Pub Date : 2024-11-23DOI: 10.1016/j.gloplacha.2024.104655
Yunping Song , Hai Xu , Kevin M. Yeager
Understanding the causes of variations in global atmospheric methane concentration (GAMC) is an important issue in the study of global climatic changes. Long-term GAMC varied rhythmically on glacial-interglacial timescales, and broadly followed the orbital/suborbital cycles in northern hemisphere solar insolation. Yet the late Holocene has witnessed an increasing GAMC trend since the mid-Holocene, which decouples with the global atmospheric CO2 concentration trend and the northern hemisphere solar insolation trend. The causes of this decoupling have been extensively studied, but remain highly debated. Here we show that the Holocene GAMC trend closely follows the long-term trend in global low latitude wetland extent as inferred from our lake-level reconstruction and from other existing hydroclimate records. We contend that changes in low latitude wetland extent play an important role in shaping the GAMC trend. We propose that reduced low latitude wetland areas during the mid-Holocene, which were likely due to the submersion of tropical wetlands by rising sea levels, and reduced low latitude wetland areas inferred from lower lake levels, could be responsible for the observed mid-Holocene GAMC drop. Increasing global low latitude wetland areas during the late Holocene are likely responsible for the contemporary increasing GAMC trend.
{"title":"Possible influence of low latitude wetland area changes on the Holocene global atmospheric methane concentration trend","authors":"Yunping Song , Hai Xu , Kevin M. Yeager","doi":"10.1016/j.gloplacha.2024.104655","DOIUrl":"10.1016/j.gloplacha.2024.104655","url":null,"abstract":"<div><div>Understanding the causes of variations in global atmospheric methane concentration (GAMC) is an important issue in the study of global climatic changes. Long-term GAMC varied rhythmically on glacial-interglacial timescales, and broadly followed the orbital/suborbital cycles in northern hemisphere solar insolation. Yet the late Holocene has witnessed an increasing GAMC trend since the mid-Holocene, which decouples with the global atmospheric CO<sub>2</sub> concentration trend and the northern hemisphere solar insolation trend. The causes of this decoupling have been extensively studied, but remain highly debated. Here we show that the Holocene GAMC trend closely follows the long-term trend in global low latitude wetland extent as inferred from our lake-level reconstruction and from other existing hydroclimate records. We contend that changes in low latitude wetland extent play an important role in shaping the GAMC trend. We propose that reduced low latitude wetland areas during the mid-Holocene, which were likely due to the submersion of tropical wetlands by rising sea levels, and reduced low latitude wetland areas inferred from lower lake levels, could be responsible for the observed mid-Holocene GAMC drop. Increasing global low latitude wetland areas during the late Holocene are likely responsible for the contemporary increasing GAMC trend.</div></div>","PeriodicalId":55089,"journal":{"name":"Global and Planetary Change","volume":"244 ","pages":"Article 104655"},"PeriodicalIF":4.0,"publicationDate":"2024-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142721908","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-22DOI: 10.1016/j.gloplacha.2024.104653
Meng Qi , Chengshuai Liu , Ting Gao , Zhengrong Wang , Yuhui Liu , Yafei Xia
Climate controls chemical weathering of silicate rocks on the transport of iron (Fe) and its isotopes from continent to the ocean, impacting the global Fe geochemical cycle. However, it's elusive if Fe isotope fractionation during silicate weathering reflects variations in climate factors. This study examines two granite-derived regolith profiles; one in Beijing (BJ), representing a temperate climate, and the other in Guangdong (GD), representing a tropical climate, to investigate their mineralogy, Fe-bearing phases, element concentrations, and Fe isotope compositions. Our results show that, despite climate differences, the two granite weathering profiles have average δ56Febulk regolith values within analytical uncertainty (0.09 ± 0.02 ‰ vs. 0.12 ± 0.04 ‰, 2SD). The δ56Febulk regolith values of temperate and tropical regolith are similar to or slightly higher than those of their respective bedrocks and remain steady along the entire weathering profile. The limited variation of Fe isotope composition in weakly weathered temperate regolith likely reflects the dissolution of primary minerals rather than the formation of secondary minerals. The Rayleigh fractionation calculations also show a Δ56Fepore solution-regolith value of ∼0 ‰ between pore solution and regolith. In contrast, in the tropical profile, despite the abundance of secondary minerals and the differences in δ56Fe values among the extracted Fe-pools exceeding 0.68 ‰, only limited Fe isotope fractionation is observed in the bulk regolith (0.01 ‰ to 0.24 ‰). These variations are likely driven by the formation of Fe oxides, relying on the atomic distribution of Fe in hematite and goethite. The linear regression analysis estimates the apparent Fe isotope fractionation factor between hematite and goethite as 0.46 ± 0.07 ‰ (Δ56Fehematite-goethite, 1SE). These findings indicate that the sensitivity of Fe isotope fractionation in bulk regolith to variations in climate factors is relatively limited. However, combined with results from other weathering profiles in different climate zones, two models suggest that changes in δ56Fe values of easily leachable and silicate-bound Fe pools are likely influenced by climate factors such as temperature and precipitation. This work advances our understanding of the Fe isotope fractionation during silicate weathering and its potential climate connection on Earth's surface.
