Research progress in clumped isotope thermometry of apatite structural carbonate

Reconstructing paleo-temperatures is of great significance for understanding the Earth's climate changes and the evolution of life. Traditional thermometry based on δ¹⁸O has uncertainties due to its reliance on the oxygen isotope composition of seawater (δ¹⁸O_w). Carbonate clumped isotope (Δ₄₇) thermometry, which was developed over the past 20 years, has become a research hotspot as it does not require prior knowledge of δ¹⁸O_w. However, carbonates, which are the most commonly used material for Δ₄₇ thermometry, are highly susceptible to diagenetic alteration, sometimes leading to the loss of original temperature information. Therefore, apatite, which contains structurally bound carbonate and exhibits strong resistance to diagenetic modification, has been an ideal material for studying deep-time paleoclimates. This paper reviews the research on apatite clumped isotopes, discussing the issues in the calibration relationships between apatite Δ₄₇ and temperature, as well as potential kinetic effects. Additionally, factors such as organic matter content, kinetic effects, and diagenetic processes (recrystallization and solid-state reordering effects) may all introduce biases in thermometric results. In the future, it will be necessary to refine the calibration relationships, integrate multi-isotope and trace element analyses to enhance data reliability. With further research, apatite clumped isotope technology is expected to bring breakthroughs to studies in deep-time paleoclimatology and related fields.