The role of the oceans in climate change is pivotal and strongly linked to the chemistry of carbon dissolved in seawater and converted into the skeletons of marine calcifying organisms (Fig. 1). Extraction of carbon from seawater to form sea-floor carbonate deposits plays a vital role in control of atmospheric CO2 on timescales of thousands of years and longer.
Figure 1 Left: the speciation of dissolved inorganic carbon in seawater and its involvement in the biogenic carbon pump (carbonic acid, H2CO3, is minor and can be ignored). The proportions of the three dissolved carbon species defines the pH of seawater. Right: Scanning electron microscope images of marine calcifying organisms; (left panel) the coccolithophore Emiliani huxleyi (diameter 5 µm) and (right panel) the foraminifer Globigerina bulloides (diameter 400 µm). Credits: P. Ziveri & H. Elderfield.
In order to understand controls on past climate we need to know how properties of the oceans changed and the record of such changes on different timescales. This information is important also for understanding future climate. For example, there have been times in the past when the oceans were more acidic than today. Working out how this occurred, and how long it took the oceans to recover, helps us to assess the impact of man-made ocean acidification.
Microscopic carbonate-secreting organisms living in seawater, like coccoliths and foraminifera, incorporates trace quantities of dissolved elements from seawater into their calcium carbonate shells during growth. The concentrations and isotopic composition of elements trapped within the calcium carbonate lattice, like lithium, boron, magnesium, strontium, provides a snapshot of past ocean chemistry. Each element captures a different aspect of seawater chemistry change. These carbonate archives of marine chemistry are preserved as fossils and can be analyzed to study the evolution of seawater chemistry through time. However, work in the area of marine calcification is almost completely divorced from work on trace element and isotopes incorporation by marine calcifiers and vice-versa.
The major focus of the research will go into marine calcification, the building block of the skeletons and shells for a large number of marine organisms. Calcification, the precipitation of the mineral phase of calcium carbonate (CaCO3) (or calcium phosphate [Ca3(PO4)2] e.g. hydroxyapatite), is an essential process found in many kingdoms of life. Calcification is sensitive to the environment, especially in aquatic systems that are susceptible to changes in ambient chemistry. For example, calcification will likely be influenced by a decrease in ocean pH associated with the increase in atmospheric carbon dioxide partial pressure (pCO2) since the beginning of industrialization. The geological record for calcification also shows no simple relationship with atmospheric CO2.
Figure 2. ‘X-ray images of Ammonia tepida from the I13 tomography beamline of the Diamond synchrotron. This techniques allows us to examine the micro-architecture of the shells, offering insights into their formation and preservation through time.
This is a key research area because: (i) storage of carbon in oceanic deposits of calcium carbonate plays a poorly understood role in controlling atmospheric CO2; (ii) trace element and isotopic compositions of marine calcifying organisms have been used for reconstructing environmental parameters (proxies) to understand past changes in climate; (iii) reduced calcification of modern ecosystems as well as enhanced dissolution of carbonate sediments will play an increasingly important role in the future chemistry of the ocean and its ability to take up atmospheric CO2
In the proposed programme we will link ocean geochemistry, biomineralization and palaeoclimate research directed at the ocean-atmosphere carbonate system in a novel way that has the potential for major advances and impact . We will explore how the present can inform about the past, and how the past can inform the present and future. The two principle domains of research can be broadly classified as chemical oceanography-biomineralization related questions and as purely palaeoclimate centirc questions. Insights from these separate components will feed information to other components and help develop a holistic view of biomineral hosted proxies of palaeo-seawater chemical changes. By bringing together the best research in these areas there is great potential for breakthroughs, and for enhancing research at Cambridge and elsewhere.