# MOJO !!! So much for my Mg comment

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#### Boomer

##### RF Staff
Just when you though it was safe to go in the water some one comes up with this

What Habib just found out today

Biological Effects in Coral Biomineralization: The Ion-Microprobe Revolution

* Meibom, A (meibom@pangea.stanford.edu) , Geological and Environmental Sciences, Stanford University, Stanford, CA 94305 United States

Scleractinian corals are among the most prolific biomineralizing organisms on Earth and massive, reef-building corals are used extensively as proxies for past variations in the global climate. It is therefore of wide interest to understand the degree to which biological versus inorganic processes control the chemistry of the coral skeleton. Early workers considered aragonitic coral skeleton formation to be a purely physiochemical process. More recent studies have increasingly emphasized the role of a skeletal organic matrix, or intercalated organic macro-molecules that control the macroscopic shape and size of the growing crystals. It is now well established that organic compounds play a key role in controlling the morphology of crystals in a wide variety of calcium carbonate biomineralization processes by binding to specific sites, thereby causing direction-specific binding energies on the crystal surfaces. Macro-molecules, such as aspartic acid-rich or glutamic proteins and sulfated polysaccharides, are known to be embedded within the aragonitic skeletal components of coral. In addition, endosymbiotic algae and the layer of cells adjacent to the mineralizing surface, the calicoblastic ectoderm, are believed to play important roles in driving and controlling hermatypic coral skeletogenesis. However, until recently, further progress has been somewhat limited because it was not possible to obtain chemical analyses of the coral skeleton with sufficiently high spatial resolution and sensitivity to correlate chemical variations with the micrometer scale organization of its different structural components. The recent emergence of new ion microprobe technology is changing this situation radically. Conventional ion microprobe and laser ablation techniques have already contributed substantially to our knowledge about the micro-distribution of key trace elements such as B, Mg, Sr, Ba and U. However, with the development of the NanoSIMS, a newly designed ion microprobe capable of trace-element and isotopic analysis with a spatial resolution down to $50-100$ nanometers, it has become possible to study the intimate relationship between the chemistry and the ultra-structure of the coral skeleton. Individual structural elements, such as centers of calcification and bundles of fibrous aragonite, can be clearly resolved and their chemical and isotopic composition mapped. In this talk preliminary results of a NanoSIMS imaging study of the aragonite skeleton of {\it Pavona clavus} will be shown. {\it Pavona clavus} is a massive reef-building coral frequently used for paleo-climate reconstructions. We find that Mg and Sr are distributed very differently in this coral. In contrast to Sr, the distribution of Mg is strongly correlated with the fine-scale structure of the skeleton and corresponds to the layered organization of aragonite fibers surrounding the centers of calcification, which have up to ten times higher Mg concentration. This could indicate a strong biological control over the Mg composition of all structural components within the skeleton. Magnesium may be used by the coral to actively control the growth of the different skeletal crystal components. Sub-micrometer scale chemical analysis will greatly advance our knowledge of the mechanisms that control the formation of the coral skeleton. However, in an effort to advance our understanding of biomineralization processes in general, the analytical capabilities of the NanoSIMS will be applied to a broad variety of mineralizing organisms. A consortium of researchers from Stanford University, the National Museum of Natural History in Paris, University of Paris XI-Orsay, LSCE in Gif sur Yvette, Centre Scientifique in Monaco, and Cameca are directly involved in these efforts

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#### mojoreef

##### Reef Keeper
Ohhh mannn, Well thanks Habib you blew my come back,lol.

Ok Now Boomer here is your HOMEWORK assignment for tonite :lol:

Distribution of magnesium in coral
http://www.cameca.fr/doc_en_pdf/mg_in_coral_skeleton_meibom_grl31_2004.pdf

Thier is a bunch more but they pretty much cover the same material, the one above has some neat pictures of formations and layering. I knew I had read up on it prior, it seems to have turned the concept of paleantology on its head.

Mike

#### Boomer

##### RF Staff
You just lucked out by coincidence . All of this data is new like 2004 ......BUT... I'll give it to you any way :lol:

I like this PDF .

I think I will drop it on Hab and Randy

Now if we could just fine one on Sr and Ba, showing the same.

#### tdwyatt

##### Member
Don't you think it is more than coincidental that Mg and Sr are both divalent (as is Calcium) and that total (not locallized) concentrations are near that of oceanic water ratios in molar terms in these skeletons?

hmmm...

Mike, interesting that this came up here, I had been looking at some other paelo articles and the site here came up on my internet search... I had the article, and it was a surprise to see your site listed as a resource... AGU has been the best source of this and related research, I guess this means that you've hit the big time, heh heh heh!!!

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#### tdwyatt

##### Member
article said:
However, it is entirely possible that Mg-rich ACC is transiently present in the coral skeleton, where it provides a controlled environment for the nucleation and growth of individual aragonite crystals in the fibrous aragonite layers as well as in COC [Cohen and McConnaughey, 2003]. The Mg-rich bands in the layered fibrous aragonite composite and the high magnesium concentration in COC (Figure 2) might in part be the trace element signature of transient ACC in both skeleton components.
Isotopic labeling and wash-out (efflux) experiments using 45Ca have provided strong evidence for the presence of an unstable calcium carbonate phase in newly formed coral skeleton [TambutteÂ´ et al., 1996]. Thus, we propose that temporally and spatially controlled release of Mg to the mineralizing surfaces plays a key role in the formation of the coral skeleton.
comments?

heh, just stirring the pot...