{"title":"Iron isotope fractionation during granite weathering under different climates","authors":"Meng Qi , Chengshuai Liu , Ting Gao , Zhengrong Wang , Yuhui Liu , Yafei Xia","doi":"10.1016/j.gloplacha.2024.104653","DOIUrl":"10.1016/j.gloplacha.2024.104653","url":null,"abstract":"<div><div>Climate controls chemical weathering of silicate rocks on the transport of iron (Fe) and its isotopes from continent to the ocean, impacting the global Fe geochemical cycle. However, it's elusive if Fe isotope fractionation during silicate weathering reflects variations in climate factors. This study examines two granite-derived regolith profiles; one in Beijing (BJ), representing a temperate climate, and the other in Guangdong (GD), representing a tropical climate, to investigate their mineralogy, Fe-bearing phases, element concentrations, and Fe isotope compositions. Our results show that, despite climate differences, the two granite weathering profiles have average δ<sup>56</sup>Fe<sub>bulk regolith</sub> values within analytical uncertainty (0.09 ± 0.02 ‰ vs. 0.12 ± 0.04 ‰, 2SD). The δ<sup>56</sup>Fe<sub>bulk regolith</sub> values of temperate and tropical regolith are similar to or slightly higher than those of their respective bedrocks and remain steady along the entire weathering profile. The limited variation of Fe isotope composition in weakly weathered temperate regolith likely reflects the dissolution of primary minerals rather than the formation of secondary minerals. The Rayleigh fractionation calculations also show a Δ<sup>56</sup>Fe<sub>pore solution-regolith</sub> value of ∼0 ‰ between pore solution and regolith. In contrast, in the tropical profile, despite the abundance of secondary minerals and the differences in δ<sup>56</sup>Fe values among the extracted Fe-pools exceeding 0.68 ‰, only limited Fe isotope fractionation is observed in the bulk regolith (0.01 ‰ to 0.24 ‰). These variations are likely driven by the formation of Fe oxides, relying on the atomic distribution of Fe in hematite and goethite. The linear regression analysis estimates the apparent Fe isotope fractionation factor between hematite and goethite as 0.46 ± 0.07 ‰ (Δ<sup>56</sup>Fe<sub>hematite-goethite</sub>, 1SE). These findings indicate that the sensitivity of Fe isotope fractionation in bulk regolith to variations in climate factors is relatively limited. However, combined with results from other weathering profiles in different climate zones, two models suggest that changes in δ<sup>56</sup>Fe values of easily leachable and silicate-bound Fe pools are likely influenced by climate factors such as temperature and precipitation. This work advances our understanding of the Fe isotope fractionation during silicate weathering and its potential climate connection on Earth's surface.</div></div>","PeriodicalId":55089,"journal":{"name":"Global and Planetary Change","volume":"244 ","pages":"Article 104653"},"PeriodicalIF":4.0,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142721909","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-22DOI: 10.1016/j.gloplacha.2024.104645
Omid Alizadeh , Morteza Mousavizadeh
The El Niño-Southern Oscillation (ENSO) is a primary driver of interannual variability in extreme precipitation in many regions worldwide. Understanding the relationship between ENSO and extreme precipitation is crucial, as it has implications for understanding the interannual variability of flood risk. We investigated the frequency of extreme daily precipitation in Southwest Asia across different seasons during El Niño and La Niña using the daily GPCP and ERA5 precipitation datasets for the period 1997–2022. Extreme precipitation at each grid point is defined as daily accumulated precipitation exceeding the 95th percentile on wet days, where a wet day is defined as one with at least 0.1 mm rainfall. El Niño is associated with an overall increase in the frequency of extreme precipitation in Southwest Asia during autumn, winter, and spring, whereas La Niña shows the opposite effect. To explore the dynamics of El Niño and La Niña teleconnections to Southwest Asia, we applied a feature tracking method on the ERA5 relative velocity at 850 hPa in different seasons. Overall, the storm track density and the mean intensity of storms increase in Southwest Asia during El Niño and decrease during La Niña in autumn, winter, and spring. In summer, El Niño favors less frequent extreme precipitation in the southern parts of Southwest Asia, where the tropical summer monsoon circulation is dominated, while La Niña is associated with more frequent extreme precipitation in this region. This pattern is expected, as the monsoon circulation is weaker during El Niño and stronger during La Niña. In line with this, we identified a decrease in the mean intensity of storms in the southern parts of Southwest Asia during El Niño, with the opposite occuring during La Niña. Our findings have important implications for understanding interannual variability of extreme precipitation in Southwest Asia and providing a framework for predicting such events.
