East Asian summer monsoon

The Japan Sea is directly influenced by the Asian monsoon, a system that transports moisture and heat across southeast Asia during the boreal summer, and is a major driver of the Earth's ocean-atmospheric circulation. Foraminiferal and facies analyses of a 460-kyr record from Integrated Ocean Drilling Program Expedition 346 Site U1427 in the Japan Sea reveal a record of nutrient flux and oxygenation that varied due to sea level and East Asian monsoon intensity. The East Asian summer monsoon (EASM) was most intense during marine isotope stage (MIS) 5e, MIS 7e, MIS 9e, and MIS 11c when the Tsushima Warm Current flowed into an unrestricted well-mixed normal salinity Japan Sea, whereas East Asian winter monsoon (EAWM) conditions dominated MIS 2, MIS 4, MIS 6, and MIS 8 when sea level minima restricted the Japan Sea resulting in low-salinity and oxygen conditions in the absence of Tsushima flow. Reduced oxygen stratified, low-salinity, and higher productivity oceanic conditions characterize Terminations TV, TIII, TII, and TI when East China Sea coastal waters breached the Tsushima Strait. Chinese loess, cave, and Lake Biwa (Japan) and U1427 proxy records suggest EASM intensification during low to high insolation transitions, whereas the strongest EAWM prevailed during lowest insolation periods or high to low insolation transitions. Ice sheet/CO 2 forcing leads to the strongest EAWM events in glacials and enhanced EASM in interglacials. Mismatches between proxy patterns suggest that latitudinal and land/sea thermal contrasts played a role in East Asian monsoon variability, suggesting that a complex interplay between ice sheet dynamics, insolation, and thermal gradients controls monsoonal intensity.

Paleoclimatic conditions associated with the East Asian monsoon are reconstructed for the Mid- to Late-Holocene using δ18O values (819 measurements) from a precisely dated (10 230Th dates) aragonite stalagmite from Lianhua Cave, Hunan Province, China. δ18O values (− 1.6‰ to − 7.0‰) are interpreted to reflect the precipitation amount effect related to the strength of summer monsoonal circulation. Throughout this period, the intensity of East Asian summer monsoonal circulation declined in response to changes in insolation and a southward shift in the Intertropical Convergence Zone (ITCZ). Punctuating this first-order trend are abrupt millennial- to decadal-scale fluctuations, the most prominent of which occurred around 3337 ± 5 yr BP and records a dramatic weakening in summer monsoonal circulation that coincides with the beginning of Neoglacial conditions. Comparisons between the δ18O values of stalagmite A1 and previously published data from stalagmite HS-4 from Heshang Cave and stalagmites D4 and DA from Dongge Cave, China, demonstrate a similar regional response to changes in East Asian monsoonal circulation. Several spectral analysis techniques and wavelet analysis were applied to these stalagmite records to evaluate the nature and character of cyclicity in the East Asian monsoon during the Holocene. Multi-Taper Method (MTM), Lomb–Scargle, and Single Spectrum Analysis (SSA) results reveal common periodicities that are unlikely to be artifacts of any single technique. The periodicities expressed in the stalagmite δ18O records occur at both solar and non-solar frequencies and support previous interpretations that variability in monsoonal circulation responds to both solar forcing and internal climatic mechanisms. Wavelet analysis demonstrates that some of these frequencies are intermittent and recur at semi-regular intervals, which may indicate long-term cyclicity that is unconstrained by the chronology of the record.

