The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Yongheng Chen - One of the best experts on this subject based on the ideXlab platform.
-
speleothem evidence for temporal spatial variation in the east asian summer monsoon since the Medieval Warm Period
Journal of Quaternary Science, 2012Co-Authors: P C Chu, Chenwu Fan, Yongheng ChenAbstract:Published annual-to-decadal-resolution stalagmite d 18 O records since AD 900 from six caves (Dongge, Furong, Heshang, Buddha, Shihua and Wanxiang) in China were analyzed to detect temporal and spatial variability of the East Asian Summer Monsoon strength, which strongly affects wet/dry conditions in eastern China. The empirical mode decomposition method was used to obtain trends of the six cave records. After the base trend was determined, d 18 O anomalies of each record were computed by subtracting the base trend. Mean d 18 O anomaly values of the detrended time series for each cave record were calculated for four Periods: (i) Medieval Warm Period (MWP; AD 900- 1250): (ii) Little Ice Age phase 1 (LIA-1; AD 1250-1550); (iii) Little Ice Age phase 2 (LIA-2; AD 1550-1850); and (iv) modern Period (MD; AD 1850-2000). From these anomalies, the temporal and spatial variability of wet/dry conditions has been identified. Positive values of the mean d 18 O anomalies indicating drier conditions appeared in the lower Yangtze River Drainage Area and Southeast Coast Area during MD-1, LIA-1 and MWP, whereas negative values existed in north, south and Yangtze areas of eastern China during LIA-2. The results agree with the dryness/wetness index reconstructed by Chinese historic records in general. These results illustrate that wet and dry conditions in different regions of eastern China could be opposite under monsoon influence, so that no single speleothem d 18 O record could represent the monsoonal climate in this vast region. Climatic patterns in the monsoonal region can be either a combination of Warm/wet and cold/dry or a combination of cold/wet and Warm/dry on annual-to- centennial scales. A 128-year Periodic cycle exists in all six cave records, whereas 64-year (possibly a harmonic of 128-year Periodicity) and 42-year Periodicities appear in Shihua, Heshang and Dongge records. These cycles may reflect the influence of solar activity on the East Asian Summer Monsoon. Copyright # 2012 John Wiley & Sons, Ltd.
-
the δ18o and δ13c records in an aragonite stalagmite from furong cave chongqing china a 2000 year record of monsoonal climate
Journal of Asian Earth Sciences, 2011Co-Authors: Zhonghong Lee, Naijung Wan, Chuanchou Shen, Daoxian Yuan, Yongheng ChenAbstract:Abstract A 7-cm long aragonite stalagmite, FR0510-1, from Furong Cave, Chongqing, was dated by 210Pb and 230Th methods, revealing a-2000-year record of climate history under the influence of the East Asian Monsoon. The FR0510-1 record resembles Dongge Cave DA record on 10–100-year scales, but quite different from the Wanxiang Cave WX42B record, indicating that while stalagmite δ18O record represents local/regional moisture change, spatial variability of the monsoonal rainfall over eastern China must take into account. During the past 2000 years, climate in Chongqing was relatively wet in the intervals of 50 BC–AD 250, AD 1150–1450 and AD 1600–1950, and relatively dry during the Periods of AD 250–1150 and AD 1450–1600. Dry conditions were prevailing over the Medieval Warm Period, whereas wet climates were dominant during the most time of the Little Ice Age in Chongqing area.
Michael G. Loso - One of the best experts on this subject based on the ideXlab platform.
