RECONSTRUCTING LATITUDINAL TERRESTRIAL TEMPERATURE GRADIENTS AT THE CRETACEOUS-PALAEOGENE BOUNDARY: TESTING THE "EQUABLE EARTH" HYPOTHESIS
Lead Research Organisation:
University of Manchester
Department Name: Earth Atmospheric and Env Sciences
Abstract
As anthropogenic atmospheric warming is forecasted to exceed 2C above preindustrial temperatures by 2100, a key uncertainty in predicting the impact of this change is the quantitative understanding of how this warming will be distributed in the oceans and atmosphere. One means of assessing this is to look to the geological past, especially the late Cretaceous to Eocene (100-34 Ma ago), when atmospheric pCO2 levels were last as high as the 700 ppmv forecasted for 2100, and global mean annual temperatures (MAT) were up to 8C warmer than today (the so-called "Greenhouse World"). Fossil data suggest that temperature-sensitive organisms, such as reptilians, were living in the Arctic-circle during this period, and led to the emergence of the "Equable Earth" hypothesis - a scenario that invokes near total collapse of the meridional, equator-to-pole temperature gradient at this time. This indicates a climate system that operated in a fundamentally different way to the modern "Icehouse World", with a different/enhanced means of transporting heat from the tropics to the poles. A fundamental problem for scientists aiming to predict future climate change, is that state-of-the-art models are not able to reproduce the degree of collapse of the global meridional temperature gradient suggested by fossil data, reflecting a problem with either the "Equable Earth" hypothesis, or with climate modelling. Either way, this uncertainty impedes our ability to confidently predict the impact of future climate change with far-reaching implications.
This research will be the first robust test of the "Equable Earth" hypothesis. We will reconstruct meridional variation in land surface MAT 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". The MATs will be reconstructed using the brGDGT palaeotemperature proxy from collected coal samples. brGDGTs are lipids produced by bacteria thriving in terrestrial environments, whose distribution is a function of land surface MAT and can be used to reconstruct land surface MATs. We have identified ten separate sites, spanning 47-75N of palaeolatitude, where coals (fossil peats) were demonstrably accumulating coevally, by the occurrence within each of the coals of the globally synchronous Iridium (Ir)-enriched layer that settled from the atmosphere after the impact of a meteorite at the K-Pg boundary. In addition to the Ir-enriched layer, the coals contain datable tephra horizons, which will constrain vertical rates of change of MAT from time-slice to time-slice. They also contain distinctive carbon isotopic events before, during and after the Ir- enriched layer, which provide additional correlatable time lines between all locations. Combined, this provides an unique opportunity to generate serial time-slice reconstructions of meridional land surface MAT gradients, spaced at sub-orbital durations, at this critical period in Earth history.
This will provide us with the opportunity to critically test the "Equable Earth" hypothesis, by placing numerical bounds on meridional MAT gradients for a series of time slices in continental interiors at this time. By generating meridional MAT gradients for multiple intervals, and by generating a tephrochronologically-based time-series through the succession, it will be possible to place bounds on the rates of change of MAT in time, from mid- to high- latitude. This will also reveal, for the first time, the dynamics in space and time of the "Greenhouse Earth" climate system, and will also allow us to assess MAT in the aftermath of meteorite impact at the K-Pg boundary, giving insight into the response of the climate system to catastrophic change, and allowing us to test competing hypotheses of climate change as the driver for the mass extinction at the K-Pg boundary.
This research will be the first robust test of the "Equable Earth" hypothesis. We will reconstruct meridional variation in land surface MAT 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". The MATs will be reconstructed using the brGDGT palaeotemperature proxy from collected coal samples. brGDGTs are lipids produced by bacteria thriving in terrestrial environments, whose distribution is a function of land surface MAT and can be used to reconstruct land surface MATs. We have identified ten separate sites, spanning 47-75N of palaeolatitude, where coals (fossil peats) were demonstrably accumulating coevally, by the occurrence within each of the coals of the globally synchronous Iridium (Ir)-enriched layer that settled from the atmosphere after the impact of a meteorite at the K-Pg boundary. In addition to the Ir-enriched layer, the coals contain datable tephra horizons, which will constrain vertical rates of change of MAT from time-slice to time-slice. They also contain distinctive carbon isotopic events before, during and after the Ir- enriched layer, which provide additional correlatable time lines between all locations. Combined, this provides an unique opportunity to generate serial time-slice reconstructions of meridional land surface MAT gradients, spaced at sub-orbital durations, at this critical period in Earth history.
