Palaeogeography, Palaeoclimatology, Palaeoecology, Oct 1, 2011
ABSTRACT In their recent paper, Hong et al. (2010; Anti-phase oscillation of Asian monsoons durin... more ABSTRACT In their recent paper, Hong et al. (2010; Anti-phase oscillation of Asian monsoons during the Younger Dryas period: Evidence from peat cellulose δ13C of Hani, Northeast China, Palaeogeography, Palaeoclimatology, Palaeoecology 297, 214–222) discuss bulk peat sample cellulose δ13C data from a fen in northeast China as a proxy for East Asian summer monsoon intensity during the Late Glacial period. Based on their own results, cited papers, and an extensive re-interpretation of sedimentological and palynological data from nearby Lake Sihailongwan, Hong et al. (2010) construct a hypothesis of contrasting moisture conditions in northern and southern China, with wet conditions in the north during the Younger Dryas period and an anti-phase behaviour of Indian- and East Asian summer monsoon intensity. However, we do not approve of the re-interpretation of our Lake Sihailongwan data by Hong et al. (2010) and must strongly reject it. We show here that neither the Hong et al. (2010) fen data, nor the Lake Sihailongwan data or any other cited data allow for the sound assumption of an intensified East Asian summer monsoon in northeastern China during the Younger Dryas. The Late Glacial variability of the fen data found by Hong et al. (2010) can be easily explained by changes in the plant assemblage down core and thus by the composition of the peat. Furthermore, the use of bulk peat cellulose δ13C data as a precipitation proxy remains unproven for that area. Hence, there is no basis for a model contrasting Indian and East Asian summer monsoons during that period.
Total organic carbon (TOC) content, total nitrogen (TN) content, stable nitrogen isotope (δ15N) a... more Total organic carbon (TOC) content, total nitrogen (TN) content, stable nitrogen isotope (δ15N) and stable organic carbon isotope (δ13Corg) ratios were continuously analysed on a high resolution sediment profile from Lake Sihailongwan (SHL), covering the time span between 16,500 and 9,500 years BP. Strong variations of the investigated proxy parameters are attributed to great climatic fluctuations during the investigated time period.
A palaeohydrological reconstruction on decadal scale for the period 15000-2000 cal. yr BP based o... more A palaeohydrological reconstruction on decadal scale for the period 15000-2000 cal. yr BP based on calculated net accumulation rates for biogenic silica (F-bSiO2) and additional proxies (sedimentological data, geochemical sediment characteristics and pollen) is derived from varved sediments of Lake Sihailongwan (SHL). In Lake SHL, F-bSiO2 is positively correlated with the inflow of nutrient-rich groundwater. Since groundwater inflow is mainly fed by seepage of summer monsoon rainfall, F-bSiO2 documents changes in summer monsoon strength. Summer monsoon rainfall was enhanced in the early Holocene around 9800 and 7800 cal. yr BP. Groundwater inflow during these periods did not reach the high level of the Lateglacial warm period (c. 14300 12500 cal. yr BP) when the vicinity of the lake was less densely covered with woody vegetation than in the Holocene. Aeolian influx of silt-sized debris was relatively higher during an overall drier period between 9500 and 8000 cal. yr BP. A mid-Holocene sedimentation interval with distinct century-scale variability in summer monsoon rainfall documents a positive correlation between rainfall and siliciclastic influx that reflects a more efficient removal of mineral aerosols for increased rainfall at an overall high dust concentration over the Asian continent. Summer monsoon rainfall reached minima around 6400, 4900, 3700 and 2200 cal. yr BP. Remarkably, aeolian siliciclastic influx peaked at the beginning and at the end of a dry interval between 4100 and 3600 cal. yr BP. Around 3600 cal. yr BP Lake SHL received substantial aeolian influx of different geochemical provenance.
