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30-Apr-2017 20:39

All these developments are beginning to contribute to our knowledge of natural climate variability on decade-to-century time scales.

Indeed, proxy indicators are now producing some of the most exciting and valuable records of variability to date.

While the degrees of accuracy and resolution available vary, the information that can be extracted is staggering.

For example (see the papers of Ruddiman and Mc Intyre, 1973; CLIMAP, 1981; and Imbrie et al., 1992 for more details), ocean proxy indicators have yielded regional information on the following characteristics: sea-surface and bottom temperature (from fossil assemblage composition), continental and landlocked ice volume and sea-level height (from oxygen isotope ratios), the partitioning of carbon between the land and oceans (from carbon isotope ratios), alkalinity of local water (from fossil preservation indices), deep-water circulation (from relative isotope compositions), surface productivity (from vertical isotope gradients), water-column stability (from radiolarian abundances), major front locations (from fossil, ice-rafted debris, and sediment-type distributions), deep-water temperature changes and surface salinity (from relative isotope compositions), vertical gradients of water-mass properties like temperature or salinity or of water-mass distributions (from analyses of sediments from different depths), deepwater velocity changes and source information (from sediment distributions near restricted passages), and predominant wind directions and intensities (from sediment compositions).

The proxy indicators represent any piece of evidence that can be used to infer climate.

Major advances have been made since then, particularly within the last few decades.