轨道尺度亚洲气候演化机理的数值模拟:历史与展望     

石正国  雷婧  周朋  任鑫 《第四纪研究》2020,(1):8-17

轨道尺度亚洲气候演化是古气候热点问题之一,其变化过程和机理对理解当前全球变暖下亚洲气候变化具有重要参考意义。最近几十年,基于黄土、石笋、湖泊等载体的轨道尺度亚洲气候重建研究获得显著进展,气候演化历史的基本框架已被构建,不同区域和指标记录之间的差异暗示了气候演化机理的复杂性。数值模拟作为研究气候动力学的重要工具之一,在轨道尺度亚洲气候变化中也得到广泛应用和快速发展。基于此,本文尝试对最近十数年轨道尺度亚洲气候演化机理的数值模拟研究做一简单总结和梳理。目前的数值模拟尚未对地质记录给出的各种变化特征、区域差异等现象,尤其是东亚夏季风的黄土和石笋差异、季风和干旱气候的耦合关系等,给出合理解释。因此,在未来工作中亟须涵盖多轨道旋回的高分辨率瞬变试验,结合良好定年的重建记录,以期对轨道尺度亚洲气候变化机理获得更深入完整的认识。  相似文献   

Luminescence and ESR dating of the sedimentary infill from the multi-level cave system of Alkerdi-Zelaieta (Navarre,N Spain)     

《Quaternary Geochronology》2022

The finding of Upper Paleolithic engravings in 2016 triggered a multidisciplinary investigation of the Alkerdi cave system (Urdazubi, N Spain). The study of the speleogenetic processes led to the identification of at least 6 paragenetic cave levels with associated sedimentary infill. In order to unravel the timing of changes in the karst dynamics and to get some insights about sediment origin, two sediment samples were collected from cave levels 4 and 1 for numerical dating purpose, using both Optically Stimulated Luminescence (OSL) and Electron Spin Resonance (ESR) methods. One additional modern-age sample was also taken from the entrance of the karst to evaluate the magnitude of the optical bleaching achieved by the quartz grains before entering the cave system. Last, one sample was collected from a flowstone for U-series dating, providing independent age control.OSL measurements were carried out using small quartz multi-grain (MG) and single-grain (SG) Single Aliquot Regenerative-dose (SAR) protocol. Initial Equivalent Dose (D_e) results show evidence of saturated OSL signal for the sample of the higher level (with ∼60% of saturated aliquots). Unlike SA data, SG analyses do not meet the usual quality criteria (e.g., relatively high recuperation ratios, only a few grains with useable signal), suggesting that corresponding dating results should be treated with caution.Hence, both MG and SG TT-OSL and MG ESR methods were subsequently employed, as the corresponding signals are known to have higher saturation levels than OSL ones. ESR analyses were based on the Multiple Centre (MC) approach using the standard multi-grain multi-aliquot additive (MAA) dose method, while TT-OSL measurements were performed following Demuro et al. (2020). The latter, however, did not return any useful results for both samples. MC ESR data show the usual D_e pattern (D_e(Al)>D_e(Ti op. D)>D_e(Ti–H)) indicating that among the three ESR signals analyzed, the Ti–H most likely provides the closest estimate to the true burial age. However, low measurement repeatability and goodness-of-of fit indicate that the reliability of the ESR results may be reasonably questioned.Results derived from this multi-technique dating approach provide the first chronological constraints for the sedimentary infill of the Alkerdi cave system. In particular, they suggest that sediment deposition in Cave Level 4 (ALK-OSL01) occurred around 130 ka, which is in good agreement with the minimum age constraint given by the speleothem (80.5 ± 9.0 ka). In comparison, the young age obtained for sample ALK-OSL02 (5.0 ± 0.9 ka) suggests recent Holocene formation of the lowest cave level 1.Finally, the MG De value obtained for the modern sample is close to zero (<1 Gy), indicating that the OSL signal is almost fully reset at a multi-grain level before entering the cave. Additionally, despite the large De overdispersion measured in this modern sample, the De values are one to two order of magnitude lower than those obtained with the same model in the other two samples. Therefore, the large OSL D_e overdispersion (OD) values of up to 64% obtained for the two samples from Cave Level 4 and 1 are most likely related to re-sedimentation processes inside the cave system.  相似文献   

Enhanced anisotropic bounding surface plasticity model considering modified spacing ratio of anisotropically consolidated clay     

Kang  Xiaosen  Liao  Hongjian  Huang  Qiangbing  Dai  Qian 《Acta Geotechnica》2022,17(6):2213-2233

