Astronomical forcing and rapid climate change in the Jurassic

Lead Research Organisation: Open University
Department Name: Environment, Earth & Ecosystems

Abstract

One of the most effective ways we can understand how the Earth works is by studying how it has behaved in the past. In particular, an understanding of how and why climate has changed over Earth history is of critical importance if we are to more fully understand how the Earth may respond to climate change in the future. Importantly, it is the geological record of rocks and fossils that provides us with the tools to understand ancient climate change beyond ~1 million years ago. A number of events in the Jurassic period (from ~200 to ~145 million years ago) have now been recognised that reveal evidence for severe and rapid climate change. Our understanding of these events relies crucially on knowing the timing, duration and rates of environmental change and defining the precise pattern, structure and detail of environmental change. In this fellowship, both these factors will be addressed in order to further understand severe climatic changes that occurred during a short interval of the Early Jurassic (the late Pliensbachian to early Toarcian stages, ~180 million years ago) and at the Middle to Late Jurassic transition (the late Callovian to early Oxfordian stages, ~160 million years ago). In marked contrast to the warm, equable and polar ice-free conditions inferred for most of the Jurassic, the Middle-Late Jurassic transition has revealed geochemical and fossil evidence for a marked deterioration of climate that resulted in a pronounced but short-lived interval of relatively cold temperatures and possible polar ice sheet growth. During the Early Jurassic interval, there is also evidence for a similar abrupt global cooling event. The cooling event of the Early Jurassic was followed by severe warming that has been associated with a marked reduction in global seawater oxygen levels, a large increase in continental weathering rates, mass extinction of marine species, and a major perturbation to the global carbon cycle. A full understanding of all these events can only be gained if their rapidity and timescale is accurately known. One way in which geologists can quantify time in successions of ancient rocks is by looking for evidence of astronomical cycles. Astronomical cycles arise because the Earth's orbit around the sun is not perfectly smooth; for example the angle of Earth's tilt and shape of its elliptical path round the sun changes through time. Importantly, these 'wobbles' in Earth's orbit are regular, and thus cause small, cyclical changes in the Earth-Sun distance with periodicities typically between ~20,000 and 400,000 years. In climatically sensitive sedimentary rocks, these climate cycles will manifest themselves as cyclic changes in rock chemistry, and these cycles can thus be counted and used to construct timescales for ancient sedimentary successions. Such cycles are a common phenomenon in the geological record, and are probably responsible for pacing the timing of the Ice Ages, which have recurred every ~100,000 years or so over the last million years or so. Critically, this also demonstrates how these cycles, although subtle, can actually drive large and severe changes in climate, probably due to feedback effects in the climate system. Nevertheless, the possibility that these cycles drove the major climate change events in the Jurassic detailed above has received little attention. In this research, I will look for evidence of astronomical cycles across the chosen study intervals in order to establish the rapidity and duration of the climate change events, whilst also assessing the potential role astronomical cycles played in driving climate change. In addition to looking for astronomical cycles, the precise causes and consequences of climate change will be assessed by making chemical measurements on rocks and fossils spanning the events. These data will be used to infer changes in seawater temperatures, weathering rates, volcanic activity, and the global carbon cycle.

Publications

10 25 50

 
Description 1. A primary focus of the grant was identifying and quantifying rates and magnitudes of rapid climate change on short (millennial) timescales in the Jurassic. Astronomical timescales typically provide the highest resolution measure of time available in rock successions of this age. It was found that the actual duration of very abrupt (i.e. millennial-scale) events cannot be reliably quantified even with astronomical techniques. A mathematical analysis of the errors indicated that assumed millennial-scale events recognised in the geological record can be longer than estimated by well over 100%, and shorter than estimated by 60%. These findings have implications for researchers seeking to accurately quantify the timescales and rates of ancient climate change and other Earth system processes.
2. A fundamental bias in the way climate is recorded in the geological record was discovered. It was found that rates of climate changes inferred from proxy data in Earth history scale with measurement timespan as an approximate power law across nearly six orders of magnitude. The scaling arises because climate change defined at the long (millennial to million year) timespans typically resolvable in the geological record does not capture the full variance of the climate system operative at shorter time-scales. This means that maximum attainable rates of climate change inferred from geological data are inevitably, and erroneously, lower than modern rates measured on shorter, annual-decadal scales. A specific implication of this finding is that rates of climate change during events like the early Toarcian and Callovian-Oxfordian cannot be compared with rates of climate change at the present day without accounting for the bias.
3. A geochemical characterisation of Early Jurassic sediments from a Panthalassa Ocean succession in Japan was conducted for the first time. This was significant because the precise pattern and global expression of climate change during this interval was hitherto uncertain owing to a Euro-centric bias of published data. Extremely abrupt (cm-scale, sub-millennial timescale) carbon isotope changes in the early Toarcian were replicated outside Europe for the first time. However, evidence for similar carbon isotope changes across the Pliensbachian-Toarcian boundary was not found. The data from Japan provide strong evidence that 12C-enriched carbon was effused to the biosphere in rapid pulses during the early Toarcian, probably from methane hydrate melting. Osmium isotope, clay and organic geochemical data further reveal that during the early Toarcian, marked changes in weathering occurred synchronously with carbon release. Taken together, the data emphasise that early Toarcian climate change was severe, global, and rapid. The findings help cement the role events like the early Toarcian can play in providing analogues for carbon release at the present day. Work on the rocks in Japan has also revealed marked changes in weather, with a likely increase in storms occurring broadly coeval with carbon release. This feature of the Toarcian event has been recognized in European and African sections, but this is the first time evidence for increased storminess has been found from the Panthalassa Ocean.
4. The environmental responses to inferred global cooling through the Callovian-Oxfordian boundary and late Pliensbachian were markedly different. Osmium isotope data across the Callovian-Oxfordian suggest that no major changes in weathering patterns occurred but that global weathering rates were low. Insights have been made into the sensitivity and limitations of the osmium isotope method. Most pertinently, data generated from rock types of subtly different type showed markedly varied osmium isotope signatures - something not predictable or cognizable a priori.
Exploitation Route The transformative potential of the work is that it provides: 1) important new geological data that contribute to anthropogenic warming debates, and 2) important new insights and caveats on the utility of such data.
The work has emphasised how the early Toarcian represents a key analogue for understanding the Earth-system responses to large-scale carbon release at the present day. This can directly impact the work of the IPCC, since they use palaeoclimate records to improve understanding of likely responses to future climate change. The completed work on abrupt Jurassic climate change provides some of the best data suitable for this task.
Additionally, the work will have an impact on how scientists determine timescales and rates of climate change in deep time. This has potential socioeconomic/political impacts because the work identified key flaws in how we compare modern climate change with geological events, and hence how we contextualise modern climate change to understand its relative severity and importance. One of the key findings related to this - that maximum rates of ancient climate change in the past were probably no slower than modern rates - resonates with an interested and informed public - as evidenced through the press release that accompanied this work.
Sectors Environment

