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I don't know the associated technical words to research this question.

There was high presence of Iron in the oceans in anoxic precambrian times, and today copper is 5 times more abundant in the oceans than iron.

Is the solubility of $\ce{Fe^{2+}}$ and $\ce{Fe^{3+}}$ and $\ce{Cu^{2+}}$ very different?

Why is there five times more Copper in seawater than Iron? Surface minerals have 1000 times higher PPM values for the latter? It's precipitating?

Why is there 4000 times less iron in seawater than Strontium? Surface minerals have 100 times higher PPM values for the iron?

Here are some measurements stated previously: https://web.stanford.edu/group/Urchin/mineral.html https://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%27s_crust

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  • $\begingroup$ There's no minerals in seawater just dissolved salts. Why would you think density of metal has any importance here? It's not like colloidal iron would be in seawater... $\endgroup$
    – Mithoron
    Feb 16, 2018 at 19:53
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    $\begingroup$ I do not see why to downvote. Why is not ok to ask why element abundance in seawater does not follow that in crust mineral whatever? OP should also link to a source for the mineral data. Obviously the iron down the nucleus shouldn't not be counted as much as that on crust. $\endgroup$
    – Alchimista
    Feb 16, 2018 at 20:04
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    $\begingroup$ Why Mark Zuckerberg is about a 1000000 times richer than me, when I'm 30% heavier? $\endgroup$ Feb 17, 2018 at 7:12
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    $\begingroup$ Come on OP id simply asking what makes the composition so different. It could have skipped any reference to weight as it was in the original answer. The question is why the abundance of ions in the sea does not reflect the abundance of elements. It would be why there is only one Zuckerberg on land and ten swimming in the oceans? To follow sarcastic comments $\endgroup$
    – Alchimista
    Feb 17, 2018 at 10:27
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    $\begingroup$ OP the various Kps of the possible combinations is one among the answers. It is not a case that Sr is heart alkali and iron is not. Nor hat the most abundant ions in sea are sodium and chlorine. If you take iron as example, it can be fixed as sulphide, etc. But as I said before you should compare abundances in seawater and a specific part of earth, probably the most outer part of the crust. The elemental composition of universe, stars, earth and earth portions is not the same. $\endgroup$
    – Alchimista
    Feb 17, 2018 at 10:43

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I'll elaborate this answer as I learn.

It's an effect owed to the low solubility of iron in the modern oxic ocean and the tendency for iron to be ‘scavenged’ from the water column by sinking particles.

Brand, L. E., Sunda, W. G. & Guillard, R. R. L. Limitation of marine phytoplankton reproductive rates by zinc, manganese and iron. Limnol. Oceanogr. 28, 1182–1198 (1983).

Cooper, L. H. N. Iron in the sea and in marine plankton. Proc. R. Soc. Lond. B 118, 419–438 (1935).

Goldberg, E. D. Marine geochemistry. 1. Chemical scavengers of the sea. J. Geol. 62, 249–265 (1954).

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