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Qian Wang - One of the best experts on this subject based on the ideXlab platform.
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effects of natural and anthropogenic changes on testate amoebae communities in an Alpine Lake over the past 2500 years
Science of The Total Environment, 2020Co-Authors: Jean Claude Ndayishimiye, Qian Wang, Xiangdong Yang, Pascaline Nyirabuhoro, Jun YangAbstract:Abstract Deep high-altitude mountain Lakes can act as a natural laboratory, and have the potential to contribute ecological data for understanding the way natural climate and anthropogenic changes that can affect the ecosystems. We present a multi-proxy record from a sediment core from such a Lake (Lake Lugu) in southwest China with emphasis on the changes in the testate amoebae community, along with sedimentological data (magnetic susceptibility, total organic carbon/TOC and total nitrogen/TN) over the last 2500 years. In total, 29 testate amoebae species belonging to eight genera (Arcella, Centropyxis, Cyphoderia, Difflugia, Netzelia, Phryganella, Pseudodifflugia and Zivkovicia) were identified. Three stages were clearly defined for the Lake based on testate amoebae community. The first stage dated to about 500 BCE–800 CE, with the testate amoebae community dominated by Centropyxis and influenced by soil erosion. The second stage (about 800–1920 CE) was characterized by a gradual increase of TOC and TN and an abrupt shift from Centropyxis-dominated to Difflugia-dominated communities. The third stage (about 1920–2010 CE) showed the pronounced impact of environmental change, high proliferation of Difflugia and a strong influence of human activities. Our results suggest that the testate amoebae assemblages in this high-altitude mountain Lake are sensitive paleoenvironmental indicators that can help to monitor Alpine Lake ecosystem change and model Lake succession under changing climate and environment. The potential causes of changes in the testate amoebae species composition and three stages of Lake Lugu succession were soil erosion and pollutants. The soil erosion led to the inwash of terrestrial particles and few testate amoebae species into Lake Lugu showing the importance of stochastic processes. The nutrient enrichment from soil erosion generated disturbances in the environment and species competition that led to the proliferation of some species and disappearance of others through niche based deterministic processes.
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temperature variations since 1750 ce inferred from an Alpine Lake in the southeastern margin of the tibetan plateau
Quaternary International, 2017Co-Authors: Jingjing Li, Qian Wang, Xiangdong Yang, Lingyang Kong, Huan Yang, Ji Shen, Cheng ZhaoAbstract:Abstract High-altitude regions are thought to be very sensitive to global climate change, especially under current global warming. However, due to the lack of paleoclimate archives such as ice core and tree-rings above the modern tree line, limited paleoclimate data have been extracted to extend instrumental data over the past few centuries, which will help understand the interannual-to decadal-scale climate variability in high-altitude regions. Here we present a high-resolution (1–6 yr) quantitative temperature record from a remote Alpine Lake at the southeastern margin of the Tibetan Plateau, by applying a novel proxy based on branched glycerol dialkyl glycerol tetraethers (brGDGTs). Contrary to the often-documented warming trend over the past few centuries, but consistent with temperature record from the northern Tibetan Plateau, our data show a gradual decreasing trend of 0.3 °C in mean annual air temperature from 1750 to 1970 CE. This result suggests a gradual cooling trend in some high altitude regions over this interval, which could provide a new explanation for the observed decreasing Asian summer monsoon. In addition, our data indicate an abruptly increased interannual-to decadal-scale temperature variations of 0.8–2.2 °C after 1970 CE, in terms of both magnitude and frequency, indicating that the climate system in high altitude regions would become more unstable under current global warming.
