Search

Dynamic fluctuations in sea surface temperature within the North Atlantic Ocean (NA-SST) exert a pivotal influence on global climate change. Yet, the specific impacts of these variations on the temperature shifts within the Qinling-Bashan Mountains (QBM) of China, remain to be fully elucidated. Furthermore, a debate surrounding the manifestation of the Little Ice Age (LIA) within the QBM is ongoing, primarily due to the scarcity of reliable, long-term, and high-resolution temperature records. To bridge these knowledge gaps, in this paper, we present a ∼ 250-year temperature reconstruction (Tmax 11 – 7) developed based on a tree-ring-width chronology from the QBM. The new reconstruction not only aligns with a local winter temperature reconstruction based on historical document evidence, but also reveals robust regional and hemispheric temperature signals. Intriguingly, the study shows that the warming trend observed in the QBM since the Industrial Era is less pronounced than that witnessed across China and the Northern Hemisphere. The Tmax 11 – 7 reconstruction provides a glimpse into the final stages of the LIA, highlighting a relatively colder 19 th century followed by a warmer 20 th century. Notably, the warming trend post-1970s remains within the bounds of the 250-year temperature framework. The research further uncovers that NA-SST has predominantly governed the QBM's temperature fluctuations over the past centuries, as evidenced by the tight positive correlation between Atlantic multidecadal Oscillation (AMO)/Atlantic multidecadal variability (AMV) and Tmax 11 – 7. However, this dominant influence of NA-SST was temporarily subdued between 1900 and 1930 CE due to the interference of Pacific Decadal Oscillation (PDO). This finding serves as a reminder that future temperature projections for the QBM must account not only for the primary role of NA-SST but also the modulating effects of the PDO. The study is essential for shaping effective environmental management and adaptation strategies in the region. • A ∼ 250-year temperature reconstruction is developed using tree rings from the QBM. • The QBM saw the last stage of the LIA and recent warming is within historical frame. • North Atlantic SST (NA-SST) played a positive and dominant role on QBM'S temperature changes. • Weakened NA-SST's impact on temperature in 1900–1930 CE was due to PDO's interference. [ABSTRACT FROM AUTHOR]

Mountain glaciers are one of the most sensitive indicators of climate change. Reconstructing past glacier extents provides valuable insights into the climate change for specific regions where instrumental records are not enough and even absent. In the paper we mapped the outlines for 691 Little Ice Age (LIA) glaciers in terms of prominent moraines beyond contemporary glaciers in the Tanggula Mountains, central Tibetan Plateau (TP). Based on these glacier outlines, we reconstructed the ice thicknesses and surfaces for the LIA glaciers in the region. Accordingly, we calculated the equilibrium-line altitudes (ELAs) for contemporary and LIA glaciers. By comparing the ELAs between the contemporary and LIA glaciers, we estimated the LIA summer temperature decreases in different subregions of the Tanggula Mountains. Since the LIA, the ELA have risen by 35.6 ± 18.8 m, 26.1 ± 17.6 m, and 63.1 ± 38.6 m in the respective western, central, and eastern subregions of the Tanggula Mountains. Assuming no change in precipitation, the LIA summer temperature would decrease by 0.22 ± 0.12 °C, 0.14 ± 0.09 °C, and 0.34 ± 0.21 °C in the three subregions, respectively. Moreover, glaciers in the western, central, and eastern subregions have lost 13.3%, 23.9%, and 42.8% of their area, 15.4%, 25.3%, and 39.6% of their length, and 20.8%, 39.0%, and 61.0% of their volume, respectively. By compiling the LIA ELA data from previous studies, we also estimated the LIA summer temperature changes for other regions of the TP. The LIA ELA and summer temperature changes relative to the present showed a decreasing trend from the edges towards the interior on the TP. • LIA glaciers and summer climate were reconstructed at the Tanggula Mountains. • LIA summers were 0.22 ± 0.12 °C, 0.14 ± 0.09 °C, and 0.34 ± 0.21 °C cooler than present in three subregions. • Summer temperature change had a decreasing trend from the edges towards the interior on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

