Corals are amazing living animals which are continually building up new layers right on top of their endoskeleton. By examining a cross section of a coral skeletons, these layers or “growth-bands” can reveal clues about the coral’s past. Much like counting annual growth rings on a tree a method using mmillimeter per year can be used for the annual growth analysis of corals.
What is interesting about coral is that there are about thirty daily bands per month and about 365 daily bands per year. By using specialized equipment scientist are able to get a deeper look at what these growth-bands mean and how this growth may have been affected by ancient weather.
Neil Tangri and his colleagues at the Stanford Linear Accelerator Center are using one of the world’s more powerful X-ray machines called a synchrotron to look deep inside a corals past. The ultra-high resolution of the synchrotron X-ray allows researchers to see a spatial resolution of about 10 microns and details down to the chemical make-up of the skeleton.
Tangri and his colleagues are studying a huge colony of Porites lutea from American Samoa and the original core sample was 18 feet long and nearly 500 years old. Porites corals can grow to be very big and very old which makes them a perfect candidate for obtaining extra old data about the past.
Researchers taking a core sample from a mature Porites lutea coral in American Samoa. (Dr. Robert B. Dunbar)
To understand more about the weather Tangri looks for the presence of trace elements, such as strontium and barium in the bands for clues about the weather. Corals skeletons are composed primarily of calcium carbonate, however, when water temperature fluctuates corals are more likely to absorb other elements found in the water column. For example corals absorb more strontium in their exoskeletons when the water is colder, so by comparing the strontium-to-calcium ratio over time, Tangri and his team are able to reconstruct ancient sea surface temperatures.
This video give us a deeper look into the secrets of our ancient climate. DEEP LOOK is a new ultra-HD (4K) short video series created by KQED San Francisco and presented by PBS Digital Studios. [KQED Science]
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