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direct versus indirect climate controls on holocene diatom assemblages in a sub tropical deep Alpine Lake lugu hu yunnan sw china
Quaternary Research, 2016Co-Authors: Qian Wang, Xiangdong Yang, N J Anderson, Xuhui DongAbstract:The reconstruction of Holocene environmental changes in Lakes on the plateau region of southwest China provides an understanding of how these ecosystems may respond to climate change. Fossil diatom assemblages were investigated from an 11,000-year Lake sediment core from a deep, Alpine Lake (Lugu Hu) in southwest China, an area strongly influenced by the southwest (or the Indian) summer monsoon. Changes in diatom assemblage composition, notably the abundance of the two dominant planktonic species, Cyclotella rhomboideo-elliptica and Cyclostephanos dubius, reflect the effects of climate variability on nutrient dynamics, mediated via thermal stratification (internal nutrient cycling) and catchment-vegetation processes. Statistical analyses of the climate–diatom interactions highlight the strong effect of changing orbitally-induced solar radiation during the Holocene, presumably via its effect on the Lake's thermal budget. In a partial redundancy analysis, climate (solar insolation) and proxies reflecting catchment process (pollen percentages, C/N ratio) were the most important drivers of diatom ecological change, showing the strong effects of climate–catchment–vegetation interactions on Lake functioning. This diatom record reflects long-term ontogeny of the Lake-catchment ecosystem and suggests that climatic changes (both temperature and precipitation) impact Lake ecology indirectly through shifts in thermal stratification and catchment nutrient exports.
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diatom seasonality and sedimentation in a subtropical Alpine Lake lugu hu yunnan sichuan southwest china
Arctic Antarctic and Alpine Research, 2015Co-Authors: Qian Wang, Xiangdong Yang, John N Anderson, Junfeng JiAbstract:Abstract The diatom succession and sedimentation during 2011 in a subtropical, deep Alpine Lake (Lugu Hu, Southwest China) were studied. The seasonal patterns in diatom assemblages were related to light, nutrient availability, and thermal regime. Peaks in the concentration of the planktonic diatoms (Asterionella formosa and Cyclotella ocellata) occurred in the metalimnion during autumn when light penetration was greater and silica concentrations were higher. The spring peak of Cyclostephanos dubius appeared to be a result of the combination of a well-mixed water column, higher nutrient concentration, and low light availability. Its sedimentation in late spring suggests that the sinking rates of C. dubius increased rapidly with the onset of stratification. However, the minimal catches of A. formosa and C. ocellata in sediment traps during autumn suggest they were still actively growing with very low sedimentation losses. The catch of benthic Fragilaria species in sediment traps during early spring and autu...
Xiangdong Yang - One of the best experts on this subject based on the ideXlab platform.
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effects of natural and anthropogenic changes on testate amoebae communities in an Alpine Lake over the past 2500 years
Science of The Total Environment, 2020Co-Authors: Jean Claude Ndayishimiye, Qian Wang, Xiangdong Yang, Pascaline Nyirabuhoro, Jun YangAbstract:Abstract Deep high-altitude mountain Lakes can act as a natural laboratory, and have the potential to contribute ecological data for understanding the way natural climate and anthropogenic changes that can affect the ecosystems. We present a multi-proxy record from a sediment core from such a Lake (Lake Lugu) in southwest China with emphasis on the changes in the testate amoebae community, along with sedimentological data (magnetic susceptibility, total organic carbon/TOC and total nitrogen/TN) over the last 2500 years. In total, 29 testate amoebae species belonging to eight genera (Arcella, Centropyxis, Cyphoderia, Difflugia, Netzelia, Phryganella, Pseudodifflugia and Zivkovicia) were identified. Three stages were clearly defined for the Lake based on testate amoebae community. The first stage dated to about 500 BCE–800 CE, with the testate amoebae community dominated by Centropyxis and influenced by soil erosion. The second stage (about 800–1920 CE) was characterized by a gradual increase of TOC and TN and an abrupt shift from Centropyxis-dominated to Difflugia-dominated communities. The third stage (about 1920–2010 CE) showed the pronounced impact of environmental change, high proliferation of Difflugia and a strong influence of human activities. Our results suggest that the testate amoebae assemblages in this high-altitude mountain Lake are sensitive paleoenvironmental indicators that can help to monitor Alpine Lake ecosystem change and model Lake succession under changing climate and environment. The potential causes of changes in the testate amoebae species composition and three stages of Lake Lugu succession were soil erosion and pollutants. The soil erosion led to the inwash of terrestrial particles and few testate amoebae species into Lake Lugu showing the importance of stochastic processes. The nutrient enrichment from soil erosion generated disturbances in the environment and species competition that led to the proliferation of some species and disappearance of others through niche based deterministic processes.
