The Experts below are selected from a list of 1152 Experts worldwide ranked by ideXlab platform
David Thomas - One of the best experts on this subject based on the ideXlab platform.
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iron and nutrient content of wind erodible sediment in the ephemeral river valleys of namibia
Geomorphology, 2017Co-Authors: Andrew Dansie, Giles F S Wiggs, David ThomasAbstract:Abstract Research concerning the global distribution of aeolian dust sources has principally focussed on salt/clay pan and desiccated lacustrine emission areas. In southern Africa such sources are identified as Etosha Pan in northern Namibia and Makgadikgadi Pans in northern Botswana. Dust emitting from ephemeral river valleys, however, has been largely overlooked. Rivers are known nutrient transport pathways and the flooding regimes of ephemeral river valleys frequently replenish stores of fine sediment which, on drying, can become susceptible to aeolian erosion. Such airborne sediment may be nutrient rich and thus be significant for the Fertilisation of marine waters once deposited. This study investigates the dust source sediments from three ephemeral river valleys in Namibia in terms of their particle size distribution and their concentrations of bioavailable N, P and Fe. We compare the nutrient content of these sediments from the ephemeral river valleys to those collected from Etosha and Makgadikgadi Pans and consider their relative Ocean fertilising potential. Our results show that the ephemeral river valleys contain fine grained sediment similar in physical character to Etosha and Makgadikgadi Pans yet they have up to 43 times greater concentrations of bioavailable iron and enriched N and P macronutrients that are each important for Ocean Fertilisation. The known dust-emitting river valleys of Namibia may therefore be contributing a greater Fertilisation role in the adjacent marine system than previously considered, and not-yet investigated. Given this finding a re-assessment of the potential role of ephemeral river valleys in providing nutrient-rich sediment into the aeolian and marine systems in other dryland areas is necessary.
Humberto González - One of the best experts on this subject based on the ideXlab platform.
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Highly variable iron content modulates iceberg-Ocean Fertilisation and potential carbon export
Nature Communications, 2019Co-Authors: Mark Hopwood, Dustin Carroll, Juan Höfer, Eric Achterberg, Lorenz Meire, Frédéric A.c. Le Moigne, Lennart Bach, Charlotte Eich, David Sutherland, Humberto GonzálezAbstract:Marine phytoplankton growth at high latitudes is extensively limited by iron availability. Icebergs are a vector transporting the bioessential micronutrient iron into polar Oceans. Therefore, increasing iceberg fluxes due to global warming have the potential to increase marine productivity and carbon export, creating a negative climate feedback. However, the magnitude of the iceberg iron flux, the subsequent fertilization effect and the resultant carbon export have not been quantified. Using a global analysis of iceberg samples, we reveal that iceberg iron concentrations vary over 6 orders of magnitude. Our results demonstrate that, whilst icebergs are the largest source of iron to the polar Oceans, the heterogeneous iron distribution within ice moderates iron delivery to offshore waters and likely also affects the subsequent Ocean iron enrichment. Future marine productivity may therefore be not only sensitive to increasing total iceberg fluxes, but also to changing iceberg properties, internal sediment distribution and melt dynamics.
Naomi E Vaughan - One of the best experts on this subject based on the ideXlab platform.
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the radiative forcing potential of different climate geoengineering options
Atmospheric Chemistry and Physics, 2009Co-Authors: Timothy M Lenton, Naomi E VaughanAbstract:Climate geoengineering proposals seek to rectify the Earth's current and potential future radiative imbalance, either by reducing the absorption of incoming solar (short- wave) radiation, or by removing CO2 from the atmosphere and transferring it to long-lived reservoirs, thus increasing outgoing longwave radiation. A fundamental criterion for evaluating geoengineering options is their climate cooling effectiveness, which we quantify here in terms of radiative forcing potential. We use a simple analytical approach, based on energy balance considerations and pulse response func- tions for the decay of CO2 perturbations. This aids trans- parency compared to calculations with complex numerical models, but is not intended to be definitive. It allows us to compare the relative effectiveness of a range of proposals. We consider geoengineering options as additional to large re- ductions in CO2 emissions. By 2050, some land carbon cycle geoengineering options could be of comparable magnitude to mitigation "wedges", but only stratospheric aerosol injec- tions, albedo enhancement of marine stratocumulus clouds, or sunshades in space have the potential to cool the climate back toward its pre-industrial state. Strong mitigation, com- bined with global-scale air capture and storage, afforestation, and bio-char production, i.e. enhanced CO2 sinks, might be able to bring CO2 back to its pre-industrial level by 2100, thus removing the need for other geoengineering. Alterna- tively, strong mitigation stabilising CO 2 at 500 ppm, com- bined with geoengineered increases in the albedo of marine stratiform clouds, grasslands, croplands and human settle- ments might achieve a patchy cancellation of radiative forc- ing. Ocean Fertilisation options are only worthwhile if sus-