This will provide us with the opportunity to critically test the "Equable Earth" hypothesis, by placing numerical bounds on meridional MAT gradients for a series of time slices in continental interiors at this time. By generating meridional MAT gradients for multiple intervals, and by generating a tephrochronologically-based time-series through the succession, it will be possible to place bounds on the rates of change of MAT in time, from mid- to high- latitude. This will also reveal, for the first time, the dynamics in space and time of the "Greenhouse Earth" climate system, and will also allow us to assess MAT in the aftermath of meteorite impact at the K-Pg boundary, giving insight into the response of the climate system to catastrophic change, and allowing us to test competing hypotheses of climate change as the driver for the mass extinction at the K-Pg boundary.
Planned Impact
The scientific and societal impact of our work will be significant and diverse. Scientific outputs will be delivered in the very top journals - a credible ambition based on the goals of the project, and track record of senior Co-Is. Communication at top international conferences (AGU, EGU etc.) will further accelerate impact.
Here we outline the specific communities who will benefit from this work, and how:
1. (Palaeo)climate modelers. The results of this study will place a new certainty on the dynamics of Earth's Climate System when operating in "Greenhouse" mode, and also how it responds to catastrophic change. The study will provide data that will inform and improve a new generation of GCM simulations of the Earth Climate System during these "Greenhouse" episodes. Because these periods are characterized by CO2 concentrations analogous to values predicted by the IPCC for as early as 2100 under continued rates of anthropogenic CO2 emissions, the results of this study provide real opportunities to impact science-based policy formulation. To this end, world-leading climate modelers Dan Lunt and Paul Valdes are embedded as project partners, who will have ongoing access to the generated dataset, and will utilise it directly as a test of, and to refine their own state-of-the-art models. Impact to the climate modelling is ensured through Dan Lunt's and Paul Valdes' international reputations and connections.
2. Palaeoecologists and palaeontologists. The results of this study will place boundare conditions on the temperatures (and their rates of change) that are associated with major floral and faunal change. This data will therefore improve understanding of the evolutionary and ecological response to climate change at a key interval in Earth history.
3. The wider public. The study benefits from the public's fascination with the dramatic events that occurred at the K-Pg boundary. Against the aesthetic appeal of this backdrop, there is a real opportunity to draw-in, engage inform the general public, and broaden their interest to the causes and nature of climate change in the past and future. This is important because communicating an understanding to the public, of the sensitivity of our planet to imposed change in the past, of the global-scale challenges posed by present and future climate change is the key to motivating science-based government policy to mitigate against anthropogenic change. Through our collaborative impact plan with the Manchester Museum, we will target the wider public at large, schools, the media, as well as the local communities on whose land the climate change we have documented happened 66 Ma ago. This direct public engagement will be undertaken during the timeframe of the project, but the aim of this engagement is to foster a future generation who subtantially more aware of evidence-based, pressing issues of environment and climate change, and its impact.
4. PDRA. The PDRA will develop practical skills in a wide range of established and novel organic geochemical and petrological techniques, sedimentology, and in the application of these techniques to solve theoretical, palaeoclimate problems over the timescale of the project. This will transfer into his/her future career and employment potential in a range of Earth Science disciplines beyond the timescale of the project.
Here we outline the specific communities who will benefit from this work, and how:
1. (Palaeo)climate modelers. The results of this study will place a new certainty on the dynamics of Earth's Climate System when operating in "Greenhouse" mode, and also how it responds to catastrophic change. The study will provide data that will inform and improve a new generation of GCM simulations of the Earth Climate System during these "Greenhouse" episodes. Because these periods are characterized by CO2 concentrations analogous to values predicted by the IPCC for as early as 2100 under continued rates of anthropogenic CO2 emissions, the results of this study provide real opportunities to impact science-based policy formulation. To this end, world-leading climate modelers Dan Lunt and Paul Valdes are embedded as project partners, who will have ongoing access to the generated dataset, and will utilise it directly as a test of, and to refine their own state-of-the-art models. Impact to the climate modelling is ensured through Dan Lunt's and Paul Valdes' international reputations and connections.
2. Palaeoecologists and palaeontologists. The results of this study will place boundare conditions on the temperatures (and their rates of change) that are associated with major floral and faunal change. This data will therefore improve understanding of the evolutionary and ecological response to climate change at a key interval in Earth history.
