Unravelling the carbon cycle using silicon isotopes in the oceans

Lead Research Organisation: University of Bristol
Department Name: Earth Sciences


With rising concerns surrounding the impacts of manmade climate change we need to look not only into the future but also into the past. By understanding how global temperatures and levels of carbon dioxide (CO2) in the atmosphere have naturally fluctuated throughout the earth's history, and the interaction with living organisms, we can take important steps towards predicting the changes that may lie ahead. It is undoubtedly a complex puzzle and there are many ways of trying to solve it.

My part of the story involves deep-sea sponges and silicon, the chemical element they use to build their glass-like opal skeletons. Sponge skeletons, or spicules, are helping me to piece together the links between the supply of vital nutrients in different parts of the ocean and the crucial role other marine organisms play in absorbing CO2 from the atmosphere and locking it away in deep sea sediments as organic carbon.
Marine sponges are one of the simplest groups of animals, living on the seafloor and feeding by filtering particles from seawater. They themselves don't play a central role in changing climates, but they do share a common need for silicon with another group of marine inhabitants that we think are vitally important to the global climate. Diatoms, a type of microscopic marine algae that live and photosynthesise at the sea surface, are responsible for sequestering nearly half the CO2 that is converted into organic carbon and sinks to the seafloor. By investigating sponges I can learn a lot about the changing availability of silicon that also makes life possible for diatoms.

Studies of ice-cores and ocean sediments tell us that over the past million years the earth's climate has cycled every 100 thousand years or so between cold ice ages, with low levels of atmospheric CO2, and warmer periods, with higher CO2 levels. My studies focus on the climate changes that took place since the end of the last ice age, around 15 thousand years ago. I can step back in time by combining analysis of living sponges brought up from the deep during research cruises at sea with fossil sponges taken from seafloor sediment samples.

I was amongst the first to show that the chemical fingerprints of sponges, in particular their silicon isotope composition, gives an accurate record of how much silicon was dissolved in the water they grew in. This opens up a unique archive stretching back millennia of the silicon levels in ocean waters down to as much as 4 km beneath the waves - the realm of sea sponges. In general, the more silicon there is supplied to the sea surface, the more diatoms can grow, and the more carbon dioxide they absorb and lock away in the seafloor sediments when they die. Building a picture of past levels of silicon in the oceans means I can test the crucial links between carbon dioxide uptake by diatoms and climate change.
Here, I plan to study key geographical areas, which have been sensitive to rapid climate change since the last ice age.
My work will provide essential insights into the dynamics of the carbon cycle and hence climate, and point to possible future scenarios and changes in ocean circulation patterns.

Planned Impact

Research into the Southern Ocean, and its role in past global climate systems, is essential for the prediction of future change. As such, the data I propose to collect will be of fundamental interest to scientists in a wide range of fields, including biogeochemists, palaeoclimatologists, climate modelers, ecologists, oceanographers and sociologists. The results will be disseminated broadly, archived and made available through publications in peer-reviewed journals and at conferences throughout the first few years of my first faculty position.
My research will compliment the output of the palaeoclimate group at Cardiff University, and would be a valuable collaboration for the geochemistry group at Bristol Isotope Group (BIG), bringing in new insight from my biogeochemical and palaeoceanographic background. I have an excellent track record developing analytical methodology on a range of instrumentation, which I believe will give me the background knowledge required for this research.
I have a strong record of teaching support, supervising and assisting both undergraduate and postgraduate students, which will continue during my first faculty position. The proposed research would path the way for future research projects for students at Cardiff, and open up opportunities for collaborative research projects at Bristol University for PhD and master students, and visiting scientists.
My research combines biogeochemistry and climate research, using the signal recorded in biogenic opal to reveal insight into the natural response to rapid climate change. The two different aspects of the research will be of interest to industry and policy makers. Biological formation of silica is an important subject area of research in the field of microtechnology, and work on silicon isotope systematics is important for understanding biomineralisation processes. This project will provide further insight into the chemical processes involved in sponge biosilica formation by constraining the relationship between its isotopic composition and environmental conditions. With the increased concern about possible manmade climate change, it is essential to understand the natural response of earth systems to rapid climate change in the past in order to predict what might happen in the future. Such future scenarios, based on high quality and open scientific findings, are integral to policy decisions about climate change prevention and mitigation that will shape the socioeconomic future of the UK. In particular, research into the response of natural algal populations in the oceans, such as outlined in this proposal, is timely given the current interest in "ocean fertilization" and geoengineering to mitigate against rising atmospheric CO2. The impact of biogeochemical cycling on climate change formed an entire chapter of the last International Panel on Climate Change assessment report (IPCC, 2007), and this project will be directly relevant for the next IPCC assessment report, due in 2013-14.
I will also actively take part in outreach activities, continuing my links with the Climate Change Consortium of Wales (C3W), and the UK Polar Network (UKPN), as a member of the Association of Polar Early Career Scientists (APECS). I intend to maintain links with the popular science radio programme "The Naked Scientists" broadcast on BBC radio and on the web in the form of podcasts, through special reports about my research (see http://www.thenakedscientists.com/HTML/podcasts/show/2006.11.19/ for links to my previous interviews). I have previously helped to run a research cruise blog in 2008 and am intending to maintain a similar website during an upcoming cruise in May 2011 (see http://censeam.niwa.co.nz/outreach/nathaniel_b._palmer).


