(MERI) Reconstructing latitudinal terrestrial environments at the Cretaceous-Palaeogene boundary; Testing the ‘Equable Earth’ hypothesis

As anthropogenic atmospheric warming is forecasted to exceed 2°C above preindustrial temperatures by 2100, it remains unclear how thermal energy will be redistributed across the globe (from equator to pole) and to what extent this will impact the terrestrial environments. One means of assessing this potential future change is to look to the geological past, especially the late Cretaceous to Eocene, when atmospheric pCO2 levels were last as high as the 700 ppmv forecasted by the ICCP for 2100, and global mean annual temperatures were as much as 8°C warmer than today. A major challenge in our understanding of the Earth’s climate dynamics during these high pCO2 “Greenhouse” episodes is the conflict between geological proxy data that invoke near total collapse of the equator-to-pole thermal gradient, and reduced seasonality in continental interiors (also known as the “Equable Earth” hypothesis), versus atmospheric General Circulation Models that consistently fail to reproduce these conditions. This highlights the need to obtain addition geochemical environmental data, particularly from horizons of comparable age and spanning a range of terrestrial environments from equator to the poles during this period in time.

This project will be a robust test of the "Equable Earth" hypothesis and the student will reconstruct meridional environmental conditions in a transect along the North American Continent, spanning mid- to high-palaeolatitude for several discrete time-equivalent instantaneous time-slices spanning the Cretaceous-Palaeogene (K-Pg) boundary - an interval in the middle of the "Greenhouse World".

To address this, the student will participate in the collection of multiple terrestrial, coal-bearing sedimentary successions from across Western Interior Basin of North America that demonstrably represent the coeval accumulation of peat across the K-Pg boundary. The locations span 49-75oN (i.e. mid- to high-) palaeolatitude, and the peats accumulated as a series of disconnected mires on alluvial plains traversing the contiguous Rocky Mountain foreland basin, which extended from the Gulf of Mexico to the Arctic Ocean. All sediments will be analysed using a wide range of advanced techniques including (in)organic geochemical and (compound specific) isotope analyses for palaeotemperature and palaeoenvironmental reconstructions. Combined with the outcomes of a recently funded NERC project (NE/S002324/1), specifically focussing on the reconstruction of terrestrial mean annual temperatures using the same sedimentary successions, this will provide data against which existing model outputs of “Greenhouse” Earth can be compared and tested, delivering a step change in our understanding of Earth’s past (and future) climate dynamics. The study will also deliver a reconstruction of changes in environmental conditions through the K-Pg boundary, testing, opposing hypotheses of climate change as the cause of mass mortality at the K-Pg boundary.

The student working on this cross-disciplinary project will gain a wide breadth of training in inorganic and organic geochemistry, isotope geochemistry, sedimentology and paleoclimate reconstruction and would suit a student with a background in any of these fields. They will have access to world-class facilities in the Williamson Research Centre for Molecular Environmental Science (SEES) and analytical facilities at Plymouth University. This project is built on a strong foundation of previous research by all involved in the recently funded NERC project and will therefore benefit directly from expertise gained and the infrastructure established. This includes the generation of a tephrachronology- and δ13C- based time-correlation framework and mean annual land surface temperature profiles. In addition, approximately half of the sedimentary successions needed will already been sampled prior to the start of the student project but it is expected that the student will participate in the second field season focussing on the Canadian part of the study area. The student will finish the project with a highly marketable skill set spanning a wide range of geochemical, petrological and data analysis techniques, which will provide a basis for a future career in the industrial, government or academic sectors, in a rapidly expanding research area of international importance.