{"title":"Impact of ENSO on extreme precipitation in Southwest Asia","authors":"Omid Alizadeh , Morteza Mousavizadeh","doi":"10.1016/j.gloplacha.2024.104645","DOIUrl":"10.1016/j.gloplacha.2024.104645","url":null,"abstract":"<div><div>The El Niño-Southern Oscillation (ENSO) is a primary driver of interannual variability in extreme precipitation in many regions worldwide. Understanding the relationship between ENSO and extreme precipitation is crucial, as it has implications for understanding the interannual variability of flood risk. We investigated the frequency of extreme daily precipitation in Southwest Asia across different seasons during El Niño and La Niña using the daily GPCP and ERA5 precipitation datasets for the period 1997–2022. Extreme precipitation at each grid point is defined as daily accumulated precipitation exceeding the 95th percentile on wet days, where a wet day is defined as one with at least 0.1 mm rainfall. El Niño is associated with an overall increase in the frequency of extreme precipitation in Southwest Asia during autumn, winter, and spring, whereas La Niña shows the opposite effect. To explore the dynamics of El Niño and La Niña teleconnections to Southwest Asia, we applied a feature tracking method on the ERA5 relative velocity at 850 hPa in different seasons. Overall, the storm track density and the mean intensity of storms increase in Southwest Asia during El Niño and decrease during La Niña in autumn, winter, and spring. In summer, El Niño favors less frequent extreme precipitation in the southern parts of Southwest Asia, where the tropical summer monsoon circulation is dominated, while La Niña is associated with more frequent extreme precipitation in this region. This pattern is expected, as the monsoon circulation is weaker during El Niño and stronger during La Niña. In line with this, we identified a decrease in the mean intensity of storms in the southern parts of Southwest Asia during El Niño, with the opposite occuring during La Niña. Our findings have important implications for understanding interannual variability of extreme precipitation in Southwest Asia and providing a framework for predicting such events.</div></div>","PeriodicalId":55089,"journal":{"name":"Global and Planetary Change","volume":"244 ","pages":"Article 104645"},"PeriodicalIF":4.0,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142700875","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Microbial sulfate reduction (MSR) and associated pyritic sulfide formation are important diagenetic processes in marine sediments. The sulfur isotopic composition of pyrite (δ34Spyr) is proven to be sensitive to changes in sedimentation rates and the content and reactivity of organic carbon, especially on the continental shelves and upper slopes (water depth < 350 m). However, the diagenetic responses of sulfur to variations in climatic and depositional conditions in the deep-sea sediments are still poorly understood. This study combines element contents and isotopes to characterize diagenetic interplays of sulfur, organic carbon, and methane in the continental slope sediments of the northern South China Sea since the mid-Pleistocene. Our data suggest that the total organic carbon (TOC) increased during glacial times, implying enhanced primary productivity due to increased nutrient supply by the East Asian Winter Monsoon, in addition to efficient transfer of organic carbon and better preservation of organic carbon due to reduced bottom water oxygen. Total sulfur and chromium reduction sulfur contents varied concomitantly with the TOC, suggesting an increased burial of organic carbon that enhanced the organoclastic sulfate reduction (OSR) and the formation of authigenic pyrite. The environmental changes did not induce a significant shift in δ34Spyr, due most likely to relatively low sedimentation rates and large fractionation in sulfur isotope through OSR during the glacial-interglacial cycles. Instead, it is hypothesized that the sulfate-driven anaerobic methane oxidation promoted the formation of a higher amount of authigenic pyrite. Consequently, it created a closed diagenetic system leading to positive excursions in δ34Spyr at the sulfate-methane transition zone. Our results suggest the vulnerability of pyrite formation and its sulfur isotopic composition to the changes in monsoon-driven primary productivity and the methane-rich fluid migrations in the continental margin sediments. This study complements the growing evidence for the local diagenetic controls on sedimentary sulfur geochemical records by highlighting the importance of early diagenesis in paleoenvironment reconstruction based on the content and sulfur isotopic composition of pyrite.
{"title":"Effects of climate change and methane-rich fluid activity on sedimentary sulfur geochemical records in the northern South China Sea since mid-Pleistocene","authors":"Junxi Feng , Yufei Zhang , Niu Li , Jianhou Zhou , Jinqiang Liang , Qianyong Liang , Shengxiong Yang , Duofu Chen , Harunur Rashid","doi":"10.1016/j.gloplacha.2024.104644","DOIUrl":"10.1016/j.gloplacha.2024.104644","url":null,"abstract":"<div><div>Microbial sulfate reduction (MSR) and associated pyritic sulfide formation are important diagenetic processes in marine sediments. The sulfur isotopic composition of pyrite (δ<sup>34</sup>S<sub>pyr</sub>) is proven to be sensitive to changes in sedimentation rates and the content and reactivity of organic carbon, especially on the continental shelves and upper slopes (water depth < 350 m). However, the diagenetic responses of sulfur to variations in climatic and depositional conditions in the deep-sea sediments are still poorly understood. This study combines element contents and isotopes to characterize diagenetic interplays of sulfur, organic carbon, and methane in the continental slope sediments of the northern South China Sea since the mid-Pleistocene. Our data suggest that the total organic carbon (TOC) increased during glacial times, implying enhanced primary productivity due to increased nutrient