The Hydrologic Cycle and Magnesium--why an abundance in the ocean?

[babyblues71]

Okay, I have an advanced question. Calcite and Dolomite are two of the most abundant carbonate materials that are found and are slowly but surely broken down via rivers in the hydrologic cycle right before this mineral-rich water makes its way into the ocean. Now then, since calcite is more abundant than dolomite, and easier to break down, why is it that there’s a greater reading of magnesium in the ocean, which is more apparent within dolomite? Am I missing another source, or when the magnesium “is” managed to be broken down from the dolomite is it in a greater quantity ppm-wise for some reason, or are the readings from the ocean like that because not as much magnesium is “needed” in the ocean when compared to calcium, and that’s why calcium tests out at 411 ppm and magnesium 1290? I've always been curious about that.....



http://www.seafriends.org.nz/oceano/seawater.htm



Brent

 

[billsreef]

Dissolved minerals from fresh water land runoff are not the only source of minerals in the Ocean Other significant sources are volcanic activity such as the deep sea rifts

 

[babyblues71]

I do realize that, but it appears that much of the volcanic activity that produces igneous rocks seems to have a distribution of both Magnesium and Iron in them at the same time, yet Iron is in very short supply in ocean water. So...now another question...what happens to all of the Iron?

http://www.dmtcalaska.org/course_dev/explogeo/class06/notes06.html

 

[billsreef]

Iron is rapidly removed by several biological process, some bacterial and most noteworthy is photosynthesis

 

[aninjaatemyshoe]

Also, only certain parts of the ocean are anemic (lack free iron). Most notably is the south pacific.