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    A microscopic approach to the pedogenic formation of palygorskite associated with Quaternary calcretes of the Adana area, southern Turkey
    (2014) Kaplan Yeşilot, Meryem; Eren, Muhsin; Kadir, Selahattin; Kapur, Selim; Huggett, Jennifer
    Quaternary calcretes in the Adana area (southern Turkey) are widespread and occur in a variety of forms such as nodular, columnar/tubular, fracture-infll, laminated hardpan, and conglomeratic crusts. Palygorskite associated with calcrete nodules, tubes, and fracture-inflls in the columnar horizon and adjacent host-rock mudstones suggests a cogenetic formation. Te β-fabric (biogenic) constituents and stable isotope values of calcretes support a pedogenic origin for calcretes and also palygorskite. Extensions of palygorskite fbre and fbre bundles from euhedral to subhedral calcite crystals in calcretes and from smectite fakes in adjacent host- rock mudstone suggest an authigenic origin related to calcretisation in which precipitation and dissolution/precipitation are the main processes for palygorskite formation, respectively. Te presence of palygorskite in subspherical aggregates containing calcite crystals, and with smectitic clay coatings around the palygorskite aggregate, similarly suggests a relationship of pedogenic evolution between the 2 clays. Palygorskite precipitated in a vadose zone from strongly evaporated alkaline water, rich in Si and Mg and low in Al and Fe, at elevated temperatures and at an advanced stage of calcrete formation. Development of palygorskite mainly on relict calcite crystals indicates its formation during or shortly following calcite formation in calcretes. Palygorskite precipitation on relative large crystal surfaces has resulted in encrusted and platy fan-like crystal morphologies, whereas its nucleation on the crystal edge relief triggers fbre- like morphologies from crystal edges.
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    Sensitivity of Reference Evapotranspiration and Soil Evaporation to Climate Change in the Eastern Mediterranean Region
    (Springer International Publishing Ag, 2019) Aydin, Mehmet; Watanabe, Tsugihiro; Kapur, Selim
    Climate data generated by a regional climate model (RCM) under the A2 scenario were used to quantify the evaporative demand of the atmosphere in the Mediterranean region of Turkey in a baseline period (1994-2003) and the future (2070-2079). The daily reference evapotranspiration and bare soil evaporation were computed using the FAO-56 Penman-Monteith and E-DiGOR models, respectively, for both periods. The sensitivity of Penman-Monteith type equations to the major climatic variables was determined. Based on decadal averages, solar radiation, air temperature, and wind-speed were projected to increase from 16.084 to 16.324 MJ m(-2) day(-1), from 19.3 degrees C to 20.7 degrees C, and from 0.75 to 0.77 m s(-1) respectively, by the period of 2070-2079 compared with the baseline period. By contrast, the relative humidity is expected to decrease from 68.1 to 67.5% (equivalent to a 0.9% reduction). The reference evapotranspiration (Eto) and potential soil evaporation (Ep) are projected to increase by 92.0 mm year(-1) and 68.6 mm year(-1) respectively by the 2070s. Conversely, the actual soil evaporation (Ea) is expected to decrease by 49.6 mm year(-1) by the same period due to the decrease in rainfall and soil wetness. The reference evapotranspiration was more sensitive to the net radiation in all seasons; followed by the air temperature in the summer months, and by the relative humidity in the winter months under both the present and future conditions. In terms of the sensitivity coefficients, the Ep responded better to the changes in climatic variables than the Eto. The sensitivity of Ep to the key climatic elements varied with the seasons: the net radiation was the most causative variable in the summer, whereas the air temperature and relative humidity were the most influential variables in the winter. The mean sensitivity coefficients for air temperature and wind-speed are projected to increase from 0.40 to 0.45 and from 0.15 to 0.19 respectively by the period of 2070-2079. A slight change in the sensitivity coefficient for relative humidity is projected. This could be explained by the expected air temperature rise and the increase in wind-speed, followed by a negligible decrease in humidity, which can increase the Ep rate. By contrast, the relative contribution of the net radiation to Ep would decrease in the future with a coefficient decreasing from 0.84 to 0.80. This outcome can be attributed to the proportionally higher increases in air temperature and wind-speed in the future, which would reduce the relative portion of the net radiation.