Global Monsoon System Research Articles

Nonlinear Response of Global Monsoon Precipitation to Atlantic Overturning Strength Variations During Marine Isotope Stage 3

AbstractMonsoon rainfall proxy records show clear millennial variations corresponding to abrupt climate events in Greenland ice cores during Marine Isotope Stage 3 (MIS3). The occurrence of these abrupt climate changes is associated with Atlantic Meridional Overturning Circulation (AMOC) strength variations which greatly impact the global oceanic energy transport. Hence, the AMOC most likely plays a key role in modulating the global monsoon rainfall at millennial time scale. No modeling work has hitherto investigated the global monsoon system response to AMOC changes under a MIS3 background climate. Using the coupled climate model CCSM3, we simulated MIS3 climate using full 38 ka before present boundary conditions and performed a set of freshwater hosing/extraction experiments. We show not only agreement between modeling results and proxies of monsoon rainfall within the global monsoon domain but also highlight a nonlinear relationship between AMOC strength and annual mean global monsoon precipitation related to oceanic heat transport constraints. During MIS3, a weakened AMOC induces a decrease in annual mean global monsoon rainfall dominated by the northern hemisphere, whereas southern hemisphere monsoon rainfall increases. Above about 16 Sverdrups a further strengthening of the AMOC has no significant impact on hemispheric and global monsoon domain annual mean rainfall. The seasonal monsoon rainfall shows the same nonlinear response like annual mean both hemispherically and globally.

Long term trends and variabilities of rainfall of the global monsoon systems during boreal and austral summer seasons

Long term trends and variabilities of rainfall of the global monsoon systems during boreal and austral summer seasons

Global monsoon systems and their modulation by the equatorial Quasi-Biennial Oscillation

Monthly-mean data of ERA-Interim reanalysis, precipitation, outgoing longwave radiation (OLR) and sea surface temperature(SST) are investigated for 40 years (1979-2018) to reveal the modulation of the global monsoon systems by the equatorial quasi-biennial oscillation (QBO), focusing only on the neutral El Niño-Southern Oscillation (ENSO) periods (in total 374 months). First, the climatology of the global monsoon systems is viewed with longitude-latitude plots of the precipitation, its proxies and lower tropospheric circulations for the annual mean and two solstice seasons, together with the composite differences between the two seasons. In addition to seasonal variations of Intertropical Convergence Zones (ITCZs), several regional monsoon systems are well identified with an anti-phase of the annual cycle between the two hemispheres. Precipitation-related quantities (OLR and specific humidity), surface conditions [i.e., mean sea level pressure (MSLP) and SST] and circulation fields related to moist convection systems show fundamental features of the global monsoon systems. After introducing eight QBO phases based on the leading two principal components of the zonal-mean zonal wind variations in the equatorial lower-stratosphere, the statistical significance of the composite difference in the precipitation and tropospheric circulation is evaluated for the opposite QBO phases. The composite differences show significant modulations in some regional monsoon systems, dominated by zonally asymmetric components, with the largest magnitudes for specific QBO-phases corresponding to traditional indices of the equatorial zonal-mean zonal wind at 20 and 50 hPa. Along the equator, significant QBO influence is characterized by the modulation of the Walker circulation over the western Pacific. In middle latitudes during boreal summer, for a specific QBO-phase, statistically significant modulation of low-pressure cyclonic perturbation is obtained over the Northern-Hemisphere western Pacific Ocean associated with statistically significant features of heavier precipitation over the eastern side of the cyclonic perturbation and the opposite lighter precipitation over the western side. During boreal winter, similar significant low-pressure cyclonic perturbations were found over the Northern-Hemisphere eastern Pacific and Atlantic Oceans for specific phases.

