A Review of the Principles and Applications of the NMR Technique for Near-Surface Characterization   总被引：2，自引：0，他引：2  

Ahmad A. Behroozmand  Kristina Keating  Esben Auken 《Surveys in Geophysics》2015,36(1):27-85

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Spatial Distribution of Carbonaceous Aerosol in the Southeastern Baltic Sea Region (Event of Grass Fires)     

Vadimas Dudoitis  Steigvilė Byčenkienė  Kristina Plauškaitė  Carlo Bozzetti  Roman Fröhlich  Genrik Mordas  Vidmantas Ulevičius 《Acta Geophysica》2016,64(3):711-731

The aerosol chemical composition in air masses affected by large vegetation fires transported from the Kaliningrad region (Russia) and southeast regions (Belarus and Ukraine) during early spring (March 2014) was characterized at the remote background site of Preila, Lithuania. In this study, the chemical composition of the particulate matter was studied by high temporal resolution instruments, including an Aerosol Chemical Speciation Monitor (ACSM) and a seven-wavelength aethalo-meter. Air masses were transported from twenty to several hundred kilometres, arriving at the measurement station after approximately half a day of transport. The concentration-weighted trajectory analysis suggests that organic aerosol particles are mainly transported over the Baltic Sea and the continent (southeast of Belarus). Results show that a significant fraction of the vegetation burning organic aerosol is transformed into oxidised forms in less than a half-day. Biomass burning aerosol (BBOA) was quantified from the ACSM data using a positive matrix factorization (PMF) analysis, while its spatial distribution was evaluated using air mass clustering approach.  相似文献   

Terrigenous plant wax inputs to the Arabian Sea: Implications for the reconstruction of winds associated with the Indian Monsoon   总被引：1，自引：0，他引：1  

Kristina A. Dahl  Delia W. Oppo  Konrad A. Hughen  Frank Sirocko 《Geochimica et cosmochimica acta》2005,69(10):2547-2558

We have determined the accumulation rates and carbon isotopic compositions (δ¹³C) of long-chain (C₂₄-C₃₂) terrigenous plant wax fatty acids in 19 surface sediment samples geographically distributed throughout the Arabian Sea in order to assess the relationship between plant wax inputs and the surrounding monsoon wind systems. Both the accumulation rate data and the δ¹³C data show that there are three primary eolian sources of plant waxes to the Arabian Sea: Africa, Asia, and the Arabian Peninsula. These sources correspond to the three major wind systems in this region: the summer (Southwest) monsoon, the winter (Northeast) monsoon, and the summer northwesterlies that blow over the Arabian Peninsula. In addition, plant waxes are fluvially supplied to the Gulf of Oman and the Eastern African margin by nearby rivers. Plant wax δ¹³C values reflect the vegetation types of the continental source regions. Greater than 75% of the waxes from Africa and Asia are derived from C₄ plants. Waxes delivered by northwesterly winds reflect a greater influence (25-40%) of C₃ vegetation, likely derived from the Mesopotamian region. These data agree well with previously published studies of eolian dust deposition, particularly of dolomite derived from the Arabian Peninsula and the Mesopotamian region, in surface sediments of the Arabian Sea. The west-to-east gradient of plant wax δ¹³C and dolomite accumulation rates are separately useful indicators of the relationship between the northwesterly winds and the winds of the Southwest monsoon. Combined, however, these two proxies could provide a powerful tool for the reconstruction of both southwest monsoon strength as well as Mesopotamian aridity.  相似文献   

Contributions of nitrogen deposition and forest regrowth to terrestrial carbon uptake     

Galina Churkina  Kristina Trusilova  Mona Vetter  Frank Dentener 《Carbon balance and management》2007,2(1):5-7

Background  

The amount of reactive nitrogen deposited on land has doubled globally and become at least five-times higher in Europe, Eastern United States, and South East Asia since 1860 mostly because of increases in fertilizer production and fossil fuel burning. Because vegetation growth in the Northern Hemisphere is typically nitrogen-limited, increased nitrogen deposition could have an attenuating effect on rising atmospheric CO₂ by stimulating the vegetation productivity and accumulation of carbon in biomass.  相似文献   

