and chloride come from rocks, from the land. they get washed into the sea. ofcourse this happens with all the other ions aswell so why does NaCl build up to such high concentrations? this is to do with residence time. the residence time is the amount of time it talke for one molecule of the substace enter and be removed from the system ie the oceans. the residence time for potassium and chloriode ions is very high . this is because there is little removing forces. therefor because it is always being added and rarely being removed it builts up causing the sea to be salty.

had to write this quick as got another blood oceanography lecture to run to hope it explains it a little.

confused? message me and i will try harder to explain

Griff

Ahhh....but NaCl is not potassium chloride. That would be KCl. NaCl is sodium chloride, which I believe is indeed the main (but not only) salt in the sea. I can understand your explanation of where water might pick up potassium on the way to the sea, but that has little to do with the ocean's content of NaCl.

 

[Charlie99]

Grif's explanation is on target, but for a 9 year old I'd simplify it even more.

Rainwater dissolves salt from the land on its way to the ocean. When the sun evaporates water from the ocean the salt stays. That evaporated water eventually becomes rain which brings more salt to the ocean. This cycle, continuously repeated keeps bringing salt to the ocean and leaving it there.


(actually, the evaporative cycle does remove some salt, but its much less than the amount of water evaporated. To use Grif's terms, the residence time is very high for the salts).

 

[Griff_1984]

Ahhh....but NaCl is not potassium chloride. That would be KCl. NaCl is sodium chloride, which I believe is indeed the main (but not only) salt in the sea. I can understand your explanation of where water might pick up potassium on the way to the sea, but that has little to do with the ocean's content of NaCl.

Sorry about the mix up i've been working on a Phosphate profiles in esturays recently guess i have P on the mind. silly mistake its corrected now. but remember salt is not just NaCl there are a huge array of metal salts including potassium salts. infact today the instruments used to measure salinity actully measure conductivity of the water. as it is the ions in the water that make it a good conductor not the water its self. more ions in the water leads to higher conductivity. Sodium and chloride make up most (55 and 30.6% respectively) potassium accounts for 1.2% of the total salts in the ocean.

it is infact a very complex subject and before now i have had to calculate such things as how deep the layer of salt would be on the sea floor if all the oceans evaporated. and the effects of increased weather of volcanic activity on the oceans salinity.

i can direct anyone who is really intrested in such subjects to relevent book and journals but it all gets a bit mathamatical!

griff

 

[rockbeauty]

This website gives a good explanation too:
http://www.utdallas.edu/~pujana/oceans/why.html

 

[SharkRider]

My 9 years old asked me the question this week end, and I could not recall of a satisfactory answer. Who has one?

There are a lot of male fish in the water without girlfriends...

 

[jeditdog]

heya guys,
just saw this one and thought i'd give the simple explenation. mineral ions such as Sodium and chloride come from rocks, from the land. they get washed into the sea. ofcourse this happens with all the other ions as well so why does NaCl build up to such high concentrations? this is to do with residence time. the residence time is the amount of time it talke for one molecule of the substace to enter and be removed from the system ie the oceans. the residence time for sodium and chloriode ions is very high (thousands of years). this is because there is little removing forces. therefor because it is always being added and rarely being removed it builts up causing the sea to be salty.

So coudl the ocean one day be too salty for the fish?

 

[Griff_1984]

jeditdog..

i have to say thats unlikely if you think about the time scales we are envolved with. it was about 250 Million years ago ( just after the premian period) when the earth started to settle out from cataclasmic techtonic activity. a lot of the salt in the oceans would have been added at this time because of the great amount of vlocanic activity and weathering. 250 million years on and undoubtably they ocenas have changed a lot but on a time scale allowing evloution to keep pase with the chages.
on the other had there are hypersaline seas around, the dead sea for example. this happens because its cut off from the rest of the oceans and has had alot of evaporation. but there is life in the dead sea, infact there is life in all the worlds seas.
fish are also very good and regulatiing salt in their bodys so i recon most will adapt if they survive long enough to see any real change in salinity.

anyway its the things we are doing to the oceans that will kill the fish. there is a theory going around now saying it wont be long unill the atlantic is anoxic, good bye fishies!

Griff