Diurnal cycle of precipitation over global monsoon systems in CMIP6 simulations

Accurate simulation of the diurnal cycle of precipitation over different climate regimes, including global monsoon systems, is an ongoing challenge for current state-of-the-art climate models. In this study, the diurnal cycles of summertime precipitation from 21 CMIP6 historical simulations are evaluated with the NASA IMERG data via the diurnal harmonic amplitude and phase from the Fourier analysis in seven regional monsoon systems: Northern and Southern Africa monsoons, South Asia monsoon, East Asia monsoon, Australia monsoon, and North and South America monsoons. Particularly, we focus on four subregions including ocean, coastal ocean, land, and coastal land considering the different underlying physical processes. It is found that the CMIP6 historical simulations perform fairly well on reproducing the diurnal cycle of precipitation over ocean and coastal ocean, while the simulated diurnal harmonic phase and amplitude over land and coastal land show larger biases and model spread compared to biases over ocean and coastal ocean. The simulation of precipitation diurnal cycle is substantially improved in the multi-model mean of both CMIP6 historical and CMIP6 AMIP simulations compared with that of CMIP5 historical simulations. But the model bias of precipitation diurnal cycle is in general similar between CMIP6 AMIP and CMIP6 historical simulations, which suggests that the impact of the interactive ocean on the simulated diurnal precipitation averaged over a large domain is generally minor. The influence of model resolution on the diurnal cycle is shown in mixed directions across various subregions, and significant improvement from the low- to high-resolution models is only notable over coastal ocean.

Deforestation Drives Desiccation in Global Monsoon Region

AbstractGlobal monsoon system is a major component of the Earth's climate system and carries about two‐thirds of the world's population. How large‐scale deforestation induced changes in water cycle and energy balance may modify global monsoon system and its underlying mechanisms are not well understood. Here, we use simulations of 11 models participating in the Land Use Model Intercomparison Project in the framework of the Coupled Model Intercomparison Project, phase 6 to study the response of global monsoon precipitation and atmospheric circulation to large‐scale deforestation. Global deforestation of about 38% induces annual precipitation reduction of about −15.01 mm yr−1 (Multi‐Model Ensemble) in global monsoon regions and −26.15 mm yr−1 in land monsoon regions. The precipitation reduction is particularly pronounced in the Northern Hemisphere Summer Monsoon (NHSM) regions with decreased precipitation by 16.83 mm in the summer monsoon season from May to September along with weakened circulation intensity. Deforestation causes asymmetrical temperature response in the northern high latitudes and Southern Hemisphere Tropics, leading to decreased hemispheric thermal contrast, which reduces the meridional pressure gradient and weakens the convergence of cross‐equatorial flows into the NHSM trough regions, thereby decreasing the NHSM circulation and precipitation intensity. The deforestation‐induced hemispheric temperature asymmetry also increases the northward cross‐equatorial atmosphere heat transport (c‐eq AHT) that drives southward shift of Intertropical Convergence Zone, which suppresses the NHSM precipitation. Our results show that the drying monsoon region in response to deforestation is fairly consistent among the models implying the adverse effects of large‐scale deforestation beyond the region of land use change.

Variability of indian monsoon and its forcing mechanisms since late quaternary

The Indian monsoon is an important part of the global monsoon system, allowing important transfers of moisture at a large geographical scale and deeply affecting human populations and economic prosperity of regions. The tropical summer monsoon in the Northern Hemisphere is generally considered to be driven by low latitude solar radiation. Therefore, the summer monsoon strength is near zero-phase to the maximum of Northern Hemisphere Summer Insolation (NHSI). However, records from the Arabian Sea and some other parts of the Indian Ocean (e.g., Andaman Sea) show that a ∼8 kyr phase difference exists between the Indian summer monsoon (ISM) strength and the northern Hemisphere Summer Insolation maxima, which is obviously different from the records of stalagmites in the East Asia and other marine sediments (e.g., Bay of Bengal). This leads to the “sea-land precession phase paradox” in indian summer monsoon research. This paper systematically summarizes the Indian monsoon variability on orbital scale indicated by various records from the Indian monsoon regions (including oceans and continents) since the late Quaternary. The orbital forcing of Indian monsoon, the potential phase difference between indian summer monsoon and northern Hemisphere Summer Insolation and its possible forcing mechanism(s) are further discussed. The observed phase lag between indian summer monsoon and northern Hemisphere Summer Insolation may be controlled by the Atlantic Meridional Overturning Circulation (AMOC), latent heat transfer between the southern Indian Ocean and the Asian continent, or caused by the lack of tightly coupling between the Arabian Sea summer monsoon proxies and the monsoon intensity. In addition, it is still unclear whether previous monsoon proxies can provide a strong constraint on the intensity of summer monsoon. Environmental magnetism has been widely used in high-resolution dating and the analysis of paleoclimate variabilities in marine and terrestrial sediments, due to its high sensitivity on the rainfall and temperature. Therefore, in order to solve these issues, it is necessary to combine magnetic parameters with geochemical and paleontological parameters for more systematic work in the future.

