The paradox of high-amplitude inter(glacial) variability across the Oligo-Miocene transition tackled using spectacular new deep-sea sediment archives

Lead Research Organisation: University of Southampton
Department Name: School of Ocean and Earth Science

Abstract

Carbon dioxide, CO2, is a powerful greenhouse gas and its concentration in Earth's atmosphere has increased by around 35% since the start of the Industrial Revolution (in a ca. 250 yr time period) to a level that is higher than at any time in the past 800 thousand years as measured in air bubbles from ice cores. If man-made (anthropogenic) CO2 emissions to the atmosphere follow projected rates, then by 2100, concentrations will reach values not seen on Earth since the Oligocene epoch ~34 to 23 million years ago (Ma). Back then, Earth is thought to have been warmer than today, featuring a genuinely green Greenland and a waxing and waning East Antarctic Ice Sheet (EAIS) that drove high amplitude sea level change (~40 m). These startling observations provide a powerful incentive to improve our understanding of the workings of that past climate system.

Our focus is arguably the most extreme event of this interval the Oligocene-Miocene transition, OMT, (~24 to 22 Ma) and presents us with a fundamental paradox on two counts:

(1) Published records indicate that the OMT was marked by a prominent 'transient' in global climate involving the inferred expansion and then retreat of Antarctic ice sheets from about half to full present-day East Antarctic ice sheet, EAIS, configuration and back again in ~400-kyr with superimposed high amplitude higher frequency orbital oscillations. Yet numerical analysis suggests that, in the absence of big changes in CO2 levels (only modest change is apparent in existing records), once formed, a large EAIS should be stable because of strong hysteresis properties associated with ice sheet geometry [to drive substantial melting of a 2 to 4 km-thick ice sheet, the snow line must ascend high into the atmosphere, well beyond the original bedrock surface where ice growth was first initiated].

(2) The imprint in these records of the influence of intricate changes Earth's orbit around the Sun on inferred glacial-interglacial cycles is unmistakable. Yet, time-equivalent oxygen isotope series from different sites show fundamentally different frequencies of orbital change- a result that contradicts the basic principles of oxygen isotope systematics if the cycles are forced by the growth and decay of large continental ice sheets.

The main factor that has limited progress in tackling this paradox has been a lack of suitable deep-sea sedimentary sections on which to work.

We propose to tackle this problem by exploiting new deep-sea sediment archives recovered from sediment drifts on the Newfoundland margin, NW Atlantic by IODP, Expedition 342 (Jun-Jul 2012; Wilson, Co-Chief Scientist; Liebrand, Stratigraphic Correlator, see Part 1, Case for Support). These sediments accumulated unusually quickly, directly in the flow path of the present day Deepwestern Boundary Current, they are clay-rich and host spectacularly well-preserved calcareous microfossils and well-sorted angular sand-sized lithic grains.

Some of the questions that we seek to address:

How reproducible are the different published oxygen isotope data series for the OMT at a site where sedimentation rates are high and microfossils are spectacularly well-preserved?

What was the nature of climate variability in the contemporaneous high-latitude North Atlantic where proximity to northern hemisphere ice sheets, sites of deep-water convection and sea ice formation make the region such an important agent in the climate system today?

Do existing CO2 records fail to capture the full amplitude of Oligo-Miocene change or do the models perhaps grossly over estimate the stability of the East Antarctic Ice Sheet?

What is the significance of the increases in CaCO3 content and organic carbon burial and then re-oxidation event inferred for the core of the OMT in our pilot study records?

Our work will shed new light on the ways in which global climate, ice sheets and the carbon cycle interact in a warm world.

Planned Impact

1. Who will benefit from this research?

This project will benefit the following specific users: Palaeoceanographers & Palaeoclimatologists; Climate and Cryosphere scientists; Earth System Scientists; the industrial hydrocarbon exploration sector of the UK economy, the wider community of scientists working on the problem of anthropogenic climate change; school children and the wider public interested in the exploration of the oceans and Earth.

