Objective The lake levels in the eastern and southern Asia are regarded as low lake-level owing to precipitation decreasing based on the records of lake-level fluctuation in the continental interior lakes since the la...Objective The lake levels in the eastern and southern Asia are regarded as low lake-level owing to precipitation decreasing based on the records of lake-level fluctuation in the continental interior lakes since the last glacial maximum（LGM）（14C 18±1 kaBP,since 20 kaBP）in the Central Asia.Higher lake-level appeared in the transition belt between western Kunlun Mountain and the central Tibetan Plateau.展开更多
Stable isotopic compositions （δ18O and 6D） have been utilized as a useful indicator for evaluating the current and historical climatic and environmental changes. Therefore, it is vital to understand the relationshi...Stable isotopic compositions （δ18O and 6D） have been utilized as a useful indicator for evaluating the current and historical climatic and environmental changes. Therefore, it is vital to understand the relationship be- tween the stable isotopic contents in lake water and the variations of lake level, particularly in Lake Qinghai, China. In this study, we analyzed the variations of isotope compositions （δ18O, 6D and d-excess） in lake water and pre- cipitation by using the samples that were collected from Lake Qinghai region during the period from 2009 to 2012. The results showed that the average isotopic contents of δ18O and 6D in lake water were higher than those in pre- cipitation, which were contrary to the variations of d-excess. The linear regression correlations between δ18O and 6D in lake water and precipitation showed that the local evaporative line （LEL） in lake water （δD=5.88δ18O-2.41） deviated significantly from the local meteoric water line （LMWL）in precipitation （δD=8.26δ18O＋16.91）, indicating that evaporative enrichment had a significant impact on isotopic contents in lake water. Moreover, we also quanti- fied the Eli ratio （evaporation-to-input ratio） in Lake Qinghai based on the lake water isotopic enrichment model derived from the Rayleigh equation. The changes of E/I ratios （ranging from 0.29 to 0.36 between 2009 and 2012） clearly revealed the shifts of lake levels in Lake Qinghai in recent years. The average E/I ratio of 0.40 reflected that water budget in Lake Qinghai was positive, and consistent with the rising lake levels and the increasing lake areas in many lakes of the Tibetan Plateau. These findings provide some evidences for studying the hydrological balance or water budget by using δ18O values of lake sedimentary materials and contribute to the reconstruction of paleo- lake water level and paleoclimate from an isotopic enrichment model in Lake Qinghai.展开更多
The formation of halite in continental basins is intimately linked to lake-level changes.Current research has revealed the connection between lake-level variations and astronomical forcing on a million-year scale.Othe...The formation of halite in continental basins is intimately linked to lake-level changes.Current research has revealed the connection between lake-level variations and astronomical forcing on a million-year scale.Other studies have also highlighted the influence of orbitally-induced climate cycles on halite deposition.However,our understanding of the impact of astronomically-paced lake-level changes on halite formation remains constrained.The Paleogene Dawenkou Formation in the Huanggang Basin of East China provides a continuous salt-bearing sedimentary record to investigate the lake-level changes in halite deposition.Lake-level fluctuations reconstructed by sedimentary noise modeling for the Middle and Upper members of the Dawenkou Formation indicate that the lake-level variations in the Huanggang Basin were linked to astronomical forcing with periods of∼2.4 Myr,∼1.2 Myr and/or∼100 kyr.Our results suggest that astronomical forcing,as a driver of lake-level variations,may have had an impact on halite deposition during the Paleogene.In the initial stage of halite formation within the Middle Member of the Dawenkou Formation,reduced heat and moisture transport during the∼1.2 Myr obliquity minima resulted in low lake levels in mid-to-high latitudes.The prolonged droughts caused by the low amplitude of∼2.4 Myr eccentricity created conditions more favorable for the development of thicker layers of halite.Subsequently,in the next halite-forming stage,a larger amplitude of∼2.4 Myr eccentricity led to a more humid climate.Warm/dry winters and cool summers paced by the∼100 kyr orbital eccentricity minima resulted in enhanced evaporation,relatively lower lake levels,and thinner halite deposition.Nevertheless,the possible transgressions may have contributed to complicated phase relationship between the lake-level change cycles and orbital cycles.This study offers an opportunity to delve deeper into the mechanism of halite deposition by objectively reconstructing lake levels using sedimentary noise modeling.展开更多
Many lakes exist in southeastern Badain Jaran Desert and its hinterland, including 110 perennial lakes and some seasonal or extinct lakes. Geomorphological, sedimentological, and bioglyph evidence obtained from field ...Many lakes exist in southeastern Badain Jaran Desert and its hinterland, including 110 perennial lakes and some seasonal or extinct lakes. Geomorphological, sedimentological, and bioglyph evidence obtained from field investigations on Badain Jaran Desert lake group, alongside measurements and dating performed on lake relic, prove that these lakes expanded while the climate was relatively wet during early and middle Holocene. The dating results suggest that the pan-lake period of the Badain Jaran Desert began at 10 cal kyr BP, before which the limnic peat period occurred(11–10 cal kyr BP). Many lakes reached their maximal water-level during 8.6–6.3 cal kyr BP and retreated or dried up in the late Holocene(about 3.5–0 cal kyr BP). During that period, the precipitation at Badain Jaran Desert may have reached 200 mm yr^(-1) for 7.7–5.3 cal kyr BP, inferred from both the age and precipitation rate of calcareous root tubes. The water balance calculation shows that wetter and warmer climate and the increase of underground water recharge were key factors in maintaining and developing the lake group at both centennial and millennial time scales. Furthermore, lake surface expansion and the increasing fresh water availability set the background for the prosperous prehistoric culture.展开更多
基金financially supported by the National Science Foundation of China(grant No.41571177)
文摘Objective The lake levels in the eastern and southern Asia are regarded as low lake-level owing to precipitation decreasing based on the records of lake-level fluctuation in the continental interior lakes since the last glacial maximum（LGM）（14C 18±1 kaBP,since 20 kaBP）in the Central Asia.Higher lake-level appeared in the transition belt between western Kunlun Mountain and the central Tibetan Plateau.
