And I assume they find that cold, deep seas produce much less in the way of limestone deposits.
Partly because, IIRC, calcium carbonate snowing down from the photosynthetic zone near-surface largely redissolves before it ever gets to a cold. deep ocean floor. Calcium carbonate is a bit odd in that respect - it's less soluble in cold water than warm. That's why it's the hot-water heater and pipes in your house that scale up if you have hard water.
Partly because, IIRC, calcium carbonate snowing down from the photosynthetic zone near-surface largely redissolves before it ever gets to a cold. deep ocean floor. Calcium carbonate is a bit odd in that respect - it's less soluble in cold water than warm. That's why it's the hot-water heater and pipes in your house that scale up if you have hard water.
Jesus Christ I'm dense! I just had a water softener installed a month ago, read all about this effect, but never put 2 and 2 together.
So let's imagine an area of very deep ocean near the equator with an abundance of water life, including algae, near the top of the water column, and with cold, dark water a couple miles below. The rain of particulate calcium carbonate skeletons from above dissolves before it reaches the sea floor. This process goes on for millenia, and one could argue that eventually the cold water at the bottom of the water column will supersaturate with dissolved calcium carbonate and that it would just precipitate out on the sea floor at a steady rate after that.
But once dissolved the calcium carbonate is much more subject to diffusion than to gravity, and so since we can assume marine geologists have in general not found significant formation of limestone layers in such regions, it must diffuse away to an extent sufficient to prevent supersaturation.
If a combination of diffusion and water currents carried such calcium carbonate rich water to shallow regions where it could warm, then the calcium carbonate would precipitate out, and this could be another factor in micrite formation.
Are we really sure that calcium carbonate is more soluble in cold water than warm? Poking about on the web definitely indicates that it is solubility that is the factor, but this makes no sense to me. I've found a couple mentions that when CO2 concentrations in water drop, which happens with higher temperature, that CaCO3 tends to precipitate out, so I don't think solubility is the whole story, but I couldn't find any details.
How does algae build its calcium carbonate shells? Does it just use calcium carbonate that's already dissolved in ocean water? Or does it create calcium carbonate? I've seen hints that they remove calcium from the water to create the shells, but no details. The world is so full of calcium carbonate that we dump it on our lawns, and there does not seem to be any large-scale inorganic source, so I expect the answer is that they create the calcium carbonate from calcium in the sea water.
Isn't this sentence from the last paragraph incorrect:
In the late Eocene the development of Antarctic glaciers resulted in colder deep sea temperatures leading to a deeper CCD.
Presumably, colder deep sea temperatures would mean that CCD is shallower, not deeper. If we can get consensus about this then we should edit the entry.
A quick Google Scholar look indicates that maybe the Wiki author is oversimplifying - carbon dioxide levels fell dramatically in the late Eocene, which both deepened the CCD and also contributed to Antartica cooling off. You are correct, though, that just colder water would mean shallower CCD.
A quick Google Scholar look indicates that maybe the Wiki author is oversimplifying - carbon dioxide levels fell dramatically in the late Eocene, which both deepened the CCD and also contributed to Antartica cooling off. You are correct, though, that just colder water would mean shallower CCD.
Well, Wiki is all about getting things right. If we can develop a concensus (hopefully Edge and Rox will chime in) then we should fix it. Here's a proposal (I went for simpler instead of more complex):
In the late Eocene a decrease in carbon dioxide levels resulted in a deeper CCD.
If we decide more information is the way to go, then how about this:
In the late Eocene a decrease in carbon dioxide levels led to the development of Antarctic glaciers and colder deep sea temperatures, which by itself would have led to a shallower CCD, but the decreased carbon dioxided levels more than compensated and caused a deeper CCD.
How does algae build its calcium carbonate shells? Does it just use calcium carbonate that's already dissolved in ocean water? Or does it create calcium carbonate? I've seen hints that they remove calcium from the water to create the shells, but no details.
It is my understanding that sea creatures (flora and fauna) take calcium from the surrounding waters and combine it with Carbon from dissolved CO2 to build their skeletons. At least that was what they taught me while I was studying for my Marine/Environmental Chemistry degree. I haven't done any research since graduating though.
One factor which can dramatically effect the rate of growth within sea creatures is the availability of Calcium in the water. Why do you think corals grow in warm seas? Warm water makes the CaCO3 much more bio-available. In cold waters they have to expend more energy to extract it and to stop it re-dissolving into the surrounding waters.
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