The vegetation history of the central Tibetan Plateau over the last two millennia provides an important baseline for exploring future vegetation evolution. In this paper, we analyze high-resolution records of pollen, grain-size, total organic carbon (TOC) and total nitrogen (TN) for a 66.5 cm deep sediment core collected from Beilei Co on the central Tibetan Plateau. Between ca. 210 CE and 1988 CE, pollen spectra together with other proxies show that the Beilei Co region was covered by alpine steppe and experienced a relatively stable environment, with only slight changes in vegetation composition and minor climatic variations. However, since 1988 CE, abundances of Artemisia and Cyperaceae have begun to increase, while those of Chenopodiaceae (current accepted Latin name is Amaranthaceae) and Asteraceae have decreased sharply. Both the pollen assemblages and other proxies show that the study area is currently undergoing a major change and that the period of vegetation stability that has characterized the past two millenia has now ended. We argue that the recent changes in the vegetation may be caused by increasing precipitation and/or thawing permafrost due to global warming. In the future, the alpine steppe around Beilei Co may be replaced by alpine meadow. • High-resolution pollen spectra covering last two millennia completed for the central Tibetan Plateau. • Vegetation of the central Tibetan Plateau is stable for most of the time until the last few decades. • The central Tibetan Plateau is experiencing an unprecedented phase of wetting. [ABSTRACT FROM AUTHOR]

In this paper, we undertake a high-resolution palynological analysis of a sediment core covering the last 1500 years obtained from Lake Ayakum in the northern Tibetan Plateau, to improve the understanding of regional climate fluctuations and their driving mechanisms. The pollen spectra are dominated by herbaceous species such as Artemisia , Chenopodiaceae, Cyperaceae and Poaceae, which grew in various alpine desert settings. Four pollen assemblage zones are identified using stratigraphically constrained cluster analysis, representing climate history at different stages. The Artemisia /Chenopodiaceae (A/C) ratio and axis score of the first principal component are used to infer regional moisture conditions and reveal a temporal pattern that is consistent with various records from central Asia. The source of Cyperaceae pollen is mainly from marsh wetlands distributed around the lake, which responded sensitively to the lake level fluctuations. In contrast, arboreal pollen is mainly a long-distance transported component, reflecting changes in regional vegetation. Our findings show that the northern Tibetan Plateau experienced relatively wet conditions during the Dark Age Cold Period and the Little Ice Age, while relatively dry conditions occurred during the Medieval Warm Period and the last two centuries. Fluctuations in moisture levels are broadly consistent with moisture records elsewhere in western China, and show a good correlation with phase changes of the North Atlantic Oscillation. The climate changes in the northern Tibetan Plateau are supposed to be primarily triggered by the NAO phases through south-north migrations of the mid-latitude westerlies during the late Holocene. • Fossil pollen based 1500-year vegetation and climate changes on the northern Tibetan Plateau. • Major pollen species were analyzed and interpreted in terms of regional moisture variations. • Four vegetation and climate stages during the late Holocene were determined accordingly. • NAO phases affected northern TP climate through south-north migrations of the westerlies. [ABSTRACT FROM AUTHOR]

In this paper, the stratigraphic occurrence of n -alkanes (C n) is investigated in three peat cores (Mildred, JPH4 and McMurray) from the ombrotrophic peatlands in northeastern Alberta, Canada, to determine their origin, biomass input, and paleoclimatic significance. The molecular composition of n -alkanes is dominated by the >C 21 medium- to long-chain homologues, with a strong odd over even predominance. A number of n -alkane-based indices (e.g. predominant n -alkane, C 23 /C 29 , C 23 /(C 27 + C 31), P aq , ACL, and CPI), show changing conditions in the organic matter (OM) input from Sphagnum species or terrestrial vascular plants, which increasingly contributed upwards in the peat profiles, and through time. P aq and C 23 /(C 27 + C 31) proxies are similar in the three cores, and allow us to infer vegetation variations that coincide with the climate alternations of the Medieval Warm Period (MWP), Little Ice Age (LIA), and modern Recent Warming (RW). The utilization of ACL-ket and (C 23 + C 25)/(C 27 + C 29 + C 31)-ket proxies, performed in comparison with n -alkane proxies, further support the biomarker-based reconstructions of paleoclimate variations over recent centuries. This study suggests that n -alkane homologues are sensitive to vegetation and climate changes and thus are reliable biomarkers for tracking past shifts in vegetation and climate variations in peat archives. • Determine organic matter source of peat sediments from n -alkane biomarkers. • C 23 /(C 27 +C 31) n -alkane proxy is proposed and can effectively characterize climate changes. • P aq proxy indication could be misleading when the contribution of Sphagnum fuscum to the peat is large. • n -Alkan-2-one proxy is studied to further confirm the biomarker-based reconstruction of paleoclimatic changes. [ABSTRACT FROM AUTHOR]

