Carbonate clumped-isotopic constraints on marine temperatures during the Cretaceous

Lead Research Organisation: University of Plymouth
Department Name: Sch of Geog Earth & Environ Sciences

Abstract

A fundamental question we can ask about the Earth's past climate is how does surface temperature respond to external forcing? Evidence suggests that the Earth's climate was warmer and more equable during the Cretaceous Period (circa 146 to 65 million years ago) than it is today - an interpretation based on the distribution of thermophylic (cold intolerant) animals, plants and geochemical proxies.

This warmth during the Cretaceous has been linked to high atmospheric CO2 concentrations. Although most evidence indicates a significantly warmer Earth, with warm polar regions (including carbonate clumped-isotope data, a new tool for reconstructing temperatures), some research has suggested a negative relationship (or decoupling) between temperature and CO2 during this period.

Although the Mesozoic is not a direct analogue for future greenhouse warming such intervals in Earth history provide important insights into processes operating in the climate system. Hence the relationship between atmospheric CO2 and temperature has added significance as we try to place the present climate in the context of predicted future scenarios. Warm polar temperatures during the Cretaceous indeed challenge our understanding of how the ocean-atmosphere system operated as they are significantly warmer than General Circulation Models can reproduce. This has important implications for the prediction of future climates as it implies we may be underestimating future climate change in such regions.

Despite the intensive study of Cretaceous marine temperatures an equator-to-pole temperature profile for the Cretaceous greenhouse world remains poorly constrained. Problems stem from the fact that traditional palaeoproxies like oxygen isotopes requires an estimate of the isotopic composition of seawater - particularly difficult to constrain at high latitudes. A more recent approach has been to sidestep this issue by using the TEX86 palaeothermometer (a temperature proxy), although with respect to the Cretaceous this technique is limited by the distribution of suitably preserved sediments, particularly at high latitudes.

This proposal aims to address this significant gap in knowledge by undertaking the first quantitative and systematic study of early Cretaceous (Valanginian-Hauterivian) marine temperatures obtained from fossil molluscs using the novel clumped-isotope palaeothermometer. These data will be integrated with new temperature data arising from other techniques. In addition to generating marine temperatures for the Cretaceous tropics, temperate and polar regions we will be able to constrain the isotopic composition of seawater and hence will also be able to provide data concerning the debate about what is the most likely mechanisms to increase the transfer of heat from the equator towards the poles. Our novel clumped-isotope derived temperatures are also expected to be of benefit to the wider community of palaeoceanographers and climate modellers by providing extensive, new data against which to test model outputs.

Planned Impact

Understanding what processes are responsible for forcing natural climate change is fundamental to our understanding of the whole Earth climate system. Therefore, the principal academic beneficiaries of this proposal will be Earth System scientists, in particular those that are involved in the reconstruction and modelling of past climate events.

It is also anticipated that beneficiaries will include government policy advisors in the Department for Energy and Climate Change and international agencies, like the Intergovernmental Panel on Climate Change (IPCC), who will develop a greater understanding of the natural climate states the planet has experienced in the past. The results will also help in the modelling and validation of past and future climate scenarios, thus expanding our understanding of these complex systems.

Given the current interest in global warming, ice melting in polar latitudes and our ability to predict future climate scenarios, along with the fact that key parallels have been identified with the Cretaceous and other past greenhouse episodes, our analysis of Cretaceous climate should therefore have a key role to play in promoting the public understanding of climate science and raising awareness of the potential consequences of global environmental change.

Finally, the PDRA assigned to this project will benefit academically from working alongside a PI and Co-I who have extensive research experience and who have an extensive publication record in the field of palaeoclimatology. Undergraduates and Masters level students will also benefit academically from the research informed teaching practices that are routinely adopted by the PI and Co-I.
 
Description Our new Cretaceous temperature and belemnite oxygen isotope data imply seawater isotope values that have a remarkably modern character in that they are similar to modern high-latitude seawater. We consider the seawater oxygen isotope values to be plausible and point to unexpected basin- or global-scale hydrologies. This finding is fundamentally different to previous date led ideas. Our work strongly implies that heterogeneous oxygen isotope equilibrium might - for a given T - occur at Kim & O'Neil (1997) plus at least 1 Permil. This is in agreement with the hypothesis of Coplen (2007) and Dietzel et al. (2009) that the equilibrium fractionation between water and calcite is at Kim & O'Neil (1997) plus 1-2Permil.
Exploitation Route Our findings are consistent with modelling results that also suggest Cretaceous surface seawater oxygen isotope values are similar in many respects to modern. So our data is of use by others who are interested in reconstructing temperatures of the past and modelling past climates
Sectors Environment

URL https://www.plymouth.ac.uk/staff/gregory-price
 
Description Marie Curie
Amount € 282,109 (EUR)
Funding ID F00002362 
Organisation Swiss Federal Institute of Aquatic Science and Technology 
Sector Public
Country Switzerland
Start 01/2015 
End 12/2017
 
Description NERC Isotope Geosciences Laboratory
Amount £26,100 (GBP)
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 06/2013 
End 06/2014
 
Description Standard Grant
Amount £582,024 (GBP)
Funding ID NE/S002324/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 03/2019 
End 03/2022
 
Description Clumped isotope analyses with University of Copenhagen & ETH Zurich 
Organisation ETH Zurich
Department Institute of Pharmaceutical Sciences
PI Contribution Exchange of data and samples
Collaborator Contribution The partner has presented new seawater temperature estimates for the Callovian to Kimmerigian interval (Middle to Upper Jurassic), from clumped isotope analyses of pristinely preserved belemnites from Staffin Bay, Isle of Skye, Scotland
Impact An abstract at EGU 2019
Start Year 2018
 
Description Clumped isotopes of the Falklands 
Organisation University of Copenhagen
Department Faculty of Science
Country Denmark 
Sector Academic/University 
PI Contribution An investigation of southern high latitude warmth during Jurassic - Cretaceous with new evidence from clumped isotope thermometry
Collaborator Contribution clumped isotope thermometry analysis
Impact EGU2018-presentation Southern high latitude climate during the Jurassic - Cretaceous: new evidence from clumped isotope thermometry by Madeleine Vickers et al.
Start Year 2018
 
Description Clumped isotopes with Frankfurt 
Organisation University of Frankfurt
Country Germany 
Sector Academic/University 
PI Contribution A research team collaboration accessing facilities undertaking clumped isotope analyses with Frankfurt University
Collaborator Contribution Exchange of data and samples
Impact no outputs or outcomes yet
Start Year 2015