Tracing Pacific-Indian Ocean heat and salt exchange by the Indonesian Throughflow and its impact on global climate variability

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.

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, 18O records only vary with sea-surface temperature (SST). In regions with variable evaporation-precipitation balance (E-P) and/or oceanic advection, 18O variations are a combination of SST and the isotopic composition of seawater (18O 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 18O allow reconstruction of past changes in 18O of seawater by subtracting the thermal component of 18O based on the Sr/Ca-SST estimates (Hennekam et al., 2018).

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).

Entry requirements
Applicants are required to hold/or expect to obtain a UK Bachelor Degree 2:1 or better in a relevant subject. The University of Leicester English language requirements apply where applicable.

How to apply
Please refer to the CENTA Studentship application information on our website for details of how to apply.As part of the application process you will need to:

• Complete a CENTA Funding form – to be uploaded to your PhD application
• Complete and submit your PhD application online. Indicate project CENTA2-GGE7-ZINK in the funding section.
• Complete an online project selection form Apply for CENTA2-GGE7-ZINK