An estuarine tidal terrace sequence at the mouth of the Kharod River, Kachchh, Western India is investigated for Pleistocene to Holocene climate and sea-level changes. Based on sedimentology, major ...element geochemistry, mineralogy, supported by optical dating, the study reports a lowered sea level during 13.8ka, followed by gradual rise in the sea level until around 6ka. This is ascribed to a combination of enhanced melt water discharge and strengthened Indian Summer Monsoon (ISM). The temporal changes in major elements (detrital proxies), suggest a fluctuating to an overall arid monsoon conditions during 5.7 to 3.1ka with a rapidly rising sea level. This is further supported by the dominance of fine textured sediment along with the occurrences of shell rich horizon. In the absence of any evidence of land-level changes, the study suggests that at around 6ka to 3ka, the sea was approximately 2m higher then present. The decline in the concentration of geochemical proxies and occurrence of Aeolian sand after 3ka is interpreted as the onset of aridity and present day like conditions. The three levels of sea stands, during – Early, Middle and Late Holocene are synchronous with various archeological (Harappan) settlements in the region.
•An estuarine tidal terrace in Western India is investigated for Pleistocene-Holocene climate / sea-level changes.•Widespread aggradation during the 13ka to 6ka under strengthened monsoonal conditions and overall fluctuating climate during the 6ka to 3ka.•The study reports that around 6ka to 3ka, the sea was approximately 2m higher then present.•The study correlates with Early to Middle Holocene Harappan archeological sites along the Gujarat coast.
Glacial–interglacial changes in the distribution of C₃/C₄ vegetation on the Chinese Loess Plateau have been related to East Asian summer monsoon intensity and position, and could provide insights ...into future changes caused by global warming. Here, we present δ13C records of bulk organic matter since the Last Glacial Maximum (LGM) from 21 loess sections across the Loess Plateau. The δ13C values (range: −25‰ to −16‰) increased gradually both from the LGM to the mid-Holocene in each section and from northwest to southeast in each time interval. During the LGM, C₄ biomass increased from <5% in the northwest to 10–20% in the southeast, while during the mid-Holocene C₄ vegetation increased throughout the Plateau, with estimated biomass increasing from 10% to 20% in the northwest to >40% in the southeast. The spatial pattern of C₄ biomass in both the LGM and the mid-Holocene closely resembles that of modern warm-season precipitation, and thus can serve as a robust analog for the contemporary East Asian summer monsoon rain belt. Using the 10–20% isolines for C₄ biomass in the cold LGM as a reference, we derived a minimum 300-km northwestward migration of the monsoon rain belt for the warm Holocene. Our results strongly support the prediction that Earth’s thermal equator will move northward in a warmer world. The southward displacement of the monsoon rain belt and the drying trend observed during the last few decades in northern China will soon reverse as global warming continues.
Central Asia comprises a vast area of arid terrain which has an important impact on the global climate system. Although still debated, the pattern of climatic variations in central Asia is regionally ...distinctive and does not appear to be strongly related to changes in insolation. To understand the climatic evolution of central Asia, as well as its forcing mechanisms, it is necessary to characterize variations in the Westerlies, which have had a major influence on climate change in the region. Past variations in the Westerlies are commonly reconstructed from records of the composition, grain-size and mass accumulation rate (MAR) of loess and the eolian component of lacustrine sediments which are commonly mixed by the signal of surface atmospheric circulation. Here we present the results of grain-size analysis of a section of last glacial and Holocene loess deposits in the Tien Shan Mountains. The results indicate that the strength of the Westerlies was weakest during the last deglacial and early Holocene (16–6 ka), strongest during the mid-Holocene (6–3.1 ka), and moderate during the late Holocene (3.1–0 ka). By comparison with an independent record of humidity, we propose that the Westerlies were an important driver of moisture variations in central Asia, with strong Westerlies circulation resulting in high precipitation and vice versa during the past 16 kyr.
•The Westerlies are reconstructed by grain-size analyses and MAR.•The Westerlies were weakest during 16–6 ka in central Asia.•The Westerlies were the dominant control of moisture variations in central Asia.