supply by the East Asian Winter Monsoon, in addition to efficient transfer of organic carbon and better preservation of organic carbon due to reduced bottom water oxygen. Total sulfur and chromium reduction sulfur contents varied concomitantly with the TOC, suggesting an increased burial of organic carbon that enhanced the organoclastic sulfate reduction (OSR) and the formation of authigenic pyrite. The environmental changes did not induce a significant shift in δ<sup>34</sup>S<sub>pyr</sub>, due most likely to relatively low sedimentation rates and large fractionation in sulfur isotope through OSR during the glacial-interglacial cycles. Instead, it is hypothesized that the sulfate-driven anaerobic methane oxidation promoted the formation of a higher amount of authigenic pyrite. Consequently, it created a closed diagenetic system leading to positive excursions in δ<sup>34</sup>S<sub>pyr</sub> at the sulfate-methane transition zone. Our results suggest the vulnerability of pyrite formation and its sulfur isotopic composition to the changes in monsoon-driven primary productivity and the methane-rich fluid migrations in the continental margin sediments. This study complements the growing evidence for the local diagenetic controls on sedimentary sulfur geochemical records by highlighting the importance of early diagenesis in paleoenvironment reconstruction based on the content and sulfur isotopic composition of pyrite.</div></div>","PeriodicalId":55089,"journal":{"name":"Global and Planetary Change","volume":"244 ","pages":"Article 104644"},"PeriodicalIF":4.0,"publicationDate":"2024-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142700893","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Recent high-resolution sediment records, such as Greenland ice cores and Chinese stalagmites, have greatly enhanced our understanding of millennial-scale climate variability during Heinrich Stadials (HSs) of the Last Glacial Period, particularly highlighting the diminished intensity of the Asian Summer Monsoon (ASM). These records reveal precise temporal correlations between high-latitude climate changes and low-latitude monsoon variability, especially in the Asian monsoon region. However, the scarcity of stalagmite records from southeastern China has limited our understanding of the spatio-temporal patterns of monsoonal precipitation variability during these abrupt climate events, as most published records are concentrated in central-northern and southwestern China. In this study, we present a high-resolution hydroclimate reconstruction based on stalagmite YXG01 from Yindi Cave, Hubei Province, China, using 42 U-Th dates and 698 δ18O and δ13C isotope measurements, spanning the 11.92–47.47 ka BP interval. Our δ18O record shows four positive excursions, indicating significantly weakened ASM intensity during the four most recent HSs (HS1 to HS4), consistent with previous studies. During these HSs, freshwater influx into the North Atlantic weakened the Atlantic Meridional Overturning Circulation, cooled Northern Hemisphere temperatures, and reduced ASM circulation/intensity, resulting in consistent positive δ18O shifts in precipitation and stalagmites across the East Asian monsoon region. We found that the amplitude of stalagmite δ18O variations during the HSs decreases progressively from Southwest China to Southeast China, a trend that aligns with simulated changes in precipitation δ18O. The smaller amplitude of δ18O shifts in southeastern China during the HSs may be linked to increased moisture contributions from the western Pacific Ocean and enhanced local precipitation. During these HSs, anti-phased variations between YXG01 δ18O and δ13C, together with temperature reconstructions and model simulations, suggest favorable hydroclimatic conditions in the mid-lower reaches of the Yangtze River Valley. Increased precipitation and moderate temperature may have enhanced vegetation growth, resulting in lower speleothem δ13C values despite the overall weakening of ASM circulation. Our new speleothem YXG01 record reveals two important observations from Southeast China: a smaller amplitude of speleothem δ18O shifts and anti-phased δ18O and δ13C variations during the HSs. Further model simulations are necessary to fully explore the underlying climate dynamics driving these patterns.
{"title":"Stalagmite records of spatiotemporal hydroclimatic variations in monsoonal China during 47–12 ka BP","authors":"Miaomiao Wang, Haiwei Zhang, Youwei Li, Rui Zhang, Jian Wang, Hanying Li, Yuteng Zhao, Xiaomei Zhang, Zeyuan Liang, Youfeng Ning, Hai Cheng","doi":"10.1016/j.gloplacha.2024.104639","DOIUrl":"10.1016/j.gloplacha.2024.104639","url":null,"abstract":"<div><div>Recent high-resolution sediment records, such as Greenland ice cores and Chinese stalagmites, have greatly enhanced our understanding of millennial-scale climate variability during Heinrich Stadials (HSs) of the Last Glacial Period, particularly highlighting the diminished intensity of the Asian Summer Monsoon (ASM). These records reveal precise temporal correlations between high-latitude climate changes and low-latitude monsoon variability, especially in the Asian monsoon region. However, the scarcity of stalagmite records from southeastern China has limited our understanding of the spatio-temporal patterns of monsoonal precipitation variability during these abrupt climate events, as most published records are concentrated in central-northern and southwestern China. In this study, we present a high-resolution hydroclimate reconstruction based on stalagmite YXG01 from Yindi Cave, Hubei Province, China, using 42 U-Th dates and 698 δ<sup>18</sup>O and δ<sup>13</sup>C isotope measurements, spanning the 11.92–47.47 ka BP interval. Our δ<sup>18</sup>O record shows four positive excursions, indicating significantly weakened ASM intensity during the four most recent HSs (HS1 to HS4), consistent with previous studies. During these HSs, freshwater influx into the North Atlantic weakened the Atlantic Meridional Overturning Circulation, cooled Northern