The tropics are the main source of the atmosphere's sensible and latent heat, and water vapour, and are therefore important for reconstructions of past climate. But long, accurately dated records of southern tropical palaeoclimate, which would allow the establishment of climatic connections to distant regions, have not been available. Here we present a 210,000-year (210-kyr) record of wet periods in

The South China Sea (SCS), characterized by a large continental shelf, is located at the edge of the Asian monsoon domain. In this study, two marine sediment cores from the northern SCS (NSCS) continental slope were investigated to construct composite vegetation and precipitation isotopic composition records based on the d 13 C and dD values of plant-wax n-alkanes throughout the Holocene (last 11,200 years; i.e. 11.2 ka). The composite d 13 C wax record indicates an overall predominance of C 3 vegetation over the last 11.2 ka. Before 8 ka BP, higher d 13 C wax values are attributed to preferential wax input from grassland and wetland biomes on the exposed continental shelf. After the inundation of the shelf by eustatic sea level rise until ca. 8 ka BP grassland and wetland biomes suffered a major size reduction and arboreal vegetation became better represented in the d 13 C wax record. The composite temperature corrected dD wax-T record suggests that moisture source variability drove precipitation isotopic composition changes during the Holocene. Lower dD wax-T values before 8.3 ka BP are interpreted as a larger moisture contribution by Pacific Ocean tropical cyclones, whereas higher dD wax-T values after 8.5 ka BP are interpreted as a larger moisture contribution from the Indian Ocean summer monsoon. Higher incidence of tropical cyclones in the NSCS during the Early Holocene was related to a temporary westward shift of the Western Pacific Warm Pool and enhanced insolation over the Northern Hemisphere. Both external and internal forcing mechanisms regulated moisture source changes in East Asia during the Holocene.

Climate model faces considerable difficulties in simulating the rainfall characteristics of southwest summer monsoon. In this study, the dynamical downscaling of European Centre for Medium-Range Weather Forecast's (ECMWF's) ERA-Interim (EIN15) has been utilized for the simulation of Indian summer monsoon (ISM) through the Regional Climate Model version 4.3 (RegCM-4.3) over the South Asia CoOrdinated Regional Climate Downscaling EXperiment (CORDEX) domain. The complexities of model simulation over a particular terrain are generally influenced by factors such as complex topography, coastal boundary, and lack of unbiased initial and lateral boundary conditions. In order to overcome some of these limitations, the RegCM-4.3 is employed for simulating the rainfall characteristics over the complex topographical conditions. For reliable rainfall simulation, implementations of numerous lower boundary conditions are forced in the RegCM-4.3 with specific horizontal grid resolution of 50 km over South Asia CORDEX domain. The analysis is considered for 30 years of climatological simulation of rainfall, outgoing longwave radiation (OLR), mean sea level pressure (MSLP), and wind with different vertical levels over the specified region. The dependency of model simulation with the forcing of EIN15 initial and lateral boundary conditions is used to understand the impact of simulated rainfall characteristics during different phases of summer monsoon. The results obtained from this study are used to evaluate the activity of initial conditions of zonal wind circulation speed, which causes an increase in the uncertainty of regional model output over the region under investigation. Further, the results showed that the EIN15 zonal wind circulation lacks sufficient speed over the specified region in a particular time, which was carried forward by the RegCM output and leads to a disrupted regional simulation in the climate model.

The South China Sea (SCS) is well connected with the western Pacific and influenced by the East Asian monsoon. We have examined temporal variations in radiocarbon marine reservoir ages (R) and regional marine reservoir corrections (ΔR) of the SCS during the Holocene using paired measurements of AMS 14C and TIMS 230Th on 20 pristine corals. The results show large fluctuations

Marine sediment core MD012394 from the Vietnam coastal upwelling area in the western South China Sea was investigated in order to reconstruct the last Quaternary monsoon upwelling based on planktic foraminifer fauna assemblages and fauna-based sea surface temperature (SST) estimates. The age model of core MD012394 was constructed using oxygen isotope stratigraphy of the planktic foraminifer G. sacculifer, with 10 accelerator mass spectrometry (AMS) 14C dating of planktic foraminifers from the sediment samples. Our studies on the relative and absolute abundances of planktic foraminifer assemblages reveal eight dominant species in core MD012394: N. dutertrei + N. pachyderma (right coiling), G. ruber, G. glutinata, G. sacculifer, P. obliquiloculata, G. menardii + G. tumida, G. calida, and G. inflata. In a Q-mode factor analysis of the fauna abundance data, the fauna factors show variations that do not parallel the glacial/interglacial changes throughout the last 135 kyr. The relative a...