Nitrogen dynamics in nontidal littoral sediments: Role of microphytobenthos and denitrification     

Kristina Sundbäck  Alison Miles  Frank Linares 《Estuaries and Coasts》2006,29(6):1196-1211

Previous measurements from cool microtidal temperate areas suggest that microphytobenthic incorporation of nitrogen (N) exceeds N removal by denitrification in illuminated shallow-water sediments. The present study investigates if this is true also for fully nontidal sediments in the Baltic Sea., Sediment-water fluxes of inorganic (DIN) and, organic nitrogen (DON) and oxygen, as well as denitrification, were measured in early autumn and spring, in light and dark, at four sites representing different sediment types. All sediments were autotrophic during the daytime both in the autumn and spring. On a 24-h time scale, they were autotrophic in the spring and heterotrophic in early autumn. Sediments funcitoned as sources of DIN and DON during the autumn and sinks during the spring, with DON fluxes dominating or being as important as DIN fluxes. Microphytobenthos (MPB) activity controlled fluxes of both DIN and DON. Significant differences between sites were found, although sediment type (sand or silt) had no consistent effect on the magnitude of MPB production or nutrient fluxes. The clearest effect related to sediment type was found for denitrification, although only in the autumn, with higher rates in silty sediments. Estimated N assimilation by MPB, based on both net primary production (0.7–6.5 mmol N m⁻² d⁻¹) and on 80% of gross primary production (1.9–9.4 mmol N m⁻² d⁻¹) far exceeded measured rates of denitrification (0.01–0.16 mmol N m⁻² d⁻¹). A theoretical calculation showed that MPB may incorporate between 40% and 100% of the remineralized N, while denitrification removes, <5%. MPB assimilation of N appears to be a far more important N consuming process than denitrification in these nontidal, shallow-water sediments.  相似文献   

A robust feldspar luminescence dating method for Middle and Late Pleistocene sediments   总被引：2，自引：0，他引：2  

Jan‐Pieter Buylaert  Mayank Jain  Andrew S. Murray  Kristina J. Thomsen  Christine Thiel  Reza Sohbati 《Boreas: An International Journal of Quaternary Research》2012,41(3):435-451

Luminescence dating is used extensively to provide absolute chronologies for Late Pleistocene sediments. Nowadays, most optical dates are based on quartz optically stimulated luminescence (OSL). However, the application of this signal is usually limited to the last ～100 ka because of saturation of the quartz luminescence signal with dose. In contrast, the feldspar infrared stimulated luminescence (IRSL) dose–response curve grows to much higher doses; this has the potential to extend the datable age range by a factor of 4–5 compared with quartz OSL. However, it has been known for several decades that this IRSL signal is unstable, and this instability often gives rise to significant age underestimation. Here we test against independent age control the recently developed feldspar post‐IR IRSL approach to the dating of sediments, which appears to avoid signal instability. A physical model explaining our observations is discussed, and the method is shown to be accurate back to 600 ka. The post‐IR IRSL signal is reduced by exposure to daylight more slowly than that from quartz and low‐temperature IRSL, preventing its general application to young (e.g. Holocene) sediments. Nevertheless, this new approach is widely applicable (feldspar of appropriate luminescence behaviour is even more ubiquitous than quartz). These characteristics make this a method of great importance for the dating of Middle and Late Pleistocene deposits.  相似文献   

Anglo American media representations, traditional medicine, and HIV/AIDS in South Africa: from muti killings to garlic cures     

Kristina Monroe Bishop 《GeoJournal》2012,77(4):571-581

Before 2000 limited media coverage of medicine in South Africa existed, yet much of what did exist centered primarily on traditional healing practices. It was not until the introduction of HIV/AIDS that traditional medicine was seen as having some potential value to the population, but only so far as the ability of traditional healers to direct patients to biomedical treatment. This article examines how the contemporary western media portrays medicine in South Africa and how the introduction of HIV/AIDS as a major news story has shifted the depiction of western and traditional medical treatment. Insights from these questions are examined in light of the colonial context of South Africa’s political struggle over medicine.  相似文献