Methane (CH 4) concentrations were measured in the water column, in sediment porewaters, and in a... more Methane (CH 4) concentrations were measured in the water column, in sediment porewaters, and in atmospheric air, in the Ría de Vigo, NW Spain, during both the onset (April 2003) and at the end of (September 2004) seasonal upwelling. In addition, CH 4 concentration and stable isotopic signatures (δ 13 CH 4) were measured in porewaters, and sediment methanogenesis and aerobic oxidation of CH 4 were determined in sediment incubations. Surface water column CH 4 (2 m depth) was in the range 3-180 nmol L-1 (110-8500 % saturation) and followed a generally landward increase but with localised maxima in both the inner and middle Ría. These maxima were consistent with CH 4 inputs from underlying porewaters in which CH 4 concentrations were up to 3 orders of magnitude higher (maximum 350 µmol l-1). Surface water CH 4 concentrations were ~ three times higher in September than in April, consistent with a significant benthic CH 4 flux driven by enhanced sediment methanogenesis following the summer productivity maximum. CH 4 and δ 13 CH 4 in sediment porewaters and in incubated sediment slurries (20 o C) revealed significant sediment CH 4 oxidation, with an apparent isotopic fractionation factor (r c) ~ 1.004. Using turbulent diffusion models of air-sea exchange we estimate an annual emission of atmospheric CH 4 from the Ría de Vigo of 18-44 × 10 6 g (1.1-2.7 × 10 6 mol). This estimate is approximately 1-2 orders of magnitude lower than a previous estimate based on a bubble transport model.
Digital data including geophysics, geotechnical and seabed sampling data is routinely acquired as... more Digital data including geophysics, geotechnical and seabed sampling data is routinely acquired as part of offshore surveys for assessing submerged landscapes. Different software packages are used for acquiring and processing the different survey elements. However, recent developments in visualisation software now allow for a more seamless integration of datasets for interpretation. The potential for Middle Palaeolithic sites to survive beneath the sea in northern latitudes has been established by intensive investigation of a part of the North Sea known within Area 240; a marine aggregate licence area situated 10km off the coast of Norfolk, England. The fortuitous discovery of Palaeolithic handaxes and other worked flint in gravel dredged from Area 240 led to a major programme of fieldwork and analysis, funded by the Aggregate Levy Sustainability Fund. The programme tested a range of methodologies to gauge their effectiveness in identifying and assessing sites of this type and produced an interpretation of the area set within its wider context. The investigations included: · Detailed re-examination of geophysical and geotechnical data from industrial surveys; · Intensive geophysical survey using four different methods of sub-bottom profiling (surface-tow boomer, pinger, chirp and parametric sonar); · Adaptation of ecological sampling methods to recover further worked flint from the seabed; · Coring to obtain complete samples of the sedimentary sequence from 10 locations in the vicinity of the site; · Paleo-environmental assessment and analysis, and scientific dating using radiocarbon and Optically Stimulated Luminescence (OSL); · Overarching synthesis and interpretation. The investigations demonstrated the presence of landscape features ranging in date from >500,000 years ago to around 8000 years ago. The handaxes and other worked flint are associated with deposits dating to the Wolstonian period, between 250,000 and 140,000 BP. The investigations confirm that the artefacts are not a ‘chance’ find, but indicate clear relationships to submerged and buried landscapes that, although complex, can be examined in detail using a variety of fieldwork and analytical methods. This paper will focus on the digital acquisition and processing of geophysical data and the integration of the geophysics results with the spatial data generated from the geotechnical data that were used to investigate the site.
Proceedings of the Geologists' Association, Dec 1, 2015
Abstract Significant progress has been made on the investigation of Quaternary submerged prehisto... more Abstract Significant progress has been made on the investigation of Quaternary submerged prehistory in the British Isles. Mainly through collaboration with industry, a considerable knowledge base has been developed on the distribution and nature of preserved palaeolandscapes of the last 1 million years in UK waters. A diverse array of material has been recovered from the seabed including bone and stone artefacts, extinct fauna, peat deposits, submerged forests and other remnants of relict landscapes from around the British Isles. Archaeological sites are rarer but Palaeolithic and Mesolithic examples are providing critical resources to reinterpret early prehistory in association with Quaternary palaeogeography.
It is well known that the North Sea conceals an extensive former landscape of Late Pleistocene an... more It is well known that the North Sea conceals an extensive former landscape of Late Pleistocene and Holocene date that was progressively submerged as result of rising post-glacial sea levels. Although an increasingly detailed picture is emerging of these submerged palaeolandscapes, well-dated palaeoenvironmental reconstructions from the North Sea Basin remain few and far between. Pollen, foraminifera, ostracod, plant macrofossil and molluscan data are presented from a radiocarbon-dated core retrieved from the site of the Dudgeon offshore wind farm, located in the southern North Sea Basin. The palaeoenvironmental analysis provides new data on changing local physical and vegetation environments in the southern North Sea Basin, occurring against a background of global climate change and rising sea levels. Subalpine plant communities gradually gave way to hazel-dominated woodland during the early Holocene, with freshwater environments replaced by increasing signs of estuarine influence from ca. 9500 to 9000 cal a BP. The thin upper peat (8411-8331 cal a BP) raises the possibility that the final inundation of the Dudgeon site may be linked to meltwater pulses following the collapse of the Laurentide Ice Sheet and the draining of the proglacial Lakes Agassiz and Ojibway.
