The global calcium (Ca) cycle is intimately linked to that of carbon (C) through carbonate weathering and precipitation of calcium carbonates. I strive to expand our understanding of marine calcium cycling via reconstructions of the Ca isotopic composition of seawater (δ44Ca) over the Cenozoic using biogenic apatite found in fossil elasmobranch (shark) tooth enameloid. (Akhtar et al., 2020)

Reconstructions of diet and trophic structures in ancient food webs often focus on geochemical analysis of fossil teeth. By focusing on non-traditional stable isotope systems (like Ca, Mg, Sr and Zn), I study shark ecology and trophic level structuring in the present day, as well as critical periods in shark evolution, including the extinction of mega-toothed sharks and the K-Pg boundary mass extinction. (Akhtar et al., 2020; Kast et al., 2022)

Shallow-water carbonates represent an important and widely used archive of the history of the global carbon cycle and chemical composition of seawater. I am interested in the formation, deposition and long-term preservation potential of coastal shallow-water carbonates, such as those found in the Great Bahama Bank and Great Barrier Reef. I work on ways to fingerprint early stage (e.g., marine) and later (e.g., meteoric) alteration of carbonate sediments via geochemical measurements (e.g. Ca and Mg isotopes) and numerical models of water-rock interactions. (Akhtar et al., 2024; Higgins et al., 2018)

The isotopic composition of calcium in (hydroxy)apatite minerals has been explored as a source of paleoenvironmental information including seawater chemistry, marine ecology and biomineralization. However, fractionation of calcium isotopes during mineral precipitation represents a significant source of uncertainty. I have been working with inorganic, lab-synthesized calcium phosphates to provide experimental constraints on Ca isotope fractionation in hydroxyaptatites at variable temperature and pH regimes.