Regional-scale Holocene sea-level reconstruction is the key to understanding natural climatic variability. The tidal flat, salt marsh, and tidal floodplain in the Yangtze River Delta were very ...sensitive to morphological changes and sea-level variation during the early Holocene. In this study, the lithology, radiocarbon ages, sediment grain size, benthic foraminifera, and ostracods of three new cores were analyzed. Twenty-four sea-level index points were extracted from incised-valley fills beneath the westernmost part of the Yangtze River Delta and used to construct a detailed relative sea-level curve for 11.03–7.25 ka. The relative sea level were − 38.90 ± 3.48 and 1.59 ± 3.28 m at 11.03 and 7.25 ka, respectively, and the average rate of sea-level rise was 10.71 mm/yr. The relative sea level gradually increased at 11.03–10.10 and 9.29–8.33 ka from 4.80 to 13.30 and 3.19 to 19.59 mm/yr, respectively. The rate of relative sea-level rise gradually decreased from 19.59 mm/yr at 8.33 ka to 13.40 mm/yr at 7.82 ka and further decreased to 5.53 mm/yr at 7.25 ka. The Yangtze River Delta recorded accelerations in the rate of sea-level rise from 8.72 to 8.18 ka of 14.2–19.59 mm/yr, corresponding to the pre-8.2 ka event. A comparison of the sea-level histories of the Yangtze River Delta and other regions indicates tectonics, glacial isostatic adjustment, and coastal levering effects caused by the marine inundation of the continental shelves. These new sea-level data contribute to the understanding of the difference in the sea-level rise rate during the early–mid Holocene.
•New and high-quality sea-level index points of the early and middle Holocene are produced for the Yangtze delta•The sea-level was -38.90 ± 3.45 m at 11.03 ka and 1.59 ± 3.28 m at 7.25 ka, the average rate of sea-level rise was 10.71 mm/yr.•The Yangtze Delta recorded accelerations in rate of sea-level rise in 8.72–8.18 ka, correspond to the pre-8.2 ka-event.
A global compilation of glacier advances and retreats for the past two millennia grouped by 17 regions (excluding Antarctica) highlights the nature of glacier fluctuations during the late Holocene. ...The dataset includes 275 time series of glacier fluctuations based on historical, tree ring, lake sediment, radiocarbon and terrestrial cosmogenic nuclide data. The most detailed and reliable series for individual glaciers and regional compilations are compared with summer temperature and, when available, winter precipitation reconstructions, the most important parameters for glacier mass balance. In many cases major glacier advances correlate with multi-decadal periods of decreased summer temperature. In a few cases, such as in Arctic Alaska and western Canada, some glacier advances occurred during relatively warm wet times. The timing and scale of glacier fluctuations over the past two millennia varies greatly from region to region. However, the number of glacier advances shows a clear pattern for the high, mid and low latitudes and, hence, points to common forcing factors acting at the global scale. Globally, during the first millennium CE glaciers were smaller than between the advances in 13th to early 20th centuries CE. The precise extent of glacier retreat in the first millennium is not well defined; however, the most conservative estimates indicate that during the 1st and 2nd centuries in some regions glaciers were smaller than at the end of 20th/early 21st centuries. Other periods of glacier retreat are identified regionally during the 5th and 8th centuries in the European Alps, in the 3rd–6th and 9th centuries in Norway, during the 10th–13th centuries in southern Alaska, and in the 18th century in Spitsbergen. However, no single period of common global glacier retreat of centennial duration, except for the past century, has yet been identified. In contrast, the view that the Little Ice Age was a period of global glacier expansion beginning in the 13th century (or earlier) and reaching a maximum in 17th–19th centuries is supported by our data. The pattern of glacier variations in the past two millennia corresponds with cooling in reconstructed temperature records at the continental and hemispheric scales. The number of glacier advances also broadly matches periods showing high volcanic activity and low solar irradiance over the past two millennia, although the resolution of most glacier chronologies is not enough for robust statistical correlations. Glacier retreat in the past 100–150 years corresponds to the anthropogenic global temperature increase. Many questions concerning the relative strength of forcing factors that drove glacier variations in the past 2 ka still remain.