The Global Monsoon Convective System as Reflected in Upper Atmosphere Gravity Waves

AbstractThe concept of a global monsoon system collectively comprising 6 tropical regions is applied to Outgoing Longwave Radiation (OLR) as a proxy for convectively generated gravity waves (GWs), leading to the global monsoon convective system (GMCS). The six tropical regions are North and South Africa, Central and South America, and the South Asia‐Pacific and Malay Archipelago/Australia‐Pacific regions. The extended GMCS is considered in terms of gravity wave momentum fluxes (GWMFs) at 30, 50, 70, and 90 km altitude during the summer season in both hemispheres between December 2016, and August 2020. The GWMFs are inferred from TIMED/SABER temperature measurements. Intermonthly, interseasonal, and interannual variations in monthly mean GWMFs are interpreted in terms of OLR as a proxy for the spatial‐temporal variability of GW sources, and in terms of MERRA2 zonal winds that quantify the influences of changes in background propagation conditions. It is found that temporal variations in GWMFs associated with the GMCS as a whole are not highly correlated with OLR, but at 30, 50, and 70 km are quantitatively linked to Doppler‐shifting effects by local winds, wind filtering at 15 km altitude, and “instrument filtering.” These effects are also compared and examined in the context of GW variances at 50 km in Southern Hemisphere summer measured by the CIPS instrument on the AIM satellite, which measures a different part of the GW spectrum. The SABER GWMF response at 90 km is irregular and variable, but sometimes consists of 3‐ and 4‐peaked structures in longitude that may reflect nonmigrating tide influences on GW propagation conditions.

The global monsoon system representation in BAM‐v1.2 and HadGEM3 climate simulations

AbstractThe features of monsoon systems in the Northern and Southern Hemispheres are analysed in climate simulations of two atmospheric models: the Brazilian Global Atmospheric Model version 1.2 (BAM‐v1.2) and the UK Met Office Hadley Centre Global Environment Model version 3 (HadGEM3). The results are compared to GPCP precipitation and ERA5 datasets. Although they have different configurations and parameterizations, the purpose is to evaluate their ability in representing key features of the global monsoon system. The spatial extent of the monsoon domains is well simulated by the models, as well as the main characteristics of the monsoons, although precipitation biases are noticed in the regions affected by the systems, consistent with vertical motion and moisture flux biases. The largest precipitation biases are found in the West Pacific Monsoon Region, extended to the east, and in the Australia Monsoon Region extended to the Maritime continent. Deficiencies in precipitation can be related to inaccuracy of vertical motion and humidity flux, as well as to the lack of air–sea interaction. However, the atmospheric circulation features at low and high levels are well represented in all monsoon regions, as well as the annual cycle of precipitation in those regions by both models. The divergence at high levels and convergence at low levels associated with ascending air movement and precipitation in monsoon regions are well represented by the models. An analysis of two monsoon indices at eight monsoon regions showed the models are generally able to simulate the relationship between precipitation and circulation features. In the majority of years, the signs of indices from the models agree with observations. Correlations of precipitation and circulation indices between models and observations show statistically significant values for some monsoon regions. The results obtained contribute to improving knowledge about global monsoon features and their representation in the two models.

