Fish Carbonates - Their dissolution potential under elevated hydrostatic pressure

A major component of the marine-atmospheric carbon cycle is the precipitation and dissolution of calcium carbonate in seawater. Calcium carbonate is the mineral that makes up rocks such as limestone and chalk. Detailed knowledge of this component is important to our understanding of the global carbon cycle, and to the Earth system as a whole. This proposal aims to explore recent findings that represent a fundamental and previously unexpected change to our understanding of the marine inorganic carbon budget. Large amounts of calcium carbonate are produced in the global oceans by marine plankton and, specifically, by microscopic organisms such as coccolithophores and foraminifera. However, recent research by the PI has highlighted the significant additional contribution to oceanic carbonate production by marine bony fish. These animals ingest sea water and are now known to also precipitate calcium carbonate within their guts and excrete these at very high rates as part of their normal functioning in seawater. This previously unrecognised source of marine carbonate is significant in its own right but, when combined with new estimates of global fish biomass, it is clear that it makes a major contribution to carbonate production on a global scale. Furthermore, due to their rather unusually high content of magnesium, these fish carbonates are predicted to be more soluble (i.e. more likely to dissolve whilst sinking) than the better know forms of calcium carbonate produced by other marine calcifying organisms. The issue of solubility is important to ocean chemistry, as carbonates that dissolve rapidly upon sinking, in the upper 500-1000 m of the ocean, will restore the alkalinity and buffer capacity of surface waters, which in turn enhances the ocean's capacity to absorb further CO2 from the atmosphere. Theoretically, the little we know about the chemistry of fish carbonates suggests they will be one of the fastest dissolving forms of this mineral. This proposal will be the first ever attempt to actually measure the influence of sinking (i.e. hydrostatic pressure) on the dissolving potential of carbonates derived from fish. This would help explain a mystery of ocean chemistry that has puzzled oceanographers for decades, i.e. the unexpectedly increase in alkalinity in the first 1000 m of depth in the Atlantic and Pacific oceans. In addition, the laboratory setting allows for the incorporation of the effect of fluid flow on the aggregates, ensuring a more realistic simulation of sinking, and consequently more accurate simulation results.