3. The wider public. The study benefits from the public's fascination with the dramatic events that occurred at the K-Pg boundary. Against the aesthetic appeal of this backdrop, there is a real opportunity to draw-in, engage inform the general public, and broaden their interest to the causes and nature of climate change in the past and future. This is important because communicating an understanding to the public, of the sensitivity of our planet to imposed change in the past, of the global-scale challenges posed by present and future climate change is the key to motivating science-based government policy to mitigate against anthropogenic change. Through our collaborative impact plan with the Manchester Museum, we will target the wider public at large, schools, the media, as well as the local communities on whose land the climate change we have documented happened 66 Ma ago. This direct public engagement will be undertaken during the timeframe of the project, but the aim of this engagement is to foster a future generation who subtantially more aware of evidence-based, pressing issues of environment and climate change, and its impact.
4. PDRA. The PDRA will develop practical skills in a wide range of established and novel organic geochemical and petrological techniques, sedimentology, and in the application of these techniques to solve theoretical, palaeoclimate problems over the timescale of the project. This will transfer into his/her future career and employment potential in a range of Earth Science disciplines beyond the timescale of the project.
Publications
O'Connor L
(2023)
Steady decline in mean annual air temperatures in the first 30 k.y. after the Cretaceous-Paleogene boundary
in Geology
Description | We have been able to show that mean annual air temperatures at two locations that were originally located at latitude 60 degrees N, increased in the last 1-5 millenia of the Cretaceous and gradually decreased over the first 5-40 millenia of the Palaeogene. This is the interval represented by a major mass extinction, and our analyses contextualise (rates of) climate change at this time. |
Exploitation Route | Episodes of rapid global warming are very interesting to society, because we are currently undergoing one. Out study provides the highest resolution data to date, of rates and absolute values of global warming that led to a mass extinction. This data provides some boundary conditions to the absolute values and rates of global warming that society and ecosystems at large could support in the future. |
Sectors | Agriculture Food and Drink Communities and Social Services/Policy Education Environment Government Democracy and Justice |
Title | Lipid biomarker palaeothermometry and carbon isotope data for eleven lignites spanning the Cretaceous-Paleogene (K-Pg) boundary in North America |
Description | The dataset consists of eleven spreadsheet tabs, each tab containing lipid biomarker palaeothermometry (air temperature reconstructions) and bulk organic carbon isotope data from individual lignites that are known to stratigraphically span the Cretaceous-Palaeogene (K-Pg) boundary. Uncalibrated, raw biomarker distributions (glycerol dialkyl glycerol tetraethers; GDGTs) are provided, as well as the calculated calibration outputs. Site coordinates are: West Bijou, Colorado (39°34'14''N, 104°18'09''W), Sussex, Wyoming (43°39'40"N, 106°19'06"W), Pyramid Butte, North Dakota (46°25'03''N, 103°58'33''W), Hell Creek Road, Montana (47°31'35"N, 106°56'23"W), Rock Creek West, Saskatchewan (49°02'20"N, 106°34'00"W), Wood Mountain Creek, Saskatchewan (49°25'20"N, 106°19'50"W), Frenchman Valley, Saskatchewan (49°20'56"N, 108°25'05"W), Knudesn's Coulee, Alberta (51°54'27"N, 113°02'57"W) Griffith's Farm, Alberta (51°54'47"N, 112°57'51"W), Coal Valley Cores (GSC CV-42-2, Cores 1 and 2), Alberta (53°05'02"N, 116°47' 40"W) Police Island, Northwest Territories (64°52'42"N, 125°12'33"W). |
Type Of Material | Database/Collection of data |
Year Produced | 2024 |
Provided To Others? | Yes |
Impact | None yet! |
URL | https://www2.bgs.ac.uk/nationalgeosciencedatacentre/citedData/catalogue/bfe2a9be-768b-4fdc-bc73-93f9... |
Description | Constraining peat accumulation rates and terrestrial mean annual temperature change at four Cretaceous-Palaeogene boundary sites in Canada |
Organisation | British Geological Survey |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | The partnership with NEIF was budgeted for in the original Standard Grant Application. The purpose of the collaboration is to generate ages of tuffs interbedded with the coals at the study sites, in order to constrain rates of peat accumulation, and therefore constrain rates of reconstructed temperature change. Our contribution is firstly to collect the tuff samples. A partial set of samples were collected in the summer of 2019, and the remainder were collected in summer 2022. We sent the set of collected samples to NEIF. Now these are processed by NEIF, the results are being integrated with the organic geochemical data, as part of the final report, and associated publications. |
Collaborator Contribution | NEIF will pick the samples for zircons, and provide absolute U-Pb ages (with uncertainties) for the collected tuffs. |
Impact | Successful generation of three ash age dates. |
Start Year | 2022 |