Orbitally forced cyclicity culminating in the alternation of glacials and interglacials is the mo... more Orbitally forced cyclicity culminating in the alternation of glacials and interglacials is the most outstanding feature of the Quaternary. At sub-orbital scale, recurrent Dansgaard–Oeschger (D/O) events are the most prominent variations of the last glacial period. First recognised in the Greenland ice core records, their global occurrence has been proven. However, unravelling effects of such rapid climate change on vegetation, including potential lead/lag relationships, remains a challenge. The results presented here from the annually laminated sedimentary sequence of Sihailongwan Lake provide the first comprehensive palaeoecological record covering the period from about ~ 65,000 to 14,000 cal yrs. BP (MIS 2-4) from monsoonal North-Eastern China. A reliable chronology has been established by both varve counting and 40 calibrated AMS 14C age determinations and a pollen sampling resolution of ~65 years allows peak-to-peak correlations between the pollen signals and 18O data from the Greenland ice cores and Chinese speleothem records. The pollen data indicate mosaic-like occurrence of woodland and steppe biotopes close to the study site during the last glacial period. Tree communities in the lake’s catchment area primarily include Betula, Larix, Alnus fruticosa, Picea and Salix - all of them constituents of taiga ecosystems and cold-deciduous forests. Beyond it, the regular occurrences of Ulmus and Fraxinus pollen grains during the pleniglacial point to the existence of favorable micro-habitats for (cool-) temperate trees not far away from the study site. Spectral analyses of pollen data derived from various taxa provide evidence of Milankovitch-, millennial- and centennial-scale climate variability during the study period. Corresponding to the precession cycle, the vegetation experienced repeated low-frequency changes characterized by the alternative growth and decline of taiga-forest and steppe biotopes. Shorter periods with ameliorated climate coincide within error margins with known D/O cycles from Greenland ice core records. An additional ~200 year periodicity of the pollen record is near the solar deVriess/Suess cycle. The new data from Sihailongwan Lake attest to changes of the East Asian monsoon system during the last Glacial over various time scales and illuminate immediate vegetations responses. The evident synchronicity of climate changes in the North Atlantic region and East Asia supports the theory of strong atmospheric coupling between both regions. Our high resolution data allows examination of response of vegetation in the context of different forcing mechanisms in more detail than has previously been possible.
In recent years enormous success has been achieved in varve counting of the Eifel maar lakes, but... more In recent years enormous success has been achieved in varve counting of the Eifel maar lakes, but a detailed correlation with the biostratigraphy has been missing. In this paper, we present new palynological results of the Lateglacial sequences from Holzmaar Lake and Meerfelder Maar Lake based on annually laminated sediments. In particular, the Meerfelder Maar has great potential, because, in contrast to the Holzmaar, the sequence between the Ulmener Maar Tephra (11 000 varve years BP) and the Laacher See Tephra (12 880 varve years BP) including the Younger Dryas is undisturbed and complete. Therefore, we currently use the Meerfelder Maar chronology (Brauer et al., 1999b) as an independent varve calendar for the biostratigraphy of the Lateglacial. The palynological signals of both maar lakes are in good agreement and can easily be correlated with one another and with type sections/type regions in northwestern Germany and Jutland. The sequences of the Eifel maar lakes have the quality of hypostratotypes with regional biozones based on an absolute time scale.
Palaeogeography, Palaeoclimatology, Palaeoecology, Oct 1, 2011
ABSTRACT In their recent paper, Hong et al. (2010; Anti-phase oscillation of Asian monsoons durin... more ABSTRACT In their recent paper, Hong et al. (2010; Anti-phase oscillation of Asian monsoons during the Younger Dryas period: Evidence from peat cellulose δ13C of Hani, Northeast China, Palaeogeography, Palaeoclimatology, Palaeoecology 297, 214–222) discuss bulk peat sample cellulose δ13C data from a fen in northeast China as a proxy for East Asian summer monsoon intensity during the Late Glacial period. Based on their own results, cited papers, and an extensive re-interpretation of sedimentological and palynological data from nearby Lake Sihailongwan, Hong et al. (2010) construct a hypothesis of contrasting moisture conditions in northern and southern China, with wet conditions in the north during the Younger Dryas period and an anti-phase behaviour of Indian- and East Asian summer monsoon intensity. However, we do not approve of the re-interpretation of our Lake Sihailongwan data by Hong et al. (2010) and must strongly reject it. We show here that neither the Hong et al. (2010) fen data, nor the Lake Sihailongwan data or any other cited data allow for the sound assumption of an intensified East Asian summer monsoon in northeastern China during the Younger Dryas. The Late Glacial variability of the fen data found by Hong et al. (2010) can be easily explained by changes in the plant assemblage down core and thus by the composition of the peat. Furthermore, the use of bulk peat cellulose δ13C data as a precipitation proxy remains unproven for that area. Hence, there is no basis for a model contrasting Indian and East Asian summer monsoons during that period.
Total organic carbon (TOC) content, total nitrogen (TN) content, stable nitrogen isotope (δ15N) a... more Total organic carbon (TOC) content, total nitrogen (TN) content, stable nitrogen isotope (δ15N) and stable organic carbon isotope (δ13Corg) ratios were continuously analysed on a high resolution sediment profile from Lake Sihailongwan (SHL), covering the time span between 16,500 and 9,500 years BP. Strong variations of the investigated proxy parameters are attributed to great climatic fluctuations during the investigated time period.
