Quantifying the Spatial Characteristics of the Moisture Transport Affecting Precipitation Seasonality and Recycling Variability in Central Asia     

Linhao ZHONG  Lijuan HUA  Zhaohui GONG  Yao YAO  Lin MU 《大气科学进展》2022,39(6):967-984

Moisture contribution and transport pathways for Central Asia(CA)are quantitatively examined using the Lagrangian water cycle model based on reanalysis and observational data to explain the precipitation seasonality and the moisture transport variation during 1979-2015.Westerly-related(northwesterly and westerly)transport explains 42%of CA precipitation and dominates in southwest CA,where precipitation is greatest in the cold season.Southeast CA,including part of Northwest China,experiences its maximum precipitation in the warm season and is solely dominated by southerly transport,which explains about 48%of CA precipitation.The remaining 10%of CA precipitation is explained by northerly transport,which steadily impacts north CA and causes a maximum in precipitation in the warm season.Most CA areas are exposed to seasonally varying moisture transport,except for southeast and north CA,which are impacted by southerly and northerly transport year-round.In general,the midlatitude westerlies-driven transport and the Indian monsoon-driven southerly-related transport explain most of the spatial differences in precipitation seasonality over CA.Moreover,the contribution ratio of local evaporation in CA to precipitation exhibits significant interdecadal variability and a meridionally oriented tripole of moisture transport anomalies.Since the early 2000s,CA has experienced a decade of anomalously low local moisture contribution,which seems jointly determined by the weakened moisture contribution from midlatitudes(the Atlantic,Europe,and CA itself)and the enhanced contribution from high latitudes(West Siberia and the Arctic)and tropical areas(South Asia and the Indian Ocean).  相似文献   

Zircon recycling and crystallization during formation of chromite- and Ni-arsenide ores in the subcontinental lithospheric mantle (Serranía de Ronda,Spain)     

《Ore Geology Reviews》2017

The ultramafic massifs of the Serranía de Ronda (namely Ronda, Ojén and Carratraca) are portions of Proterozoic (∼1.2–1.8 Ga) subcontinental lithospheric mantle (SCLM) affected by partial melting and infiltration of melts. The latter of these events was broadly coeval with the tectonic emplacement of the peridotites into the continental crust in the Early Miocene. This resulted in the formation of chromite and Ni-arsenide ores (Cr-Ni) associated with orthopyroxenites and cordieritites. Six zircons recovered from a massive chromitite sample from the Ronda massif yield both concordant and discordant ages between 2309 ± 37 Ma and 109 ± 15 Ma, and δ¹⁸O between 8.3‰ and 9.4‰. Two Proterozoic ages obtained for zircons of this population (1815 ± 9 Ma and 1794 ± 17 Ma) are identical, within error, to those of zircons reported previously in the garnet pyroxenites of Ronda (1783 ± 37 Ma). Similarly, concordant Early Jurassic (192 ± 13 Ma) and Cretaceous ages (109 ± 15 Ma) obtained from the core and rim, respectively, of a single zircon from the chromitite are also consistent with the ages (180 ± 5 Ma, 178 ± 6 Ma, and 131 ± 3 Ma) already reported for magmatic zircons from corunudum-bearing garnet pyroxenites in the Ronda massif. The observation that chromitites and garnet-pyroxenites contain similar populations of zircons suggests that the parental melts of chromitites inherited zircons from their protolithic garnet pyroxenites, representing relics of oceanic/arc crust recycled in the mantle. Eleven zircons recovered from a massive cordieritite associated with chromitite in the Ronda massif yield scattered concordant and discordant ages between 568 Ma and 21 Ma, with correspondingly variable δ¹⁸O (4.8–13.5‰) and unradiogenic Hf-isotope ratios (ε_Hf(t) from −12.36 to −4.43). The youngest age is concordant at 21.18 ± 0.4 Ma and matches the ages of zircons from the chromitite (weighted average age of 20.4 ± 0.87 Ma, n = 4) and a plagioclasite dyke (scattering between 20.1 ± 0.2 Ma and 17.9 ± 0.1 Ma; n = 11) associated with the Cr-Ni mineralization in the Ojén massif. These zircons show similar unradiogenic Hf-(ε_Hf(t) between −14.5 and −7.6) and heavy O-isotope compositions (δ¹⁸O = 11.3–12.4‰). A sample of the massive cordieritite hosting the chromitites contains abundant zircons that yield scattered concordant, sub-concordant and discordant U-Pb ages varying from 33.8 ± 1 Ma to 781 ± 10 Ma; these zircons (n = 21) have variable U-contents (105–13900 ppm) and Th/U ratios (0.003–0.8). On the basis of O- and Hf-isotope compositions, these zircons define three populations independently of their ages: (1) grains with consistent high δ¹⁸O (6.1–12.7‰) and negative ε_Hf(t) (from −14.42 to −6.88); (2) grains with high δ¹⁸O (7.6–11.1‰) and positive ε_Hf(t) (3.10–4.84); and (3) grains with δ¹⁸O < 5.5‰ typical of mantle values. We suggest that zircons from this cordieritite with U-Pb ages older than Miocene are inherited, and were incorporated physically into the SCLM by fluids or melts produced during dehydration-melting of the crustal rocks wrapping the peridotite massifs. The population of Early Miocene zircons found in the chromitites and associated cordieritites and the plagioclasite dyke in the mineralization of the Ojén massif date the crustal emplacement of the peridotites and, therefore, the formation of the Cr-Ni ores. We propose a model in which the unique Cr-Ni mineralizations found in the ultramafic rocks of the Serranía de Ronda were formed as a result of contamination of the SCLM with crustal components.  相似文献   

