Reducing Greenhouse Climate Proxy Uncertainty

On current trajectories, the concentration of atmospheric carbon dioxide (CO2) will exceed 550 ppm by the middle of this century. Such high carbon dioxide concentrations last occurred over 25 million years ago during the "greenhouse" climates of the early Cenozoic. In particular, the early Eocene epoch (~55 to 48 million years ago) was characterized by the warmest climates of the past 65 million years, with no ice sheets on Antarctica, polar regions ~20-40 degrees C warmer and sea levels ~50 to 70m higher than present. These warm Eocene climates can be simulated using the same climate models that are used to predict future climate change, such as those used in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (2013-14). In this report, climate model simulations of the Eocene were compared against temperature estimates from the geological record to test the accuracy of modelled warming in Polar regions at greatly increased CO2.

PI Dunkley Jones was responsible for collating the Eocene temperature estimates used and figured in the IPCC AR5 report. This work is now being substantially improved ahead of the next IPCC report within a collaborative international project to run IPCC-class climate models with a consistent set of boundary conditions and Eocene geographies, as part of the "Deep-time Model-data Intercomparison Project" (DeepMIP). Significant improvements in the accuracy of the critical geological data used to test these models - Eocene surface temperatures and atmospheric CO2 concentrations - are, however, more difficult to establish. Current moderately reliable estimates of ocean surface temperatures for the early Eocene are limited to only seven locations globally, and, at high latitudes, can diverge by up to 20 degrees C depending on the proxy method used. Current estimates of early Eocene CO2 concentrations are even more uncertain, ranging from ~300 ppm to in excess of 2000 ppm. There is only one sound early Eocene data point based on the CO2 proxy methods highlighted by the IPCC as having particular promise - those based on foraminiferal boron isotopes and alkenone carbon isotope compositions.

Here we aim to make a step-change improvement in these "proxy" estimates by taking advantage of two new opportunities. The first, is the serendipitous discovery of a remarkable suite of very well preserved, unaltered marine microfossils, made of calcium carbonate, alongside similarly well-preserved organic molecular biomarkers produced by Eocene marine algae and bacteria. The chemistry of this fossil material is the basis for proxy temperature and/or atmospheric CO2 estimation. The quality of this material is so high that we propose to generate ~170 alkenone-based CO2 estimates for the early Eocene, where previously there were none, and 15 boron-isotope based estimates to test the single data point currently available. The rare co-occurrence of these substrates and their abundance also provides the opportunity to use multiple independent methods to estimate both ocean temperatures (4 methods) and atmospheric CO2 (2 methods) on the same sample set, and so directly compare estimates from different methodologies at the same time and place.

The second key opportunity is a new collaboration between the PI Dunkley Jones and astrophysicists with advanced expertise in data analysis, statistical modelling and signal processing. With the generation of the largest ever dataset of proxy-to-proxy comparisons from any Greenhouse climate, this new collaboration will maximise our ability to draw robust conclusions about systematic errors within any given proxy method. This is vital for the reconstruction of warm climate states where there are persistent discrepancies between temperature reconstructions based on different proxy methods. Here, we will be able to directly compare methods from the same samples and with uniformly excellent preservation.

Following the NERC Handbook, here we address Pathways to Impact sections a & b: who could potentially benefit from the proposed research and how might the potential beneficiaries benefit?

INDUSTRIAL IMPACT

Core 16/28-Sb01 was funded and acquired by the Irish Petroleum Infrastructure Programme (PIP) at a cost of c. £550k. The original drilling aim was to confirm the Cenozoic and Mesozoic stratigraphy of Rockall Trough, an exploration frontier. PIP and their industrial partners will receive direct benefit from our proposed work program. Our new organic geochemical and micropaleontological data will provide down-core constraints on early Cenozoic environments of the Rockall Trough region. Our work will directly feed into a new project, contracted by PIP to Merlin Energy Resources (Merlin), to integrate all existing biostratigraphic and micropaleontological data from across the Irish Basins. The project team, lead by the PI, already has an excellent working relationship with Merlin Energy Resources, including the co-supervision of a PhD project in Birmingham on the Jurassic Basins of Northern Ireland with their Director Dr Phil Copestake, and also with their associated team for the specific PIP project, including Dr Haydon Bailey who teaches on the University of Birmingham MSc course in Applied Micropaleontology. We also have strong links with key industry partners through PP Harrington of Petrostrat Ltd, who originally studied the Rockall Cores for palynological content. Between PPs PIP, Haughton (University College Dublin) and Harrington (Petrostrat) we will directly link our results into the most current industry data integration for the Rockall area. Further, this collaboration will also be of benefit for the Project Team, as we seek to expand the search for well-preserved material from the Late Cretaceous and Neogene on the Irish Shelf. Collaboration with industry data integration and with PIP is likely to be a productive mutual collaboration for both industry understanding of regional geology and paleoclimate science. To ensure the best possible communication between our project team, other relevant academics (Haughton) and industry end-users, we propose a Dublin-based workshop, co-hosted with PIP and the Irish Shelf Petroleum Studies Group (ISPSG) to discuss how our results relate to frontier deep-water paleoenvironments. In particular, do they provide new constraints on industry source-sink analysis that aim to predict erosion sites, sediment transport pathways and foci of sand deposition. As well as this, we have also made a commitment report on this project at PIP's annual conference each November.

EDUCATIONAL IMPACT

Cenozoic palaeoceanographic research embodies international scientific collaboration and the deployment of specialized engineering and technological solutions against a backdrop of dramatic ocean environments. This strong aesthetic appeal gives scientists leverage for communicating their work to the public, including young people, educators and policy makers. In the case of our proposal, the appeal is enhanced by the juxtaposition of the familiar with the exotic: the NE Atlantic and western coast of the British Isles during the last super Greenhouse world. The same ocean, the same land mass, but subject to dramatically different sea-levels, persistently hot temperatures and replete with para-tropical rainforests harbouring vegetation such as Palms and Bombacoideae trees (whose modern taxa include the Baobabs and Durian fruit trees). Palaeoclimatic research can be inspirational for the public, and our impact plan will ensure that our message about climate change reaches this audience. Through our collaborative impact plan with the Lapworth Museum of Geology, we will target schools, the media and the wider public.