Juillet - Leclerc, A., and G. Schmidt, 2001: A calibration of the oxygen isotope paleothermometer of coral aragonite from Porites. (pubs.giss.nasa.gov)
As to the technical parts, as described in many sources, we have lots of paleothermometers for the central Greenland ice cores over the last 100,000 years, providing multiple validation and high confidence that temperatures have been estimated accurately. (dotearth.blogs.nytimes.com)
Unlike previous methods, the clumped isotope paleothermometer technique does not rely on assumptions about the isotopic composition of seawater. (sciencedaily.com)