understanding changes in cenozoic carbonate chemistry | Ocean and Earth Science, National Oceanography Centre Southampton

Ocean and Earth Science, National Oceanography Centre Southampton

Research project: Understanding changes in Cenozoic carbonate chemistry

Currently Active:: Yes

One of the most enigmatic fluctuations in marine chemistry on geological timescales is the cyclic variation in the abundance of the dominant cations magnesium (Mg), calcium (Ca) and strontium (Sr) that have a major control upon the dominant form of calcium carbonate (CaCO3) precipitated - the oceans appear to regularly switch between ‘aragonite seas' and ‘calcite seas'. Determining the biological, environmental and tectonic processes responsible for these changes will significantly improve our understanding of the factors that control oceanic composition, as well better determine the impact of climate change on CaCO3 formation and preservation throughout the geological record.

Project Overview

The principal reactions governing carbonate precipitation in the oceans, and how this interacts with the marine Mg, Ca and Sr cycles. (Source: C.R. Pearce) — Ocean carbonate precipitation

Objectives

This project will provide new constraints on the processes that control the cation composition of the oceans, and establish how these mechanisms varied over the Cenozoic. The main objectives of this research are:

To improve our understanding of the marine Mg, Ca and Sr cycles using a non-traditional stable isotope approach.
To better characterise cation incorporation into carbonates.
To determine variations in the Mg, Ca and Sr stable isotopic composition of seawater over the Cenozoic to ascertain what caused the observed shift in Mg/Ca and Sr/Ca ratios.

Approach

δ ^26/24 Mg, δ ^44/40 Ca and δ ^88/86 Sr records from inorganic CCVs will be used to determine how the cation isotopic composition of seawater has varied over the last 180 Ma. Combining the CCV isotopic and elemental records will enable changes in marine fluxes to be characterised in a manner not achievable using element ratios alone, as each isotopic system responds differently to marine processes. Computer modelling will be used to combine and interpret the results from each system.