Search

The abrupt weakening of the East Asian summer monsoon (EASM) during Younger Dryas (YD) has been attributed to freshwater discharge into the North Atlantic ocean and resultant Northern Hemisphere cooling. Recent studies have found that sea ice variability in the Nordic Sea during the YD exerted a great influence upon the northern high-latitude climate. However, the influence of sea ice upon EASM evolution during YD event remains unclear. In this paper, we report two precisely-dated speleothem oxygen isotope records from the EASM-dominated region of central China. Our records archive abrupt changes in EASM variability during the YD event. Initially, there was a significant strengthening of the EASM during the mid-YD following the gradually increased Atlantic meridional overturning circulation (AMOC). Later this trend reversed at ∼12.15 ka due to northern high-latitude sea ice fluctuations and a consequent reduction of AMOC. At the YD termination, abrupt intensification of the EASM was synchronous with the rapid decline of sea-ice and recovery of the AMOC indicating that sea ice variability was a significant influence on high latitude climate and EASM variation during the YD. • A new speleothem δ18O record show significant EASM strengthening during mid-YD. • Mid-YD oscillation in EASM linked with NH sea ice variability. • Abrupt EASM intensification at YD termination synchronous with the rapid decline of sea ice. • Drier interval following the YD termination in central China. [ABSTRACT FROM AUTHOR]

Abstract Floral communities in terrestrial habitats such as steppes are highly sensitive to regional climate changes. Here, we generated carbon and nitrogen isotope profiles for soil organic matter (SOM) in the Weinan loess-paleosol section in order to investigate changes in floral communities on the Chinese Loess Plateau (CLP) and their relationship to climate variation since 75 ka. δ13C SOM at Weinan ranges from −23.6 to −18.0‰ and δ15N SOM ranges from +3.4 to +5.5‰. Modeling based on the δ13C SOM record suggests that the proportion of C4 plants (%C4) has varied from lower during cold intervals (with minima of 24–32% at 73.1 ka, 20.9 ka (LGM), and 0.6 ka) to higher during warm intervals (with maxima of 62–64% at 53.0 ka and 8.2 ka). The δ13C SOM and δ15N SOM profiles are strongly correlated (r = +0.82; p(α) <0.001), suggesting that the N-isotope composition of SOM was also largely controlled by inputs of C4 versus C3 plants, consistent with known patterns of N-isotope variation among modern plants. The %C4 profile exhibits significant covariation with reconstructed mean annual temperatures (MAT) (r = +0.42; p(α) <0.001), mean annual precipitation (MAP) (r = +0.42; p(α) <0.001), and summer monsoon intensity (r = +0.50; p(α) <0.001), suggesting that paleovegetation was controlled by each of these climate variables to a degree. Comparing the Weinan record to SOM profiles across the CLP region, we identified three zones of varying monsoonal influence, with the East Asian Summer Monsoon (EASM) exerting the strongest influence on the southeastern margin of the CLP, and the East Asian Winter Monsoon (EAWM) greater influence on its northwestern margin. This paper provides new insights into deciphering paleovegetation patterns and their links to paleoclimate change on the basis of paired C- and N-isotope records. Highlights • Analysis of δ13C and δ15N of soil organics in Weinan section, Chinese Loess Plateau • δ13C SOM and δ15N SOM profiles exhibit strong correspondence since 75 ka • Both C- and N-isotope compositions controlled mainly by inputs of C3 vs C4 plants • Paleovegetation type strongly influenced by summer monsoon intensity [ABSTRACT FROM AUTHOR]

To achieve a sufficient understanding of the spatial dynamics of terrestrial climate variability, new proxies and networks of data that cover thousands of years and run up to the present day are needed. Here we show the first Gram-negative bacterial 3-hydroxy fatty acid (3-OH-FA) based temperature and hydrological records from any paleoclimate archive globally. The data, covering the last 9 ka before present (BP), are generated from an individual stalagmite, collected from Heshang Cave, located on a tributary of the Yangtze River, central China (30°27′N, 110°25′E; 294 m). Our results indicate a clear early-to-middle Holocene Climatic Optimum (8.0–6.0 ka BP) followed by a long-term monotonic cooling and increasing variability over the last 0.9 ka BP. The hydrological record shows two relatively long wet periods (8.8–5.9 ka BP and 3.0–0 ka BP) and one relatively dry period (5.9–3.0 ka BP) in central China. We show that 3-OH-FA biomarkers hold promise as independent tools for paleoclimate reconstruction, with the potential to deconvolve temperature and hydrological signals from an individual stalagmite. [ABSTRACT FROM AUTHOR]

Droughts and floods caused by extreme hydroclimatic events in East Asian monsoon area often have serious effects on human society. The Poyang Lake region has always been one of the most severe floods and droughts in East China. In order to explore the relationship between monsoon climate change and occurrence of drought/flood, this study rebuilt a high-resolution (~ 10 yr) of temperature and aridity change history of the past 1000 years. Phytolith assemblages together with the climatic indices revealed 3 phases of paleoenvironmental changes over the last millennium: (1) Medieval Warm Period (MWP) during 900–1370 AD witnessed increased monsoon precipitation and frequent floods corresponding to strong El Niño–like state; (2) Little Ice Age (LIA) during 1370–1800 AD experienced severe droughts coupling with decreased monsoon precipitation and intensive La Niña–like state; (3) Current Warm Period (CWP) during 1800–2003 AD encountered highly frequent floods related to the increased monsoon precipitation modulated by strong El Niño–like state. Our results confirmed that there is a connection between solar irradiance, ENSO activity and monsoon precipitation in the subtropical East China. On interannual-decadal timescales, due to the modulation of ENSO on the location of the Western Pacific Subtropical High (WPSH) and Meiyu Belt, the occurrences of droughts and floods affected by ENSO-related monsoon precipitation has significantly affected not only the sedimentary environment, but also human activities, which is significant for the prediction of future prevention of droughts and floods in the East Asian monsoon region against the background of global warming. • Medieval Warm Period witnessed increased monsoon precipitation and frequent floods. • Little Ice Age experienced severe droughts and decreased monsoon precipitation. • Drought and flood occurrences were modulated by ENSO-related monsoon precipitation. [ABSTRACT FROM AUTHOR]

Abstract: Lipid biomarkers in stalagmites have potential in palaeoenvironmental reconstruction, but glycerol dialkyl glycerol tetraethers (GDGTs) in stalagmites have rarely been investigated. We report the occurrence of archaeal isoprenoid GDGTs and bacterial branched GDGTs in Heshang Cave stalagmites in central China. The archaeal component, crenarchaeol, dominated bacterial branched GDGTs in the stalagmites and on the weathered parent rock surface collected inside the cave. In contrast, the distribution of GDGTs in the overlying soil shows that branched GDGTs dominated archaeal GDGTs. Hence, the majority of archaeal GDGTs in stalagmites may be produced by Crenarchaeota inhabiting the cave rather than being inherited from the overlying soil. Bacterial branched GDGT distributions, expressed as MBT and CBT indices, showed remarkable differences between stalagmite and soil samples, implying that most branched GDGTs may also be produced in situ in the cave. The TEX86 or values were found to increase with more depleted δ 18O values representing much stronger monsoon and therefore usually higher temperatures, in the study region. However, the MBT/CBT index in stalagmites may be influenced by a variety of factors besides palaeotemperature. [ABSTRACT FROM AUTHOR]