Overview

Project Highlights:

  • Study a set of unique coral cores covering up to 250 years of ocean climate history from Ashmore-Cartier archipelago in NW Australia, a global choke point in heat and salt exchange controlling global climate
  • Carry out research with cutting edge stable isotope and trace element geochemistry
  • Undertake innovative climate and geochemical proxy data analysis and develop paleoclimate reconstructions of temperature and hydroclimate

 

Overview:

The Indonesian Throughflow (ITF) is the only low latitude Pacific-Indian Ocean connection, and has a profound impact on the (re)distribution of heat, salt and dissolved anthropogenic-CO2 between these basins. Hence, it modulates global ocean circulation, global climate variability, and ocean acidification. Long-term (>200 year) information on the ITF is sparse (Hennekam et al., 2018), but this is a prerequisite for understanding (1) long-term ITF variability, (2) the impact of ongoing anthropogenic climate change on major climate phenomena (e.g. ENSO, IOD, Asian Monsoon), and (3) anthropogenic impact on the Pacific-Indian Ocean carbon inventory. To fill this knowledge gap, we propose to use giant Porites corals as natural archives of thermohaline conditions and circulation patterns, focusing on key locations in the eastern Indian Ocean ITF leakage. Coral δ18O-Sr/Ca measurements will be used to disentangle salinity (δ18O-Sr/Ca) and SST (Sr/Ca), as thermohaline conditions in the eastern Indian Ocean are linked to changes in ITF dynamics. Our pilot coral data show the potential to produce unique, long ITF records (Hennekam et al., 2018).

The aim of this project is to produce long (two centuries) climate records from Ashmore and Cartier island in the southeastern Indian Ocean Timor Sea (Fig. 1) with bimonthly temporal resolution in order to unravel natural changes in the teleconnectivity with the tropical Pacific. We, therefore, propose to build a 250 year climate data base for the ITF outflow into the Indian Ocean through a seasonally resolved multi-proxy geochemical study of corals complemented by instrumental climate data analysis.

Figure 1: Location of coral core sampling sites in southeastern Indian Ocean off NW Australia affected by the Indonesian Throughflow (ITF) transporting fresh and warm water from the Western Pacific Warm Pool (WPWP) feeding the South Equatorial Current (SEC) in the Indian Ocean. Map indicates salinity in March and September seasons. Red stars indicates Ashmore and Cartier Island archipelago (12S, 123E) where exceptionally old corals have been drilled in 2011 by the Australian Institute of Marine Science right in the outflow of the ITF. Right) massive 5m tall Porites sp. coral and drilling of cores.

Methodology

We will use the oxygen isotope composition of coral carbonate, which is the most widely used tool in coral paleoclimatology, in combination with trace element abundances to resolve temperature and salinity variations recorded by the corals (Hennekam et al., 2018). In regions with a constant hydrological balance, d18O records only vary with sea-surface temperature (SST). In regions with variable evaporation-precipitation balance (E-P) and/or oceanic advection, d18O variations are a combination of SST and the isotopic composition of seawater (d18O seawater). Sr/Ca-ratios have been shown to be the most robust thermometer in corals unaffected by seawater variations (Zinke et al., 2015). Consequently, coupled measurements of coral Sr/Ca ratios and d18O allow reconstruction of past changes in d18O of seawater by subtracting the thermal component of d18O based on the Sr/Ca-SST estimates (Hennekam et al., 2018).

 

Training and Skills

In the first year, the student will be trained in a single cohort on environmental science, research methods and core skills. You will become proficient in experimental design and protocols, in use of sophisticated analytical equipment including inductively coupled mass spectrometry, stable isotopes, XRD, X-ray and CT-scanning (most at University of Leicester), as well as fieldwork experience. This combination of innovative methods and state-of-the-art analytical equipment will provide you with a truly unique set of skills that will be attractive to both industrial and academic employers. You will join a thriving community of palaeoclimatologists at University of Leicester and have use of a recently refurbished Laboratories.

Timeline

Year 1: Get aquainted with the research methods and corals as climate archives through intensive literature study. Determine the sampling strategy for the long cores, based on X-ray and UV-imaging provided by Australian colleagues (AIMS). Use of milling machine to obtain powders from the first long core. Check core parts for diagenesis with XRD and thin sections. Perform test measurements in stable isotope and ICP-MS labds before starting with real samples. Join a fieldtrip at end of year 1 or start of year 2 to Australia with partner Curtin University (either Exmouth or Kimberleys). Commence analysis of first real samples end of year 1.

Year 2: Continue the sampling and geochemical data acquisition on core 1 and start with core 2 and core 3. Collect instrumental climate data and perform initial correlation/regression analysis with climate indices to check for climate relationships in the 20th/21st century. Get aquainted with data analysis toolkits (R, Matlab, climate explorer). Aim for first presentation of initial data at national or international conference mid-end year 2.

Year 3: Application of data analysis toolkits to entire dataset. Interpretation of geochemical data and working out climate drivers at regional and global scale. Synthesis of data for global climate teleconnections. Publication of papers and conference presentations, including the opportunity to present at international meetings, will be part of the schedule from year 2 onwards.

Partners and collaboration (including CASE)

The student will work under supervision of newly-appointed Professor Jens Zinke, an expert in coral paleoclimatology and geochemistry, supported by Dr Arnoud Boom, an expert in stable isotope mass spectrometry and its application to tropical archives. Both supervisors are based at the University of Leicester (UOL). Furthermore, we will work in close collaborations with Dr Tiffany Barry who leads the ICP-MS laboratory at UOL. Dr Janice Lough, a world-famous coral core expert, at the Australian Institute of Marine Science is our partner providing the core, growth parameters and getting involved in publishing. International analytical exchange and fieldwork is envisaged with Prof. Zinke’s long-term collaborators at Curtin University (Dr Brown, Dr MacIlwain) and the University of Western Australia (Dr O’Leary).

Further Details

Contact Jens Zinke, University of Leicester, jz262@le.ac.uk