Cumulative impacts on seabed habitats: An indicator for assessments of good environmental status     

Samuli Korpinen  Manuel MeidingerMaria Laamanen 《Marine pollution bulletin》2013

The European seas are under anthropogenic pressures impacting the state of water quality, benthic habitats and species. The EU Marine Strategy Framework Directive (MSFD) requires the Member States to assess the impacts of pressures and make a programme of measures leading to good environmental status (GES) by 2020. This study presents a method for assessing the quantity and distribution of anthropogenic impacts on benthic habitats in the Baltic Sea by using spatial data of human pressures and benthic habitats. The southern sub-basins were more extensively impacted than the northern sub-basins. Over the entire sea area, deep sea habitats were more impacted than shallower infralittoral and circalittoral habitats. Sand and coarse sediments were the seabed types relatively most impacted in the Baltic Sea scale. A comparison against tentative thresholds for GES showed that in the sub-basin scale only one third of the habitat types was in GES.  相似文献   

OBSERVATIONS ON THE HINTEREIS AND VERNAGTFERNER     

H. SCHATZ 《水文科学杂志》2013,58(1):94-96

Abstract

Adequate water resources management at the basin level needs quality downscaling of climate change scenarios for application to impact assessment and adaptation work. This study evaluates the ability of a regional climate model (RegCM3) to simulate the present-day climate and regional water balance over the Niger River Basin (NRB). RegCM3 gives a good simulation of the NRB hydroclimatic features. The mean bias error for monthly temperature is 1.5°C, 0.3 mm d^-1 for rainfall, and 0.4 mm d^-1 for runoff. Moderate to high correlations (0.66–0.95) were found between the modelled and the observed variables. RegCM3-based water cycling indices were not statistically different from the observation. Seasonal moistening efficiency (m) ranges between 19% and 37%; 66% of the available atmospheric moisture over NRB precipitates between June and September, of which 21% originates from local evaporation. The result suggests that the moisture sink period is July to October with very high precipitation efficiency over the basin. The model reproduces the hydroclimatology of the NRB and hence is a suitable tool for further studies relating to the assessment of climate change impacts on river basin water systems.