Unravelling the carbon cycle using silicon isotopes in the oceans

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.

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).