Final Report Summary - VOLCANIC WEATHERING (Fresh volcanic deposits as a sink for atmospheric carbon: a laboratory, field, and modelling approach to quantifying variation in chemical weathering rates)
The Marie Curie Intra-European Fellowship undertaken by Morgan Jones at the University of Iceland entitled VOLCANIC WEATHERING (PIEF-GA-2009-254495) was a resounding success. The work focused on the particulate riverine fluxes of elements from volcanic terrains, and their behaviour upon arrival in coastal and estuarine waters. Initially, this work considered Icelandic field sites and samples for laboratory experiments, but in the second part of the fellowship the scope of the study was expanded to consider a wide variety of river sediments from around the world.
The overriding conclusions of this work are that there are clear indications of non-conservative transfer of elemental concentrations and isotopic signatures from rivers to the oceans, and that the dissolution of particulate material upon arrival in seawater is a key component of global element cycles. This has important consequences for the changes to river systems by human activity, including the decline in particulate transport due to the construction of dams, or the increase due to deforestation and erosion. Moreover, the impact of the fluxes of nutrients to the oceans and the subsequent effect on carbon dioxide (CO2) removal from the atmosphere through biological and weathering activity is likely to be incorrectly quantified at present. The methods combined in these studies typify the originality and innovative nature required of a Marie Curie fellowship. The success of this fellowship is borne out in the five published articles and two articles currently in submission, arising from this work.
Project report
The project had three principal objectives. Part one was to compare and contrast two lavas of similar age and geographical extent but markedly different lithologies to assess the role of lava chemistry on the weathering process. Part two was to measure the fluid geochemistry of a rhyolite catchment in central Iceland, to compare with catchments of basaltic lithology. Part three was to assess the impacts of weathering of volcanic terrains on the carbon cycle using a global climate model.
A reconnaissance field trip to the lavas of Harfntinnuhraun and Eldgjá showed that contrary to the suggestions of the part one of the proposal, even though there is a close geographical proximity between the two sample sites (25 km), the climatic differences due to varying altitude and precipitation meant that the level of weathering and soil formation were not controlled by lithology alone. This meant that there were too many variables to be able to conduct a quantitative scientific analysis of the lavas. Similarly, difficulties with adapting the source code of the global circulation model meant that it was unable to be used as a useful tool for measuring the effect of increased weathering on the global carbon cycle.
In order to fulfil the project objectives through alternative means, more emphasis was placed on part 2 of the proposal. Instead of solely considering the geochemical fluxes from a rhyolite catchment in Iceland, samples were collected from a range of river catchments from around the world. The work focused on particulate material, and their behaviour upon arrival in coastal and estuarine waters.
A suite of batch reactor experiments were conducted on riverine particulates mixed with seawater, measuring the changes in elemental concentrations and isotopic compositions through time. In particular, measurements of changes to isotopic ratios of strontium (87Sr/86Sr) and neodymium ((epsilon)Nd) were able to quantify the amount of particulate dissolution and precipitation occurring in the experiments. Comparisons with riverine and estuarine particles demonstrated that initial release of elements occurs in a remarkably short time frame, while the global dataset highlighted the importance of the much more reactive basaltic particles than sediment from older continental catchments. The scope of the study was extended to investigate whether it was possible to observe the reactions of particulate material with seawater in nature. Transects were conducted in Borgarfjörður estuary and Hvítá river in western Iceland, to measure the variations in elemental concentrations and 87Sr/86Sr compositions of the fluid, suspended solid, and bedload solid phases. As with the experimental results, the field evidence demonstrated rapid Sr release from the riverine particulates, calculated to be greater than the corresponding dissolved flux from the river.
Therefore, there is conclusive evidence of non-conservative transfer of elemental concentrations and isotopic signatures from rivers to the oceans, and that the dissolution of particulate material upon arrival in seawater is a key component of global element cycles. If the field and laboratory evidence of Sr and Nd release can be applied to other elements, as is likely, then particulate material dissolution is integral to the marine budgets of many elements. This changes our understanding of coastal productivity, and has important consequences for the changes to river systems by human activity, including the decline in particulate transport due to the construction of dams, or the increase due to deforestation and erosion. Moreover, the impact of the fluxes of nutrients to the oceans and the subsequent effect on CO2 removal from the atmosphere through biological and weathering activity is likely to be incorrectly quantified at present. This clearly has wider socio-economic impacts, including climate monitoring, ecosystem health and preservation, fish reserves, land use, river management, and pollution dispersion.