Double-plunge structure of the East Asian summer monsoon during Heinrich stadial 1 recorded in Xianyun Cave, southeastern China

The interhemispheric anti-phase relationship of monsoon precipitation on the millennial timescale has been widely verified and is generally attributed to the migration of the mean position of the Intertropical Convergence Zone (ITCZ). However, previous high-resolution records showed that the interhemispheric monsoon climate could have been decoupled within Heinrich stadial 1 (HS1), creating a two-fold subdivision in the Asian summer monsoon and a double-plunge structure in the South American summer monsoon. In this study, we present a high-resolution and precisely dated composite stalagmite oxygen-isotope record exhibiting a clear double-plunge structure during HS1 from southeastern China, the frontal zone predominantly influenced by the East Asian summer monsoon (EASM). Our new record characterizes a weak EASM period corresponding to HS1, divided into two weak periods (HS1c, 17.89–17.01 ka B.P.; HS1a, 15.94–14.76 ka B.P.) by a relatively strong phase (HS1b, 17.01–15.94 ka B.P.). Comparisons with other records from global monsoon systems suggest the double-plunge structure of HS1 is widespread in the low latitudes of monsoon domains, and the interhemispheric anti-phase relationship of the monsoonal hydroclimate still holds on the sub-millennial timescale. This structure could be closely linked with two meltwater pulses in the North Atlantic, separated by a weak period and a brief rerouting of the main freshwater input produced by the Laurentide ice sheet from subpolar North Atlantic to the Gulf of Mexico. The change in the interhemispheric thermal gradient during HS1b likely pulled/pushed the ITCZ northward briefly and induced the synchronous and reverse change in the interhemispheric monsoon climate.

Monsoon driven ecosystem and landscape change in the 'Top End' of Australia during the past 35 kyr

The Indo-Australian Summer Monsoon (IASM) is the dominant climate feature of northern Australia, affecting rainfall/runoff patterns over a large portion of the continent and exerting a major control on the ecosystems of Australia's Top End, including the viability of wetland ecosystems and the structure of the woody savanna. We examined the behaviour the IASM from 35 kyr using proxy data preserved in the sediments of Table Top Swamp, a small seasonal swamp in northern Australia. Elemental data, stable C and N isotopes, pollen and sedimentary data were combined to develop a picture of monsoon activity and landscape and ecosystem response. Results demonstrated that between 35 and 25 ka conditions were drier and more stable than present, with a more grass dominated savanna and limited wetland development, implying reduced IASM activity. After ~25 ka, there is evidence of increased moisture at the study site, but also increased IASM variability. However, despite evidence of at least periodic increases in moisture, including periods of wetland establishment, the IASM displayed a subdued response to peak precession insolation forcing by comparison to the other global monsoon systems. Instead, the greatest change occurred from ~10 ka when the continental shelf flooded, increasing moisture advection to the study site and resulting in establishment of a quasi-permeant wetland. Whereas the early Holocene was marked by both the onset of pollen preservation and a wetter vegetation mosaic, indicative of a consistently active IASM, the mid-late Holocene was marked by drier vegetation, increased fire, but also increased C 3 vegetation and runoff, implying increased IASM variability. Holocene changes in ecosystem dynamics occur coincident with an expansion in human population, which likely also influenced vegetation and landscape response at the study site. • Wetlands were likely limited across the Top End and northern Australia before 25 ka with savanna more grass dominated. • The IASM became more effective from 9 ka, with ecosystem developing their current configuration after this time. • There is evidence of human resource use impacting vegetation assemblages in the Top End from the early to mid-Holocene. • There is evidence of both increasing moisture and aridity in the mid- to late-Holocene in the Top End. • Sea level appears to be the major control of IASM strength in the Top End over the past 35 kyr.