Hemisphere temperatures, and reduced ASM circulation/intensity, resulting in consistent positive δ<sup>18</sup>O shifts in precipitation and stalagmites across the East Asian monsoon region. We found that the amplitude of stalagmite δ<sup>18</sup>O variations during the HSs decreases progressively from Southwest China to Southeast China, a trend that aligns with simulated changes in precipitation δ<sup>18</sup>O. The smaller amplitude of δ<sup>18</sup>O shifts in southeastern China during the HSs may be linked to increased moisture contributions from the western Pacific Ocean and enhanced local precipitation. During these HSs, anti-phased variations between YXG01 δ<sup>18</sup>O and δ<sup>13</sup>C, together with temperature reconstructions and model simulations, suggest favorable hydroclimatic conditions in the mid-lower reaches of the Yangtze River Valley. Increased precipitation and moderate temperature may have enhanced vegetation growth, resulting in lower speleothem δ<sup>13</sup>C values despite the overall weakening of ASM circulation. Our new speleothem YXG01 record reveals two important observations from Southeast China: a smaller amplitude of speleothem δ<sup>18</sup>O shifts and anti-phased δ<sup>18</sup>O and δ<sup>13</sup>C variations during the HSs. Further model simulations are necessary to fully explore the underlying climate dynamics driving these patterns.</div></div>","PeriodicalId":55089,"journal":{"name":"Global and Planetary Change","volume":"244 ","pages":"Article 104639"},"PeriodicalIF":4.0,"publicationDate":"2024-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142718380","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-19DOI: 10.1016/j.gloplacha.2024.104642
Jiang Yi-ao Zhang , Xiaotong Xiao , Ruediger Stein , Wenshen Xiao , Rujian Wang , Yang Ding , Lupeng Nie , Meixun Zhao
Sea ice is an essential component in polar regions and plays an important role in global climate changes. Knowing sea-ice variabilities on long-term time scales is critical to understand the rapid sea-ice decline in recent decades and to predict future Arctic changes. In this study, a suite of biomarkers including highly branched isoprenoids (IP25 and HBI III (Z)) and sterols (brassicasterol and dinosterol) were measured in 55 surface sediments from the Bering-Chukchi Sea to central Arctic Ocean transect. PIP25 indices were calculated with sea-ice biomarker IP25 and phytoplankton biomarkers (brassicasterol, dinosterol and HBI III (Z)). The new data were combined with published data (n = 875) to complete the pan-Arctic dataset of biomarkers (n = 1062) in surface sediments. The compiled extended total data in general support previous pan-Arctic PIP25 studies and by this the reliability of the PIP25 approach for (paleo) sea-ice reconstructions. Furthermore, this study provides an extended basis for semi-quantitative paleo-sea-ice reconstruction in different regions of the Arctic Ocean. Phytoplankton biomarkers HBI III (Z) display highest values near the winter sea ice (WSI) edge in the pan-Arctic, reflecting the ice-edge conditions. PIIIIP25 show significant correlations with satellite spring/summer and autumn sea-ice concentration in the Pacific Sector of the pan-Arctic dataset (Bering-Chukchi Sea shelves, Chukchi Borderland and Canada Basin), and with spring/autumn sea-ice concentration in the Atlantic sector of the pan-Arctic dataset (Fram Strait, East Greenland shelf and Barents Sea). PIIIIP25 index seems to be reliable to reconstruct the paleo-sea-ice conditions in the Pan-Arctic, as well as PBIP25 and PDIP25 (using brassicasterol and dinosterol as phytoplankton biomarker, respectively). Furthermore, regional calibrations of comprehensive biomarker and PIP25 datasets against known sea-ice conditions would add further confidence in their application for paleo-sea-ice reconstruction. Based on our extended HBI III dataset we did not find that the HBI TR25 index was a reliable proxy for phytoplankton spring blooms on pan-Arctic scales. Certainly, deciphering the origin of certain biomarkers (e.g. HBI III (Z) and (E)) is still crucial for their application in further validation of PIP25 and TR25 indices application.
{"title":"New Sea-ice biomarker data from Bering-Chukchi Sea surface sediments and its significance for pan-Arctic proxy-based sea-ice reconstruction","authors":"Jiang Yi-ao Zhang , Xiaotong Xiao , Ruediger Stein , Wenshen Xiao , Rujian Wang , Yang Ding , Lupeng Nie , Meixun Zhao","doi":"10.1016/j.gloplacha.2024.104642","DOIUrl":"10.1016/j.gloplacha.2024.104642","url":null,"abstract":"<div><div>Sea ice is an essential component in polar regions and plays an important role in global climate changes. Knowing sea-ice variabilities on long-term time scales is critical to understand the rapid sea-ice decline in recent decades and to predict future Arctic changes. In this study, a suite of biomarkers including highly branched isoprenoids (IP<sub>25</sub> and HBI III (Z)) and sterols (brassicasterol and dinosterol) were measured in 55 surface sediments from the Bering-Chukchi Sea to central Arctic Ocean transect. PIP<sub>25</sub> indices were calculated with sea-ice biomarker IP<sub>25</sub> and phytoplankton biomarkers (brassicasterol, dinosterol and HBI III (Z)). The new data were combined with published data (<em>n</em> = 875) to complete the pan-Arctic dataset of biomarkers (<em>n</em> = 1062) in surface sediments. The compiled extended total data in general support previous pan-Arctic PIP<sub>25</sub> studies and by this the reliability of the PIP<sub>25</sub> approach for (paleo) sea-ice reconstructions. Furthermore, this study provides an extended basis for semi-quantitative paleo-sea-ice reconstruction in different regions of the Arctic Ocean. Phytoplankton biomarkers HBI III (Z) display highest values near the winter sea ice (WSI) edge in the pan-Arctic, reflecting the ice-edge conditions. P<sub>III</sub>IP<sub>25</sub> show significant correlations with satellite spring/summer and autumn sea-ice concentration in the Pacific Sector of the pan-Arctic