Interpretation of palaeomonsoon dynamics on the Eastern Tibetan Plateau from a 10 kyr peat record of dust deposition and regional atmospheric model simulations

The Holocene evolution of the Asian monsoon remains poorly constrained due to the lack of information on past wind trajectories and intensities in central Asia. Mineral dust mobilized from aeolian deposits, transported by atmospheric currents and deposited in environmental archives such as peatlands, offers the potential to elucidate past changes in monsoon dynamics. This thesis examines the history of palaeomonsoon circulation in central Asia during the Holocene through the study of the fluxes and sources of dust deposited in a peatland on the eastern Tibetan Plateau, and the use of this record to constrain numerical simulations of dust transport. Different Asian dust sources capable of providing material to the peat deposit were characterized geochemically to establish a framework of provenance tracers for their identification. Rare earth element-based proxies were shown to be effective geochemical tracers to distinguish between them. These proxies were measured in a 9,500 year old peat core from Hongyuan to reconstruct the history of mineral dust deposition in this region. Results suggest that the deposits of northern and northwestern China dominated dust input to the peat throughout the Holocene and particularly during the last 5 kyr, with earlier deposition also governed by high local contributions. All geochemical proxies indicate that the northern sources dominated between 3.1-2.7 and 1.7-0.9 kyr BP, accompanied by a large increase in dust fluxes. These changes are interpreted as a strengthening of the East Asian winter monsoon, in agreement with other studies in the region. Annual fluxes and sources simulated with a regional atmosphere-chemistry/aerosol climate model show good agreement with the geochemical data. These results provide the first uninterrupted interpretation of atmospheric circulation patterns in central Asia during the Holocene and confirm the potential of peatlands as reliable repositories of dust deposition and as high-quality datasets against which regional model simulations can be evaluated

Interpretation of palaeomonsoon dynamics on the Eastern Tibetan Plateau from a 10 kyr peat record of dust deposition and regional atmospheric model simulations

The Holocene evolution of the Asian monsoon remains poorly constrained due to the lack of information on past wind trajectories and intensities in central Asia. Mineral dust mobilized from aeolian deposits, transported by atmospheric currents and deposited in environmental archives such as peatlands, offers the potential to elucidate past changes in monsoon dynamics. This thesis examines the history of palaeomonsoon circulation in central Asia during the Holocene through the study of the fluxes and sources of dust deposited in a peatland on the eastern Tibetan Plateau, and the use of this record to constrain numerical simulations of dust transport. Different Asian dust sources capable of providing material to the peat deposit were characterized geochemically to establish a framework of provenance tracers for their identification. Rare earth element-based proxies were shown to be effective geochemical tracers to distinguish between them. These proxies were measured in a 9,500 year old peat core from Hongyuan to reconstruct the history of mineral dust deposition in this region. Results suggest that the deposits of northern and northwestern China dominated dust input to the peat throughout the Holocene and particularly during the last 5 kyr, with earlier deposition also governed by high local contributions. All geochemical proxies indicate that the northern sources dominated between 3.1-2.7 and 1.7-0.9 kyr BP, accompanied by a large increase in dust fluxes. These changes are interpreted as a strengthening of the East Asian winter monsoon, in agreement with other studies in the region. Annual fluxes and sources simulated with a regional atmosphere-chemistry/aerosol climate model show good agreement with the geochemical data. These results provide the first uninterrupted interpretation of atmospheric circulation patterns in central Asia during the Holocene and confirm the potential of peatlands as reliable repositories of dust deposition and as high-quality datasets against which regional model simulations can be evaluated.EThOS - Electronic Theses Online ServiceRoyal Society and Mineralogical SocietyGBUnited Kingdo

