Fieldwork in the Atacama Desert, Chile

Thursday, 13 December 2012

Cladocora caespitosa; from reefs to crystals (in pictures)

 As this will likely be my last post of the year and nobody wants too much science this close to Christmas, I thought I'd just use it to show some pretty pictures of the corals (Cladocora caespitosa) I've been working on. As you scroll down the level of zoom increases from full reef to microscopic crystal scale, enjoy...
Mljet C. caespitosa bank, Croatia; the only known example of a modern C. caepitosa buildup comparable to a tropical reef (Photo courtesy of P. Kruzic)

Living C. caespitosa with extended feeding polyps (Photo courtesy of P. Kruzic)

Mid-Holocene (6-10,000 years old) fossil C. caespitosa, Mavra Litharia Reef, Greece (trowel for scale), they don't look quite so nice by the time I get to them as they've been dead for a few thousand years and uplifted out of the sea.

Sample hacked off the above locality

Sectioned isolated corallite, ready for analysis (approx. 45mm long)

Optical binocular microscope images of sectioned corallite showing the complex internal structure of the septa, the brown staining is most likely due to contamination from iron-rich groundwaters percolating through the porous septa and so these regions must be removed before analysis to leave just the solid outer wall behind (corallite is approx. 8mm wide)

False colour optical image of a horizontally cross sectioned modern corallite stem showing the spoke-like structure of the septal region (larger sample approx. 7.5mm diameter)

Same cross sections as above but viewed under the scanning electron microscope (SEM) , lower image shows secondary cements infilling some of the pore spaces between the septa showing that these areas do not all grow at the same time.

SEM image of the septa seen from side view
SEM images zoomed right in to see the individual crystals of primary aragonite that make up the coral. The primary aragonite is unstable and prone to breaking down over time, if this happens the original geochemical signals recorded by the growing coral are lost and they are useless to me, but these look like very good samples for analysis.

If the aragonite does break down, more stable secondary calcite crystals (shown here) replace them, this sample would be too altered to be of any use for analysis.

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