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the radiative forcing potential of different climate geoengineering options
Atmospheric Chemistry and Physics, 2009Co-Authors: Timothy M Lenton, Naomi E VaughanAbstract:Abstract. Climate geoengineering proposals seek to rectify the Earth's current and potential future radiative imbalance, either by reducing the absorption of incoming solar (shortwave) radiation, or by removing CO2 from the atmosphere and transferring it to long-lived reservoirs, thus increasing outgoing longwave radiation. A fundamental criterion for evaluating geoengineering options is their climate cooling effectiveness, which we quantify here in terms of radiative forcing potential. We use a simple analytical approach, based on energy balance considerations and pulse response functions for the decay of CO2 perturbations. This aids transparency compared to calculations with complex numerical models, but is not intended to be definitive. It allows us to compare the relative effectiveness of a range of proposals. We consider geoengineering options as additional to large reductions in CO2 emissions. By 2050, some land carbon cycle geoengineering options could be of comparable magnitude to mitigation "wedges", but only stratospheric aerosol injections, albedo enhancement of marine stratocumulus clouds, or sunshades in space have the potential to cool the climate back toward its pre-industrial state. Strong mitigation, combined with global-scale air capture and storage, afforestation, and bio-char production, i.e. enhanced CO2 sinks, might be able to bring CO2 back to its pre-industrial level by 2100, thus removing the need for other geoengineering. Alternatively, strong mitigation stabilising CO2 at 500 ppm, combined with geoengineered increases in the albedo of marine stratiform clouds, grasslands, croplands and human settlements might achieve a patchy cancellation of radiative forcing. Ocean Fertilisation options are only worthwhile if sustained on a millennial timescale and phosphorus addition may have greater long-term potential than iron or nitrogen Fertilisation. Enhancing Ocean upwelling or downwelling have trivial effects on any meaningful timescale. Our approach provides a common framework for the evaluation of climate geoengineering proposals, and our results should help inform the prioritisation of further research into them.
Mark Hopwood - One of the best experts on this subject based on the ideXlab platform.
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Highly variable iron content modulates iceberg-Ocean Fertilisation and potential carbon export
Nature Communications, 2019Co-Authors: Mark Hopwood, Dustin Carroll, Juan Höfer, Eric Achterberg, Lorenz Meire, Frédéric A.c. Le Moigne, Lennart Bach, Charlotte Eich, David Sutherland, Humberto GonzálezAbstract:Marine phytoplankton growth at high latitudes is extensively limited by iron availability. Icebergs are a vector transporting the bioessential micronutrient iron into polar Oceans. Therefore, increasing iceberg fluxes due to global warming have the potential to increase marine productivity and carbon export, creating a negative climate feedback. However, the magnitude of the iceberg iron flux, the subsequent fertilization effect and the resultant carbon export have not been quantified. Using a global analysis of iceberg samples, we reveal that iceberg iron concentrations vary over 6 orders of magnitude. Our results demonstrate that, whilst icebergs are the largest source of iron to the polar Oceans, the heterogeneous iron distribution within ice moderates iron delivery to offshore waters and likely also affects the subsequent Ocean iron enrichment. Future marine productivity may therefore be not only sensitive to increasing total iceberg fluxes, but also to changing iceberg properties, internal sediment distribution and melt dynamics.
Chien Wang - One of the best experts on this subject based on the ideXlab platform.
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enhanced marine sulphur emissions offset global warming and impact rainfall
Scientific Reports, 2015Co-Authors: Benjamin S Grandey, Chien WangAbstract:Artificial Fertilisation of the Ocean has been proposed as a possible geoengineering method for removing carbon dioxide from the atmosphere. The associated increase in marine primary productivity may lead to an increase in emissions of dimethyl sulphide (DMS), the primary source of sulphate aerosol over remote Ocean regions, potentially causing direct and cloud-related indirect aerosol effects on climate. This pathway from Ocean Fertilisation to aerosol induced cooling of the climate may provide a basis for solar radiation management (SRM) geoengineering. In this study, we investigate the transient climate impacts of two emissions scenarios: an RCP4.5 (Representative Concentration Pathway 4.5) control; and an idealised scenario, based on RCP4.5, in which DMS emissions are substantially enhanced over Ocean areas. We use mini-ensembles of a coupled atmosphere-Ocean configuration of CESM1(CAM5) (Community Earth System Model version 1, with the Community Atmosphere Model version 5). We find that the cooling effect associated with enhanced DMS emissions beneficially offsets greenhouse gas induced warming across most of the world. However, the rainfall response may adversely affect water resources, potentially impacting human livelihoods. These results demonstrate that changes in marine phytoplankton activity may lead to a mixture of positive and negative impacts on the climate.