Details of Award
NERC Reference : NE/V001213/1
Atmospheric fluxes of mineral dust-derived soluble trace elements to the ocean using thorium isotopes (ThorMap)
Grant Award
- Principal Investigator:
- Professor AR Baker, University of East Anglia, Environmental Sciences
- Co-Investigator:
- Professor G Henderson, University of Oxford, Earth Sciences
- Grant held at:
- University of East Anglia, Environmental Sciences
- Science Area:
- Atmospheric
- Earth
- Marine
- Terrestrial
- Overall Classification:
- Panel B
- ENRIs:
- Biodiversity
- Environmental Risks and Hazards
- Global Change
- Science Topics:
- Climate & Climate Change
- Biogeochemical Cycles
- Ocean - Atmosphere Interact.
- Abstract:
- Biological productivity (the growth of phytoplankton) is limited by the availability of iron (Fe) in at least 30% of the ocean. Fe is so insoluble in seawater that the large amounts entering from rivers cannot be transported far from the continental margins. The supply of Fe from dust falling on the ocean becomes the primary way to add Fe (and other elements important to life such as phosphorus) to the open ocean. The pattern and flux of Fe from the atmosphere to the surface ocean is therefore important for ocean ecosystems, and for the global carbon cycle (because ocean life consumes carbon). Despite this importance, the flux of dust and of its incorporated metals to the ocean is poorly known. It is challenging to measure this flux directly, and other observational approaches require quite fundamental assumptions, which limit accuracy. At present, therefore, most estimates of dust flux rely on atmospheric models, and are generally considered to be uncertain by a factor of ten, particularly in remote regions. In the proposed work, we will assess and use a new approach to quantify the inputs of dust and its associated micronutrients to the ocean. This approach relies on measurements of two biologically inactive, partially soluble components of dust: thorium (Th) and aluminium (Al). Two isotopes of Th are used in this assessment. 232Th, is present in continental rocks. If found dissolved in the open ocean, 232Th must have been recently added by dissolution of dust transported from the continents. Another isotope, 230Th, is formed within seawater by the decay of a uranium isotope. Its concentration in seawater reflects a competition between this known rate of formation, and removal due to its insoluble nature. We can therefore use 230Th to assess the removal rate of Th, including 232Th, from seawater. The 232Th removed must be replaced by input from dust to maintain the observed 232Th concentrations, so we can calculate the input of dust. There are two main challenges to the reconstruction of dust fluxes from Th isotopes. One is that the solubility of Th in dust, a critical term in the flux calculation, is not well known. Our new results indicate that Th is amongst a small group of elements whose solubility is very little impacted by transport of dust through the atmosphere, while the solubilities of Fe, Al and several other biologically active elements are all altered greatly during transport. Using aerosol samples collected on a series of research cruises, and at a sampling tower on Bermuda, we will assess the solubility of Th, the controls on how that varies during atmospheric transport, and its relationship to changes in Al and Fe solubility. We will also conduct laboratory studies on desert dust parent soils aimed at better understanding the unusual Th solubility in dust aerosols. Dust fluxes can also be calculated from dissolved Al concentrations, but these estimates are affected by changes in Al solubility during atmospheric transport. The second challenge is that we do not know how far 232Th from the continents might travel after input at the coast. We will address this by incorporating 232Th into an ocean model. Such models have a proven ability to reconstruct 230Th, and we will develop them to also model 232Th, and to indicate where 232Th is dominated by coastal inputs rather than by dust. These models will also be used to assess the uncertainty in using Th isotopes to reconstruct dust inputs. A large number of observations of Th isotopes in seawater has recently been measured during an international programme: GEOTRACES. We will add data from two further cruises, to complete a detailed coverage of Th and Al measurements for the Atlantic Ocean. Combined use of the Th and Al tracers will therefore allow us to produce robust maps of dust inputs (from Th) and soluble Fe inputs (by taking account of the changes in solubility during transport using Al) for the Atlantic (with associated maps of uncertainty).
- NERC Reference:
- NE/V001213/1
- Grant Stage:
- Awaiting Completion
- Scheme:
- Standard Grant FEC
- Grant Status:
- Active
- Programme:
- Standard Grant
This grant award has a total value of £583,846
FDAB - Financial Details (Award breakdown by headings)
| DI - Other Costs | Indirect - Indirect Costs | DA - Investigators | DA - Estate Costs | DI - Staff | DA - Other Directly Allocated | DI - T&S |
|---|---|---|---|---|---|---|
| £63,848 | £204,928 | £38,672 | £58,610 | £192,101 | £3,415 | £22,274 |
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