Acta Geotechnica - The critical state of anisotropically consolidated clay is not well captured by the classical anisotropic bounding surface plasticity model without considering the real...  相似文献   

Holocene and Eemian climatic optima in the Korean Peninsula based on textural and carbon isotopic records from the stalagmite of the Daeya Cave,South Korea     

Kyoung-nam Jo  Kyung Sik Woo  Hyoun Soo Lim  Hai Cheng  R. Lawrence Edwards  Yongjin Wang  Xiuyang Jiang  Ryeon Kim  Jae Il Lee  Ho Il Yoon  Kyu-Cheul Yoo 《Quaternary Science Reviews》2011,30(9-10):1218-1231

Textural and stable isotopic records from the absolute-dated stalagmite of the Daeya Cave (DY-1) provide new insights into the climatic evolution of the Korean Peninsula during the Holocene and Eemian climatic optima. The stalagmite yielded ages of 8572 ± 227 to 5907 ± 158 and 1,23,456 ± 535 to 1,19,837 ± 1089 years, which coincide with the Holocene and Eemian climatic optima, respectively. The stalagmite’s δ¹³C record closely resembles previously reported Chinese speleothem δ¹⁸O data. Thus it can be suggested that textural and geochemical results of the DY-1 reflect East Asian monsoon intensity, which is forced by summer insolation patterns in the northern hemisphere. Lighter carbon isotopic compositions, well-developed fibrous calcite crystals, and their relatively faster growth rate in the stalagmite sample are interpreted to reflect the warmest and wettest climate conditions of the Holocene and Eemian interglacials. Both climatic optima took place when insolation was decreasing from its maximum level, temperature in Greenland was highest, and sea level approached its maximum level. These climatic optima also coincide with decreasing Antarctic temperatures. Compared the DY-1 data to other proxies, it is suggested that the Holocene and Eemian climatic optima developed through a balance among boreal insolation, monsoon intensity, and sea level (also continental ice volume), which are the main climatic forcing factors in the northern hemisphere. These trends also follow the bi-polar seesaw mechanism as previously described.  相似文献   

Ocean current estimation using a Multi-Model Ensemble Kalman Filter during the Grand Lagrangian Deployment experiment (GLAD)     

《Ocean Modelling》2015

In the summer and fall of 2012, during the GLAD experiment in the Gulf of Mexico, the Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE) used several ocean models to assist the deployment of more than 300 surface drifters. The Navy Coastal Ocean Model (NCOM) at 1 km and 3 km resolutions, the US Navy operational NCOM at 3 km resolution (AMSEAS), and two versions of the Hybrid Coordinates Ocean Model (HYCOM) set at 4 km were running daily and delivering 72-h range forecasts. They all assimilated remote sensing and local profile data but they were not assimilating the drifter’s observations. This work presents a non-intrusive methodology named Multi-Model Ensemble Kalman Filter that allows assimilating the local drifter data into such a set of models, to produce improved ocean currents forecasts. The filter is to be used when several modeling systems or ensembles are available and/or observations are not entirely handled by the operational data assimilation process. It allows using generic in situ measurements over short time windows to improve the predictability of local ocean dynamics and associated high-resolution parameters of interest for which a forward model exists (e.g. oil spill plumes). Results can be used for operational applications or to derive enhanced background fields for other data assimilation systems, thus providing an expedite method to non-intrusively assimilate local observations of variables with complex operators. Results for the GLAD experiment show the method can improve water velocity predictions along the observed drifter trajectories, hence enhancing the skills of the models to predict individual trajectories.  相似文献   

Effect of plant life form on relationship between δD values of leaf wax n-alkanes and altitude along Mount Taibai, China     

Zhang Pu  Liu Weiguo 《Organic Geochemistry》2011,42(1):100-107

We present δD_wax values from different forms of plants and soils, and δD_sw values from soil water along the northern slope of Mount Taibai, China. The results show a highly negative linear correlation of the δD_wax values for soils with altitude (R² 0.74) and we observed the same correlation for δD_sw values of soil water with altitude (R² 0.68). The δD_wax of living plants behaves like the soil, but does not exhibit a significant linear correlation with altitude (R² 0.11). The δD_wax values of woody plants and grasses also show a similar trend with respect to altitude with significant and no linear correlation, respectively (R² 0.50 for woody plants and 0.17 for grass), which suggest that the “altitude effect” can not be well documented for the δD_wax values of living plants, which may be due to differences in plant type and/or evapotranspiration controlled by the plant microclimate. The ε_wax-sw values of woody plants, grasses and soil show minor fluctuations with altitude. However, the ε_wax-sw and δD_wax values of woody plants are roughly 51‰ and 50‰ more positive, respectively, than those of grasses, suggesting that an “altitude effect” could be documented in the δD_wax of woody plants and grasses, with each responding independently to changes in precipitation along the altitude transect. Additionally, the ε_wax-sw values of soil are relatively constant with altitude, suggesting that the altitudinal change in the proportions between woody plant and grass input to soils will likely change the relationship between the δD_wax values of soil n-alkanes and altitude.  相似文献   