#### mojoreef

##### Reef Keeper
Tom so good to see ya buddy, I have dearly missed our conversations. OK must go dust off the thinking cap its been a while, hehehe.

If your refering to Boomers post wth coincidence comment that was for me, he said I got lucky, lol. This is all based on a conversation in regards to the new oceanic salt have a very high Mag concentration, I said that it would effect the corals skeliton.

In reading other articles the coarl seems to use magenesium as a control device from what I am gathering, It intakes it through the polyps via zoox and allows it to go in the voids between tissue and skeliton. I am not sure about this though as magnesium is also a nutrient (macro) and is used to stabilize ribosomes as well as to bind ATP to enzymes, and is a component of chlorophyll .

I will have to read more, HEY wat is the date on that study??? 2003??

good to see ya Tom, I hope you hang out a bit.

MIke

#### Boomer

##### RF Staff
Tommy nice to see you around

Don't you think it is more than coincidental that Mg and Sr are both divalent (as is Calcium) and that total (not locallized) concentrations are near that of oceanic water ratios in molar terms in these skeletons?

This statement is not new it is old, been around for a few years but the debate is still there. Some say both Sr and Mg many control corals allometric growth rate, while others are arguing no, both Sr and Mg , to include Ba, are just substituting cations for Ca, being that the diameter of the ion fits into the Aragonite lattice real easy. You may want to look at some of the other data on coral depth and species. We posted a bunch on our chem forum, where most is all on Sr.

http://reefcentral.com/forums/showthread.php?s=&threadid=89625&highlight=strontium

http://reefcentral.com/forums/showt...6&perpage=25&highlight=strontium&pagenumber=1

I would be very carful of comparing paleo articles with recent coral, you will get yourself in trouble. Fossil corals, not recent corals beached somewhere are not made of Aragonite but Calcite. Aragonite is not found in fossils, it is altered to Calcite. Furthermore, the fossil corals have no Sr as it does not fit into the Calcite lattice. The Sr is "pushed" out and replaced by Ca during ACT (Aragonite to Calcite Transition) phase.

See;

Carbonate Sedimentology by Tucker ( textbook)

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#### Boomer

##### RF Staff
More from Randy

In this article:

The Chemical & Biochemical Mechanisms of Calcification in Corals
http://www.advancedaquarist.com/issues/apr2002/chem.htm

I discuss how organics may impact and control calcification. Magnesium (and/or strontium strontium) may be used in similar ways:

"The Role of Organics

Organic molecules are known to play a substantial role in the formation of calcium carbonate in many organisms, including abalone shells and other mollusk shells. These materials can be proteins, glycoproteins, mucopolysaccharides, and phospholipids (and likely others that have not yet been identified). They help to induce the nucleation and growth of aragonite and are often referred to as the "organic matrix" because much of skeleton of corals is comprised of these organic materials.

In the case of corals, we have relatively little information about exactly what these organic materials are doing. The structures of some of these proteins contain an unusually large number of aspartic acid residues. These amino acids are capable of binding to calcium, but whether that is a critical function or not has not been established. Here is some speculation about what these organics might be doing with respect to calcification:

1. They may help control the concentration of free calcium in the ECF, and thereby help control the rate of precipitation of CaCO3.

2. They may control the location of crystal growth by binding free calcium and ferrying it to the location where the coral wants precipitation to take place.

3. They may bind to the aragonite crystal face and thereby control the rate of precipitation.

4. They may bind to the aragonite crystal face and thereby prevent precipitation in places where the coral does not want the skeleton to grow.

5. They may bind to the aragonite crystal face and thereby inhibit binding of magnesium, phosphate, or other ions that are known to inhibit the growth of calcium carbonate crystals.

Regardless of the mechanisms involved, the need for these organics in calcification is easily verified. Allemand et al14 have studied the role of such materials in Stylophora pistillata. Interestingly, they find that inhibitors of protein synthesis reduce the rate of calcification considerably. For example, reducing protein synthesis by 60-85% reduced calcification by 50%. A similar result was found by inhibiting glycoprotein synthesis. These results did not come about because of reduced metabolism, but rather by specific effects of reduced protein and glycoprotein synthesis. The most important conclusion in their paper may be that the rate of skeletogenesis may be more limited by the rate of biosynthesis and exocytosis of organic matrix proteins rather than by calcium deposition.
Interestingly, the apparently large need for a particular amino acid (aspartic acid) to synthesize these proteins is satisfied by external sources, not by either the coral itself or the zooxanthellae. For this reason, it might be interesting to see what added aspartic acid does to calcification rates in reef tanks."

#### Boomer

##### RF Staff
I said that it would effect the corals skeliton

Yah but you where comparing solution kenetics to bio-kenetics, so you where only half right :lol:

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