Overview

Project Highlights:

  • Join a world-leading team striving to understand how carbon cycles around Earth's surface during extreme climatic warmth
  • Learn cutting-edge geochemical analyses for reconstructing past carbon cycling and climatic change
  • Test hypotheses that the size and volatility of carbon reservoirs at or near Earth’s surface vary with background climate state1
  • Determine the deep-sea temperature response to large-scale perturbations of the carbon cycle1,2 during Eocene extreme greenhouse warmth

 

During the early Eocene epoch, Earth witnessed its warmest temperatures of the past 90 million years, with the deep oceans up to 14°C warmer than today2,3. These greenhouse climates have traditionally been regarded as uniformly warm and climatically stable, or ‘equable’. However, the last decade has seen the discovery of a number of ‘hyperthermals’ (Fig. 1; rapid global warming events not dissimilar to our current anthropogenic warming) driven by large-scale releases of carbon from some as yet unknown source(s)1,2, challenging these traditional views of equability, and instead suggesting that greenhouse climates may be marked by pronounced instability.

The most well-studied hyperthermals occur during a ~6 million year-long interval of progressive global warming culminating in the peak warmth of the early Eocene from 52 to 50 Myr ago1 (Fig. 1). The occurrence and relative size of these hyperthermals have been explained by a thermodynamic threshold for carbon release and a decrease in the size of carbon reservoirs during times of extreme warmth1. However, these hypotheses have proven difficult to test owing to the lack of continuous records from within the early Eocene and from the subsequent climatic cooling during the middle Eocene. This project will test hypotheses that the size and volatility of isotopically depleted carbon reservoirs should diminish during extreme global warmth1 and the corollary hypothesis that these carbon reservoirs should grow and become more volatile with subsequent cooling into the middle Eocene (an interval for which almost no high resolution records exist, Fig. 1). It will also evaluate the deep-sea temperature response2,4 to these carbon cycle-driven hyperthermals to provide valuable information on the sensitivity of Earth’s climate to large-scale carbon releases.

This project will take advantage of new sequences from the Atlantic Ocean with the highest sedimentation rates available for the Eocene to allow an evaluation of the sensitivity of climate and the carbon cycle to Earth’s orbital cycles during extreme greenhouse warmth1,2,4 & subsequent global cooling

Benthic 18O data3 (red) showing peak early Eocene warmth and subsequent middle Eocene cooling, with existing high resolution benthic foraminifer 13C data records2,4 (green). Note absence of high resolution benthic isotope data during peak warmth and for much of the cooler middle Eocene.

Methodology

The successful candidate will reconstruct orbital-scale variability in deep-sea temperatures and carbon cycling using high resolution isotope analyses of benthic foraminifera2,4 from expanded sequences from the equatorial Atlantic (IODP Exp. 207) and North Atlantic (IODP Exp. 342). O and C isotope (d13C, d18O) analyses will be performed on the in-house Thermo-Scientific Delta+ stable isotope mass spectrometer.

This project will also use ultra-high resolution X-Ray Fluorescence (XRF) scanning of the chemical elemental contents of sediment cores housed at Bremen to develop detailed astronomical age models.

Because of the excellent preservation of planktic foraminifera, opportunity also exists to reconstruct the response of the surface ocean and thermocline across hyperthermal events and their longer-term response to the termination of the early Eocene greenhouse and onset of climatic cooling.

Training and Skills

CENTA students are required to complete 45 days training throughout their PhD including a 10 day placement. In the first year, students will be trained as a single cohort on environmental science, research methods and core skills. Throughout the PhD, training will progress from core skills sets to master classes specific to CENTA research themes.

The student will receive training in all aspects of state-of-the-art, high-precision stable isotope analyses in world-class geochemical laboratories. Training will also be provided in foraminifer taxonomy and taphonomy. There may also be opportunity for the student to participate in an IODP drilling expedition.

Timeline

Year 1: Training in laboratory protocols, processing of sediment samples, and taxonomy of benthic and planktic foraminifera. Picking benthic foraminifera from samples. Visit IODP core repository in Bremen to take additional samples from Exp. 342 and Exp. 207 cores. Training in stable isotope analytical techniques. Analyse first batches of benthic foraminifera.

Year 2: Generate majority of stable isotope data. Pick planktic foraminifera in targeted intervals and analyse for d13C & d18O. Visit Bremen for XRF datasets. Construct astronomically calibrated age models. Process and interpret data. Prepare manuscript #1.

Year 3: Finish remaining analytical work, continue data processing and interpretation. Present results at an international conference. Prepare manuscripts #2 and #3. Possible opportunity for involvement in IODP expedition. Write up PhD thesis. Contribute to wider IODP synthesis efforts.

Partners and collaboration (including CASE)

Project results will help meet the ambitious scientific goals of IODP Exp. 342 (comprising some of the target sequences), and the successful candidate will have opportunities to interact and collaborate with IODP Exp. 342 scientists. Results from this project will form an integral part of the broader goals of an international consortium of nine different institutions (the Eocene Stable Isotope Consortium [ESIC]) formed on IODP Exp. 342 (http://iodp.tamu.edu/scienceops/expeditions/newfoundland_sediment_drifts.html) with the ambitious aim of developing the first comprehensive, high-resolution, astronomically tuned benthic foraminiferal d13C and d18O time series for the entire Eocene epoch.

Results from this project will also complement other datasets of Eocene pCO2 that are currently being produced by a large multi-institution consortium (http://descentintotheicehouse.org.uk) that, together, will transform our understanding of Eocene climate evolution.

Beyond the Supervisory team, key project collaborators are:

Prof. Heiko Pälike, Ursula Röhl & Thomas Westerhold (astronomical age model construction, XRF core scanning; Bremen, Germany)

Dr Sandra Kirtland-Turner (Stable Isotope geochemistry, numerical modelling of the carbon cycle; UC Riverside, USA)

Further Details

Students should have a strong background in, and enthusiasm for, Earth science, oceanography and/or chemistry. The student will join a well-established team researching Earth system processes during past warm climates at the Open University.

Please contact Philip Sexton (philip.sexton@open.ac.uk) for further information.

Applications should include:

Apologies that some bits of information are requested multiple times on different forms. Please fill in everything requested.

Applications should be sent to

STEM-EEES-PhD-Student-Recruitment@open.ac.uk  

by 5 pm on 25th January 2017