-
Summer temperatures during the Medieval Warm Period and Little Ice Age inferred from varved proglacial lake sediments in southern Alaska
Journal of Paleolimnology, 2008Co-Authors: Michael G. LosoAbstract:For the heavily glaciated mountains of southern Alaska, few high-resolution, millennial-scale proxy temperature reconstructions are available for comparison with modern temperatures or with the history of glacier fluctuations. Recent catastrophic drainage of glacier-dammed Iceberg Lake, on the northern margin of the Bagley Icefield, exposed subaerial outcrops of varved lacustrine sediments that span the Period 442–1998 AD. Here, an updated chronology of varve thickness measurements is used to quantitatively reconstruct melt-season temperature anomalies. From 1958 to 1998, varve thickness has a positive and marginally significant correlation with May–June temperatures at the nearest coastal measurement stations. Varve sensitivity to temperature has changed over time, however, in response to lake level changes in 1957 and earlier. I compensate for this by log-transforming the varve thickness chronology, and also by using a 400-year-long tree-ring-based temperature proxy to reconstruct melt-season temperatures at Iceberg Lake. Regression against this longer proxy record is statistically weak, but spans the full range of occupied lake levels and varve sensitivities. Reconstructed temperature anomalies have broad confidence intervals, but nominally span 1.1°C over the last 1500+ years. Maximum temperatures occurred in the late twentieth century, with a minimum in the late sixth century. The Little Ice Age is present as three cool Periods between 1350 and 1850 AD with maximum cooling around 1650 AD. A Medieval Warm Period is evident from 1000 to 1100 AD, but the temperature reconstruction suggests it was less Warm than recent decades—an observation supported by independent geological evidence of recent glacier retreat that is unprecedented over the Period of record.
Jianguo Huang - One of the best experts on this subject based on the ideXlab platform.
-
a 2 326 year tree ring record of climate variability on the northeastern qinghai tibetan plateau
Geophysical Research Letters, 2003Co-Authors: Qibin Zhang, Guodong Cheng, Tandong Yao, Xingcheng Kang, Jianguo HuangAbstract:[1] High-resolution climate proxy records covering the last two millennia on the Qinghai-Tibetan Plateau are scarce yet essential to evaluation of the patterns, synchroneity and spatial extent of past climatic changes including those in the Medieval Warm Period (MWP) and the Little Ice Age (LIA). Here we present a 2326-year tree-ring chronology of Sabina przewalskii Kom. for Dulan area of northeastern Qinghai-Tibetan Plateau. We find that the annual growth rings mainly reflect variations in regional spring precipitation. The greatest change in spring precipitation during the last two millennia seems to occur in the second half of the 4th century. The North Atlantic MWP was accompanied by notable wet springs in the study region during A.D. 929–1031 with the peak occurring around A.D. 974. Three intervals of dry springs occurred in the Period of LIA. Our tree-ring data will facilitate intercontinental comparisons of large-scale synoptic climate variability for the last two millennia.
Barbara Kutchko - One of the best experts on this subject based on the ideXlab platform.
-
a 2000 year varve based climate record from the central brooks range alaska
Journal of Paleolimnology, 2009Co-Authors: Broxton W Bird, Mark B Abbott, Bruce P Finney, Barbara KutchkoAbstract:Varved minerogenic sediments from glacial-fed Blue Lake, northern Alaska, are used to investigate late Holocene climate variability. Varve-thickness measurements track summer temperature recorded at Atigun Pass, located 41 km east at a similar elevation (r2 = 0.31, P = 0.08). Results indicate that climate in the Brooks Range from 10 to 730 AD (varve year) was Warm with precipitation inferred to be higher than during the twentieth century. The varve-temperature relationship for this Period was likely compromised and not used in our temperature reconstruction because the glacier was greatly reduced, or absent, exposing sub-glacial sediments to erosion from enhanced precipitation. Varve-inferred summer temperatures and precipitation decreased after 730 AD, averaging 0.4°C above the last millennial average (LMA = 4.2°C) from 730 to 850 AD, and 0.1°C above the LMA from 850 to 980 AD. Cooling culminated between 980 and 1030 AD with temperatures 0.7°C below the LMA. Varve-inferred summer temperatures increased between 1030 and 1620 AD to the LMA, though the Period between 1260 and 1350 AD was 0.2°C below the LMA. Although there is no equivalent to the European Medieval Warm Period in the Blue Lake record, two Warm intervals occurred from 1350 to 1450 AD and 1500 to 1620 AD (0.4 and 0.3°C above the LMA, respectively). During the Little Ice Age (LIA; 1620 to 1880 AD), inferred summer temperature averaged 0.2°C below the LMA. After 1880 AD, inferred summer temperature increased to 0.8°C above the LMA, glaciers retreated, but aridity persisted based on a number of regional paleoclimate records. Despite Warming and glacial retreat, varve thicknesses have not achieved pre-730 AD levels. This reflects limited sediment availability and transport due to a less extensive retreat compared to the first millennium, and continued relative aridity. Overall, the Blue Lake record is similar to varve records from the eastern Canadian Arctic that document a cool LIA and twentieth century Warming. However, the occurrence and timing of events, such as the LIA and Medieval Warm Period, varies considerably among records, suggesting heterogeneous climatic patterns across the North American Arctic.