dataset (Bering-Chukchi Sea shelves, Chukchi Borderland and Canada Basin), and with spring/autumn sea-ice concentration in the Atlantic sector of the pan-Arctic dataset (Fram Strait, East Greenland shelf and Barents Sea). P<sub>III</sub>IP<sub>25</sub> index seems to be reliable to reconstruct the paleo-sea-ice conditions in the Pan-Arctic, as well as P<sub>B</sub>IP<sub>25</sub> and P<sub>D</sub>IP<sub>25</sub> (using brassicasterol and dinosterol as phytoplankton biomarker, respectively). Furthermore, regional calibrations of comprehensive biomarker and PIP<sub>25</sub> datasets against known sea-ice conditions would add further confidence in their application for paleo-sea-ice reconstruction. Based on our extended HBI III dataset we did not find that the HBI TR<sub>25</sub> index was a reliable proxy for phytoplankton spring blooms on pan-Arctic scales. Certainly, deciphering the origin of certain biomarkers (e.g. HBI III (Z) and (E)) is still crucial for their application in further validation of PIP<sub>25</sub> and TR<sub>25</sub> indices application.</div></div>","PeriodicalId":55089,"journal":{"name":"Global and Planetary Change","volume":"244 ","pages":"Article 104642"},"PeriodicalIF":4.0,"publicationDate":"2024-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142700876","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-19DOI: 10.1016/j.gloplacha.2024.104640
Lin Chen , Youliang Huang , Menghan Qiu , Zhilun Li , Rui Yang , Mengjing Li , Huiling Sun , Lixiong Xiang , Shanjia Zhang , Xiaozhong Huang , Aifeng Zhou
The dual pressures of global warming and increased anthropogenic activities pose significant threats to terrestrial vegetation ecosystems. To better understand the impacts of climate change and human activities on terrestrial vegetation ecosystems, we reconstructed the changes in vegetation and plant biomass over the past 4500 years using n-alkane records from sediments of two alpine lakes in northwestern China: Xiannv Lake and Tianchi Lake. Our results indicate that changes in the spatial variability of plant biomass are not related to temperature and precipitation. Furthermore, CO2 fertilization and nutrient inputs from dust contributed to the observed changes in plant biomass. We also compared the history of human activities in the Tianshan Mountains, the eastern Silk Road, and the Hunsandak Sandy Land, and find that the demand for plant resources—whether for human settlement, military construction, or warfare—may have caused a sudden decline in terrestrial vegetation, thereby disrupting the positive effects of dust on plant biomass growth.
{"title":"Human settlement and destructive activities disrupt the positive contribution of dust to plant biomass growth over the past 2000 years","authors":"Lin Chen , Youliang Huang , Menghan Qiu , Zhilun Li , Rui Yang , Mengjing Li , Huiling Sun , Lixiong Xiang , Shanjia Zhang , Xiaozhong Huang , Aifeng Zhou","doi":"10.1016/j.gloplacha.2024.104640","DOIUrl":"10.1016/j.gloplacha.2024.104640","url":null,"abstract":"<div><div>The dual pressures of global warming and increased anthropogenic activities pose significant threats to terrestrial vegetation ecosystems. To better understand the impacts of climate change and human activities on terrestrial vegetation ecosystems, we reconstructed the changes in vegetation and plant biomass over the past 4500 years using <em>n</em>-alkane records from sediments of two alpine lakes in northwestern China: Xiannv Lake and Tianchi Lake. Our results indicate that changes in the spatial variability of plant biomass are not related to temperature and precipitation. Furthermore, CO<sub>2</sub> fertilization and nutrient inputs from dust contributed to the observed changes in plant biomass. We also compared the history of human activities in the Tianshan Mountains, the eastern Silk Road, and the Hunsandak Sandy Land, and find that the demand for plant resources—whether for human settlement, military construction, or warfare—may have caused a sudden decline in terrestrial vegetation, thereby disrupting the positive effects of dust on plant biomass growth.</div></div>","PeriodicalId":55089,"journal":{"name":"Global and Planetary Change","volume":"244 ","pages":"Article 104640"},"PeriodicalIF":4.0,"publicationDate":"2024-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142700915","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-17DOI: 10.1016/j.gloplacha.2024.104636
Yanan Zhang , Gang Li , Jimin Yu , Yi Zhong , Jianghui Du , Xun Gong , Xiaodong Jiang , Congcong Gai , Shiying Li , Qingsong Liu
Despite its critical role in regulating the global climate and carbon cycle, the evolution of deep Pacific circulation has not been fully deciphered during the last glacial cycle. The effect of deep Pacific hydrographic change (e.g. oxygenation and circulation) on atmospheric CO2 variation is still uncertain. Here, we study redox-sensitive elements including V-U-Mn and benthic foraminiferal δ13C at the HYIV2015-B9 site in the southern South China Sea (SCS) to reconstruct the oxygenation and δ13C signals of water masses during the last glacial cycle. The intra-basin benthic foraminiferal δ13C gradient suggests enhanced stratification of the deep Pacific during the glacial compared to the interglacial, implying sluggish abyssal Pacific overturning. This is consistent with weak Pacific Deep Water (PDW) ventilation, as indicated by high contents of authigenic V and U, and low authigenic Mn. The inferred sluggish abyssal Pacific overturning is probably associated with less transport of Lower Circumpolar Deep Water, facilitating the expansion of respired carbon storage in the glacial deep Pacific. Meanwhile, the atmospheric CO2 rise is closely related to active abyssal Pacific overturning since late MIS 5, particularly when considering the impact of Southern Ocean upwelling modulated by Earth's obliquity. Overall, our data indicate the critical role of abyssal Pacific overturning in the carbon cycle, revealing the potential pathway for deep carbon dioxide outgassing in the North Pacific.
