Trace element and isotope partitioning in carbonates in simulated biological environments

Many marine organisms produce calcium carbonate structures e.g. corals produce skeletons, bivalves produce shells and foraminifera (single-celled organisms) produce tests. These mineral structures provide organisms with tissue support and/or protection from predators and the physical environment. The chemistry of calcium carbonate is affected by environment. In particular seawater temperatures affect how trace elements substitute in place of calcium and the ratio of oxygen isotopes (forms of oxygen with different masses) in the mineral structure. Thus the geochemistry of the calcium carbonate structures provides information on the temperature and chemistry of seawater at the time the organism lived and grew. The mineral structures are preserved after the death of the organism e.g. as coral reefs, and the analysis of fossil specimens offers an excellent route to reconstruct records of past environmental conditions. Such records help us to understand past changes and interactions in global climate and to predict 21st century climate change. Understanding how other factors affect the chemistry of the shells and reefs is key to accurate interpretation of the climate information recorded in fossil specimens.

Coral skeletons and foraminifera tests form at specialist calcification sites, either in or adjacent to the organism. The calcification sites contain both soluble and insoluble organic biomolecules (e.g. proteins, lipids), which control and guide the precipitation and growth of the mineral. These biomolecules also affect the chemistry of the mineral. In this research we will analyse modern and fossil corals and foraminifera to determine how the concentrations and compositions of organic biomolecules at the calcification site have varied throughout time. We will then precipitate CaCO3 minerals in vitro under conditions replicating those of past and present calcification sites to determine how variations in biomolecules affect mineral chemistry. In particular we will explore how biomolecules interact with other ions at the calcification site over a range of temperature to control mineral chemistry. We will calculate how relationships between coral skeleton and foraminifera test chemistry and seawater temperature have varied throughout time. By applying these calculations to fossils, we will optimise the accuracy of past seawater temperature estimates. We will also use advanced microscopy techniques to visualise the structure of the mineral precipitated under different conditions and to watch the formation of minerals in real time. These observations will help us to understand how variations in the calcification environment affect the incorporation of trace elements and isotopes in calcium carbonate.

Our improved palaeoproxy calibrations will increase the accuracy of past seawater temperature for surface and deep ocean waters and ice volume estimates. These data will facilitate understanding of past climate by improving models which explore how interactions in the ocean and atmosphere drive climate change. Such models underpin our current predictions of the magnitude and geography of future climate change. Increasing the accuracy of these models enables us to plan for future climate change more efficiently.

Researchers studying biomineralisation and the impact of future changes in seawater temperature and pCO2 (ocean acidification) will benefit from our research which will demonstrate how biomolecules can facilitate or suppress calcium carbonate precipitation over different temperatures and pH. Understanding this aspect of biomineralisation is crucial to estimating the future behaviours of calcareous organisms which are of key economic importance e.g. shallow and deep water corals provide important habitat space for fisheries while bivalves are a food source. Approximately 1 in 6 people on the planet rely on coral reefs for their livelihoods and understanding the coral biomineralisation processes is fundamental for predicting their futures.

The UK government is committed to reducing UK greenhouse gas emissions by investing in low-carbon energy sources, improving fuel standards in cars and increasing energy efficiency wherever possible. Encouraging the general public to reduce their carbon footprint will be key to successfully implementing these greenhouse gas reductions. Raising awareness of the negative impacts of CO2 emissions at a local and global scale is an important component of this. Our research, exploring the relationships between temperature, pH and biocarbonate production, provides an excellent route to highlight the negative effects of increasing atmospheric CO2 (and ocean acidification) and to demonstrate their wider impacts e.g. reduction in coral reef production and associated loss of tourism income, coastal protection and fisheries, impacts on UK bivalve aquaculture etc. We will communicate our research to school children (through the University of St. Andrews Geobus) and to the general public through exhibits at Dundee Science Centre (Sensations) and the University of St. Andrews Science open day.