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temperature variations since 1750 ce inferred from an Alpine Lake in the southeastern margin of the tibetan plateau
Quaternary International, 2017Co-Authors: Jingjing Li, Qian Wang, Xiangdong Yang, Lingyang Kong, Huan Yang, Ji Shen, Cheng ZhaoAbstract:Abstract High-altitude regions are thought to be very sensitive to global climate change, especially under current global warming. However, due to the lack of paleoclimate archives such as ice core and tree-rings above the modern tree line, limited paleoclimate data have been extracted to extend instrumental data over the past few centuries, which will help understand the interannual-to decadal-scale climate variability in high-altitude regions. Here we present a high-resolution (1–6 yr) quantitative temperature record from a remote Alpine Lake at the southeastern margin of the Tibetan Plateau, by applying a novel proxy based on branched glycerol dialkyl glycerol tetraethers (brGDGTs). Contrary to the often-documented warming trend over the past few centuries, but consistent with temperature record from the northern Tibetan Plateau, our data show a gradual decreasing trend of 0.3 °C in mean annual air temperature from 1750 to 1970 CE. This result suggests a gradual cooling trend in some high altitude regions over this interval, which could provide a new explanation for the observed decreasing Asian summer monsoon. In addition, our data indicate an abruptly increased interannual-to decadal-scale temperature variations of 0.8–2.2 °C after 1970 CE, in terms of both magnitude and frequency, indicating that the climate system in high altitude regions would become more unstable under current global warming.
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the response of cladocerans to recent environmental forcing in an Alpine Lake on the se tibetan plateau
Hydrobiologia, 2017Co-Authors: Lingyang Kong, Xiangdong Yang, Giri Kattel, N J Anderson, Zhujun HuAbstract:Global environmental change has affected aquatic ecosystems of the southeast Tibetan Plateau during the past 200 years, altering the composition and biomass of primary producers (e.g. algae). However, the response of primary consumers (e.g. cladocerans) to this recent environmental forcing is not well documented. Samples of cladoceran remains from sediment traps (1-year deployment), surface sediments covering a range of water depths and a short 22.5-cm sediment core were analysed in a small, remote Alpine Lake (Moon Lake) in Sichuan Province (SW China). Littoral forms, notably Chydorus sphaericus and Acroperus harpae, together with Daphnia pulex dominated the cladoceran community. Remains of these cladocerans were well represented in the sediment core assemblages as indicated by their relative abundance in the surface sample. There was a marked increase in the abundance of D. pulex and total cladoceran fluxes in the sediment core from ca. 1880 AD, coinciding with the changes in diatom assemblages and pigments. Analysis of the multi-proxy data (cladocerans, diatom, pigment, total organic carbon, C/N ratio, air temperature and atmospheric NO3 − records) suggests that both direct and indirect climatic forcing, coupled with enhanced nutrient supply (e.g. NO3 − deposition) effects on primary producers have changed cladoceran community dynamics in Moon Lake over the last ~200 years.
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direct versus indirect climate controls on holocene diatom assemblages in a sub tropical deep Alpine Lake lugu hu yunnan sw china
Quaternary Research, 2016Co-Authors: Qian Wang, Xiangdong Yang, N J Anderson, Xuhui DongAbstract:The reconstruction of Holocene environmental changes in Lakes on the plateau region of southwest China provides an understanding of how these ecosystems may respond to climate change. Fossil diatom assemblages were investigated from an 11,000-year Lake sediment core from a deep, Alpine Lake (Lugu Hu) in southwest China, an area strongly influenced by the southwest (or the Indian) summer monsoon. Changes in diatom assemblage composition, notably the abundance of the two dominant planktonic species, Cyclotella rhomboideo-elliptica and Cyclostephanos dubius, reflect the effects of climate variability on nutrient dynamics, mediated via thermal stratification (internal nutrient cycling) and catchment-vegetation processes. Statistical analyses of the climate–diatom interactions highlight the strong effect of changing orbitally-induced solar radiation during the Holocene, presumably via its effect on the Lake's thermal budget. In a partial redundancy analysis, climate (solar insolation) and proxies reflecting catchment process (pollen percentages, C/N ratio) were the most important drivers of diatom ecological change, showing the strong effects of climate–catchment–vegetation interactions on Lake functioning. This diatom record reflects long-term ontogeny of the Lake-catchment ecosystem and suggests that climatic changes (both temperature and precipitation) impact Lake ecology indirectly through shifts in thermal stratification and catchment nutrient exports.