2. How will they benefit from this research?

This project will make a significant scientific advancement towards understanding the stability of an interval in Earth's history when existing records suggest that Antarctic ice sheets underwent repeated large scale growth and retreat despite little apparent change in atmospheric carbon dioxide levels and the ice sheet stability predicted by numerical climate models. The records to be generated are from the Newfoundland margin in the North Atlantic Ocean and will be of higher fidelity than those previously obtained for this interval. We will sample drill-cores of sediments recovered from the deep ocean by Integrated Ocean Drilling Program Expedition 342 (Wilson, Co Chief Scientist). These sediments have unusually high rates of deposition, hosting spectacularly well-preserved fossils and the distal signal of sediment transport from Greenland and North America by ocean currents and perhaps ice rafting. Improved knowledge of the stratigraphy of the Newfoundland sediment drifts and global glacial-interglacial cycles acquired during our project will also be used to improve the UK Industrial knowledge base that underpins techniques used to discover new petroleum reserves in deep-water settings.

3. What will be done to ensure that they benefit?

i) Our results will be made available for peer and public scrutiny by presentation in scientific meetings and publication in the scientific literature.
ii) Follow-up dissemination to the wider public will be achieved in the first instance through media interviews including to global news networks (eg., AP, Reuters) are among the most efficient channels for high impact and can ultimately result in spin-out feature articles (eg. http://www.newscientist.com/issue/2661) and the University of Southampton and NOCS news websites (http://www.noc.soton.ac.uk/index.php).
iii) Rapid dissemination to the Earth System Science community during the course of the project will be achieved by presentations at international meetings and participation in workshops.
iv) Meetings in Soton and Abingdon with Mr Andrew Davies, Neftex to discuss the implications of our work for improving the knowledge base that underpins training in the key skill set used to discover new hydrocarbon reserves in deep-water settings.
v) Our results will be incorporated into NOCS "Ocean & Earth" day activities used to enthuse young people in science and wider participation in Higher Education.
vi) We will leverage UK/NERC Impact from IODP investment in two dedicated scientific outreach professionals who participated in Exp 342 and produced and disseminated a series of 10 min-long video clips during the expedition and have already resulted in >10,000 viewings. A 20 min. documentary featuring will debue At Fall AGU 2012 and the PI has secured funding for a follow up that will cover the post-cruse phase of IODP Exp 342.

Publications

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Ladant J (2018) Meridional Contrasts in Productivity Changes Driven by the Opening of Drake Passage in Paleoceanography and Paleoclimatology

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Liebrand D (2018) Orbitally Forced Hyperstratification of the Oligocene South Atlantic Ocean. in Paleoceanography and paleoclimatology

 
Description We reconstruct changes in atmospheric CO2 record for the middle Miocene Climatic Optimum (MCO) between 15.5 and 17 million years ago. Our record shows pronounced variability between 300 ppm and 500 ppm on a roughly 100 thousand year time scale during the MCO. These CO2 changes reconstructed for the Miocene are ~2 times larger in absolute terms (300 to 500 ppm compared to 180 to 280 ppm) than those associated with the late Pleistocene and ~15% larger in terms of climate forcing. In contrast, however, variability in proxy record of global climate are two thirds the amplitude of that seen during the late Pleistocene. These observations indicate a lower overall sensitivity to CO2 forcing for Miocene (Antarctic only) ice sheets than their late Pleistocene (Antarctic plus lower latitude northern hemisphere) counterparts. Our records point to the existence of two reservoirs of ice on Antarctica. One of these reservoirs appears stable, while a second reservoir shows a level of dynamism that contradicts the results of coupled climate-ice sheet model experiments given the CO2 concentrations that we reconstruct.
Exploitation Route To inform policy in response to human-driven climate change.
Sectors Environment

 
Description Integrated Ocean Drilling Program 
Organisation International Ocean Discovery Programme (IODP)
Country United States 
Sector Charity/Non Profit 
PI Contribution I co-lead IODP Expedition 342 and ODP Legs 199 & 207, three multi-million dollar multi-international collaboration as co-chief scientist and/or senior proponent. I participated in IODP Expedition 320. Members of my research group participated in these and many other (I)ODP expeditions
Collaborator Contribution see above and scientific papers arising
Impact many scientific publications. IODP is multi-international and multi-disciplinary
 
Description Online educational film documentaries 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact We instigated and participated in a series of eight online film documentaries of the scientific process at sea and post-cruise . The films have been viewed tens of thousands of times and sparked follow up questions and discussions.
Year(s) Of Engagement Activity 2012,2013,2015
URL https://www.youtube.com/watch?v=A3ot11rBYXM