School of Geography & Geosciences
Department of Geography & Sustainable Development

Greenhouse gas and sediment dynamics in the coastal intertidal zone

Coastal marine ecosystems are believed to be sinks for atmospheric CO_2, accounting for the equivalent of approximately one-quarter of anthropogenic CO₂ emissions worldwide. Coastal intertidal habitats, such as mudflats and saltmarshes, are particularly significant for carbon storage, with sequestration rates as much as 10 times that of other wetlands. These ecosystems are sinks for carbon not only because of their high primary productivity, but also because they are active depositional systems that sequester carbon via anaerobic sediment burial. However, despite these systems acting as sinks for carbon, the anaerobic conditions mean that intertidal habitats potentially act as significant sources of non-CO₂ greenhouse gases (GHGs), such as methane (CH₄) and nitrous oxide (N₂O). In order to understand the overall GHG budget of these ecosystems, and thus their global warming potentials, we need to evaluate their potential to act both as sources and sinks of carbon, as well as producers of radiatively important GHGs such as CH₄ and N₂O. This PhD project will explore the potential of coastal intertidal habitats to act as sources or sinks of GHGs, sediment, and carbon using atmospheric, biogeochemical, sedimentological, and geophysical measurement techniques. Fieldwork will be conducted in the estuaries of eastern Scotland (e.g, Eden, Forth, or Tay). This project is deliberately pitched to be broad in scope, with the actual project focus determined by the successful candidate’s interests and expertise. Principally we are seeking an enthusiastic natural scientist with a background in ecology, earth science, environmental science, or other cognate discipline.

Exploring the temporal stability of Terrestrial-Marine teleconnections between the Central Pacific and higher latitudes

The El Niño/Southern Oscillation (ENSO) influences global climate at interannual time-scales and is often linked with extreme weather events such as flooding and drought and associated socio-economic problems. One of the key issues is how the ENSO system will respond to global warming. However, the instrumental record is not long enough to place recent changes in ENSO variability in a longer-term context. An understanding of the variability of the central Pacific (CP) over recent centuries must therefore rely upon palaeoclimate reconstructions to provide information on changes in mean state and variability prior to measured observations. However, a recent review (by primary supervisor) and re-analysis of available proxy data highlighted the difficulties of reconstructing past ENSO variability, especially when relying on different proxy archives (corals vs. tree-rings) and purported teleconnections.

This PhD project will utilise both instrumental and proxy data to assess the temporal stability of teleconnected relationships with the CP over the last 500 years. As coral archives are restricted in length, tree-rings are key archives, but of course, none are located in the CP. There are multiple regions, teleconnected with the CP, where substantial tree-ring (TR) data exist (e.g. American south-west, South America, and New Zealand). This project will focus on these regions and will not only assess how well the TR data coheres with the CP instrumental and coral data, but will also examine how data from these four regions cohere with each other – spatially and temporally. This project will benefit from work being conducted though NERC grant NE/H009957/1 (PI - Tudhope), which includes analysis of ENSO teleconnections over the past 5,000 years.

The signature of drought in river corridors

Links between hydrology and vegetation in the riparian corridor are well appreciated, but the details of vegetation response to physical boundary conditions, such as water availability in floodplains, are not well constrained. Thus, we have a poor quantitative understanding of how riparian vegetation responds to climate change (e.g., shifts toward increasing drought). This shortcoming can limit the ability of scientists and resource managers to anticipate species crashes and shifts in species composition in riparian zones, which affect ecosystem functioning. The proposed research will investigate the response of riparian forests to climate by employing stable isotope geochemistry to measure temporal changes in water sources delivered to the root zone of co-occurring trees with contrasting rooting depths. The postgraduate student will identify the signatures of source waters used by trees to construct tree ring cellulose and will investigate corresponding chronologies of tree growth over decadal timescales, in conjunction with time series of instrumental climate records. The student will analyze O and C isotopes to interrogate the relationships between growth history of riparian trees in floodplains and available water sources. Depending on the applicant’s abilities, there is also opportunity to develop simple physically based numerical models of water table fluctuations to provide physical explanations for floodplain water availability and corresponding isotopic signatures and/or to investigate remote sensing data on water storage and tree health, if the applicant possessed these desirable skills. The field component of this research will be carried out along the Rhone River basin of France and the Sacramento River of California, USA.