基金financially supported by the National Natural Science Foundation of China (41130640, 91425301, 41321001, 41401057)the projects from the State Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing Normal University
文摘Stable isotopic compositions （δ18O and 6D） have been utilized as a useful indicator for evaluating the current and historical climatic and environmental changes. Therefore, it is vital to understand the relationship be- tween the stable isotopic contents in lake water and the variations of lake level, particularly in Lake Qinghai, China. In this study, we analyzed the variations of isotope compositions （δ18O, 6D and d-excess） in lake water and pre- cipitation by using the samples that were collected from Lake Qinghai region during the period from 2009 to 2012. The results showed that the average isotopic contents of δ18O and 6D in lake water were higher than those in pre- cipitation, which were contrary to the variations of d-excess. The linear regression correlations between δ18O and 6D in lake water and precipitation showed that the local evaporative line （LEL） in lake water （δD=5.88δ18O-2.41） deviated significantly from the local meteoric water line （LMWL）in precipitation （δD=8.26δ18O＋16.91）, indicating that evaporative enrichment had a significant impact on isotopic contents in lake water. Moreover, we also quanti- fied the Eli ratio （evaporation-to-input ratio） in Lake Qinghai based on the lake water isotopic enrichment model derived from the Rayleigh equation. The changes of E/I ratios （ranging from 0.29 to 0.36 between 2009 and 2012） clearly revealed the shifts of lake levels in Lake Qinghai in recent years. The average E/I ratio of 0.40 reflected that water budget in Lake Qinghai was positive, and consistent with the rising lake levels and the increasing lake areas in many lakes of the Tibetan Plateau. These findings provide some evidences for studying the hydrological balance or water budget by using δ18O values of lake sedimentary materials and contribute to the reconstruction of paleo- lake water level and paleoclimate from an isotopic enrichment model in Lake Qinghai.
基金supported by the Deep Earth Probe and Mineral Resources Exploration—National Science and Technology Major Project of China(No.2024ZD1001105).
文摘The formation of halite in continental basins is intimately linked to lake-level changes.Current research has revealed the connection between lake-level variations and astronomical forcing on a million-year scale.Other studies have also highlighted the influence of orbitally-induced climate cycles on halite deposition.However,our understanding of the impact of astronomically-paced lake-level changes on halite formation remains constrained.The Paleogene Dawenkou Formation in the Huanggang Basin of East China provides a continuous salt-bearing sedimentary record to investigate the lake-level changes in halite deposition.Lake-level fluctuations reconstructed by sedimentary noise modeling for the Middle and Upper members of the Dawenkou Formation indicate that the lake-level variations in the Huanggang Basin were linked to astronomical forcing with periods of∼2.4 Myr,∼1.2 Myr and/or∼100 kyr.Our results suggest that astronomical forcing,as a driver of lake-level variations,may have had an impact on halite deposition during the Paleogene.In the initial stage of halite formation within the Middle Member of the Dawenkou Formation,reduced heat and moisture transport during the∼1.2 Myr obliquity minima resulted in low lake levels in mid-to-high latitudes.The prolonged droughts caused by the low amplitude of∼2.4 Myr eccentricity created conditions more favorable for the development of thicker layers of halite.Subsequently,in the next halite-forming stage,a larger amplitude of∼2.4 Myr eccentricity led to a more humid climate.Warm/dry winters and cool summers paced by the∼100 kyr orbital eccentricity minima resulted in enhanced evaporation,relatively lower lake levels,and thinner halite deposition.Nevertheless,the possible transgressions may have contributed to complicated phase relationship between the lake-level change cycles and orbital cycles.This study offers an opportunity to delve deeper into the mechanism of halite deposition by objectively reconstructing lake levels using sedimentary noise modeling.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41371114 & 41530745)
文摘Many lakes exist in southeastern Badain Jaran Desert and its hinterland, including 110 perennial lakes and some seasonal or extinct lakes. Geomorphological, sedimentological, and bioglyph evidence obtained from field investigations on Badain Jaran Desert lake group, alongside measurements and dating performed on lake relic, prove that these lakes expanded while the climate was relatively wet during early and middle Holocene. The dating results suggest that the pan-lake period of the Badain Jaran Desert began at 10 cal kyr BP, before which the limnic peat period occurred(11–10 cal kyr BP). Many lakes reached their maximal water-level during 8.6–6.3 cal kyr BP and retreated or dried up in the late Holocene(about 3.5–0 cal kyr BP). During that period, the precipitation at Badain Jaran Desert may have reached 200 mm yr^(-1) for 7.7–5.3 cal kyr BP, inferred from both the age and precipitation rate of calcareous root tubes. The water balance calculation shows that wetter and warmer climate and the increase of underground water recharge were key factors in maintaining and developing the lake group at both centennial and millennial time scales. Furthermore, lake surface expansion and the increasing fresh water availability set the background for the prosperous prehistoric culture.
