Geochemical Proxy Systems in Marine CaCO₃ Biominerals Record Both Environmental Changes and Biomineralisation Processes

The isotopic and elemental composition of calcium carbonate formed by marine organisms underpins a substantial portion of our knowledge of past climates. These geochemical ‘proxy’ systems have revolutionised our understanding of palaeoenvironmental change, but remain largely rooted in empiricism because of poorly understood biological ‘vital effects’. Here, we outline how this is both a problem and an opportunity—while some proxies have their basis in biological processes, this is the root cause of uncertainty in others. Moreover, integrating geochemistry into biomineralisation models provides additional constraint on cellular mechanisms; geochemical data have untapped potential in the field of biomineralisation and could be used to simultaneously understand the proxies in question and to determine why biomineralising organisms are sensitive to environmental change.