Dynamics of arable land requirements for food in South Africa: From 1961 to 2007

Food consumption puts pressure on natural resources and arable land. In the present study, we examined the dynamics of land requirements for food in South Africa from 1961 to 2007 and investigated the relationships between dietary patterns, yield, cropping intensity, population and the area of required land using the thought experiment method. Strong population growth and the development of agricultural technology (indicated by yield) accounted for more than a 2.5-fold increase in the total land requirements for food from 1961 to 2007. Before the 1990s, the increase in crop yields enabled constant land requirements, whereas, after the 1990s, the combined effect of agricultural technology and population growth, together with a small contribution from dietary changes, led to an increase in the land requirements for food. Our findings confirm that the variation in land requirements for food is a complex, non-linear function of agricultural production techniques, population growth and dietary patterns and show that the complex relationship between dietary pattern changes, and economic development challenges future predictions of land requirements for food in South Africa

Lead atmospheric deposition rates and isotopic trends in Asian dust during the last 9.5 kyr recorded in an ombrotrophic peat bog on the eastern Qinghai-Tibetan Plateau

International audienceA full understanding of the atmospheric Pb cycle in Asia during the Holocene is key to palaeoclimate studies of past atmospheric circulation patterns, as well as to assess the impact of increasing industrial activities in this region. However, long-term records of atmospheric Pb isotopic trends in Asia are still sparse. Consequently, we study changes in the concentrations, fluxes and isotopic signature of deposited Pb contained in a 14C-dated peat core from the eastern Qinghai-Tibetan Plateau, dating back to 9.5 kyr BP, and present the first peat record of the changing isotopic composition of atmospheric Pb in dust in Asia during this time. Lead concentrations and fluxes vary between 2.96-21.58 lg g 1 and 0.06-3.52 mg m 2 y 1, respectively, with an average Pb baseline of 6.80 ± 4.18 lg g 1. These values agree with other Pb studies of lake and peat archives in China but are one order of magnitude larger than early and mid-Holocene values measured in Europe. Lead isotopic variability throughout the core is small, varying between 206Pb/207Pb = 1.190-1.197, 206Pb/204Pb = 18.648-18.786, 207Pb/204Pb = 15.666-15.694 and 208Pb/204Pb = 38.890-39.090. The application of Bayesian trans-dimensional changepoint modelling to the Pb dataset enabled the identification of eight significant changes in the isotopic composition of the deposited Pb. Such changes mark different phases of atmospheric Pb deposition, and hence variations in atmospheric circulation patterns and environmental conditions. Temporal variations in the potential natural and/or anthropogenic Pb sources are assessed based on the 206Pb, 207Pb, 208Pb and 204Pb isotopic composition and the 1/[Pb] ratio of the peat samples. Our results suggest that Pb deposition throughout the Holocene was governed by local deposition and long-range input from natural dust sources in northwestern (Taklamakan desert and Qaidam basin) and northern China (Badain Jaran and Tengger deserts). Input from the northern sources seems to have been particularly important between 3.1-2.7 kyr BP and 1.7-0.9 kyr BP, suggesting a possible strengthening of the East Asian winter monsoon, in agreement with previous reconstructions in Asia. Based on the Pb/Sc and isotopic composition profiles we do not note any evidence for anthropogenic Pb derived from the thriving mining or smelting activities in northern and eastern China in the last few millennia, suggesting that atmospheric deposition to this region of the eastern Tibetan Plateau was dominated by natural Pb fluxes. These can serve as a true Asian "background" value against which anthropogenic impacts can be quantified. Our results confirm that the combination of radiogenic isotopes (Pb) and trace elements in peat bogs enables observational reconstructions of changes in past regional atmospheric circulation. Such records will enable more refined interpretations of marine and terrestrial palaeorecords in Asia and the Pacific and consequently provide further constraints for changes in ocean and atmospheric circulation and for the testing of palaeoclimate models of circulation patterns

Lead atmospheric deposition rates and isotopic trends in Asian dust during the last 9.5 kyr recorded in an ombrotrophic peat bog on the eastern Qinghai-Tibetan Plateau