P C Chu - One of the best experts on this subject based on the ideXlab platform.
-
speleothem evidence for temporal spatial variation in the east asian summer monsoon since the Medieval Warm Period
Journal of Quaternary Science, 2012Co-Authors: P C Chu, Chenwu Fan, Yongheng ChenAbstract:Published annual-to-decadal-resolution stalagmite d 18 O records since AD 900 from six caves (Dongge, Furong, Heshang, Buddha, Shihua and Wanxiang) in China were analyzed to detect temporal and spatial variability of the East Asian Summer Monsoon strength, which strongly affects wet/dry conditions in eastern China. The empirical mode decomposition method was used to obtain trends of the six cave records. After the base trend was determined, d 18 O anomalies of each record were computed by subtracting the base trend. Mean d 18 O anomaly values of the detrended time series for each cave record were calculated for four Periods: (i) Medieval Warm Period (MWP; AD 900- 1250): (ii) Little Ice Age phase 1 (LIA-1; AD 1250-1550); (iii) Little Ice Age phase 2 (LIA-2; AD 1550-1850); and (iv) modern Period (MD; AD 1850-2000). From these anomalies, the temporal and spatial variability of wet/dry conditions has been identified. Positive values of the mean d 18 O anomalies indicating drier conditions appeared in the lower Yangtze River Drainage Area and Southeast Coast Area during MD-1, LIA-1 and MWP, whereas negative values existed in north, south and Yangtze areas of eastern China during LIA-2. The results agree with the dryness/wetness index reconstructed by Chinese historic records in general. These results illustrate that wet and dry conditions in different regions of eastern China could be opposite under monsoon influence, so that no single speleothem d 18 O record could represent the monsoonal climate in this vast region. Climatic patterns in the monsoonal region can be either a combination of Warm/wet and cold/dry or a combination of cold/wet and Warm/dry on annual-to- centennial scales. A 128-year Periodic cycle exists in all six cave records, whereas 64-year (possibly a harmonic of 128-year Periodicity) and 42-year Periodicities appear in Shihua, Heshang and Dongge records. These cycles may reflect the influence of solar activity on the East Asian Summer Monsoon. Copyright # 2012 John Wiley & Sons, Ltd.
-
temporal and spatial variation of δ18o in china since Medieval Warm Period
2010Co-Authors: P C ChuAbstract:High-resolution δO data (yearly) since AD 900 from six caves (Dongge, Furong, Heshang, Wanxiang, Buddha, Shihua) in China was analyzed to detect decadal and centennial variability of wet/dry in the Asian Monsoon region. The empirical mode decomposition method (Huang et al., 1998) was used to obtain trends for the six cave data. The nine-year running average was conducted on the detrened data (ΔδO, called anomaly) to filter out high-frequency fluctuation such as the interannual variability. Mean values of anomaly for each cave were calculated for 5 Periods: (1) Medieval Warm Period (MWD, AD 900 –AD 1100), (2) little ice age phase-1 (LIA-1, AD 1250 – AD 1550), (3) little ice age phase-2 (LIA-2, AD 1550 – AD 1850), (4) modern Period-1 (MD-1, AD 1850 – AD 1950), and (5) modern Period-2 (MD-2, AD 1950-2000). Anomalies in MWP and LIA-2 has opposite signs: negative anomaly (strong monsoon) in MWP and positive anomaly (weak monsoon) in LIA-2 in (Dongge, Wanxiang) cave data otherwise in (Budda, Furong, Heshang, Shihua) cave data. In LIA-1, all the six caves have positive anomalies (weak monsoon). In MD-1 (AD 1850-AD 1950), all the six caves have negative anomalies; and in MD-2 (AD 1950 – AD 2000), all the caves except Buddha have negative anomalies. It implies strong monsoon with global Warming trend. Spectral analysis was also conducted on the detrended data of the six caves. The above observational studies show the following results: (1) Monsoon strength has spatial variations; (2) Stronger monsoon occurred under both Warm and cold climatic conditions. One should not use the relationship of Warm condition ― stronger summer monsoon to interpret monsoonal climates in short time scales (less than centennial scale); and (3) Monsoon strengthening continues.