Climate modeller and isotope geochemist
Postdoc research
PlioGate: investigating the role of marine gateways in modelled Pliocene warmth
PhD Thesis
Did closure of the Mediterranean 6-5 Ma affect global climate?
Undergraduate Dissertation
Linking continental-slope failure, clathrate instability and the methane pulse associated with the Palaeocene-Eocene Thermal Maximum.
We - Paul Valdes (Univeristy of Bristol), Alan Haywood (University of Leeds) and myself - were awarded a NERC Small Grant to investigate the role of the Bering Straits and the Gibraltar Straits in modelling global climate processes. The project targets areas of current disagreement between model output and geologic data; focussing on climate in the Pliocene Epoch, around 5.3-2.6 million years ago. This is thought to be the last time that atmospheric CO2 levels were as high as today, so it is interesting that although models can simulate the general climate trends quite well, they are unable to reproduce regional patterns (especially in the North Atlantic-Arctic region). PlioGate aims to address the discrepency between the models and geologic data, improving our ability to faithfully simulate warm climate processes.
The project started in November 2012 and will contribute towards work being carried out by:
Thesis pdf also available to download from my Publications and Presentations page.
Background & Rationale More than five million years ago there were two Mediterranean-Atlantic gateways: one through northern Morocco (Rifian Corridor) and the other through southern Spain (Betic Corridor) (Fig.). Progressive tectonic restriction and closure of these marine corridors led to extreme salinity fluctuations in the Mediterranean 5-6 million years ago, resulting in the deposition of both several kilometres of salt and brackish water sediments. The pattern of circulation through these gateways is thought to have varied considerably. At times, all Atlantic inflow may have flowed through the Moroccan corridor while Mediterranean outflow was funnelled through southern Spain. At others, two-way flow through one or both gateways is envisaged. The Mediterranean's outflow flux is an important control on Mediterranean salinity, because it is the main mechanism for removing salt from the system. However, Mediterranean outflow water is also thought to be one of the drivers controlling the pattern and vigour of thermohaline circulation in the North Atlantic and hence has a wider climatic significance. |
 Fig. During the Messinian, the Mediterranean was connected. |
Project Aims
With respect to water exchanged through the Mediterranean-Atlantic gateway(s):
*HadCM3 is the UK Met Office's fully coupled atmosphere-ocean General Circulation Model
Project supervisors:
Key Findings
Evidence was collated from all DSDP, IODP and ODP Initial Results volumes containing sediments deposited ~ 65 - 45 Ma to assemble a database of continental-slope failures across the Palaeocene-Eocene Thermal Maximum (PETM).
A peak in mass movement was observed ~ 55 Mya, concurrent with a negative spike in d18O of benthic foraminifera and a CIE at ODP Site 865 (assumed to represent a global and rapid increase in ocean bottom waters and the oceanic/atmospheric methane pulse, respectively). Analysis of data from BRIDGE-run simulations, of benthic d18O and eustatic sea level curves suggests that temperature and pressure conditions at the seafloor were conducive to thermal dissociation of clathrates, causing methane to be released to the oceans and atmosphere.
Implications
The results of the investigation support the postulation that continental-slope failure, the climate optimum and the methane pulse observed during the PETM are causally linked through submarine methane hydrate dissociation. However, it is unclear whether mass movement pre-dated, coincided with or post-dated the surmised destabilisation of marine clathrates due to dating inaccuracies and associated low temporal resolution. Also, the focus of coring expeditions hitherto has hindered the assemblage of a representative database of mass movement events and it seems likely that much evidence has been permanently obliterated by the processes of subduction and erosion.
 Fig. Schematic of the Bouma Sequence, which, when recorded in a |
Although it remains unknown whether submarine slope failure was a cause or consequence (or both) of clathrate dissociation, it is evident that the system presents a severe threat to society - particularly the coastal regions of Europe, North America and North Asia - considering potential future climate change. Continuing the Work Future work will use complimentary methodologies to extend this database of continental slope failure during the PETM. In this way, research into the causes and consequences of the PETM is expected to move further away from unsubstantiated speculation, providing a more solid foundation for our understanding of the causal mechanisms underlying and the processes triggered by the PETM. Project advisor:
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