NERC Open Research Archive

    The SALTMED model calibration and validation using field data from Morocco

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    The objective of this study was to calibrate and validate the SALTMED model using field data of three growing seasons of quinoa (Chenopodium quinoa Willd.), chickpeas (Cicer arietinum) and sweet corn (Zea mays Saccharata) which were grown in the south of Morocco and subjected to six treatments of deficit irrigation with treated wastewater. The calibration focussed primarily on soil moisture related to quinoa in the field, measured yield and dry matter. The validation process of biomass production was based on use of the calibrated photosynthesis efficiency value of the control treatment. Plant parameters such as plant height and rooting depth, duration of each growth stage, sowing date, harvesting date, harvest index and leaf area index were based on field measurements and records. Crop coefficients Kc, Kcb, Fc were based on FAO56 paper. Soil parameters such as water retention curves were based on laboratory measurements. Initial soil water content and salinity were based on measurements either in the laboratory or in the field. Fine tuning of some crop and soil parameters was carried out in order to obtain a good calibration. Following successful calibration and validation, the SALTMED model proved its ability to predict soil moisture, yield and total dry matter for three growing seasons under several deficit irrigation strategies using treated wastewater. The model showed a very good agreement between the observed and simulated data, as well as being able to reveal the same difference between deficit irrigation strategies in terms of measured yield and total dry matter

    Environmental geographic basis for the Protected Area System

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    Mixed biosiliceous-terrigenous sedimentation under the Antarctic Circumpolar Current, Scotia Sea

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    Sediment supply to the Scotia Sea is controlled by the east-flowing Antarctic Circumpolar Current (ACC) with some Weddell Gyre influence in the south. Near-bottom flow is unsteady with frequent changes in flow direction and episodic benthic storms. Near the North Scotia Ridge, mounds of sediment up to 1 km thick have accumulated on lower Miocene ocean floor. The basins farther south contain up to 2 km of sediment which is flat-lying or draped rather than mounded. Sediment cores exhibit a biogenic-terrigenous cyclicity related to glacial-interglacial cycles. Grain-size data suggest that ACC flow was stronger during glacials than interglacials

    Changes in heavy metals in Antarctic snow from Coats Land since the mid-19th to the late-20th century

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    V, Cr, Mn, Cu, Zn, Co, Ag, Cd, Ba, Pb, Bi and U have been measured in a series of dated snow samples, covering the period from 1834 to 1990, collected at remote, low accumulation sites in Coats Land, Antarctica. They were determined by ultrasensitive inductively coupled sector field mass spectrometry in ultraclean conditions. Concentrations are found to be extremely low, down to 3 x 10(-15) g/g, for most metals, then confirming the high purity of Antarctic snow. The results show contrasting time trends for the different metals. For Mn, Co, Ba, and possibly V and Cd, no clear time trends are observed. For Cr, Cu, Zn, Ag, Pb, Bi and U, on the other hand, pronounced enhancements are observed during the recent decades. They are attributed to emissions of heavy metals to the atmosphere from human activities in Southern America, Southern Africa and Australia, especially non-ferrous metal mining and smelting in Chile, Peru, Zaire, Zambia and Australia. It shows that atmospheric pollution for heavy metals in the remote Antarctic continent is not limited to Pb and Cu, as previously thought, but also affects several other metals. It is a further indication that atmospheric pollution for heavy metals is really global

    Solar cycle changes in daytime VLF subionospheric attenuation

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    Observations of field strengths of signals from a number of VLF transmitters, after propagation over long paths in the Earth–ionosphere waveguide, have been used to examine changes in the daytime attenuation rate in the course of a solar cycle. The measurements reported were recorded in the period 1986–1996. The paths studied range in length over about 8–14 Mm; they included NLK (Seattle) and NPM (Hawaii) to Dunedin, NZ, and NAA (Cutler, Maine) and NSS (Annapolis, Maryland) to Faraday, Antarctica. The frequencies monitored were mainly in the range 21–25 kHz but measurements near 10 kHz of Omega Hawaii at Faraday were also used. The daytime VLF attenuation rates at solar minimum were found to be greater by about 0.3 dB/Mm than at solar maximum

    Generalized Maxwell Love numbers

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    Dust and sea salt variability in central East Antarctica (Dome C) over the last 45 kyrs and its implications for southern high-latitude climate

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    A detailed record of non-sea-salt calcium, a proxy for dust, and sea-salt sodium, a proxy for sea salt, covering the last 45 kyr is presented. It shows that in the first part of the transition from the last glacial period to the Holocene (18-15 kyr BP), the changes in dust flux mainly reflect changes at the dust source, namely vegetation cover and local climate. The changes in the later part of the transition (12-11 kyr BP) are similar in extent to the changes seen in sea salt and most likely reflect a reorganization of the atmospheric circulation. During the last glacial period, considerable variation of dust but not of sea salt is observed, pointing to climatic changes in Patagonia, the main dust source for Dome C. A comparison of the glacial records from Dome C and Taylor Dome suggests that similar influences controlled aerosol input at both sites during this period
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