Orbital Tuning

Orbital tuning is an important dating technique climatologists use to study past climate. This refers to a procedure of linking cycles of incoming solar radiation with the Earth's ice volume responses to determine age. As discussed earlier regarding the Milankovitch cycles, astronomers have calculated the solar radiation signal over time and have determined that cycles at 41,000 and 23,000 years have produced regular climatic responses. Because of this correlation, these predictable climate cycles can be used as time clocks for dating purposes. Scientists have also determined that ice volume response in the Earth's ice sheets always lags behind these orbital forcings by a consistent amount, allowing them to date climate records in ocean sediments in relation to the known timing of the orbital changes. They are able to correlate this through the detection and analysis of oxygen-18, because 518O is a good index of ice volume. Every 32.8 feet (10 m) of change in global sea level causes a 0.1 percent change in 518O. Scientists can also date the reversals of Earth's magnetic field in ocean sediment cores to add additional absolute dates to a profile. In fact, many climate experts regard the timescales derived from orbital tuning chronometry for the last several million years to be more accurate than those based solely on radio-metric dating techniques.

It is also a versatile technique—it can be applied to any ocean sediment core containing §18O. When this timescale is established in the higher (polar) latitudes, it is often correlated at lower latitudes to reconstruct orbital-scale monsoon activity at 23,000-year cycles as well as decay of ice-sheets at both middle and high latitudes. Climate change back to 5 million years has been established using this technique.

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