What property of ice core samples helps scientists determine the average global temperature over the last 160,000 years?

The 1H/2H ratio, which refers to the ratio of the two hydrogen isotopes present in water (protium and deuterium), is a critical factor in analyzing ice core samples for deducing average global temperatures over extensive periods, such as the last 160,000 years. As temperatures change, the ratio of these isotopes in ice also changes due to fractionation processes during evaporation and precipitation.

When temperatures are warmer, the ratio typically indicates a higher proportion of the lighter hydrogen isotope, 1H, because lighter isotopes preferentially evaporate more readily. Conversely, during cooler periods, there is relatively more of the heavier isotope, 2H. By analyzing the isotopic composition of the gas bubbles trapped in the ice core, scientists can infer past temperatures. This information is instrumental in constructing climate models and understanding long-term climate changes.

In contrast, while the depth of the ice layers can provide a timeline of accumulation and periods of melting, it does not directly relate to temperature measurements. The density of the ice may indicate compaction and the history of accumulation but does not correlate as directly with temperature changes. Similarly, the color of the ice layers can reflect certain environmental conditions or impurities but is not a direct indicator of