Reconstructing Intermediate Water Temperature Response to Pliocene-Pleistocene Climates

Lead Research Organisation: Durham University
Department Name: Geography

Abstract

Projections of future climate change under higher atmospheric carbon dioxide concentrations rely upon our understanding of the relationships and feedbacks that operate between different climate components, either as processes (ocean circulation, ice-sheet behaviour) or regions (e.g. low versus high latitudes). A number of key variables within the modern climate system have been linked to major climate transitions in the past, but whether they drove, amplified, or responded to climate events remains a topic of intense debate.

In this project we propose to investigate the response of the intermediate waters of the ocean to the growth of large ice-sheets in the northern hemisphere and falling atmospheric CO2 conditions over the last 4 million years. Intermediate waters are found at around 500 - 1500 m water depth. They are important for connecting large areas of the ocean, because they are formed first by the sinking of surface waters in the high-latitudes (e.g. the Southern Ocean), but extend to reach the equator where they may then return to the surface ocean by the process of upwelling. This means that changes in temperature, salinity, and nutrients can be transported from the polar regions to the tropics. It is thought that during the retreat of the ice-sheets, these water masses were extremely important for releasing carbon dioxide into the atmosphere and acting as a "feedback" for rapid climate change.

Despite the importance of intermediate waters for global climate, their response to significant events in the climate system since 4 million years ago is unclear. We also know that over the last 4 million years there have been a large number of extinction events in organisms called foraminifera that live in intermediate waters. Although these extinction events are global in extent, their cause is not known but may have been linked to the temperature of the intermediate waters. We propose a thorough investigation of intermediate water temperatures and foraminifera assemblages over the last 4 million years to assess the cause of the extinction events. We will generate the first record of intermediate water temperature from the SW Pacific that extends back to 4 million years ago. Our chosen site sits within the most important intermediate water mass of the present day (Antarctic Intermediate Water). We will use the trace metal composition of a key species of foraminifera that did not become extinct and which lives in intermediate waters, to calculate past temperatures. We will assess the causes of any changes in intermediate water properties by generating records of sea-surface temperature which reflect the surface ocean circulation in the area of intermediate formation in the Southern Ocean. We will use specific organic remains (alkenones) from marine algae to determine past sea-surface temperature values. We therefore aim to not only reconstruct intermediate water temperatures, but also investigate what caused any changes that are observed. At present, there are large gaps in time between samples in the foraminifera extinction record. By reducing these gaps and reconstructing foraminifera assemblages, we will more precisely determine the links between foraminifera extinctions and changing intermediate water properties. As a result of this thorough approach, this research programme will answer key questions about the processes that connected the low- and high-latitudes and caused widespread marine extinction events over the last 4 million years.

Planned Impact

The main beneficiaries of the proposed research beyond the academic realm will be young people and the local public in the region of the host institution (North-East England) and the British Geological Survey (Nottingham). These communities will benefit via an increased understanding of the scientific approaches taken to understanding earth history, the key questions that drive palaeoclimate science, the unresolved questions around important marine extinction events, and our current knowledge of natural climate variability. As a result, they will be ensured of engagement with UK Science and an introduction to scientific methods. Our engagement with undergraduate students will contribute to the basic training of the next generation of young scientists and policy makers in the UK.

Our regional activities will draw on existing and strong links with schools and teachers developed by the PI as part of her co-ordination of both Newcastle University Geography Outreach programmes and the North-East Quaternary Association (NEQUA), and links with the celebrated natural history arm of the Great North Museum. Furthermore, the British Geological Survey is also committed to outreach programmes which include visits to schools by BGS scientists, and participation at the annual British Science Association "Science Week". All of these events engage school pupils, teachers and the general public in scientific and geographical/geoscience research. They require no extra cost to this research project.