The overriding conclusions of this work are that there are clear indications of non-conservative transfer of elemental concentrations and isotopic signatures from rivers to the oceans, and that the dissolution of particulate material upon arrival in seawater is a key component of global element cycles. This has important consequences for the changes to river systems by human activity, including the decline in particulate transport due to the construction of dams, or the increase due to deforestation and erosion. Moreover, the impact of the fluxes of nutrients to the oceans and the subsequent effect on carbon dioxide (CO2) removal from the atmosphere through biological and weathering activity is likely to be incorrectly quantified at present. The methods combined in these studies typify the originality and innovative nature required of a Marie Curie fellowship. The success of this fellowship is borne out in the five published articles and two articles currently in submission, arising from this work.
Project report
The project had three principal objectives. Part one was to compare and contrast two lavas of similar age and geographical extent but markedly different lithologies to assess the role of lava chemistry on the weathering process. Part two was to measure the fluid geochemistry of a rhyolite catchment in central Iceland, to compare with catchments of basaltic lithology. Part three was to assess the impacts of weathering of volcanic terrains on the carbon cycle using a global climate model.
A reconnaissance field trip to the lavas of Harfntinnuhraun and Eldgjá showed that contrary to the suggestions of the part one of the proposal, even though there is a close geographical proximity between the two sample sites (25 km), the climatic differences due to varying altitude and precipitation meant that the level of weathering and soil formation were not controlled by lithology alone. This meant that there were too many variables to be able to conduct a quantitative scientific analysis of the lavas. Similarly, difficulties with adapting the source code of the global circulation model meant that it was unable to be used as a useful tool for measuring the effect of increased weathering on the global carbon cycle.
In order to fulfil the project objectives through alternative means, more emphasis was placed on part 2 of the proposal. Instead of solely considering the geochemical fluxes from a rhyolite catchment in Iceland, samples were collected from a range of river catchments from around the world. The work focused on particulate material, and their behaviour upon arrival in coastal and estuarine waters.
A suite of batch reactor experiments were conducted on riverine particulates mixed with seawater, measuring the changes in elemental concentrations and isotopic compositions through time. In particular, measurements of changes to isotopic ratios of strontium (87Sr/86Sr) and neodymium ((epsilon)Nd) were able to quantify the amount of particulate dissolution and precipitation occurring in the experiments. Comparisons with riverine and estuarine particles demonstrated that initial release of elements occurs in a remarkably short time frame, while the global dataset highlighted the importance of the much more reactive basaltic particles than sediment from older continental catchments. The scope of the study was extended to investigate whether it was possible to observe the reactions of particulate material with seawater in nature. Transects were conducted in Borgarfjörður estuary and Hvítá river in western Iceland, to measure the variations in elemental concentrations and 87Sr/86Sr compositions of the fluid, suspended solid, and bedload solid phases. As with the experimental results, the field evidence demonstrated rapid Sr release from the riverine particulates, calculated to be greater than the corresponding dissolved flux from the river.
Therefore, there is conclusive evidence of non-conservative transfer of elemental concentrations and isotopic signatures from rivers to the oceans, and that the dissolution of particulate material upon arrival in seawater is a key component of global element cycles. If the field and laboratory evidence of Sr and Nd release can be applied to other elements, as is likely, then particulate material dissolution is integral to the marine budgets of many elements. This changes our understanding of coastal productivity, and has important consequences for the changes to river systems by human activity, including the decline in particulate transport due to the construction of dams, or the increase due to deforestation and erosion. Moreover, the impact of the fluxes of nutrients to the oceans and the subsequent effect on CO2 removal from the atmosphere through biological and weathering activity is likely to be incorrectly quantified at present. This clearly has wider socio-economic impacts, including climate monitoring, ecosystem health and preservation, fish reserves, land use, river management, and pollution dispersion.