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climate and tectonic effects on holocene development of an Alpine Lake muge co se margin of tibet
The Holocene, 2016Co-Authors: Xiangdong Yang, John N Anderson, Zhujun Hu, Enlou Zhang, Rong Wang, Richard T JonesAbstract:South-west China is an important area for determining variability of the SW Asian Monsoon; it is, however, also tectonically very active. Palaeolimnological studies in this region generally focus on climate as a direct driver of ecological change, rarely considering the effects of tectonic activity and catchment ontogeny. We present diatom and organic matter data from a Holocene sediment record from Muge Co, an Alpine Lake located on an active fault zone in the southeast margin of Tibet, and explore the possible drivers of ecological change. A major change occurred at 9000 cal. BP, when the diatom assemblage switched from benthic to predominantly planktonic forms, and organic matter content decreased rapidly. Comparison of the Holocene diatom record with a regional data set of Lake surface sediments using detrended canonical correspondence analysis (DCCA) suggests that this change in diatom development was mainly associated with changing water depth, most likely linked to a seismically triggered landslide...
Ulrich Von Grafenstein - One of the best experts on this subject based on the ideXlab platform.
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palaeoecology of late glacial and holocene profundal ostracoda of pre Alpine Lake mondsee austria a base for further palaeo biological research
Palaeogeography Palaeoclimatology Palaeoecology, 2015Co-Authors: Tadeusz Namiotko, Stefan Lauterbach, Achim Brauer, Nils Andersen, Dan L Danielopol, Matthias Huls, Krystyna Milecka, Ulrich Von Grafenstein, Angel Baltanas, Walter GeigerAbstract:Succession of profundal ostracod palaeoassemblages in response to environmental changes during the Late Glacial and Holocene was studied in a similar to 15-m-long sediment sequence from pre-Alpine Lake Mondsee (Austria). First local ostracod assemblage zone LOAZ-1 (prior to 15,700 a BP), with low abundances of Leucocythere mirabilis and Limnocytherina sanctipatricii followed by Cytherissa lacustris, corresponds to the Pleniglacial phase of clastic-detrital sedimentation at relatively high rates. Most of the key species of LOAZ-2 (15,590 to 13,940 a BP, including the Pleniglacial-Late Glacial transition), i.e. limnocytherids, Fabaeformiscandona cf. harmsworthi, F. tricicatricosa, C. lacustris and Candona candida, reveal the significant association with high Al contents and low sedimentation rates and are classified as preferring low-productivity conditions. In contrast, Candona neglecta, dominant in LOAZ-3 (13,820 to 9960 a BP, palynologically defined as Balling-Early Holocene) and in the last LOAZ-4 (9780 a BP to present) as well as Cypria ophtalmica (second key species in LOAZ-4) show relationship with higher productivity, elevated sedimentation rates and decreasing Al contents. Furthermore, valve biodegradation and shape disparity at different time periods and in relation to sedimentation rate changes were investigated in A-3 juveniles of Candona neglecta. The highest percentage of valves biodegraded by Actinobacteria was recorded during the Allerod, Younger Dryas and Early Holocene, when the lowest sedimentation rates occurred, whereas significantly lower frequencies of biodegraded valves were recorded during the mid-Holocene and Late Holocene, when sediment accumulation was much higher. It is also hypothesised that the degree of the valve shape variation was related to the Lake productivity. During the Allerod, Younger Dryas and Early Holocene a valve shape variation significantly lower than that recorded during Late Holocene intervals, characterised by intensified Lake productivity, was observed. Additionally, an agenda of potential questions and approaches that should be considered and form the core of further (palaeo-)biological research projects is offered. (C) 2014 Elsevier B.V. All rights reserved.
