REIMAGINATION: REconstructing and understanding the IMplications of surface 14C AGe changes In the North Atlantic for overturning circulaTION

The Atlantic Ocean's conveyor belt circulation is a fundamental component of the global climate system, transporting heat from low to high latitudes, and thus warming Northern Europe. The strength of this circulation is thought to have varied abruptly in the past, giving rise to rapid climate changes of more than 10 degrees C in a decade during the last glacial period. Changes of this nature today would have a severe impact on society, so we want to know more about the sensitivity of this circulation. In order to do this, we will study intervals of rapid climate and circulation change in the past.

To better understand these past circulation changes we will reconstruct the concentration of radiocarbon in surface and deep waters in the North Atlantic Ocean. This is known as a radiocarbon reservoir age, and it is highly sensitive to the rate of ocean circulation. Therefore, by reconstructing reservoir ages, we can tell how quickly the ocean was circulating during intervals of rapid climate change.

We also need to know what the reservoir age was in the past if we want to use radiocarbon as a dating tool, to tell the age of geological and archeological objects and events. Radiocarbon can be thought of as a stopwatch for a geological sample. For a marine sample, however, there is already some time on the clock when we press go. This extra time before starting the clock is the reservoir age, and we must know what it is in order to accurately tell geological time.

By reconstructing reservoir ages, we will therefore improve understanding of rapid circulation and climate change, and also improve the most important dating tool used in earth and archeological sciences.

To reconstruct radiocarbon reservoir ages we need to measure the radiocarbon content of a sample, and also to know its age independently, so we can work out what was already on the clock when the sample formed.
To do this we will make radiocarbon measurements on shells taken from sediment cores from the North Atlantic, and pair them with a range of exciting new techniques that can tell their age. Firstly we will look for layers of volcanic ash in the sediment cores, which we can date using their argon content, and match to precisely dated ash layers in ice cores and on Iceland. Secondly we can look at changes in sea surface temperature records, and match these to the same events that are precisely dated in ice cores. Thirdly we will use the concentration of thorium in sediments to tell how much sediment accumulated between these ash and temperature tie points. Fourthly, we will combine all this information using statistical modelling, which will also provide a good measure of the uncertainty in our results.

This work will create maps of reservoir ages and how they changed in the North Atlantic over the last 10 to 50 thousand years, with a special focus on times of rapid climate change. To help us link the reservoir ages to different circulation regimes, we will use a climate model that can simulate radiocarbon. We will make this model's ocean circulation operate in different ways, and see which circulations best match our data. This will allow us to better understand how ocean circulation changed in the past to cause rapid climate change, and improve confidence in how ocean circulation may operate in the future.

Finally, we will package our reservoir age maps into a tool that can be used by earth scientists and archeologists to improve their radiocarbon dating.

Our work is focused on topics of significant interest to policy makers and the general public: rapid climate change, and radiocarbon dating. We will capitalise on this to deliver broad and lasting impact to the following groups:

1. Public and Policy makers - understanding of climate tipping points
"Tipping points" in the climate system, such as the rapid AMOC shifts we are studying, are a major concern for policy makers and the general public. Although the chances of AMOC shutdown in the next century are unlikely, the severity of the potential impact on society makes this a crucial tipping point to understand. Our radiocarbon reservoir age data, and accompanying circulation state modelling, will provide a thorough framework in which to test model skill in reproducing rapid circulation and climate changes. The ability of climate models to reproduce the circulation regimes we reconstruct will improve our confidence in their predictive abilities, and thus their utility for policy decision making.

2. High school students and teachers - climate change education delivered through Geobus
High school students, teachers, and their families will benefit from educational outreach on climate change that we will undertake as part of the University of St Andrew's highly successful Geobus initiative. Geobus provides teaching and resources in the earth and environmental sciences to high schools across Scotland and the North of England. Climate-focussed workshops have been particularly welcomed by Geobus staff and teachers, given the perception of climate science as a "new" subject and a "hot topic". The topical nature of climate change also makes it an excellent topic with which to engage students in STEM subjects, a key goal for UK education and economic development. Geobus has an excellent track record of impact to date: since its establishment in 2012, it has delivered material to over 20,000 pupils in 160 schools, and has grown its funding pool from an initial £50k provided by NERC, to >£350k till 2016 through industry sponsorship.

3. Radiocarbon users - new products, interlab collaboration, technical development
Radiocarbon dating is a tool with wide multi-disciplinary applications across the environmental and archeological sciences, and in both research and commercial sectors. The proposed work will have broad impact on the radiocarbon community by providing the first systematic regional assessment of radiocarbon reservoir ages in the North Atlantic across the whole datable interval (10-50 ka). The project will also promote continued interlab calibration and technical development for two key UK radiocarbon facilities.

4. Students, teachers, and general public
Our project website will include a photo gallery resource which will provide a tool for students and teachers to learn about how records of past ocean circulation changes are developed. This will include a photo gallery (and short videos) of the recovery of a marine sediment core, sampling and picking of foraminifera, and processing in the AMS 14C facility with text explaining each.

5. Young women considering STEM subjects - break down gender bias perceptions
STEM subjects have suffered from perceptions of gender bias. The female PI Andrea Burke and CoI Paula Reimer will help address this by providing tours of the Queens University Belfast Accelerator Mass Spectrometry facility to female high school students. Burke and Reimer will act as role models to encourage young women to consider STEM subjects.

6. Training and networking of highly skilled researchers
The project will contribute to the UK's skill set through the training and professional development of an undergraduate student and a PDRA. The strong and diverse team of project partners will facilitate the integration of PI Andrea Burke and CoI James Rae into the UK and European research communities, which will help further spread the impact of this research