A palaeohydrological reconstruction on decadal scale for the period 15000-2000 cal. yr BP based o... more A palaeohydrological reconstruction on decadal scale for the period 15000-2000 cal. yr BP based on calculated net accumulation rates for biogenic silica (F-bSiO2) and additional proxies (sedimentological data, geochemical sediment characteristics and pollen) is derived from varved sediments of Lake Sihailongwan (SHL). In Lake SHL, F-bSiO2 is positively correlated with the inflow of nutrient-rich groundwater. Since groundwater inflow is mainly fed by seepage of summer monsoon rainfall, F-bSiO2 documents changes in summer monsoon strength. Summer monsoon rainfall was enhanced in the early Holocene around 9800 and 7800 cal. yr BP. Groundwater inflow during these periods did not reach the high level of the Lateglacial warm period (c. 14300 12500 cal. yr BP) when the vicinity of the lake was less densely covered with woody vegetation than in the Holocene. Aeolian influx of silt-sized debris was relatively higher during an overall drier period between 9500 and 8000 cal. yr BP. A mid-Holocene sedimentation interval with distinct century-scale variability in summer monsoon rainfall documents a positive correlation between rainfall and siliciclastic influx that reflects a more efficient removal of mineral aerosols for increased rainfall at an overall high dust concentration over the Asian continent. Summer monsoon rainfall reached minima around 6400, 4900, 3700 and 2200 cal. yr BP. Remarkably, aeolian siliciclastic influx peaked at the beginning and at the end of a dry interval between 4100 and 3600 cal. yr BP. Around 3600 cal. yr BP Lake SHL received substantial aeolian influx of different geochemical provenance.
Orbitally forced cyclicity culminating in the alternation of glacials and interglacials is the mo... more Orbitally forced cyclicity culminating in the alternation of glacials and interglacials is the most outstanding feature of the Quaternary. At sub-orbital scale, recurrent Dansgaard–Oeschger (D/O) events are the most prominent variations of the last glacial period. First recognised in the Greenland ice core records, their global occurrence has been proven. However, unravelling effects of such rapid climate change on vegetation, including potential lead/lag relationships, remains a challenge. The results presented here from the annually laminated sedimentary sequence of Sihailongwan Lake provide the first comprehensive palaeoecological record covering the period from about ~ 65,000 to 14,000 cal yrs. BP (MIS 2-4) from monsoonal North-Eastern China. A reliable chronology has been established by both varve counting and 40 calibrated AMS 14C age determinations and a pollen sampling resolution of ~65 years allows peak-to-peak correlations between the pollen signals and 18O data from the Greenland ice cores and Chinese speleothem records. The pollen data indicate mosaic-like occurrence of woodland and steppe biotopes close to the study site during the last glacial period. Tree communities in the lake’s catchment area primarily include Betula, Larix, Alnus fruticosa, Picea and Salix - all of them constituents of taiga ecosystems and cold-deciduous forests. Beyond it, the regular occurrences of Ulmus and Fraxinus pollen grains during the pleniglacial point to the existence of favorable micro-habitats for (cool-) temperate trees not far away from the study site. Spectral analyses of pollen data derived from various taxa provide evidence of Milankovitch-, millennial- and centennial-scale climate variability during the study period. Corresponding to the precession cycle, the vegetation experienced repeated low-frequency changes characterized by the alternative growth and decline of taiga-forest and steppe biotopes. Shorter periods with ameliorated climate coincide within error margins with known D/O cycles from Greenland ice core records. An additional ~200 year periodicity of the pollen record is near the solar deVriess/Suess cycle. The new data from Sihailongwan Lake attest to changes of the East Asian monsoon system during the last Glacial over various time scales and illuminate immediate vegetations responses. The evident synchronicity of climate changes in the North Atlantic region and East Asia supports the theory of strong atmospheric coupling between both regions. Our high resolution data allows examination of response of vegetation in the context of different forcing mechanisms in more detail than has previously been possible.
In recent years enormous success has been achieved in varve counting of the Eifel maar lakes, but... more In recent years enormous success has been achieved in varve counting of the Eifel maar lakes, but a detailed correlation with the biostratigraphy has been missing. In this paper, we present new palynological results of the Lateglacial sequences from Holzmaar Lake and Meerfelder Maar Lake based on annually laminated sediments. In particular, the Meerfelder Maar has great potential, because, in contrast to the Holzmaar, the sequence between the Ulmener Maar Tephra (11 000 varve years BP) and the Laacher See Tephra (12 880 varve years BP) including the Younger Dryas is undisturbed and complete. Therefore, we currently use the Meerfelder Maar chronology (Brauer et al., 1999b) as an independent varve calendar for the biostratigraphy of the Lateglacial. The palynological signals of both maar lakes are in good agreement and can easily be correlated with one another and with type sections/type regions in northwestern Germany and Jutland. The sequences of the Eifel maar lakes have the quality of hypostratotypes with regional biozones based on an absolute time scale.
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