Scientists use a hydraulic drill to take a coral core sample.

Certain species of tropical reef corals form annual growth bands, samples of which can be obtained through underwater coring with rock drills. Analysis of these samples allows scientists to estimate historical sea surface temperature and salinity, and to study the movement of surface water masses and deep-ocean mixing. Some of these coral records are centuries old. By following these patterns over time, we can better understand the natural variability of the El Nino/Southern Oscillation (ENSO), the single most important cause of inter-annual climate variation on the planet. Understanding ENSO could lead to improved climate predictions that might help save money and ease the suffering of millions worldwide.

Coral forms in layers like an onion. Here, each year is marked with a black line.

Additionally, the chemistry of coral bands in the equatorial Pacific is closely correlated with tree-ring widths over northern Mexico and the southwestern USA. This amazing long-range biological connection between the growth dynamics of coral reefs and forests is orchestrated by the global ocean-atmospheric interaction referred to as ENSO, and illustrates the interconnectedness of the Earth ecosystem.

Polar Archives

	Glacial ice is formed by the accumulation, compression, and re-freezing of snowfall over many years.

The annual layers of ice preserved in glaciers also provide interesting records of past climate. In Antarctica, scientists have cored over 3 kilometers down through the ice, uncovering a climatic record that stretches back over 400,000 years. Some of the most convincing evidence for global warming can be found in these glacial archives of climate. At the same time, many glaciers worldwide are undergoing massive retreat. The recession of mountain glaciers has also been particularly dramatic, and the high-elevation tropical glacier found on Mt. Kilamanjaro in Africa may soon disappear completely.
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Photos: Marilyn & Maris Kazmers / SharkSong Photography; Rob Dunbar, Rice University; John T. Andrews, UC Boulder