Additional project-specific events will also introduce participants to results which investigate and challenge existing ideas about natural climate variability and the causes of widespread extinction events in the recent geological past. Through the generation of online A-level revision and teaching materials, we will introduce young people to the exciting scientific developments taking place in palaeoclimate research. Our project website will be used to release these materials, and provide additional resources for the media and academic researchers. The PDRA will attend the NERC media training programme, and will be listed as a Newcastle University "expert" for climate science.

The direct societal or economic impact of this research is difficult to quantify, but through the generation of high-quality new data sets that have implications for understanding climate feedbacks and the causes of evolutionary events, this research programme will ensure that the UK remains an important centre for tackling key earth system science questions. This project thus contributes to the UK knowledge economy, and ultimately to a 'green economy' via scientific investigation of climate change.

Publications

10 25 50
 
Description We have tested and proved the viability of a new method to reconstruct water temperature below the sea surface (here, we reconstruct the properties of an important water mass - Antarctic Intermediate Water - which connects the high latitudes with the tropics).

We have provided the first continuous record of sea surface temperature evolution from the mid latitudes of the Pacific Ocean spanning the last 4 million years (the only other record which exists is from the Atlantic Ocean). We combine this with the first ever reconstruction of Antarctic Intermediate Water temperatures over the same time interval. We show that a complex evolution of Southern Ocean circulation marks the transition from the warm Pliocene climates of 3-4 million years ago with the large ice ages of the last ~2.7 million years.

We provided the first comprehensive test of whether a seafloor extinction event at ~1 million years ago was because of cooling, changes corrosivity of the water masses, or changing food supply. Our data reject the first two factors, and indicate for the first time that a specific change in phytoplankton (living at the sea surface) probably caused the extinction of around 90 fauna living on the seafloor.
Exploitation Route the results are largely academic at this stage, but we propose several hypotheses which should be tested on how the southern high latitudes have evolved over the last 4 million years. We also present a new hypothesis to explain a seafloor extinction event, which requires testing across multiple sites and with global reach.
Sectors Education,Environment

 
Description European Geosciences Union Ambassador Award
Amount € 960 (EUR)
Organisation European Geosciences Union 
Sector Charity/Non Profit
Country Germany
Start 08/2013 
End 10/2013
 
Description Climate Change: A prehistoric window on Earth's future? 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact Contributions to a BBC Futures article discussing evolution of climate, the Pliocene warm period, and how we reconstruct past climates.

In this article by Sarah Cruddas, published by the BBC, the importance of understanding past climates, and specifically the Pliocene ~3 million years ago, is outlined.
Year(s) Of Engagement Activity 2013
 
Description Conference on Pliocene Climate 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact 70 researchers attended a workshop in which a small set of plenary talks was followed by three different sets of discussion groups, who were set tasks of considering future research directions and potential syntheses. I was a co-organiser of this event and we secured funding from a range of international sponsors.

Outcomes from the meeting include:
- proposal to submit a working group application to the PAGES framework
- future reviews and syntheses of Pliocene climate by designated groups
- future workshop to assess progress in 2 years
Year(s) Of Engagement Activity 2014
URL http://jornades.uab.cat/plioclim/
 
Description Geological Society Presentation 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Presentation focussed on the new data from this grant, and led to questions and discussion with the audience both immediately after the talk and in the subsequent discussion session.

Advice on the corrections to be made for one of the temperature reconstructions was used to formulate the pending publication from this award.
Year(s) Of Engagement Activity 2014
URL http://www.lifeandplanet.net/2014-co-evolution-of-life-and-planet.html
 
Description Publicly available Research Project website 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Our project website (hosted through our department research pages) gives a brief outline of the research project and what our aims are. This has been noted as interesting and useful for applicants to PhD and post-doctoral research positions, who can get a flavour of what the research in our department involves.

Informally, PhD and post-doctoral research associate applications have noted the value in seeing what kinds of research projects are available in our department.
Year(s) Of Engagement Activity 2012,2013,2014
URL http://www.dur.ac.uk/geography/research/research_projects/?mode=project&id=530