The East Asian climate history during the Neogene is a complicated and contentious issue, in particular because of its bearing on the development of the East Asian monsoon and Tibetan uplift chronology. Here we present a paleoprecipitation analysis based on mean molar tooth height (hypsodonty) of large herbivorous mammals to investigate the spatial pattern of climate zonation in East Asia during the middle Miocene. We show a generally humid and uniform situation before the late middle Miocene, replaced by a mid-latitude ...

Received 23 July 2006; revised 18 September 2006; accepted 19 October 2006; published 20 December 2006. [1] The impact of the Atlantic Multidecadal Oscillation (AMO) on the Asian summer monsoon is investigated using a coupled atmosphere-ocean global general circulation ...

A coupled approach based on clay mineral assemblages and isotopic data (Sr and Nd) of sediment from Ocean Drilling Program (ODP) Site 1145 has been used to trace the sources of sediment feeding the northern part of the South China Sea, and to investigate the evolution of East Asian monsoon intensity over the last 450 ky. Clay mineral assemblages are dominated by illite and smectite, with lesser abundance of chlorite and kaolinite. 87Sr / 86Sr and ɛNd(0) isotopic data, combined with the smectite / (illite + chlorite) ratio, indicate that the Pearl River is the main contributor for detrital material to the northern margin of the SCS, with variable continental input of volcanic material derived from the erosion of the Luzon Arc. These inputs follow the low-latitude solar insolation with a 23 ky periodicity, as recorded by a periodic change of the clay mineralogy. For the first time, this study presents a SCS deep-sea sediment high-resolution record of climatic changes in the last 450 ky, showing that smectite / (illite + chlorite) variations are mainly related to changes in the East Asian summer monsoon intensity. Because the mineralogical record is independent of other external forcing phenomena such as global glacial/interglacial oscillations, the smectite / (illite + chlorite) ratio has been used here as a proxy to reconstruct past changes of the South-East Asian summer monsoon intensity.

High-resolution siliciclastic grain size and bulk mineralogy combined with clay mineralogy, rubidium, strontium, and neodymium isotopes of Core MD01-2393 collected off the Mekong River estuary in the southwestern South China Sea reveals a monsoon-controlled chemical weathering and physical erosion history during the last 190,000 yr in the eastern Tibetan Plateau and the Mekong Basin. The ranges of isotopic composition are limited throughout sedimentary records:87Sr/86Sr = 0.7206–0.7240 andεNd(0) = −11.1 to −12.1. These values match well to those of Mekong River sediments and they are considered to reflect this source region. Smectites/(illite + chlorite) and smectites/kaolinite ratios are used as indices of chemical weathering rates, whereas the bulk kaolinite/quartz ratio is used as an index of physical erosion rates in the eastern Tibetan Plateau and the Mekong Basin. Furthermore, the 2.5–6.5 μm/15–55 μm siliciclastic grain size population ratio represents the intensity of sedimen...

High-resolution study of clay mineralogy and major element geochemistry has been derived from high sedimentation rate cores collected in the south China sea (SCS) (MD01-2393 and MD97-2150) in order to reconstruct the erosion and weathering history of Mekong river basin and the evolution of the East Asian monsoon. Chronology is assessed by oxygen isotope measurements and AMS 14C dating performed on planktonic foraminifera G. ruber. Clay minerals and major element results suggest the Mekong River and the Indonesian Islands Arc as the main source. Illite/kaolinite and K/Si ratios permit to reconstruct the physical erosion of the eastern Tibetan Plateau. Kaolinite/chlorite and chemical index of alteration (CIA) permit to reconstruct the history of the chemical weathering in the Mekong River Basin. MISs 5 and 2 are clearly characterized by a decrease of the chemical weathering and an increase of the physical erosion. The evolution of the East Asian monsoon is obtained by the smectite/ill...