 
Description Daiwa Foundation Small Grant
Amount £2,500 (GBP)
Funding ID 10960/12369 
Organisation Daiwa Foundation Small Grants 
Sector Charity/Non Profit
Country United Kingdom
Start 01/2017 
End 01/2018
 
Description NERC Facilities Grant
Amount £47,150 (GBP)
Funding ID IP-1673-116 
Organisation Natural Environment Research Council 
Department NERC Isotope Geosciences Laboratory
Sector Academic/University
Country United Kingdom
Start 11/2016 
End 11/2018
 
Description Sasakawa Foundation of Great Britain Grant
Amount £1,600 (GBP)
Funding ID 4883 
Organisation The Great Britain Sasakawa Foundation 
Sector Charity/Non Profit
Country United Kingdom
Start 03/2016 
End 03/2016
 
Description Expression of the Toarcian OAE in shallow marine sediments of China 
Organisation University of Lille
Department Earth Sciences
Country France 
Sector Academic/University 
PI Contribution Carried out XRF analysis of sedimentary rocks as part of this collaboration.
Collaborator Contribution Undertook fieldwork and geochemical analyses of sedimentary rocks from Toarcian successions in southwest China.
Impact Paper in EPSL in 2018: Han, Z., Hu, X., Kemp, D.B. & Li, J. 2018. Carbonate platform response to the Toarcian Oceanic Anoxic Event in the Tibetan Himalaya: Implications for environmental change and biotic platform demise, Earth and Planetary Science Letters, 489, 59-71, doi:10.1016/j.epsl.2018.02.017
Start Year 2016
 
Description Geologic controls on sedimentation rate scaling laws 
Organisation University of California, Riverside
Country United States 
Sector Academic/University 
PI Contribution Sedimentation rate data were analysed to assess climatic controls on sedimentation useful for understanding palaeoenvironmental change
Collaborator Contribution Provision sedimentation rate data for analysis, and expertise in data handling
Impact 10.1111/sed.12112
Start Year 2010
 
Description Osmium isotope analysis of Jurassic mudrocks 
Organisation National Research Centre for Geoanalysis, Beijing
Country China 
Sector Public 
PI Contribution Provision of samples, analysis of data
Collaborator Contribution Osmium isotope analysis of samples and expertise in data interpretation
Impact Work has now ended. Data were not suitable for publication
Start Year 2012
 
Description Phase-specific oxygen isotope analysis of clay minerals for discerning palaeohydrology of abrupt climate change 
Organisation Western University
Country Canada 
Sector Academic/University 
PI Contribution Provision of samples, analysis of data.
Collaborator Contribution Analysis of samples for phase-specific oxygen isotopes
Impact Work is ongoing
Start Year 2013
 
Description Toarcian climate change from the Panthalassa margin 
Organisation University of Tokyo
Country Japan 
Sector Academic/University 
PI Contribution Field and laboratory work has been completed on Toarcian sedimentary rocks from the Toyora area of Japan, which formed part of the Panthalassa Ocean margin in the Early Jurassic. Multiproxy geochemical analysis has been carried out on these rocks
Collaborator Contribution Collaborator at University of Tokyo provided logistical support, field guidance, and scientific expertise that facilitated the research.
Impact 4 papers now published:Kemp, D.B., Fraser, W.T. & Izumi, K. 2018. Stratigraphic completeness and resolution in an ancient mudrock succession, Sedimentology, doi:10.1111/sed.12450. Izumi, K., Kemp, D.B., Itamiya, S. & Inui, M. 2018. Sedimentary evidence for enhanced hydrological cycling in response to rapid carbon release during the early Toarcian oceanic anoxic event, Earth and Planetary Science Letters, 481, 162-170, doi:10.1016/j.epsl.2017.10.030. Izumi, K., Endo, K., Kemp, D.B. & Inui, M. 2017. Ocean redox conditions through the late Pliensbachian to early Toarcian in the northwestern Panthalassic margin: Insights from pyrite and geochemical data, Palaeogeography Palaeoclimatology Palaeoecology, doi:10.1016/j.palaeo.2017.12.024. Kemp, D.B., & Izumi, K. 2014. Multiproxy geochemical analysis of a Panthalassic margin record of the early Toarcian oceanic anoxic event (Toyora area, Japan), Palaeogeography Palaeoclimatology Palaeoecology, 414, p. 332-341
Start Year 2013