The Kumaun region of India in the northwestern Himalaya experiences complex rainfall patterns, receiving precipitation both during the summer monsoon (June to September) as well as during winter months dominated by westerlies (October to March). In this paper, we present a multi-proxy palaeoclimate record spanning the last ∼1500 years from Tadag Taal, an intermontane lake in Kumaun, India. Our dataset (stable isotope ratios, grain size, trace element ratios) suggests the occurrence of four long-term precipitation cycles of high and low rainfall coinciding with the Dark Ages Cold Period (DACP, ∼475–850 CE), Medieval Climate Anomaly (MCA ∼900–1300 CE), Little Ice Age (LIA, ∼1450–1800 CE) and Current Warm Period (CWP, ∼1850 CE to Present). We infer multi-decadal to centennial-scale shifts in the Indian summer monsoon co-varying with changes in El Niño-Southern Oscillation (ENSO) activity superimposed by changes in solar insolation. To correlate our time-series from the northwestern Himalaya with the Core Monsoon Zone and understand coherency in precipitation between the two regions, we applied the Wavelength Coherency Test. Our data suggest wet conditions during the early phase of the LIA (∼1450–1640 CE) and dry conditions in the later phase of the LIA from ∼1640–1800 CE. The wet conditions in the early LIA were perhaps driven by increased winter precipitation. This is in contrast to Central India that witnessed dry conditions during the entire duration of the LIA. This study thus suggests that monsoon strength was different during earlier and later phase of the LIA. Further, the LIA did not witness uniform climate variability through its duration as has been reported in some European and Chinese proxy records. • Study of proxy record from Tadag Taal lake, northwestern Himalaya since CE 475. • Both dry and wet events have been reported during the MCA and LIA. • The early part of LIA (∼1450–1640 CE) was wet and later LIA (∼1640–1800 CE) was dry. • During the MCA, C 3 -type vegetation was predominant. [ABSTRACT FROM AUTHOR]

In this paper, we use δ 13 C and δ 15 N of serial samples of dentine collagen from archaeological springbok teeth as a novel high-resolution but short-term palaeoenvironmental proxy. Two adult and seven juvenile springbok ( Antidorcas marsupialis ) teeth from the archaeological site SK400 were analyzed. This site, located in the Namaqualand desert on the west coast of South Africa has yielded a large number of small-medium bovids, likely all springbok. These springbok were killed in a single episode between 1438 and 1641 CE, during the Little Ice Age (LIA). The juvenile springbok were significantly more depleted in 13 C and enriched in 15 N compared with the adults. During the four to six months over which their teeth developed, the juveniles consumed a higher proportion of C 3 plants and were exposed to greater aridity than the adults at equivalent ages. Based on dental wear, the adults are estimated to be between 3.5 and 7.5 years old at death, so the isotope values in their teeth record diet and environmental conditions several years earlier. In addition, the juveniles (but not the adults) show a trend towards more negative δ 13 C values and very high δ 15 N (up to + 18.9‰) during the period of tooth formation, truncated by the animals' death. We infer that the animals were killed during an extreme drought. Informed by the archaeological evidence, we surmise that this was probably a herd of springbok on ‘trek’ in search of food and water, as this species is known to do during droughts. Although palaeoenvironmental proxies for the region as a whole suggest that Namaqualand was cool and wet during the Little Ice Age, this study indicates at least one period of drought, contributing to the developing picture of highly variable climates in southern Africa during the Holocene. [ABSTRACT FROM AUTHOR]

This paper provides a high-resolution temperature reconstruction for the last Millennium from Lake Atnsjøen, SE Norway (61°52′31″N, 10°10′37″E). The sedimentary record reveals strong influence of the large-scale global climate patterns on the local climate in southern part of Eastern Norway. We reconstructed mean July air temperature using Chironomidae-based transfer function and fossil Chironomidae assemblages. The reconstruction was supported by a selection of climate-sensitive geochemical and paleoecological sedimentary proxies of terrestrial and aquatic origin, including Cladocera, pollen and macrofossils. Presented results revealed that summer temperatures were 1–2 °C warmer than the mean Millennial temperatures during the 11th, 13th, 15th and 20th centuries and 1–2 °C lower during the 12th, 14th, 17th–18th centuries. A persistent cold period, the Little Ice Age (LIA), occurred between 1550 and 1800 CE, was interrupted by a short warming at 1650 CE. The recognized regional climate fluctuations during the last Millennium affected the lake and its catchment, of which the strongest impact was caused by the LIA cooling. During the LIA the catchment vegetation was impacted by climate deterioration and the lake productivity reached its lowest level during the last Millennium. The current temperature reconstruction is in agreement with a previous continental scale temperature reconstruction for Europe. From obtained results it emerges that during the LIA the climate of western Scandinavia has been dictated by the atmospheric patterns originating from the North Atlantic. [ABSTRACT FROM AUTHOR]