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Description Sedimentary and ice-core records show that the past 800 thousand years of earth's climate has cycled between cold glacials, characterized by low atmospheric carbon dioxide levels (pCO2 ~ 200 ppmV) and warmer interglacials, with higher pCO2 (~ 280 ppmV) on a timescale of approximately 100 thousand years. The same records show that previous glacial cycles were punctuated by abrupt (millennial) climate change events. The Southern Ocean is linked with these climatic events, in part because it exerts a primary control on the distribution of nutrients to a large portion of the modern ocean, which in turn regulates algal population structure and carbon uptake.
My overall aim was to investigate changes in the flow of Southern Ocean water into the Atlantic over the last glacial cycle. I addressed a number of outstanding questions:
Question 1: What was the geographical extent of Southern Ocean intermediate waters in the Atlantic over the last glacial cycle?
I have found evidence that the concentration of silicic acid (likely sourced from the Southern Ocean) at intermediate depths was similar in the glacial compared to today; however there were higher concentrations in the North Atlantic during millennial scale climate events (Hendry et al., 2014; Hendry et al., in prep).
Question 2: To what extent did high silicic acid waters reach the surface of the North Atlantic, and important upwelling regions of the Equatorial Atlantic over the last glacial cycle, and to what extent was the silicic acid utilised by diatoms?
I have found that there were significant near surface ecological changes in different regions of the North Atlantic during millennial scale climate events, according to algal assemblages and geochemical archives (Hendry et al., 2014; Pike, Hendry & Eastwood, in prep).
Understanding how the ocean has responded to deglacial warming, and abrupt climate change, in the past will elucidate how ocean nutrient cycling may respond in the future.
Exploitation Route Further research into the ecological impacts of abrupt climate change (palaeoclimate, modern observations and future projections), with implications for environment and fisheries.
Potential investigation of carbon sequestration and marine biological uptake of carbon during climate change (so-called 'ocean fertilization').
Sectors Agriculture

Food and Drink




URL http://www.pressreleasepoint.com/research-finds-fundamental-marine-ecosystem-change-during-rapid-climate-change-events
Description Benthic foraminiferal stable isotopes during the late glacial and last glacial termination of the NE Atlantic
Amount £680 (GBP)
Organisation Cardiff University 
Sector Academic/University
Country United Kingdom
Start 05/2013 
End 08/2013
Description Cardiff Undergraduate Research Opportunities Programme (CUROP)
Amount £1,360 (GBP)
Organisation Cardiff University 
Sector Academic/University
Country United Kingdom
Start 06/2013 
End 09/2013
Description Comprehensive Calibration of Critical Paleoceanographic Proxies
Amount £12,500 (GBP)
Funding ID IP-1298-0512 
Organisation Research Councils UK (RCUK) 
Sector Public
Country United Kingdom
Description From micro to macro: the fractionation of silicon isotopes during biogenic opal formation
Amount £150,000 (GBP)
Organisation The Royal Society 
Sector Charity/Non Profit
Country United Kingdom
Start 03/2014 
End 03/2017
Description Royal Society University Research Fellowship
Amount £450,000 (GBP)
Organisation The Royal Society 
Sector Charity/Non Profit
Country United Kingdom
Start 09/2013 
End 10/2018
Description Southern Ocean Sponges: The link between biogeography and geochemistry
Amount £75,000 (GBP)
Funding ID RPG-2012-615 
Organisation The Leverhulme Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 09/2013 
End 09/2016
Description Starter Grant
Amount € 2,000,000 (EUR)
Funding ID ERC-2015-StG - 678371_ICY-LAB 
Organisation Research Councils UK (RCUK) 
Sector Public
Country United Kingdom
Start 04/2016 
End 04/2021
Description Silicon isotopes in the oceans 
Organisation University of California, Santa Barbara
Country United States 
Sector Academic/University 
PI Contribution Analyses and personnel.
Collaborator Contribution Writing a funded proposal for ship time for sample collection, and other analytical costs.
Impact Funded National Science Foundation proposal Review paper (see publications)
Start Year 2012
Description Early Career Workshop 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Participants in your research and patient groups
Results and Impact I organised an Early Career Workshop 'Thinking outside the climate envelope' for Early Career Researchers (ECRs) working in various aspects of climate research, from social sciences to natural sciences (note: this was funded as the impact plan for this NERC New Investigator Grant). The aim was to engage with ECRs, and to get them to think about different applications of their skills to the wider field. Guest speakers were Kirsty Edgar from Cardiff University, Tim Kruger from Oxford Geoengineering, and Paul Halloran from the MetOffice.

We had excellent feedback from the participants. Written feedback included:
'I was pleased to get a lot of discussion out of the talk I gave' (from a senior scientist);
'I would certainly be interested in attending similar events again' (from a masters student);
'I have learn a lot from a wide range of topics given during the meeting. I also use the opportunities to talk to different people. I will meet some of them from Cardiff University and see whether we can work together on the climate change and water resources' (from a PhD student);
'My horizons have been broadened' (from guest speaker).
Year(s) Of Engagement Activity 2012
URL http://c3wales.org/uncategorized/summer-2012-newsletter/
Description Soapbox Science 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact I informally presented my research on biogenic silica during Soapbox Science, during which members of the public could listen in, ask questions, and discuss my research and the related topics. I also wrote two blogs about me, my career and my research. The event is especially geared at promoting women in science.

As a direct consequence of my blogging activities, I was interviewed for a Nature News article.
Year(s) Of Engagement Activity 2014
URL http://soapboxscience.org/?page_id=823