Mesolithic settlement sites preserved on the northeast coast of England and in southeast Scotland... more Mesolithic settlement sites preserved on the northeast coast of England and in southeast Scotland drive questions about the relationship between early human settlement and the Holocene palaeogeography of 'Doggerland'. Palaeogeographical reconstructions before 8000 years ago have been restricted by a lack of sea-level index points and particularly by sparse nearshore geophysical and geological datasets required for such reconstructions. This paper presents new high-resolution geophysical survey data from Northumberland's nearshore 'white ribbon' which provide a foundation for more accurate palaeogeographical reconstructions within which early prehistoric settlement sites can be more readily understood. High-resolution bathymetry data collected in the nearshore adjacent to the Mesolithic house site at Howick are integrated with coastal LiDAR, seismic, geological and archaeological datasets to underpin palaeogeographical reconstructions. The reconstructions illustrate changing coastal landscapes during Early Holocene sea-level rise. The data and interpretations provide a 'source-to-sea' context for understanding the archaeology at important sites such as Howick and Low Hauxley. Furthermore, they provide a basis for enhancing management of at-risk coastal prehistoric archaeology and a framework to prospect for and protect further vulnerable nearshore archaeological heritage.
Abstract Significant progress has been made on the investigation of Quaternary submerged prehisto... more Abstract Significant progress has been made on the investigation of Quaternary submerged prehistory in the British Isles. Mainly through collaboration with industry, a considerable knowledge base has been developed on the distribution and nature of preserved palaeolandscapes of the last 1 million years in UK waters. A diverse array of material has been recovered from the seabed including bone and stone artefacts, extinct fauna, peat deposits, submerged forests and other remnants of relict landscapes from around the British Isles. Archaeological sites are rarer but Palaeolithic and Mesolithic examples are providing critical resources to reinterpret early prehistory in association with Quaternary palaeogeography.
Methane (CH 4) concentrations were measured in the water column, in sediment porewaters, and in a... more Methane (CH 4) concentrations were measured in the water column, in sediment porewaters, and in atmospheric air, in the Ría de Vigo, NW Spain, during both the onset (April 2003) and at the end of (September 2004) seasonal upwelling. In addition, CH 4 concentration and stable isotopic signatures (δ 13 CH 4) were measured in porewaters, and sediment methanogenesis and aerobic oxidation of CH 4 were determined in sediment incubations. Surface water column CH 4 (2 m depth) was in the range 3-180 nmol L-1 (110-8500 % saturation) and followed a generally landward increase but with localised maxima in both the inner and middle Ría. These maxima were consistent with CH 4 inputs from underlying porewaters in which CH 4 concentrations were up to 3 orders of magnitude higher (maximum 350 µmol l-1). Surface water CH 4 concentrations were ~ three times higher in September than in April, consistent with a significant benthic CH 4 flux driven by enhanced sediment methanogenesis following the summer productivity maximum. CH 4 and δ 13 CH 4 in sediment porewaters and in incubated sediment slurries (20 o C) revealed significant sediment CH 4 oxidation, with an apparent isotopic fractionation factor (r c) ~ 1.004. Using turbulent diffusion models of air-sea exchange we estimate an annual emission of atmospheric CH 4 from the Ría de Vigo of 18-44 × 10 6 g (1.1-2.7 × 10 6 mol). This estimate is approximately 1-2 orders of magnitude lower than a previous estimate based on a bubble transport model.