Number of glacial advances, temperature reconstruction and climatic forcings. (A) Total solar irradiance anomalies (Steinhilber et al., 2009). (B) Reconstructed global volcanic aerosol forcing from sulfate composite records from tropical (bipolar) eruptions (Sigl et al., 2015). (C) Multi-proxy temperature reconstruction of the Northern Hemisphere (CE 1–1979 (red) with its 80-yr component (blue) and the instrumental record (green) (Moberg et al., 2005). (D) Number of glacial advances normalized and inverted (averaged for the high and mid latitudes of the Northern and Southern hemispheres and from the tropics, cumulative curves). Display omitted
•The LIA was a global phenomenon with maximum extents varying in time in different regions.•Global coherence of glacier advances are recognized in the 2nd millennium CE.•Glacier fluctuations broadly correspond with temperature in the past 2 ka.•Coherence of glacier advances with volcanic eruptions and solar variability in the past 1 ka.•No analogues of modern global glacier recession is recognized in the past 2 ka.
A continuous high-resolution record from a precisely-dated stalagmite spanning the last precessional cycle provides new insight into the dynamics of climate change from orbital to centennial scales. ...A 600-mm length stalagmite (LS46) collected from the Luoshui Cave, Hubei Province, Central China, was well-dated (a total of 24 230Th dates) and high-resolved sampled for oxygen and carbon stable isotopic measurements (2047 subsamples in total). The stalagmite LS46 δ18O is consistent with other published stalagmite δ18O time series in monsoonal China, and closely tracks changes in the Northern Hemisphere summer insolation (NHSI) on July 21st throughout the past 23.5 kyr. Besides, the stalagmite LS46 δ18O shows significant correlations with the reconstructed Dali lake-level history and tree-ring δ18O records in the marginal monsoon regions. On this basis, we interpret that the stalagmite LS46 δ18O reflects the large-scale monsoon circulation with a superimposed local climate signal that might be related to effective humidity. Furthermore, the stalagmite LS46 δ18O exhibited four long-lasting extremely weak monsoon events since 7 kyr B.P.. These four weak monsoon events corresponded well with the tree-ring record in the northwestern fringe of the East Asian summer monsoon (EASM) region. Notably, the good correspondence between the stalagmite record and the tree-ring record also provides a good chronological support for our assessment of the climate and cultural evolution during the middle-late Holocene transition, the medieval warm period (MWP) and Little Ice Age (LIA). During the early-middle Holocene, the detrended δ18O profile revealed 10 multi-centennial monsoon cycles with a duration of nearly 500 yr and the amplitude of ∼0.8‰. The wavelet analysis further discloses that the EASM has nearly 500 yr and 200 yr periodic oscillations in the early-middle Holocene, research indicated that the solar activity and the North Atlantic Oscillation (NAO)/North Atlantic Deep Water (NADW) jointly drive the dominant nearly 500 yr cycle of the Asian monsoon.
•A successive stalagmite δ18O/δ13C series from Central China over the past 23.5 kyr.•Stalagmite δ18O coincides with tree ring δ18O and lake level.•LS46 δ18O records 4 weak monsoon events since 7 kyr B.P. and corresponds well to the tree ring data in NW China.•∼500 yr periodicity of AM during the Early-Mid Holocene was forced by solar activity and the NAO.
The Holocene temperature discrepancy between paleoclimate reconstructions and climate model simulations—known as the Holocene temperature conundrum—calls for new high‐quality Holocene temperature ...records at high elevations. Here, we present a quantitative Holocene mean annual air temperature record based on a site‐specific branched glycerol dialkyl glycerol tetraethers calibration from a small remote alpine lake on the southeastern Tibetan Plateau. The record reveals a temperature history comprising a relatively cool early Holocene (before 7 ka) followed by a warmer mid‐ to late‐Holocene (after 7 ka), which was likely linked to increasing local annual insolation and greenhouse gases. Three cold events punctuated the general warming trend ca. 10.4 ka, 3.7 ka, and 1.7 ka BP, and correspond closely in time to ice rafting events in the North Atlantic, and to episodes of volcanism and/or unusual solar activity. The entire Holocene temperatures are cooler than the previously identified anthropogenic warming from 1990–2015 AD.
