Biomineralization and 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
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
- 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?
Benthic foraminifera grown in culture and fed a mixture of green, red and brown algae
Summer Student Fellow Nadine Eisenkolb working
with WHOI scientist Joan Bernhard in her benthic foraminiferal culture
lab. (Tom Kleindist)
Click to enlarge
Diagram of 8-mL culture chamber for benthic foraminifera (C. Hintz, Univ. South Carolina).
» Microscopy Center at MBL