A full understanding of the atmospheric Pb cycle in Asia during the Holocene is key to palaeoclimate studies of past atmospheric circulation patterns, as well as to assess the impact of increasing industrial activities in this region. However, long-term records of atmospheric Pb isotopic trends in Asia are still sparse. Consequently, we study changes in the concentrations, fluxes and isotopic signature of deposited Pb contained in a (14)C-dated peat core from the eastern Qinghai-Tibetan Plateau, dating back to 9.5 kyr BP, and present the first peat record of the changing isotopic composition of atmospheric Pb in dust in Asia during this time. Lead concentrations and fluxes vary between 2.96-21.58 mu g g(-1) and 0.06-3.52 mg m(-2) y(-1), respectively, with an average Pb baseline of 6.80 +/- 4.18 mu g g(-1). These values agree with other Pb studies of lake and peat archives in China but are one order of magnitude larger than early and mid-Holocene values measured in Europe. Lead isotopic variability throughout the core is small, varying between (206)Pb/(207)Pb = 1.190-1.197, (206)Pb/(204)Pb = 18.648-18.786, (207)Pb/(204)Pb = 15.666-15.694 and (208)Pb/(204)Pb = 38.890-39.090. The application of Bayesian trans-dimensional changepoint modelling to the Pb dataset enabled the identification of eight significant changes in the isotopic composition of the deposited Pb. Such changes mark different phases of atmospheric Pb deposition, and hence variations in atmospheric circulation patterns and environmental conditions. Temporal variations in the potential natural and/or anthropogenic Pb sources are assessed based on the (206)Pb, (207)Pb, (208)Pb and (204)Pb isotopic composition and the 1/[Pb] ratio of the peat samples. Our results suggest that Pb deposition throughout the Holocene was governed by local deposition and long-range input from natural dust sources in northwestern (Taklamakan desert and Qaidam basin) and northern China (Badain Jaran and Tengger deserts). Input from the northern sources seems to have been particularly important between 3.1-2.7 kyr BP and 1.7-0.9 kyr BP, suggesting a possible strengthening of the East Asian winter monsoon, in agreement with previous reconstructions in Asia. Based on the Pb/Sc and isotopic composition profiles we do not note any evidence for anthropogenic Pb derived from the thriving mining or smelting activities in northern and eastern China in the last few millennia, suggesting that atmospheric deposition to this region of the eastern Tibetan Plateau was dominated by natural Pb fluxes. These can serve as a true Asian &quot;background&quot; value against which anthropogenic impacts can be quantified. Our results confirm that the combination of radiogenic isotopes (Pb) and trace elements in peat bogs enables observational reconstructions of changes in past regional atmospheric circulation. Such records will enable more refined interpretations of marine and terrestrial palaeorecords in Asia and the Pacific and consequently provide further constraints for changes in ocean and atmospheric circulation and for the testing of palaeoclimate models of circulation patterns.</p

Solution structure of APETx2, a specific peptide inhibitor of ASIC3 proton-gated channels

Acid-sensing ion channels (ASIC) are proton-gated sodium channels that have been implicated in pain transduction associated with acidosis in inflamed or ischemic tissues. APETx2, a peptide toxin effector of ASIC3, has been purified from an extract of the sea anemone Anthopleura elegantissima. APETx2 is a 42-amino-acid peptide cross-linked by three disulfide bridges. Its three-dimensional structure, as determined by conventional two-dimensional 1H-NMR, consists of a compact disulfide-bonded core composed of a four-stranded β-sheet. It belongs to the disulfide-rich all-β structural family encompassing peptide toxins commonly found in animal venoms. The structural characteristics of APETx2 are compared with that of PcTx1, another effector of ASIC channels but specific to the ASIC1a subtype and to APETx1, a toxin structurally related to APETx2, which targets the HERG potassium channel. Structural comparisons, coupled with the analysis of the electrostatic characteristics of these various ion channel effectors, led us to suggest a putative channel interaction surface for APETx2, encompassing its N terminus together with the type I-β turn connecting β-strands III and IV. This basic surface (R31 and R17) is also rich in aromatic residues (Y16, F15, Y32, and F33). An additional region made of the type II′-β turn connecting β-strands I and II could also play a role in the specificity observed for these different ion effectors