Time: Jul 21, 2020 14:00-16:00 British Summer Time
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1. A welcome and introduction to this series from the organisers
Organisers
Jen O'Keefe (Morehead State University)
Nichola Strandberg (University of Southampton)
Yoshi Maezumi (University of Amsterdam)
Limi Mao (Nanjing Institute of Geology and Palaeontology)
2. Talks
( 1/3 ) Jing Wu
(Institute of Geology and Geophysics, Chinese Academy of Sciences)
Shrinkage of East Asia winter monsoon since the Mid‐Holocene indicated by pollen records from lakes in Northeast China
Abstract
Instrumental records indicate a close relationship between the El Niño‐Southern Oscillation and the East Asian winter monsoon (EAWM) on interannual to decadal time scales. However, few studies have examined possible links between them on centennial/millennial time scales. In Northeast China, modern observations show that the immigration of temperate forest trees such as Pinus (pine) and Quercus (oak) into cold temperate boreal forest is sensitive to changes in winter temperature. Here we present a continuous high‐resolution pollen record from Lake Moon in the central part of the Great Khingan Mountain Range, Northeast China. The record reveals increasing contents of Pinus and Quercus pollen after ~6.0 ka cal. BP, which may indicate a gradual weakening of the EAWM. It is broadly coupled with an increasing El Niño frequency since the middle Holocene, and we observe a statistically significant correlation between the percentages of Pinus and Quercus and a time series of El Niño events. On the centennial to millennial time scale, the results of wavelet analysis and band‐pass filtering show that the occurrence and development of El Niño have also promoted a weaker EAWM after ~6.0 ka cal. BP, which is inversely correlated with the variation of the ca. 500‐year cycle originated from changes in solar output. These results imply that the climate transition in the mid‐Holocene is caused by the change of variations in solar activity and amplified by ocean circulation El Niño‐Southern Oscillation to influence the East Asian Monsoon system, especially the EAWM, and finally change the vegetation in Great Khingan Mountain Range.
Location of Lake Moon
Simplified pollen percentage diagram for Lake Moon
Wavelet spectrum and band‐pass filtering calculated on pollen records and El Niño‐Southern Oscillation index
Pollen from the Lake Moon published elsewhere: 1. Larix, 2. Pinus, 3. Picea/Abies, 4. Alnus, 5, 6 Betula, 7. Carpinus, 8. Corylus, 9. Ulmus, 10. Tilia, 11. Quercus, 12. Salix, 13. Spiraea [Wu et al., 2019. Characteristics of the Younger Dyas event in the Great Khingan Mountains area. Quaternary Science 39:985-993, in Chinese with English abstract ]
Pollen from the Lake Moon published elsewhere: 1. Ephedra, 2. Thalictrum , 3. Ranunculaceae , 4. Chenopodiaceae/Amaranthaceae, 5. Potentilla, 6. Sanguisorba, 7. Poaceae,8. Artemisia , 9, 13,14. Asteraceae (9, 13. Aster type, 14.Taraxacum type),10. Brassicaceae, 11. Polygonum, 12. Cyperaceae [Note: Pollen from the Lake Moon published in elsewhere (Wu et al., 2019. Characteristics of the Younger Dyas event in the Great Khingan Mountains area. Quaternary Science 39:985-993, in Chinese with English abstract]
( 2/3 ) Vitor Gomes
(Federal University of Pará - UFPA)
What pollen can tell us about Amazonian tree species distribution?
Abstract
Aim: To (a) assess the environmental suitability for rainforest tree species of Moraceae and Urticaceae across Amazonia during the Mid-Late Holocene and (b) determine the extent to which their distributions increased in response to long-term climate change over this period.
Location: Amazonia.
Taxon: Tree species of Moraceae and Urticaceae.
Methods: We used MaxEnt and inverse distance weighting interpolation to produce environmental suitability and relative abundance models at 0.5-degree resolution for tree species of Moraceae and Urticaceae, based on natural history collections and a large plot dataset. To test the response of the Amazon rainforest to long-term climate change, we quantified the increase in environmental suitability and modelled species richness for both families since the Mid-Holocene (past 6,000 years). To test the correlation between the relative abundance of these species in modern vegetation
versus modern pollen assemblages, we analysed the surface pollen spectra from 46 previously published paleoecological sites.
Results: We found that the mean environmental suitability in Amazonia for species of Moraceae and Urticaceae showed a slight increase (6.5%) over the past 6,000 years, although southern ecotonal Amazonia and the Guiana Shield showed much higher increases (up to 68%). The accompanied modelled mean species richness increased by as much as
120% throughout Amazonia. The mean relative abundance of Moraceae and Urticaceae correlated significantly with the modern pollen assemblages for these families.
Main Conclusions: Increasing precipitation between the Mid- and Late Holocene expanded suitable environmental conditions for Amazonian humid rainforest tree species of Moraceae and Urticaceae, leading to rainforest expansion in ecotonal areas of Amazonia, consistent with previously published fossil pollen data.
Current modelled relative abundance for Moraceae and Urticaceae
Current mean modelled environmental suitability and modelled species richness for Moraceae and Urticaceae
Percentage of increase in mean modelled environmental suitability and species richness during the Mid-Late Holocene
Relationship between predicted relative abundance and modern pollen assemblages of Moraceae and Urticaceae
( 3/3 ) Shaohua Yu
(Guangzhou Marine Geological Survey)
Pollen record in the northern western continental shelf of the South China Sea in the past 82 ka: Paleoenvironment changes in the last glacial period
Abstract
The northwestern continental shelf of the South China Sea (SCS) is in a geographic location that was sensitive to the global paleoenvironmental change during the last glacial period. Here we present a high resolution palynological record of Core ZBW (100.65 m in length) from the continental shelf of the SCS in the past 82 ka. In contrast to results for the northern SCS, the core’s pollen assemblage was dominated by arboreal trees between MIS5a and MIS1, even during the glacial period. Pollen provenance analyses indicated it was mainly from the drainage basin of the Red River, the Yungui Plateau and Tibetan Plateau. Between 66 and 64 ka, the contribution of Pinus fell while that of Cyclobalanopsis and trilete spores increased, indicating a drier and cooler climate. Conversely, during MIS3, the contributions of Pinus and lowland trees were high, indicating a warm and wet climate. The sedimentary environment in core ZBW alternated between coastal marine and river alluvial or shore facies. A sedimentary hiatus between 42 and 13 ka coincided with a significant fall in sea levels. Seismic data indicate that the Hainan paleo-river Delta (HPRD) process occurred at the core site between 65 and 56 ka, with extremely high rates of sediment deposition. Pollen data indicate the HPRD process was coincided with a transition period from cooler and drier climate to warmer and wetter climate, and lower sea levels to higher sea levels.
Study area and the location of the ZBW core site.
Pollen data for the ZBW core (northwestern SCS), the MD05-2906 core, and ODP site 1144
Comparison of proxies' variations
Pollen from the ZBW core. 1: Dicranopteris. 2: Cyperaceae . 3, 6, 14, 17, 22: Cycloblanopsis. 4: Artemisia. 5: Lindsaea. 7:
Euphorbiaceae. 8: Hamamelidaceae. 9–10: Alnus. 11: Lygodium. 12: Athyrium. 13: Poaceae (1970–1980 cm). 15: Juglans. 16: Humata. 18: Chenopodiaceae. 19, 23: Altingia. 20: Cibotium. 21: Polypodiaceae. 24: Pinus. 25: Anacardiaceae . 26: Dacrydium. 27: Tsuga. 28: Abies.
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