尽管太平洋深层环流在调节全球气候和碳循环方面起着至关重要的作用，但在上一个冰川周期期间，太平洋深层环流的演变尚未完全被破解。太平洋深层水文变化（如含氧量和环流）对大气二氧化碳变化的影响仍不确定。在此，我们研究了中国南海南部HYIV2015-B9站点的氧化还原敏感元素（包括V-U-Mn）和底栖有孔虫δ13C，以重建上一个冰川周期期间水团的含氧量和δ13C信号。盆地内底栖有孔虫的δ13C梯度表明，与间冰期相比，冰川期太平洋深层的分层作用增强，这意味着太平洋深海翻腾作用减弱。这与太平洋深水（PDW）通气较弱是一致的，高自生 V 和 U 含量以及低自生 Mn 含量表明了这一点。推断出的太平洋深海翻腾缓慢可能与下极圈深水的输送较少有关，从而促进了太平洋冰川深海呼吸碳储存的扩大。同时，大气中二氧化碳的上升与自 MIS 5 晚期以来活跃的太平洋深海翻腾密切相关，特别是在考虑到南大洋上涌受地球纬度影响的情况下。总之，我们的数据表明了太平洋深海翻腾在碳循环中的关键作用，揭示了北太平洋深海二氧化碳排气的潜在途径。
{"title":"Response of atmospheric CO2 changes to the Abyssal Pacific overturning during the last glacial cycle","authors":"Yanan Zhang , Gang Li , Jimin Yu , Yi Zhong , Jianghui Du , Xun Gong , Xiaodong Jiang , Congcong Gai , Shiying Li , Qingsong Liu","doi":"10.1016/j.gloplacha.2024.104636","DOIUrl":"10.1016/j.gloplacha.2024.104636","url":null,"abstract":"<div><div>Despite its critical role in regulating the global climate and carbon cycle, the evolution of deep Pacific circulation has not been fully deciphered during the last glacial cycle. The effect of deep Pacific hydrographic change (e.g. oxygenation and circulation) on atmospheric CO<sub>2</sub> variation is still uncertain. Here, we study redox-sensitive elements including V-U-Mn and benthic foraminiferal δ<sup>13</sup>C at the HYIV2015-B9 site in the southern South China Sea (SCS) to reconstruct the oxygenation and δ<sup>13</sup>C signals of water masses during the last glacial cycle. The intra-basin benthic foraminiferal δ<sup>13</sup>C gradient suggests enhanced stratification of the deep Pacific during the glacial compared to the interglacial, implying sluggish abyssal Pacific overturning. This is consistent with weak Pacific Deep Water (PDW) ventilation, as indicated by high contents of authigenic V and U, and low authigenic Mn. The inferred sluggish abyssal Pacific overturning is probably associated with less transport of Lower Circumpolar Deep Water, facilitating the expansion of respired carbon storage in the glacial deep Pacific. Meanwhile, the atmospheric CO<sub>2</sub> rise is closely related to active abyssal Pacific overturning since late MIS 5, particularly when considering the impact of Southern Ocean upwelling modulated by Earth's obliquity. Overall, our data indicate the critical role of abyssal Pacific overturning in the carbon cycle, revealing the potential pathway for deep carbon dioxide outgassing in the North Pacific.</div></div>","PeriodicalId":55089,"journal":{"name":"Global and Planetary Change","volume":"244 ","pages":"Article 104636"},"PeriodicalIF":4.0,"publicationDate":"2024-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142700916","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-17DOI: 10.1016/j.gloplacha.2024.104634
Yixuan Zhu , Zhoutao Zheng , Guang Zhao , Juntao Zhu , Bo Zhao , Yihan Sun , Jie Gao , Yangjian Zhang
Evapotranspiration (ET) is a crucial component of both the water cycle and energy balance, with vegetation being a key factor influencing ET. Vegetation impacts ET primarily through two modes: vegetation growth change (VGC) and vegetation type conversion (VTC). Despite the different mechanisms by which VGC and VTC influence ET, previous studies have rarely differentiated their individual effects. This has left the relative contributions of VGC and VTC to ET changes unclear. To address this gap, this study focuses on the arid and semi-arid regions of China (ASAC), where substantial vegetation changes have been observed. The spatiotemporal patterns of ET in ASAC were analyzed using remote sensing ET data from 2001 to 2018. The leaf area index (LAI) and land use/land cover (LULC) data were incorporated to perform pairwise comparison and contribution analysis to investigate the specific effects of VGC and VTC on ET. The results revealed a significant increase in mean annual ET across ASAC, with a rate of 4.5 mm/yr (p < 0.05). This increase was more pronounced in forest land and cropland compared to grasslands. ET increased across all seasons, with the largest increase occurring in summer, accounting for approximately 50 % of the annual ET increment. The pairwise comparison and contribution analysis indicated that ET in ASAC is more sensitive to vegetation greening than to VTC. VTC played a moderating role in ET changes, with relative contribution ranging from 1.3 % to 57.8 % across different LULC change types. These findings enhance our understanding of how vegetation changes influence ET. They can also provide valuable insights for land management strategies in ASAC, aiming to optimize vegetation construction and promote ecosystems sustainability.