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orbital and solar forcing of shifts in mid to late holocene flood intensity from varved sediments of pre Alpine Lake ammersee southern germany
Quaternary Science Reviews, 2013Co-Authors: Markus Czymzik, Achim Brauer, Peter Dulski, Ulrich Von Grafenstein, Birgit Plessen, R Naumann, Raphael SchefflerAbstract:Abstract Microfacies analyses and X-ray fluorescence scanning (μ-XRF) at sub-mm resolution were conducted on the varved Mid- to Late Holocene interval of two sediment profiles from pre-Alpine Lake Ammersee (southern Germany). The coring sites are located in a proximal (AS10prox) and distal (AS10dist) position towards the main tributary River Ammer, in 1.8 km distance from each other. To shed light on sediment distribution within the Lake, particular emphasis was (1) the detection of intercalated detrital layers and their micro-sedimentological features, and (2) intra-basin correlation of these event deposits. Detrital layers were dated by microscopic varve counting, verified by accelerator mass spectrometry 14C dating of terrestrial plant macrofossils. Since ∼5500 varve years (vyr) BP, in total 1573 detrital layers were detected in either one or both of the investigated sediment profiles. Based on their microfacies, geochemistry, and proximal-distal deposition pattern, detrital layers were interpreted as River Ammer flood deposits. Earlier studies on flood layer seasonality have proven that flood layer deposition occurs predominantly during spring and summer, the flood season at Lake Ammersee. Most prominent features of the record are the onset of regular flood layer deposition at ∼5500 vyr BP in AS10prox and ∼2800 vyr BP in AS10dist as well as three major increases in mean flood layer thickness at ∼5500, 2800, and 400 vyr BP. Integrating information from both sediment profiles allowed to interpret these changes in terms of shifts towards higher mean flood intensity. Proposed triggering mechanisms are gradual reduction in Northern Hemisphere orbital summer forcing and superimposed centennial-scale solar activity minima. Likely responses to this forcing are enhanced equator-to-pole temperature gradients and changes in synoptic-scale atmospheric circulation. The consequences for the Ammersee region are more intense cyclones leading to extremer rainfall and flood events in spring and summer.
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environmental responses to lateglacial climatic fluctuations recorded in the sediments of pre Alpine Lake mondsee northeastern alps
Journal of Quaternary Science, 2011Co-Authors: Stefan Lauterbach, Achim Brauer, Nils Andersen, Dan L Danielopol, Peter Dulski, Matthias Huls, Krystyna Milecka, Tadeusz Namiotko, Milena Obremska, Ulrich Von GrafensteinAbstract:Investigation of the sedimentary record of pre-Alpine Lake Mondsee (Upper Austria) focused on the environmental reaction to rapid Lateglacial climatic changes. Results of this study reveal complex proxy responses that are variable in time and influenced by the long-term evolution of the Lake and its catchment. A new field sampling approach facilitated continuous and precisely controlled parallel sampling at decadal to sub-annual resolution for µ-XRF element scanning, carbon geochemistry, stable isotope measurements on ostracods, pollen analyses and large-scale thin sections for microfacies analysis. The Holocene chronology is established through microscopic varve counting and supported by accelerator mass spectrometry 14C dating of terrestrial plant macrofossils, whereas the Lateglacial age model is based on δ18O wiggle matching with the Greenland NGRIP record, using the GICC05 chronology. Microfacies analysis enables the detection of subtle sedimentological changes, proving that depositional processes even in rather large Lake systems are highly sensitive to climate forcing. Comparing periods of major warming at the onset of the Lateglacial and Holocene and of major cooling at the onset of the Younger Dryas reveals differences in proxy responses, reflecting threshold effects and ecosystem inertia. Temperature increase, vegetation recovery, decrease of detrital flux and intensification of biochemical calcite precipitation at the onset of the Holocene took place with only decadal leads and lags over a ca. 100 a period, whereas the spread of woodlands and the reduction of detrital flux lagged the warming at the onset of the Lateglacial Interstadial by ca. 500-750 a. Cooling at the onset of the Younger Dryas is reflected by the simultaneous reaction of δ18O and vegetation, but sedimentological changes (reduction of endogenic calcite content, increase in detrital flux) were delayed by about 150-300 a. Three short-term Lateglacial cold intervals, corresponding to Greenland isotope substages GI-1d, GI-1c2 and GI-1b, also show complex proxy responses that vary in time. Copyright © 2011 John Wiley & Sons, Ltd.
Achim Brauer - One of the best experts on this subject based on the ideXlab platform.
