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- Guo, Benhong, et al.
(författare)
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Dominant precessional forcing of the East Asian summer monsoon since 260 ka
- 2022
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Ingår i: Geology. - : Geological Society of America. - 0091-7613 .- 1943-2682. ; 50:12, s. 1372-1376
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Tidskriftsartikel (refereegranskat)abstract
- One of the most perplexing problems in paleoclimate research is how orbital cyclicities force East Asian summer monsoon (EASM) precipitation variation over the middle to late Quaternary. Chinese loess records suggest that EASM precipitation was dominated by 100 k.y. cycles controlled by Northern Hemisphere ice sheet forcing. In contrast, speleothem records suggest that EASM precipitation was dominated by 23 k.y. cycles caused by Northern Hemisphere summer insolation forcing. In order to resolve this inconsistency, we present high-resolution paleoclimate records from Xijin drill cores on the western Chinese Loess Plateau for the past 260 k.y., the rough upper limit of luminescence dating. Magnetic susceptibility (χ) shows clear 23 k.y. precessional cycles over interglacials but has constant low values over glacials. This is interpreted as indicating a lack of pedogenesis, such that χ cannot record EASM precipitation variations, rather than an absence of EASM variation itself. To circumvent this issue, we use inversed sand content as an alternative proxy for EASM precipitation over glacials and splice this with the interglacial logarithmic χ from Xijin drill cores. This new record reveals dominant 23 k.y. cycles over both interglacials and glacials, consistent with speleothem δ18O data and dominant insolation forcing. These findings allow a consistent understanding of EASM variability and forcing mechanisms from both loess and speleothem archives, resolving one of the largest debates in past monsoon research. These results challenge suggestions of high-latitude ice sheet forcing of the EASM based on slowly accumulated loess records from the central Loess Plateau.
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| 2. |
- Li, Guoqiang, et al.
(författare)
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A comprehensive dataset of luminescence chronologies and environmental proxy indices of loess-paleosol deposits across Asia
- 2024
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Ingår i: npj Climate and Atmospheric Science. - : Springer Nature. - 2397-3722. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- Loess-paleosol sequences have been used in Asia to study climate and environmental changes during the Quaternary. The scarcity of age control datasets and proxy indices analysis data for Asian loess has limited our understanding of loess depositional processes and the reconstruction of paleoclimatic changes from loess-paleosol records. In this study, we present a dataset that includes 1785 quartz optically stimulated luminescence ages and 1038 K-feldspar post-infrared infrared stimulated luminescence ages from 128 loess-paleosol sequences located in different regions of Asia. We generate 38 high-resolution age-depth models of loess records based on the provided datasets. We provide data on 12,365 grain size records, 14,964 magnetic susceptibility records, 2204 CaCO3 content records, and 3326 color reflection records. This dataset contains the most detailed and accurate chronologies and proxy index data for loess records in Asia yet published. It provides fundamental data for understanding the spatial-temporal variations in loess depositional processes and climatic changes across the continent during the mid-late Quaternary.
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| 4. |
- Rasmussen, Christian F., et al.
(författare)
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High-resolution OSL dating of loess in Adventdalen, Svalbard : Late Holocene dust activity and permafrost development
- 2023
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Ingår i: Quaternary Science Reviews. - 0277-3791 .- 1873-457X. ; 310
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Tidskriftsartikel (refereegranskat)abstract
- There is considerable uncertainty over the nature and causes of Holocene dust activity in the Arctic, and its links to climatic changes. Loess deposits act as near-source archives of dust deposition and provide a means to address these uncertainties. Here we develop a fully independent age model for a loess core taken in Adventdalen, Svalbard, based on 136 quartz luminescence ages taken at 2 cm intervals. This represents the most detailed luminescence dating analysis undertaken to date on a sedimentary archive. Extensive laboratory tests and stratigraphic consistency indicate that the quartz luminescence ages are reliable. Together with grain size and cryostratigraphic analyses, as well as stratigraphic investigation of an adjacent loess exposure, the exceptional detail of the chronology combined with Bayesian age modelling uniquely allows changes in loess accumulation rates, particle size and permafrost development to be reconstructed over the last 3000 yrs on 101–103 yr timescales. The results show that loess deposition was mostly continuous over this interval, albeit with a short period of reworking or non-aeolian sedimentation during the Little Ice Age. Permafrost development in the loess is dominantly syngenetic, with ice contents increasing with depth. There is considerable variability in loess mass accumulation rate over the late Holocene, with peaks occurring during the last 250 yrs, as well as at 750–900, 1050–1200, 1400–1600, 1900–2450 and possibly 2700–3000 a. These peaks generally coincide with increased coarse silt deposition, potentially suggesting a link with greater wind activity. However, the peaks also seem to coincide with possible warm phases on Svalbard, which would rather imply that temperature-driven sediment availability in glaciofluvial source areas is the main control on dustiness in Adventdalen. In any case, the rates of loess deposition in the Adventdalen core are exceptionally high globally (up to 0.35 cm yr−1/2900 g m−2 yr−1 sedimentation and mass accumulation rates, respectively), and if representative of wider patterns across Svalbard, may suggest that the archipelago is a more important high latitude dust source than previously realised.
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