Climate proxy optimization - quantifying factors controlling growth, geochemistry and micro/nanostructural design of bivalve mollusk shells

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The planned project aims at a better understanding of the environmental and biological factors governing incremental growth, crystal structures and chemistry of bivalve mollusk shells. Bivalves are increasingly used as proxies of past climates. Yet, the underlying mechanisms of how bivalves actually record environmental conditions in their shells (growth rate, trace and minor element and isotope geochemistry, micro/nanostructural design) are poorly understood. Most models describing the relation between shell growth and environment were inductively inferred and not supported by experiments. The planned project will address this insufficiency by analyzing shell formation under natural and laboratory conditions. Main foci are (1) the timing at which bivalves accrete calcium carbonate to their shells, (2) the role of biological clocks and physiology in shell secretion, (3) factors that influence shell nanostructures and growth rate and (4) the chemical and stable isotopic composition of the shells in relation to that of the ambient water. Will growth rate and chemistry of the shells vary still if external factors remain constant (constant temperature, food supply, food quality, light etc.)? To what extent is shell growth, chemistry and crystal structures governed by biological clocks, physiology or physiochemical controls? Results of the planned study will significantly improve our understanding of how to interpret climate proxies preserved in shells of bivalve mollusks. It will help optimizing models on information retrieval and offer a means of quantifying (new) environmental proxies obtained from bivalve mollusk shells.