Description | Constraining rates of peat accumulation and terrestrial mean annual temperature change at four Cretaceous-Palaeogene boundary sites in Canada (NEIF 2318.0920) |
Organisation | University of Glasgow |
Department | NERC SUERC CIAF Cosmogenic Isotope Analysis Facility |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | The partnership with NEIF was budgeted for in the original Standard Grant Application. The purpose of the collaboration is to generate ages of tuffs interbedded with the coals at the study sites, in order to constrain rates of peat accumulation, and therefore constrain rates of reconstructed temperature change. Our contribution is firstly to collect the tuff samples. A partial set of samples were collected in the summer of 2019, and the remainder were due to have been collected in summer 2020 (this was not done for reasons of COVID restrictions). We sent the partial set of collected samples to NEIF. Once processed by NEIF, we will integrate the results with the organic geochemical data, as part of the final report, and associated publications. |
Collaborator Contribution | NEIF will pick the samples for sanidines, irradiate the sanidines and provide absolute ages (with uncertainties) for the collected tuffs. |
Impact | The project failed to produce useful Ar/Ardates from the tuffs on completion. Multidisciplinary: inorganic stable isotopes, organic geochemistry, stratigraphy. |
Start Year | 2021 |
Description | Manchester Festival of Climate Action - Panel Discussion on "What can the past tell us about our future" (Panellist: PDRA O'Connor). |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Public/other audiences |
Results and Impact | The Festival of Climate Action was an university run outreach activity, where members of the public were able to engage in discussions with experts on topics relating to climate and sustainability. Experts were able to give brief presentations on their research and how it informs debates around climate, sustainability and society. |
Year(s) Of Engagement Activity | 2021 |
URL | https://www.manchester.ac.uk/climate-festival/ |
Description | Poster by PDRA O'Connor "To include or not to include? Assessing brGDGT distributions in deep-time lignite records", 2nd international GDGT Workshop. |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Postgraduate students |
Results and Impact | Poster titled "To include or not to include? Assessing brGDGT distributions in deep-time lignite records" |
Year(s) Of Engagement Activity | 2023 |
Description | Talk by Co-I Price at the European Geophysical Union Annual General Meeting, Vienna (Online) 2021, "A terrestrial temperature peak in the first millennia after the Cretaceous-Paleogene Boundary". |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | Presentation of interim results to a major international interdisciplinary geosciences conference. |
Year(s) Of Engagement Activity | 2021 |
URL | https://meetingorganizer.copernicus.org/EGU21/EGU21-12647.html |
Description | Talk by Co-I Van Dongen at the International Meeting on Organic Geochemisty, Montpellier (Online) 2021, "Terrestrial temperatures peak in the first millennia after the Cretaceous-Paleogene Boundary". |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | Conference presentation of the interim results of the project to the main international conference on Organic Geochemistry. |
Year(s) Of Engagement Activity | 2021 |
URL | https://eage.eventsair.com/imog-2021/ |
Description | Talk by PDRA O'Connor "A millennial-scale record of mean annual air temperatures spanning 70 ka over the Cretaceous-Paleogene boundary", EGU General Assembly |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Postgraduate students |
Results and Impact | Talk titled "A millennial-scale record of mean annual air temperatures spanning 70 ka over the Cretaceous-Paleogene boundary". |
Year(s) Of Engagement Activity | 2023 |
Description | Talk by PDRA O'Connor "Abrupt cooling event 30 ka before the K-Pg: a link between terrestrial climate & Deccan volcanism?", Nederlands Aardwetenschappelijk Congres. |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Postgraduate students |
Results and Impact | A talk titled "Abrupt cooling event 30 ka before the K-Pg: a link between terrestrial climate & Deccan volcanism?" |
Year(s) Of Engagement Activity | 2024 |
Description | Talk by PDRA O'Connor, "Last ~100 ka of the Cretaceous characterised by global warming", 31st International Meeting on Organic Geochemistry. |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Postgraduate students |
Results and Impact | Talk titled "Last ~100 ka of the Cretaceous characterised by global warming" |
Year(s) Of Engagement Activity | 2023 |
Description | Talk by PI Jerrett at the British Sedimentological Research Group AGM, Edinburgh 2018: "Reconstructing land mean annual temperatures in the ancient record: implications for future climate change, and understanding sediment budgets in the past." |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Professional Practitioners |
Results and Impact | Presented a session on "Sedimentology and Society" which was a new session included at the British Sedimentological Research Group to encourage non-commerical benefits of research in sediments and sedimentary rocks. |
Year(s) Of Engagement Activity | 2018 |
URL | http://www.lyellcentre.ac.uk/docs/57thBSRGAbstract.pdf |