NERC - CIRCE: Combining Isotopes in Radiolarians to Constrain the Evolution of the Coupled Carbon-Silica Cycle
Lead Research Organisation:
University of Bristol
Abstract
CIRCE: Combining Isotopes of Radiolaria to Characterise the Evolution of the coupled carbon and silica cycles
Circe was a sorceress in ancient Greek mythology, known for her transformational mastery of the natural world around her.
The drawdown of atmospheric carbon during the chemical weathering of silicate rocks has long been considered the main way Earth’s climate is stabilised on geological timescales. More recently, the Si released to the ocean in these chemical reactions is increasingly recognised as a regulator of Earth’s climate, through its effect on ocean productivity (which shuttles C away in the deep ocean) and by setting the rates of so-called ‘reverse weathering’ – where fresh clay minerals are formed at the seafloor. Because reverse weathering reduces ocean alkalinity and keeps more dissolved carbon in seawater in the form of CO2, this can influence – and likely has influenced – Earth’s climate. A key control on ocean Si concentration besides weathering is how much Si gets locked away by silicifying organisms like sponges, radiolarians and diatoms. Crucially, our current methods of reconstructing Si concentrations and biotic Si uptake in the past are extremely limited, meaning we cannot confidently decipher the interplay between Si cycling, carbon cycling, biotic innovation and climate.
CIRCE will address this by developing new isotopic tools and methods (O, Si and B) to reconstruct ocean temperature, ocean silica cycling, and ocean carbon cycling from the silica shells of radiolaria – establishing a whole new geochemical proxy archive with the potential to go back half a billion years of Earth history. We will then apply our new tools – together with cGENIE (carbon-centric Grid-Enabled Integrated Earth system) Earth system modelling – to two key intervals in the geological past, to constrain when biotic innovations (namely the rise to dominance of diatoms) transformed the coupled Si-C cycle from one where Si-fuelled reverse weathering acted in opposition to the silicate weathering feedback, to one where efficient C drawdown by diatoms and reduced alkalinity consumption by reverse weathering lowered atmospheric CO2 more effectively. This question is central to understanding the interplay between Earth’s biota and climate, how the Earth’s climate is moderated on geological timescales, and what drove some of the major climatic transitions in Earth history.
We propose to do this with a team made up of world experts in Si, B and O isotopes, an RcL with extensive experience in radiolarian taxonomy, physiology and ecology, and an RIA who has previously implemented new geochemical cycles in cGENIE. CIRCE will use labs at the University of Bristol (UoB) and BGS that are set up with state-of-the-art tools primed to do the work. In particular, brand new analytical facilities at BGS will allow us to generate our radiolarian proxy records from a fraction of the sample sizes previously required, making this project particularly timely. In establishing a whole new proxy archive with which to address critical questions in palaeoceanography, CIRCE aims to have a transformational effect on the field worthy of its ancient Greek namesake, who reshaped the world around her to suit her needs.
Circe was a sorceress in ancient Greek mythology, known for her transformational mastery of the natural world around her.
The drawdown of atmospheric carbon during the chemical weathering of silicate rocks has long been considered the main way Earth’s climate is stabilised on geological timescales. More recently, the Si released to the ocean in these chemical reactions is increasingly recognised as a regulator of Earth’s climate, through its effect on ocean productivity (which shuttles C away in the deep ocean) and by setting the rates of so-called ‘reverse weathering’ – where fresh clay minerals are formed at the seafloor. Because reverse weathering reduces ocean alkalinity and keeps more dissolved carbon in seawater in the form of CO2, this can influence – and likely has influenced – Earth’s climate. A key control on ocean Si concentration besides weathering is how much Si gets locked away by silicifying organisms like sponges, radiolarians and diatoms. Crucially, our current methods of reconstructing Si concentrations and biotic Si uptake in the past are extremely limited, meaning we cannot confidently decipher the interplay between Si cycling, carbon cycling, biotic innovation and climate.
CIRCE will address this by developing new isotopic tools and methods (O, Si and B) to reconstruct ocean temperature, ocean silica cycling, and ocean carbon cycling from the silica shells of radiolaria – establishing a whole new geochemical proxy archive with the potential to go back half a billion years of Earth history. We will then apply our new tools – together with cGENIE (carbon-centric Grid-Enabled Integrated Earth system) Earth system modelling – to two key intervals in the geological past, to constrain when biotic innovations (namely the rise to dominance of diatoms) transformed the coupled Si-C cycle from one where Si-fuelled reverse weathering acted in opposition to the silicate weathering feedback, to one where efficient C drawdown by diatoms and reduced alkalinity consumption by reverse weathering lowered atmospheric CO2 more effectively. This question is central to understanding the interplay between Earth’s biota and climate, how the Earth’s climate is moderated on geological timescales, and what drove some of the major climatic transitions in Earth history.
We propose to do this with a team made up of world experts in Si, B and O isotopes, an RcL with extensive experience in radiolarian taxonomy, physiology and ecology, and an RIA who has previously implemented new geochemical cycles in cGENIE. CIRCE will use labs at the University of Bristol (UoB) and BGS that are set up with state-of-the-art tools primed to do the work. In particular, brand new analytical facilities at BGS will allow us to generate our radiolarian proxy records from a fraction of the sample sizes previously required, making this project particularly timely. In establishing a whole new proxy archive with which to address critical questions in palaeoceanography, CIRCE aims to have a transformational effect on the field worthy of its ancient Greek namesake, who reshaped the world around her to suit her needs.