Biomineralization &
Geochemistry of Biogenic Carbonates

Much of what we know about past climate variability comes from information stored in the carbonate skeletons of marine organisms preserved in deep-sea sediments or fossil reefs.

Variations in ocean chemistry and temperature are recorded as changes in the isotopic and elemental composition of skeletons, shells or tests as they grow, and we have developed sophisticated techniques to measure small changes in carbonate composition with extremely high precision (see related links below). Nevertheless, formation of the shell or skeleton is a biological process and information about the oceanic environment is processed through a “biological filter”. Therefore our estimates of past ocean variability are only as good as our understanding of the various factors that influence shell chemistry.

To separate the biological and environmental influences on shell chemistry, we are using a combination of inorganic carbonate precipitation experiments and culturing of live corals and foraminifera under controlled conditions. This experimental approach allows us to identify, isolate and manipulate the individual environmental factors that influence shell growth and composition.  The goal of this work is to provide a framework within which to understand and accurately interpret the composition of coral skeletons and foraminfera shells in terms of the environmental conditions under in which they grew.

Some of our research questions are:

• What factors control the partitioning of elements and isotopes between seawater and CaCO₃ that precipitates from it?
• For certain elements and isotopes, there are significant differences between biological carbonates and inorganic carbonates grown under the same conditions. What is the origin(s) of these “vital effects”? Do these effects change with age (ontogeny) of the organism or colony?
• Seawater is supersaturated with respect to calcite and aragonite (two polymorphs of CaCO₃) yet kinetic barriers prevent spontaneous precipitation of CaCO₃ from seawater. By what mechanism do marine calcifiers overcome these barriers to build their skeletons?
• What are the main factors affecting the biomineralization (calcification) process?Do the same factors that affect nucleation and growth rates of inorganic CaCO₃, i.e., temperature and seawater saturation state, also affect nucleation and growth of crystals by corals and foraminifera?
• How will changes in ocean temperature and seawater saturation state (i.e., ocean acidification) over the next century affect the ability of corals and foraminifera to build their skeletons?

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