Variation in n-alkane δD values from terrestrial plants at high latitude: Implications for paleoclimate reconstruction     

Hong Yang  Weiguo Liu  Qin Leng  Michael T. Hren  Mark Pagani 《Organic Geochemistry》2011,42(3):283-288

The molecular hydrogen isotope composition (δD) of leaf waxes from terrestrial plants is increasingly used to infer hydrological characteristics of ancient high latitude climates. Analysis of the hydrogen isotope composition of n-alkanes (δD_n-alkane) from a global dataset of individual plants growing at low and middle latitudes indicates that plant ecological life form is an important factor in determining the hydrogen isotope fractionation. However, environmental and biological controls of high latitudinal leaf wax δD values are poorly understood because of a lack of δD records from modern flora in these regions. We previously noticed smaller apparent hydrogen isotope fractionations between n-alkanes and environmental water (ε_alk-water) in deciduous trees growing at high latitudes (>59°N; Liu, W.-G., Yang, H., 2008. Multiple controls for the variability of hydrogen isotopic compositions in higher plant n-alkanes from modern ecosystems. Global Change Biology 14, 2166-2177.) To further examine these issues, we measured δD_n-alkane from a variety of plants that inhabit high latitude environments and added critically needed leaf wax δD data from grass and herbs to the existing global δD_n-alkane database. Inclusion of these new data with the existing global dataset (n = 408) confirms plant ecological life form as an important control for leaf wax δD variation for terrestrial plants living at high latitudes. Our results suggest that, while precipitation δD is captured in these high latitude plants, physiological characters such as leaf area, venation pattern and hydraulic system, that enhance transpiration rate during summer growth, may impart δD_n-alkane differences among plants with different ecological life forms.  相似文献   

Chronostratigraphy and lake-level changes of Laguna Cari-Laufquén, Río Negro, Argentina     

Alyson Cartwright  Jay Quade  Scott Stine  Kenneth D. Adams  Wallace Broecker  Hai Cheng 《Quaternary Research》2011,76(3):430-440

Evidence from shoreline and deep-lake sediments show Laguna Cari-Laufquén, located at 41°S in central Argentina, rose and fell repeatedly during the late Quaternary. Our results show that a deep (> 38 m above modern lake level) lake persisted from no later than 28 ka to 19 ka, with the deepest lake phase from 27 to 22 ka. No evidence of highstands is found after 19 ka until the lake rose briefly in the last millennia to 12 m above the modern lake, before regressing to present levels. Laguna Cari-Laufquén broadly matches other regional records in showing last glacial maximum (LGM) highstands, but contrasts with sub-tropical lake records in South America where the hydrologic maximum occurred during deglaciation (17–10 ka). Our lake record from Cari-Laufquén mimics that of high-latitude records from the Northern Hemisphere. This points to a common cause for lake expansions, likely involving some combination of temperature depression and intensification of storminess in the westerlies belt of both hemispheres during the LGM.  相似文献   

应用瞬变电磁法小线框大电流探测隐伏断层   总被引：1，自引：0，他引：1  

杨农合  王辉  徐小林  吴朝俊  杨宁宁  王宝深 《物探与化探》2011,35(1):80-85

瞬变电磁法小线框、大电流技术在金属矿勘探和地下水的探测中已趋成熟。在长期实践的基础上,分析断层上方出现的感应二次场V2 负值现象和成因,提出断层和次新断层以及地质塌陷的探测方法和数据处理的要点,总结出利用小线框、大电流瞬变电磁法探测隐伏断层的技术方法。钻井验证表明,该方法施工快速轻便,断层点定位准确。  相似文献   

古火灾历史重建的研究进展     

占长林  曹军骥  韩永明  安芷生 《地球科学进展》2011,26(12):1248-1259

火是地球系统的重要组成部分,与气候、植被、生物地球化学循环和人类活动密切相关。火对全球气候和生态系统的影响已成为目前全球变化研究的一个热点。火灾发生后会在周围的环境中留下许多燃烧产物,如黑碳、木炭屑、多环芳烃、左旋葡萄糖等,它们广泛存在于海洋、湖泊、河流、土壤和陆地风成沉积物中;还会留下一些火灾痕迹,如树木火疤、土壤磁...  相似文献