Weathering and climate: New insights from the marine records of Li, Nd and Os
Lead Research Organisation:
The Open University
Department Name: Environment, Earth & Ecosystems
Abstract
Since 65 million years ago, there have been huge changes in Earth's climate. Back then, the Earth was a 'greenhouse'; the Arctic was devoid of permanent ice and supported luxuriant forests, while the low latitudes were seasonally arid. Today, the Earth experiences 'icehouse' conditions, characterized by extensive permanent polar ice sheets. It isn't clear what caused the transition from a greenhouse to an icehouse world, but there is growing evidence that amongst the primary controls is the concentration of atmospheric carbon dioxide, the principal greenhouse gas. Weathering of continental silicate rocks regulates levels of atmospheric carbon dioxide because it leads to drawdown of CO2. Silicate weathering rates are controlled primarily by temperature and rainfall, creating a dynamic link between weathering and climate: for example, higher global temperatures accelerate weathering of silicates causing drawdown of atmospheric CO2, which in turn leads to cooler temperatures through reduced greenhouse warming. Such 'feedback' processes are important for regulating Earth's climate system. On long timescales (>100,000 years), silicate weathering also responds to tectonically-driven changes in continental topography; for example, uplift and erosion of the Himalaya-Tibet plateau is believed to be associated with intensified silicate weathering and long-term cooling over the past 40 million years or so. Thus far most of our information about how silicate weathering rates have changed over the past 65 million years has come from the temporal record of the strontium (Sr) isotopic composition of the oceans. However, in recent years this proxy has been widely criticized because shifts in Sr isotopes may reflect changes in the Sr isotopic composition of the rocks being weathered, rather than a simple change in the silicate weathering flux. Furthermore, the Sr isotopic composition of seawater changes very slowly (on timescales of >100,000 years), so the Sr isotope record cannot capture the short-term events that can influence Earth's long-term climate evolution. At the Open University, we have been developing new ways of tracing past changes in silicate weathering. Our preliminary studies show that seawater lithium (Li) concentrations respond to long-term changes in the silicate weathering flux, while seawater Li isotope ratios reflect weathering intensity. Meanwhile, the osmium (Os) isotopic composition of seawater tells us about short-term changes in the weathering flux and also the Os isotopic composition of the rocks that are weathered. Finally, the neodymium (Nd) isotopic composition of seawater responds rapidly to changes in the isotopic composition of the continental source. Thus, considered together, the temporal records of seawater Li concentrations and Li, Os and Nd isotopes can provide valuable information as to past changes in weathering rates and processes, on both long and short timescales. The aim of this proposal is to generate records of seawater Li concentrations and Li, Os and Nd isotopes for the past 65 million years. We will then integrate these records with those of global temperature, ice volume etc, in order to better understand the links between weathering and climate.
Publications
Anand P
(2008)
Coupled sea surface temperature-seawater d 18 O reconstructions in the Arabian Sea at the millennial scale for the last 35 ka
in Paleoceanography
Austin, W.E.N.; James, R.H.
(2008)
Biogeochemical Controls on Palaeoceanographic Environmental Proxies: Special Publication
Bowe C
(2015)
Positive externalities, knowledge exchange and corporate farm extension services; a case study on creating shared value in a water scarce area
in Ecosystem Services
Elderfield H
(2006)
Calibrations for benthic foraminiferal Mg/Ca paleothermometry and the carbonate ion hypothesis
in Earth and Planetary Science Letters
Pogge Von Strandmann P
(2006)
Riverine behaviour of uranium and lithium isotopes in an actively glaciated basaltic terrain
in Earth and Planetary Science Letters
Rachael James (Author)
(2008)
Utility of Li and Li isotopes as tracers of continental weathering.
