PhD Title: The biomineralogy of marine calcifying organisms and ocean acidification.

Supervisors: Harry Elderfield, Simon Redfern and Jean-Pierre Gattuso (Laboratoire d'Océanographie, Villefranche-sur-Mer)

Description: My project aims to provide a mineralogical assessment of the effects of ocean acidification on calcium carbonate shells.  Anthropogenic CO2 emissions are altering the carbon chemistry of our surface ocean ("ocean acidification"), creating an environment that should be hostile to shell-producing organisms.  At present, we know that this "acidification" effects marine calcifyers (see links below), but the effects are complex and vary dramatically between and within groups of organisms.  Several major research programs are investigating this complex problem, studying live organisms and ancient fossils to try and predict the response of these important organisms to future ocean acidification.  I am approcahing the problem from a mineralogical standpoint.

I began investating bulk-scale shell mineralogy using X-Ray powder diffraction techniques, but found them insufficient to examine the complex structure of biominerals.  I have since moved to a variety of synchrotron X-ray techniqes, that give the necessary spatial resolution to investigating the internal and external structures of biominerals, and their fine-scale chemistry.  The techniques I am using include Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy (at ALS, Berkeley), X-ray computed tomography and ptychography (at Diamond, Oxford) and total X-ray scattering (Diamond, Oxford).  I am using these techniques to examine the microstructure of foraminiferal tests (shells), to reveal aspects of their mineralisation mechanisms that will inform our use of palaeoproxies

I study the mineral microstructure of biologically produced calcite and aragonite, and how this microstructure varies with environmental conditions.  The fine-scale mineral-organic structure of shells determines their physical characteristics (e.g. strength, flexibility) and their susceptibility to dissolution.  The survival of shelled organisms depends largely on the integrity of their shells, and if environmental changes render them incapable of producing viable shells, their survival will be threatened.  The trace chemistry of shells is known to vary considerably with environmental changes, which hints at underlying micro-structural variations.  I study the effects of environmental perturbations on biologically produced calcite and aragonite from a structural perspective.  My research can be summed up by several questions: 

  • Does biomineral microstructure vary with changes in the external environment, and if so how do these changes effect the physical characteristics of the biominerals?
  • How do the trace elements we use as palaeoenvironmental proxies get into biominerals - is it thermodynamically or biologically mediated (or both)?
  • What is the structure of the 'Amorphous Calcium Carbonate' precursor that many (most?) organisms employ in calcification, and what can this tell us about their calcification mechanisms?

 

Cool Stuff: 

   

 A 3D model of Globigerinella aequilateralis constructed from X-ray tomography data collected at beamline I13 (Diamond Light Source synchrotron).

 

Links: 

Ocean Acidification Research: 

EPOCA - The European Project on OCean Acidification

UKOA - The UK Ocean Acidification research program

BIOACID - The Biological Impacts of Ocean ACIDification (German program) 

Other: 

The Cost Of Knowledge - petition against the excessive cost of accessing publicly funded academic research


Last updated on 18-Oct-12 16:08