Plain Language Summary
The scarcity of high‐quality, quantitative Holocene temperature records from terrestrial archives, especially at high elevations, such as the Tibetan Plateau, limits our understanding of the temperature history of the Holocene. Here, we present a molecular fossil‐based mean annual air temperature record for the last 12,000 years from sediments preserved in a small remote alpine lake. The new record shows that the early Holocene was relatively cool and was followed by a warmer mid‐ to late‐ Holocene, which is consistent with results from climate modeling studies. This Holocene warming trend was probably due to increases in regional annual solar radiation and additional radiative forcing of greenhouse gases. The reconstruction captures the anthropogenic warming of the past 25 years (1990–2015 AD) and shows it to be unusual during the past 12,000 years.
Key Points
An unreported cooler early Holocene (before 7 ka BP) temperature record was presented at high elevations on the southeastern Tibetan Plateau
The entire Holocene mean annual temperatures are cooler than the previously identified anthropogenic warming at this site from 1990 to 2015 AD
Three multi‐centennial cold events centered on 10.4, 3.7, and 1.7 ka BP are observed in the record
Identifying the position of the Current Warm Period (CWP) in the context of the long‐term climatic trend is vital for understanding the impact of human activity on climate change. Reconstructions of ...summer temperature and precipitation in eight subregions of China over the past 22,000 years show that the CWP summer temperature and precipitation in these subregions are all lower than in the Early to Middle Holocene. The timing of the Holocene temperature and precipitation peaks in northern China (including Northwest China, North China, and Northeast China) is mainly determined by orbital forcing. Greenhouse gas forcing and the land ice‐sheet help to fine‐tune the timing of the climate maxima. These findings show that the climate since the Last Glacial Maximum in northern China is more sensitive to nonanthropogenic external forcings, whereas the summer precipitation in Southwest China since the early 20th century is controlled more by anthropogenically forced changes.
Plain Language Summary
Reconstructions of past climate are essential for understanding current warming trends and reasons under the natural climate and anthropogenic forcings. We provide a climate reconstruction in China over the past 22,000 years using a novel method combining proxy data and model simulations. Our results show that the summer temperature and precipitation during the Current Warm Period in the eight subregions of China are both significantly lower than those in the Early and Middle Holocene, and the long‐time summer temperature and precipitation variations are highly sensitive to orbital forcing. These results highlight the regional consistency in the climate response to external forcings.
Key Points
Summer temperature and precipitation during the Current Warm Period in China are not unprecedented over the past 22,000 years
The Holocene maxima of summer temperature and precipitation in different regions of China occur at about the same time (8.1–7.6 ka)
The variations of summer temperature and precipitation in northern China are mainly determined by insolation
Fire occurrence is driven by a complex interplay between vegetation, climatic, landform and human factors making it challenging to separate the individual effect of each variable. Here we present a ...reconstruction of the Holocene biomass burning history of two regions located in the Central European temperate zone that differ in the timing of the Middle Holocene expansion of broadleaf-dominated forest communities. This allowed us to investigate the effect of biotic changes on past fire activity. Multiple-site charcoal accumulation records were used to estimate regional-scale trends in biomass burning and to compare them with major trajectories of vegetation development. Extensive 14C-dated soil charcoal records collected within both regions were amalgamated using a cumulative probability function to identify a stand-scale proxy of past fire occurrence. Our results suggest that rising vegetation productivity driven by rapid Early Holocene climate amelioration enhanced biomass burning. The increased fire activity during this period was driven by both a drier- and warmer-than-present climate and easily flammable fuels produced by conifer-dominated vegetation. We identified an inhibiting effect of the concomitant Fagus sylvatica expansion on levels of biomass burning that occurred asynchronously between our mountain and mid-elevation sandstone regions 6500 cal yr BP and 4900 cal yr BP, respectively. The amount of compositional change in plant communities was more related to the transformation of major vegetation types than to fluctuations in fire activity levels. The divergent timing of the fire decline in response to the Fagus sylvatica expansion implies biotic control over biomass burning that is independent of a direct climatic influence.
•Pronounced inter-regional differences in fire history have been identified across Central Europe.•Increased fire activity during the Early Holocene was driven by both the climate and conifer-dominated vegetation.•An expansion of Fagus sylvatica during the Middle Holocene induced a marked decrease in biomass burning.•Broad-leaved trees exert significant control over biomass burning that is independent of a direct climatic influence.
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