Abstract: This paper documents the occurrence of the Little Ice Age (LIA) in the El Azufre and El Peñón glaciers at 35°S and in the Las Choicas and Las Damas glaciers at 34°55′S in the headwaters of the Rio Grande basin in the Central Andes of Argentina. Moraine morphology, stratigraphic relationships, radiocarbon ages obtained from peat on these glacial deposits and the proximity to the active glaciers enabled us to reconstruct the LIA advance in this area. The LIA maximum advance occurred between cal. yr 1550 and 1720 AD, and a readvance occurred around cal. yr 1830 AD. In addition, glacier fluctuations of the Las Vacas and Güssfeltd glaciers (33°S) and El Peñón and El Azufre glaciers were documented from the end of the 19th century to the present based on historical and aerial photographs, and satellite images. The glaciers showed a marked retreat during 1894–2007. Minor readvances occurred in the 1980s and 1990s, which could be related with strong warm ENSO events during these decades. Our results are consistent with observations made by other authors in the region. [Copyright &y& Elsevier]

Abstract: This paper presents an updated, extensive review of glacier fluctuations during the past 1000years in the extratropical Andes of South America between ca. 17° and 55°S. Given the variety of environmental conditions and evidence available for glacier fluctuations across this wide latitudinal range, regional accounts are given for the Desert Andes (∼17°–31°S), the Andes of central Chile and Argentina (31°–36°S), and the North (36°–45°S) and South (45°–55°S) Patagonian Andes. The techniques, dating limitations, and interpretations of the glacier records along this transect are also discussed. Information on glacier fluctuations in the Desert Andes is limited to the 20th century. Documentation on past glacier variations is more abundant in the Central Chilean-Argentinean Andes, but the number of chronologies dealing with glacier fluctuations prior to the 1900s is also limited. Most records indicate that glaciers were generally more extensive prior to the 20th century, with dates of maximum expansion ranging from the 16th to the 19th centuries. The number and extent of glaciers increase significantly in the Patagonian region, where the evidence available for dating glacier variations during the past centuries is more abundant and the dating control for glacier events is generally better than in the northern parts of the study area. For some Patagonian glaciers, maximum Little Ice Age (LIA) or post-LIA advances have been precisely dated by dendro-geomorphological determinations or in situ measurements. However, for most sites, the evidence available is still preliminary and there is considerable variability in the extent and timing of events related to the maximum LIA expansion identified in most areas between the 16th and 19th centuries. Evidence is starting to appear at a growing number of sites for glacier advances during the first half of the past millennium. These events were generally less extensive than the LIA maximum pulses. Despite the occurrence of several post-LIA readvances over the past 100–110years, most areas in the Andes of extratropical South America have experienced a general pattern of glacier recession and significant ice mass losses. The differences in the glacier histories observed at local and regional scales probably reflect the inherent limitations associated with the glacier records and/or the dating techniques used in each case together with the varying dominance of precipitation, temperature and other climatic and non-climatic factors on glacier mass balance and glacier dynamics. These differences indicate that the late Holocene glacier history of southern South America is more complex than commonly assumed. The evidence discussed in this study highlights not only the immense potential for glaciological studies of this region but also a significant need for an increased number of detailed, well-dated records of glacier fluctuations. [Copyright &y& Elsevier]

Semi-arid regions are among the most vulnerable areas prone to the negative impacts of climate change. Long-term high-resolution proxy climate data will enable us to put the recent climate trends into a long-term context of natural climate variability. We developed the hitherto first regional ring-width chronology (1450–2015C.E.) from Cupressus sempervirens L. in the Zagros Mountains, western Iran and reconstructed precipitation variability for the semi-arid region during the period 1560–2015C.E. Climate-growth relationships revealed that precipitation and minimum temperatures are positively correlated with radial growth, whereas maximum temperatures reveal negative impacts. Spatial correlations with gridded precipitation data, Palmer drought severity index (PDSI), and standardized precipitation-evapotranspiration index (SPEI 01) further indicate that the climate signals contained in tree-ring width variations capture the precipitation variability in the Near East and other eastern Mediterranean regions. The southern Zagros Mts. experienced multiple megadroughts during the reconstructed period. The longest dry period occurred from 1956 to 1971 and the highest frequency of dry events occurred in the 20th century. In addition, documented famines in Iran occurred within prolonged droughts. The southern Zagros Mts. has experienced high frequency of extreme/severe dry events and long dry phases during the Little Ice Age (1560–1850C.E.). The reconstructed dry and wet events occurred irregularly, and one-year and two-year drought/wet events showed the highest frequency during the reconstructed period, highlighting the importance of sustainable water management strategies for the semi-arid southern Zagros region. • Mediterranean cypress are reliable proxies for climate reconstructions in SW Iran. • C. sempervirens growth is mainly limited by precipitation and maximum temperatures. • High frequencies of extreme dry and wet events have occurred in the 20th century. • One-year and two-year drought/wet years showed the highest frequencies. • Large-scale climate indices have strong influence on rainfall patterns in SW Iran. [ABSTRACT FROM AUTHOR]