348 resultados para Ice storage studies
em Publishing Network for Geoscientific
Resumo:
Accumulation rates in the eastern part of Ronne Ice Shelf were determined by isotopic stratigraphy (18O). The samples were taken from snow-pits dug during the Filchner I and II operations in 1984 and 1986. In general, the accumulation rate decreases towards the south; the greatest decrease, from 21.3 to 13.3 g/cm**2/a, was observed between Filchner Station and measuring point 341, sited 270 km up-stream of the ice edge. The d18O values of the near-surface layers vary between -25 and -29 per mil. The 18O content in the more southerly part is progressively depleted in the direction of Möllereisstrom, paralleling a decrease in the accumulation rate. Near the ice edge the 18O content decreases to the west. A 100 m ice core drilled in 1984 at point 340, 22 km from the ice edge, probably goes back to A.D. 1460; it has been dated by isotopic stratigraphy. The accumulation rate up-stream of the drilling site was deduced from the sequence of annual layers, using a simple ice-flow model. The accumulation shows strong variations over the last 200 years, which may be caused in part by local variations in the accumulation on Ronne Ice shelf.
Resumo:
Agricultural pesticide use has increased worldwide during the last several decades, but the long-term fate, storage, and transfer dynamics of pesticides in a changing environment are poorly understood. Many pesticides have been progressively banned, but in numerous cases, these molecules are stable and may persist in soils, sediments, and ice. Many studies have addressed the question of their possible remobilization as a result of global change. In this article, we present a retro-observation approach based on lake sediment records to monitor micropollutants and to evaluate the long-term succession and diffuse transfer of herbicides, fungicides, and insecticide treatments in a vineyard catchment in France. The sediment allows for a reliable reconstruction of past pesticide use through time, validated by the historical introduction, use, and banning of these organic and inorganic pesticides in local vineyards. Our results also revealed how changes in these practices affect storage conditions and, consequently, the pesticides' transfer dynamics. For example, the use of postemergence herbicides (glyphosate), which induce an increase in soil erosion, led to a release of a banned remnant pesticide (dichlorodiphenyltrichloroethane, DDT), which had been previously stored in vineyard soil, back into the environment. Management strategies of ecotoxicological risk would be well served by recognition of the diversity of compounds stored in various environmental sinks, such as agriculture soil, and their capability to become sources when environmental conditions change.
Resumo:
At mid- to high-latitude marine sites, ice-rafted debris (IRD) is commonly recognized as anomalously coarse-grained terrigenous material contained within a fine-grained hemipelagic or pelagic matrix (e.g., Conolly and Ewing, 1970; Ruddiman, 1977, doi:10.1130/0016-7606(1977)88<1813:LQDOIS>2.0.CO;2; Krissek, 1989, doi:10.2973/odp.proc.sr.104.114.1989; Jansen et al., 1990; Bond et al., doi:10.1038/360245a0, 1992; Krissek, 1995, doi:10.2973/odp.proc.sr.145.118.1995). The presence of such ice-rafted material is a valuable indicator of the presence of glacial ice at sea level on an adjacent continent, whereas the composition of the IRD can often be used to identify the location of the source area (e.g., Goldschmidt, 1995, doi:10.1016/0025-3227(95)00098-J). Because the amount of core recovered during Leg 163 was very limited, this shore-based, postcruise study focuses on materials recovered at a nearby site during Leg 152. In particular, this study examines sediments recovered at Site 919; these sediments were described as containing a significant ice-rafted component in the Leg 152 Initial Reports volume (Larsen, Saunders, Clift, et al., 1994, doi:10.2973/odp.proc.ir.152.1994). In this study, the sedimentary section from Site 919 has been examined with the goal of providing a detailed history of glaciations on Greenland and other landmasses adjacent to the Norwegian-Greenland Sea; this history ultimately will be calibrated using an oxygen isotope stratigraphy (Flower, 1998, doi:10.2973/odp.proc.sr.152.219.1998), although that calibration has not been completed at this time. Because ice-core studies of the Greenland Ice Sheet (GIS) have shown that the GIS changed dramatically, and in some cases extremely rapidly, during at least the last interglacial stage (GRIP Members, 1993, doi:10.1038/364203a0), a detailed IRD record from the Southeast Greenland margin should provide insight into the longer term behavior of this sensitive component of the Northern Hemisphere climate system.
Resumo:
Precise knowledge of the phase relationship between climate changes in the two hemispheres is a key for understanding the Earth's climate dynamics. For the last glacial period, ice core studies have revealed strong coupling of the largest millennial-scale warm events in Antarctica with the longest Dansgaard-Oeschger events in Greenland through the Atlantic meridional overturning circulation. It has been unclear, however, whether the shorter Dansgaard-Oeschger events have counterparts in the shorter and less prominent Antarctic temperature variations, and whether these events are linked by the same mechanism. Here we present a glacial climate record derived from an ice core from Dronning Maud Land, Antarctica, which represents South Atlantic climate at a resolution comparable with the Greenland ice core records. After methane synchronization with an ice core from North Greenland, the oxygen isotope record from the Dronning Maud Land ice core shows a one-to-one coupling between all Antarctic warm events and Greenland Dansgaard-Oeschger events by the bipolar seesaw. The amplitude of the Antarctic warm events is found to be linearly dependent on the duration of the concurrent stadial in the North, suggesting that they all result from a similar reduction in the meridional overturning circulation.
Resumo:
The data collection "Deep Drilling of Glaciers: Soviet-Russian projects in Arctic, 1975-1995" was collected by the following basic considerations: - compilation of deep (>100 m) drilling projects on Arctic glaciers, using data of (a) publications; (b) archives of IGRAN; (c) personal communication of project participants; - documentation of parameters, references. Accuracy of data and techniques applied to determine different parameters are not evaluated. The accuracy of some geochemical parameters (up to 1984 and heavy metalls) is uncertain. Most reconstructions of ice core age and of annual layer thickness are discussed; - digitizing of published diagrams (in case, when original numerical data were lost) and subsequent data conversion to equal range series and adjustment to the common units. Therefore, the equal-range series were calculated from original data or converted from digitized chart values as indicated in the metadata. For the methodological purpose, the equal-range series obtained from original and reconstructed data were compared repeatedly; the systematic difference was less then 5-7%. Special attention should be given to the fact, that the data for individual ice core parameters varies, because some parameters were originally measured or registered. Parameters were converted in equal-range series using 2 m steps; - two or more parameter values were determined, then the mean-weighted (i.e. accounting the sample length) value is assigned to the entire interval; - one parameter value was determined, measured or registered independently from the parameter values in depth intervals which over- and underlie it, then the value is assigned to the entire interval; - one parameter value was determined, measured or registered for two adjoining depth intervals, then the specific value is assigned to the depth interval, which represents >75% of sample length ; if each of adjoining depth intervals represents <75% of sample length, then the correspondent parameter value is assigned to both intervals of depth. This collection of ice core data (version 2000) was made available through the EU funded QUEEN project by S.M. Arkhipov, Moscow.