{"title":"Evapotranspiration increase is more sensitive to vegetation greening than to vegetation type conversion in arid and semi-arid regions of China","authors":"Yixuan Zhu , Zhoutao Zheng , Guang Zhao , Juntao Zhu , Bo Zhao , Yihan Sun , Jie Gao , Yangjian Zhang","doi":"10.1016/j.gloplacha.2024.104634","DOIUrl":"10.1016/j.gloplacha.2024.104634","url":null,"abstract":"<div><div>Evapotranspiration (ET) is a crucial component of both the water cycle and energy balance, with vegetation being a key factor influencing ET. Vegetation impacts ET primarily through two modes: vegetation growth change (VGC) and vegetation type conversion (VTC). Despite the different mechanisms by which VGC and VTC influence ET, previous studies have rarely differentiated their individual effects. This has left the relative contributions of VGC and VTC to ET changes unclear. To address this gap, this study focuses on the arid and semi-arid regions of China (ASAC), where substantial vegetation changes have been observed. The spatiotemporal patterns of ET in ASAC were analyzed using remote sensing ET data from 2001 to 2018. The leaf area index (LAI) and land use/land cover (LULC) data were incorporated to perform pairwise comparison and contribution analysis to investigate the specific effects of VGC and VTC on ET. The results revealed a significant increase in mean annual ET across ASAC, with a rate of 4.5 mm/yr (<em>p</em> < 0.05). This increase was more pronounced in forest land and cropland compared to grasslands. ET increased across all seasons, with the largest increase occurring in summer, accounting for approximately 50 % of the annual ET increment. The pairwise comparison and contribution analysis indicated that ET in ASAC is more sensitive to vegetation greening than to VTC. VTC played a moderating role in ET changes, with relative contribution ranging from 1.3 % to 57.8 % across different LULC change types. These findings enhance our understanding of how vegetation changes influence ET. They can also provide valuable insights for land management strategies in ASAC, aiming to optimize vegetation construction and promote ecosystems sustainability.</div></div>","PeriodicalId":55089,"journal":{"name":"Global and Planetary Change","volume":"244 ","pages":"Article 104634"},"PeriodicalIF":4.0,"publicationDate":"2024-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142672809","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-17DOI: 10.1016/j.gloplacha.2024.104638
Xiaoling Wu , Chenglai Wu , Zhaohui Lin , Mingzhu Yang
Dust activity in East Asia has shown multi-scale temporal variations in the past. Many studies have been devoted to the interannual variations of dust activity, but little attention is paid to its variations at the intra-seasonal scale and our knowledge on this is still limited. Several dust storms have occurred over East Asia in spring 2023, which is taken as a good example for us to explore the intra-seasonal variations of dust activity. Based on station observations of dust events, meteorology reanalysis, and satellite observations of surface vegetation cover, here we find that there is much difference in dust storm activity between March and April of 2023 in terms of both the location and intensity. Dust storms mainly occurred in the central and eastern parts of Inner Mongolia and in the central and northern parts of Tarim Basin in March. In contrast, they mainly occurred in the western part of Inner Mongolia, eastern part of Northwest China, and a large region of Tarim Basin. For the regional mean number of dust storm days (NDS), it is significantly higher than the climatological mean value of 2003–2022 in April but lower for March of 2023. Further analysis reveals that the frequency of strong wind is below (above) the climatological mean for March (April) in the Tarim Basin and Gobi Deserts, indicating that wind speed may play a key role in the intra-seasonal variations of dust storm activity, although its effect is offset or enhanced by that of soil moisture and vegetation cover to a lesser extent. The shift of wind field is closely related to the evolution of geopotential height from positive anomaly in March to negative anomaly in April in Mongolia Plateau and southern Central Siberia at 500 hPa. Overall these results highlight the intra-seasonal variation of dust activity in spring 2023 in East Asia and the essential role of associated atmospheric circulation in driving this.
{"title":"Intra-seasonal variations of dust activity over East Asia in spring 2023 and their mechanisms","authors":"Xiaoling Wu , Chenglai Wu , Zhaohui Lin , Mingzhu Yang","doi":"10.1016/j.gloplacha.2024.104638","DOIUrl":"10.1016/j.gloplacha.2024.104638","url":null,"abstract":"<div><div>Dust activity in East Asia has shown multi-scale temporal variations in the past. Many studies have been devoted to the interannual variations of dust activity, but little attention is paid to its variations at the intra-seasonal scale and our knowledge on this is still limited. Several dust storms have occurred over East Asia in spring 2023, which is taken as a good example for us to explore the intra-seasonal variations of dust activity. Based on station observations of dust events, meteorology reanalysis, and satellite observations of surface vegetation cover, here we find that there is much difference in dust storm activity between March and April of 2023 in terms of both the location and intensity. Dust storms mainly occurred in the central and eastern parts of Inner Mongolia and in the central and northern parts of Tarim Basin in March. In contrast, they mainly occurred in the western part of Inner Mongolia, eastern part of Northwest China, and a large region of Tarim Basin. For the regional mean number of dust storm days (N<sub>DS</sub>), it is significantly higher than the climatological mean value of 2003–2022 in April but lower for March of 2023. Further analysis reveals that the frequency of strong wind is below (above) the climatological mean for March (April) in the Tarim Basin and Gobi Deserts, indicating that wind speed may play a key role in the intra-seasonal variations of dust storm activity, although its effect is offset or enhanced by that of soil moisture and vegetation cover to a lesser extent. The shift of wind field is closely related to the evolution of geopotential height from positive anomaly in March to negative anomaly in April in Mongolia Plateau and southern Central Siberia at 500 hPa. Overall these results highlight the intra-seasonal variation of dust activity in spring 2023 in East Asia and the essential role of associated atmospheric circulation in driving this.</div></div>","PeriodicalId":55089,"journal":{"name":"Global and Planetary Change","volume":"244 ","pages":"Article 104638"},"PeriodicalIF":4.0,"publicationDate":"2024-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142700892","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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