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palaeoecology of late glacial and holocene profundal ostracoda of pre Alpine Lake mondsee austria a base for further palaeo biological research
Palaeogeography Palaeoclimatology Palaeoecology, 2015Co-Authors: Tadeusz Namiotko, Stefan Lauterbach, Achim Brauer, Nils Andersen, Dan L Danielopol, Matthias Huls, Krystyna Milecka, Ulrich Von Grafenstein, Angel Baltanas, Walter GeigerAbstract:Succession of profundal ostracod palaeoassemblages in response to environmental changes during the Late Glacial and Holocene was studied in a similar to 15-m-long sediment sequence from pre-Alpine Lake Mondsee (Austria). First local ostracod assemblage zone LOAZ-1 (prior to 15,700 a BP), with low abundances of Leucocythere mirabilis and Limnocytherina sanctipatricii followed by Cytherissa lacustris, corresponds to the Pleniglacial phase of clastic-detrital sedimentation at relatively high rates. Most of the key species of LOAZ-2 (15,590 to 13,940 a BP, including the Pleniglacial-Late Glacial transition), i.e. limnocytherids, Fabaeformiscandona cf. harmsworthi, F. tricicatricosa, C. lacustris and Candona candida, reveal the significant association with high Al contents and low sedimentation rates and are classified as preferring low-productivity conditions. In contrast, Candona neglecta, dominant in LOAZ-3 (13,820 to 9960 a BP, palynologically defined as Balling-Early Holocene) and in the last LOAZ-4 (9780 a BP to present) as well as Cypria ophtalmica (second key species in LOAZ-4) show relationship with higher productivity, elevated sedimentation rates and decreasing Al contents. Furthermore, valve biodegradation and shape disparity at different time periods and in relation to sedimentation rate changes were investigated in A-3 juveniles of Candona neglecta. The highest percentage of valves biodegraded by Actinobacteria was recorded during the Allerod, Younger Dryas and Early Holocene, when the lowest sedimentation rates occurred, whereas significantly lower frequencies of biodegraded valves were recorded during the mid-Holocene and Late Holocene, when sediment accumulation was much higher. It is also hypothesised that the degree of the valve shape variation was related to the Lake productivity. During the Allerod, Younger Dryas and Early Holocene a valve shape variation significantly lower than that recorded during Late Holocene intervals, characterised by intensified Lake productivity, was observed. Additionally, an agenda of potential questions and approaches that should be considered and form the core of further (palaeo-)biological research projects is offered. (C) 2014 Elsevier B.V. All rights reserved.
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orbital and solar forcing of shifts in mid to late holocene flood intensity from varved sediments of pre Alpine Lake ammersee southern germany
Quaternary Science Reviews, 2013Co-Authors: Markus Czymzik, Achim Brauer, Peter Dulski, Ulrich Von Grafenstein, Birgit Plessen, R Naumann, Raphael SchefflerAbstract:Abstract Microfacies analyses and X-ray fluorescence scanning (μ-XRF) at sub-mm resolution were conducted on the varved Mid- to Late Holocene interval of two sediment profiles from pre-Alpine Lake Ammersee (southern Germany). The coring sites are located in a proximal (AS10prox) and distal (AS10dist) position towards the main tributary River Ammer, in 1.8 km distance from each other. To shed light on sediment distribution within the Lake, particular emphasis was (1) the detection of intercalated detrital layers and their micro-sedimentological features, and (2) intra-basin correlation of these event deposits. Detrital layers were dated by microscopic varve counting, verified by accelerator mass spectrometry 14C dating of terrestrial plant macrofossils. Since ∼5500 varve years (vyr) BP, in total 1573 detrital layers were detected in either one or both of the investigated sediment profiles. Based on their microfacies, geochemistry, and proximal-distal deposition pattern, detrital layers were interpreted as River Ammer flood deposits. Earlier studies on flood layer seasonality have proven that flood layer deposition occurs predominantly during spring and summer, the flood season at Lake Ammersee. Most prominent features of the record are the onset of regular flood layer deposition at ∼5500 vyr BP in AS10prox and ∼2800 vyr BP in AS10dist as well as three major increases in mean flood layer thickness at ∼5500, 2800, and 400 vyr BP. Integrating information from both sediment profiles allowed to interpret these changes in terms of shifts towards higher mean flood intensity. Proposed triggering mechanisms are gradual reduction in Northern Hemisphere orbital summer forcing and superimposed centennial-scale solar activity minima. Likely responses to this forcing are enhanced equator-to-pole temperature gradients and changes in synoptic-scale atmospheric circulation. The consequences for the Ammersee region are more intense cyclones leading to extremer rainfall and flood events in spring and summer.
