Reconstruction of environmental responses to climate change using sediment cores from the Pacific Ocean (NERC EAO DTP)

With carbon dioxide increasing in the atmosphere, much interest has turned to how the Earth system has changed climatically over geological time. Scientists turn to sample archives to investigate these past climates and environments. One such archive is aeolian deposits, which have the potential to record changes in dust flux, sources and properties. These archives are ubiquitously present across the Earth’s surface: on land sea and ice, but are best archived within oceanic sediments.

The aim of this project is to use sediment cores from the Pacific Ocean to understand the complex system of continental land mass erosion and dust provenance, oceanic deposition and input from volcanic sources. One excellent tracer for differentiating between these sources and quantifying deposition rate is helium isotopic measurements. By combining existing magnetic records with geochemical tracers, this project aims to provide fundamental new insights into palaeoclimate over the last million years and how these variations relate to and provide feedback to global climate cycles.

This project will make use of a combination of tracers to understand past climate change in the Pacific Ocean. Specifically, the student will investigate how ocean sediment core from drilling programmes in the Pacific Ocean can be used to quantify the variable contribution of different dust sources to the oceanic sediment overall flux. Our overall aim is to undertake a thorough investigation into the age, origin and flux of oceanic sediment which changed rapidly during the Quaternary due to sensitive responses to climatic variations. In addition, dust transport and deposition may also feedback into climate modification by radiative forcing when airborne.

This project involves a multi-tracer approach which will document the sources of and processes by which sediments are deposited in the Pacific. Helium abundances and isotopic ratios are a key tracer in this area of work (e.g. McGee et al., 2016) and will be the principle analytical tool in this project. 4He is produced by radioactive decay of U and Th, hence it is relatively abundant in continental rocks. With good chronostratigraphic information, this can be used to determine sediment fluxes and deposition rates to the ocean. In contrast, 3He in sediment core comes from either cosmic ray interactions with elements within specific minerals or potentially from interplanetary dust particles loaded with 3He by implantation from the solar wind. This is relatively constant (or can be corrected for), hence it can quantify sediment deposition rate. In combination, the 3He/4He may help to differentiate between sediment from weathered crust verses active volcanic origin. Particularly for 4He, diffusive loss is an issue that requires correction, therefore these sediments are size sorted to allow quantification of this process. Similarly, understanding of the specific sites that retain He and other tracers is also critical to correct interpretation of these data - this will also be investigated. In addition, particle “focusing” (concentration before deposition), interpreted from He, measurements can occur because of processes within the water column, stripping by settling organic matter or local movements at the seabed (e.g., remobilisation by slope failure and subsequent deposition in basins between abyssal hills). The latter can potentially be evaluated from geophysical data, such as seismic reflection and multibeam sonar, which you will able to assess with the assistance of the Marine Geophysics group in Manchester.

Additional techniques (SEM, electron probe mapping) are available in Manchester and other geochemical evidence such as stable isotopes and trace element analyses could potentially be utilised in the project depending on the focus of the work (to be be directed ultimately by the student). The student will take advantage of the world-class analytical instruments including a dedicated noble gas mass spectrometer at Manchester University and the stable isotope and world-leading magnetic facilities at Lancaster University. Specialist training will be given in a range of sample preparation and analytical techniques. The student will also receive training in transferable and professional skills.

The project is principally in the field of palaeoclimate and geochemistry and is suitable for a numerate student with a background in geology/geoscience or a physical science. Previous laboratory experience is an asset but is not essential.