Digital data including geophysics, geotechnical and seabed sampling data is routinely acquired as... more Digital data including geophysics, geotechnical and seabed sampling data is routinely acquired as part of offshore surveys for assessing submerged landscapes. Different software packages are used for acquiring and processing the different survey elements. However, recent developments in visualisation software now allow for a more seamless integration of datasets for interpretation. The potential for Middle Palaeolithic sites to survive beneath the sea in northern latitudes has been established by intensive investigation of a part of the North Sea known within Area 240; a marine aggregate licence area situated 10km off the coast of Norfolk, England. The fortuitous discovery of Palaeolithic handaxes and other worked flint in gravel dredged from Area 240 led to a major programme of fieldwork and analysis, funded by the Aggregate Levy Sustainability Fund. The programme tested a range of methodologies to gauge their effectiveness in identifying and assessing sites of this type and produced an interpretation of the area set within its wider context. The investigations included: · Detailed re-examination of geophysical and geotechnical data from industrial surveys; · Intensive geophysical survey using four different methods of sub-bottom profiling (surface-tow boomer, pinger, chirp and parametric sonar); · Adaptation of ecological sampling methods to recover further worked flint from the seabed; · Coring to obtain complete samples of the sedimentary sequence from 10 locations in the vicinity of the site; · Paleo-environmental assessment and analysis, and scientific dating using radiocarbon and Optically Stimulated Luminescence (OSL); · Overarching synthesis and interpretation. The investigations demonstrated the presence of landscape features ranging in date from >500,000 years ago to around 8000 years ago. The handaxes and other worked flint are associated with deposits dating to the Wolstonian period, between 250,000 and 140,000 BP. The investigations confirm that the artefacts are not a ‘chance’ find, but indicate clear relationships to submerged and buried landscapes that, although complex, can be examined in detail using a variety of fieldwork and analytical methods. This paper will focus on the digital acquisition and processing of geophysical data and the integration of the geophysics results with the spatial data generated from the geotechnical data that were used to investigate the site.
Proceedings of the Geologists' Association, Dec 1, 2015
Abstract Significant progress has been made on the investigation of Quaternary submerged prehisto... more Abstract Significant progress has been made on the investigation of Quaternary submerged prehistory in the British Isles. Mainly through collaboration with industry, a considerable knowledge base has been developed on the distribution and nature of preserved palaeolandscapes of the last 1 million years in UK waters. A diverse array of material has been recovered from the seabed including bone and stone artefacts, extinct fauna, peat deposits, submerged forests and other remnants of relict landscapes from around the British Isles. Archaeological sites are rarer but Palaeolithic and Mesolithic examples are providing critical resources to reinterpret early prehistory in association with Quaternary palaeogeography.
It is well known that the North Sea conceals an extensive former landscape of Late Pleistocene an... more It is well known that the North Sea conceals an extensive former landscape of Late Pleistocene and Holocene date that was progressively submerged as result of rising post-glacial sea levels. Although an increasingly detailed picture is emerging of these submerged palaeolandscapes, well-dated palaeoenvironmental reconstructions from the North Sea Basin remain few and far between. Pollen, foraminifera, ostracod, plant macrofossil and molluscan data are presented from a radiocarbon-dated core retrieved from the site of the Dudgeon offshore wind farm, located in the southern North Sea Basin. The palaeoenvironmental analysis provides new data on changing local physical and vegetation environments in the southern North Sea Basin, occurring against a background of global climate change and rising sea levels. Subalpine plant communities gradually gave way to hazel-dominated woodland during the early Holocene, with freshwater environments replaced by increasing signs of estuarine influence from ca. 9500 to 9000 cal a BP. The thin upper peat (8411-8331 cal a BP) raises the possibility that the final inundation of the Dudgeon site may be linked to meltwater pulses following the collapse of the Laurentide Ice Sheet and the draining of the proglacial Lakes Agassiz and Ojibway.
Mesolithic settlement sites preserved on the northeast coast of England and in southeast Scotland... more Mesolithic settlement sites preserved on the northeast coast of England and in southeast Scotland drive questions about the relationship between early human settlement and the Holocene palaeogeography of 'Doggerland'. Palaeogeographical reconstructions before 8000 years ago have been restricted by a lack of sea-level index points and particularly by sparse nearshore geophysical and geological datasets required for such reconstructions. This paper presents new high-resolution geophysical survey data from Northumberland's nearshore 'white ribbon' which provide a foundation for more accurate palaeogeographical reconstructions within which early prehistoric settlement sites can be more readily understood. High-resolution bathymetry data collected in the nearshore adjacent to the Mesolithic house site at Howick are integrated with coastal LiDAR, seismic, geological and archaeological datasets to underpin palaeogeographical reconstructions. The reconstructions illustrate changing coastal landscapes during Early Holocene sea-level rise. The data and interpretations provide a 'source-to-sea' context for understanding the archaeology at important sites such as Howick and Low Hauxley. Furthermore, they provide a basis for enhancing management of at-risk coastal prehistoric archaeology and a framework to prospect for and protect further vulnerable nearshore archaeological heritage.
Abstract Significant progress has been made on the investigation of Quaternary submerged prehisto... more Abstract Significant progress has been made on the investigation of Quaternary submerged prehistory in the British Isles. Mainly through collaboration with industry, a considerable knowledge base has been developed on the distribution and nature of preserved palaeolandscapes of the last 1 million years in UK waters. A diverse array of material has been recovered from the seabed including bone and stone artefacts, extinct fauna, peat deposits, submerged forests and other remnants of relict landscapes from around the British Isles. Archaeological sites are rarer but Palaeolithic and Mesolithic examples are providing critical resources to reinterpret early prehistory in association with Quaternary palaeogeography.
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Papers by Louise Tizzard