Stewart J
(2016)
Influence of the Amazon River on the Nd isotope composition of deep water in the western equatorial Atlantic during the Oligocene-Miocene transition
in Earth and Planetary Science Letters
Stewart J
(2012)
Geochemical assessment of the palaeoecology, ontogeny, morphotypic variability and palaeoceanographic utility of "Dentoglobigerina" venezuelana
in Marine Micropaleontology
Stewart J
(2017)
Silicate Weathering and Carbon Cycle Controls on the Oligocene-Miocene Transition Glaciation
in Paleoceanography
Description | Since 65 million years ago, there have been huge changes in Earth's climate. Back then, the Earth was a 'greenhouse'; the Arctic was devoid of permanent ice and supported luxuriant forests, while the low latitudes were seasonally arid. Today, the Earth experiences 'icehouse' conditions, characterized by extensive permanent polar ice sheets. It isn't clear what caused the transition from a greenhouse to an icehouse world, but there is growing evidence that amongst the primary controls is the concentration of atmospheric carbon dioxide, the principal greenhouse gas. Weathering of continental silicate rocks regulates levels of atmospheric carbon dioxide because it leads to drawdown of CO2. Silicate weathering rates are controlled primarily by temperature and rainfall, creating a dynamic link between weathering and climate: for example, higher global temperatures accelerate weathering of silicates causing drawdown of atmospheric CO2, which in turn leads to cooler temperatures through reduced greenhouse warming. Such 'feedback' processes are important for regulating Earth's climate system. On long timescales (>100,000 years), silicate weathering also responds to tectonically-driven changes in continental topography; for example, uplift and erosion of the Himalaya- Tibet plateau is believed to be associated with intensified silicate weathering and long-term cooling over the past 40 million years or so. Thus far most of our information about how silicate weathering rates have changed over the past 65 million years has come from the temporal record of the strontium (Sr) isotopic composition of the oceans. However, in recent years this proxy has been widely criticized because shifts in Sr isotopes may reflect changes in the Sr isotopic composition of the rocks being weathered, rather than a simple change in the silicate weathering flux. Furthermore, the Sr isotopic composition of seawater changes very slowly (on timescales of >100,000 years), so the Sr isotope record cannot capture the short-term events that can influence Earth's long-term climate evolution. At the Open University, we have been developing new ways of tracing past changes in silicate weathering. Our preliminary studies show that seawater lithium (Li) concentrations respond to long-term changes in the silicate weathering flux, while seawater Li isotope ratios reflect weathering intensity. Meanwhile, the osmium (Os) isotopic composition of seawater tells us about short-term changes in the weathering flux and also the Os isotopic composition of the rocks that are weathered. Thus, considered together, the temporal records of seawater Li concentrations and Li and Os isotopes can provide valuable information as to past changes in weathering rates and processes. The aim of this proposal is to generate records of seawater Li concentrations and Li and Os isotopes for the past 65 million years. We will then integrate these records with those of global temperature, ice volume etc, in order to better understand the links between weathering and climate. |
Sectors | Environment |
Description | Academic publications and international conferences. |
First Year Of Impact | 2006 |
Sector | Environment |
Impact Types | Societal |
Description | LOSCAR |
Organisation | University College London |
Department | RCN-SEES consortium (Research Coordination Network -- Science, Engineering, and Education for Sustainability) |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | The results of our work on the taxonomy, ecology and geochemistry of 'D.' venezuelana is of crucial importance for the palaeoceanographic community because we have demonstrated that morphological variations within the morphospecies are not accompanied by changes in test chemistry. Thus all variants may be used for trace element and isotope work. This work is now widely cited by this community. |
Collaborator Contribution | We are also now working in collaboration with climate modellers (Prof. Heiko Paelike, Prof. Andy Ridgewell) to quantify the effects of continental weathering on levels of pCO2 and climate. This is being done using the LOSCAR (Long-term Ocean-atmosphere-Sediment Carbon cycle Reservoir) model |
Impact | Pending |
Start Year | 2011 |
Description | Sands of Time |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Public/other audiences |
Results and Impact | The results of this work were part of an exhibit 'Sands of Time' which was designed to introduce the public to the importance of ocean drilling. The exhibit included a series of posters (one concerning this project), a 'hands-on' sediment core demonstration and examination of microfossils under the microscope. The tied PhD student presented this exhibit at three local schools, as well as the Intech science centre (Winchester), the Cheltenham Science Festival, the Summer Science Exhibition (London), and the Stokes Bay Festival (Gosport). All of these events took place in 2009. The overall cost of the exhibit was £4000, some of which was contributed by the NOC's 'Ocean on Wheels' outreach programme, and some of which was contributed by the UK Integrated Ocean Drilling Programme. Well received by organisers |
Year(s) Of Engagement Activity | 2010 |