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environmental responses to lateglacial climatic fluctuations recorded in the sediments of pre Alpine Lake mondsee northeastern alps
Journal of Quaternary Science, 2011Co-Authors: Stefan Lauterbach, Achim Brauer, Nils Andersen, Dan L Danielopol, Peter Dulski, Matthias Huls, Krystyna Milecka, Tadeusz Namiotko, Milena Obremska, Ulrich Von GrafensteinAbstract:Investigation of the sedimentary record of pre-Alpine Lake Mondsee (Upper Austria) focused on the environmental reaction to rapid Lateglacial climatic changes. Results of this study reveal complex proxy responses that are variable in time and influenced by the long-term evolution of the Lake and its catchment. A new field sampling approach facilitated continuous and precisely controlled parallel sampling at decadal to sub-annual resolution for µ-XRF element scanning, carbon geochemistry, stable isotope measurements on ostracods, pollen analyses and large-scale thin sections for microfacies analysis. The Holocene chronology is established through microscopic varve counting and supported by accelerator mass spectrometry 14C dating of terrestrial plant macrofossils, whereas the Lateglacial age model is based on δ18O wiggle matching with the Greenland NGRIP record, using the GICC05 chronology. Microfacies analysis enables the detection of subtle sedimentological changes, proving that depositional processes even in rather large Lake systems are highly sensitive to climate forcing. Comparing periods of major warming at the onset of the Lateglacial and Holocene and of major cooling at the onset of the Younger Dryas reveals differences in proxy responses, reflecting threshold effects and ecosystem inertia. Temperature increase, vegetation recovery, decrease of detrital flux and intensification of biochemical calcite precipitation at the onset of the Holocene took place with only decadal leads and lags over a ca. 100 a period, whereas the spread of woodlands and the reduction of detrital flux lagged the warming at the onset of the Lateglacial Interstadial by ca. 500-750 a. Cooling at the onset of the Younger Dryas is reflected by the simultaneous reaction of δ18O and vegetation, but sedimentological changes (reduction of endogenic calcite content, increase in detrital flux) were delayed by about 150-300 a. Three short-term Lateglacial cold intervals, corresponding to Greenland isotope substages GI-1d, GI-1c2 and GI-1b, also show complex proxy responses that vary in time. Copyright © 2011 John Wiley & Sons, Ltd.
Xuhui Dong - One of the best experts on this subject based on the ideXlab platform.
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direct versus indirect climate controls on holocene diatom assemblages in a sub tropical deep Alpine Lake lugu hu yunnan sw china
Quaternary Research, 2016Co-Authors: Qian Wang, Xiangdong Yang, N J Anderson, Xuhui DongAbstract:The reconstruction of Holocene environmental changes in Lakes on the plateau region of southwest China provides an understanding of how these ecosystems may respond to climate change. Fossil diatom assemblages were investigated from an 11,000-year Lake sediment core from a deep, Alpine Lake (Lugu Hu) in southwest China, an area strongly influenced by the southwest (or the Indian) summer monsoon. Changes in diatom assemblage composition, notably the abundance of the two dominant planktonic species, Cyclotella rhomboideo-elliptica and Cyclostephanos dubius, reflect the effects of climate variability on nutrient dynamics, mediated via thermal stratification (internal nutrient cycling) and catchment-vegetation processes. Statistical analyses of the climate–diatom interactions highlight the strong effect of changing orbitally-induced solar radiation during the Holocene, presumably via its effect on the Lake's thermal budget. In a partial redundancy analysis, climate (solar insolation) and proxies reflecting catchment process (pollen percentages, C/N ratio) were the most important drivers of diatom ecological change, showing the strong effects of climate–catchment–vegetation interactions on Lake functioning. This diatom record reflects long-term ontogeny of the Lake-catchment ecosystem and suggests that climatic changes (both temperature and precipitation) impact Lake ecology indirectly through shifts in thermal stratification and catchment nutrient exports.