East Asian winter monsoon variation during the last 3000 years as recorded in a subtropical mountain lake, northeastern Taiwan

The East Asian Winter Monsoon (EAWM) is a fundamental part of the global monsoon system that affects nearly one-quarter of the world’s population. Robust paleoclimate reconstructions in East Asia are complicated by multiple sources of precipitation. These sources, such as the EAWM and typhoons, need to be disentangled in order to understand the dominant source of precipitation influencing the past and current climate. Taiwan, situated within the subtropical East Asian monsoon system, provides a unique opportunity to study monsoon and typhoon variability through time. Here we combine sediment trap data with down-core records from Cueifong Lake in northeastern Taiwan to reconstruct monsoonal rainfall fluctuations over the past 3000 years. The monthly collected grain-size data indicate that a decrease in sediment grain size reflects the strength of the EAWM. End member modelling analysis (EMMA) on sediment core and trap data reveals two dominant grain-size end-members (EMs), with the coarse EM 2 representing a robust indicator of EAWM strength. The downcore variations of EM 2 show a gradual decrease over the past 3000 years indicating a gradual strengthening of the EAWM, in agreement with other published EAWM records. This enhanced late-Holocene EAWM can be linked to the expansion of sea-ice cover in the western Arctic Ocean caused by decreased summer insolation.

The connection of east Asia and southwestern north America in climate change mode since the last glacial maximum at various timescales

Climate change modes between East Asia and southwestern North America are interlinked; however, little research has been done in comparing the underlying mechanisms between time scales. Here we present a comprehensive study using modern observations, paleoclimate records, and PMIP3/CMIP5 simulations to investigate the multi-timescale wet/dry changes in East Asia and southwestern North America and its relationship in climate change modes since the Last Glacial Maximum. Results show that wet/dry conditions in the monsoon and non-monsoon regions of East Asia and southwestern North America all have reverse changes at different timescales. On the millennial-scale the two continents are linked through the factors of insolation, greenhouse gas concentrations, El Niño-Southern Oscillation, and the northern hemisphere ice sheet. On the modern interannual and interdecadal scales the two climate systems are interlinked through the atmosphere-ocean interaction and precipitation and temperature patterns of both continents. This study provides a new perspective for the linkage study between different continents on a long-term scale, as well as a new recognition to global monsoon system.

Potential Influences of Volcanic Eruptions on Future Global Land Monsoon Precipitation Changes

AbstractThe global monsoon system is of exceptional socioeconomic importance owing to its impacts on two‐thirds of the globe’s population. Major volcanic eruptions strongly influence global land monsoon (GLM) precipitation change. By using 60 plausible eruption scenarios sampled from reconstructed volcanic proxies over the past 2,500 years, 21st century volcanic influences on GLM precipitation projections are examined with an Earth system model under a moderate emission scenario. The decadal‐scale ensemble spread with realistic eruptions (VOLC) increases by 17.5% and 20.1% compared to no‐volcanic (NO‐VOLC) and constant background‐volcanic (VOLC‐CONST) scenarios, respectively. Compared with NO‐VOLC, the centennial mean VOLC GLM precipitation shows a 10% overall reduction and regionally, Asia is the most impacted. Changes in atmospheric circulation in the aftermath of large volcanic eruptions match the global warming response patterns well with opposite sign, with the North American monsoon precipitation enhanced following large volcanic eruptions, which is in sharp contrast to the robust decrease in Asian monsoon rainfall. Volcanic activity could delay the time of emergence of anthropogenic influence by five years on average over about 60% of the GLM area. Our results demonstrate the importance of statistical representation of potential volcanism for the projections of future monsoon variability. Quantifying volcanic impacts on regional climate projections and their socioeconomic influences on infrastructure planning, food security, and disaster management should be a priority of future work.

FIO-ESM v2.0 Outputs for the CMIP6 Global Monsoons Model Intercomparison Project Experiments

Three tiers of experiments in the Global Monsoons Model Intercomparison Project (GMMIP), one of the endorsed model intercomparison projects of phase 6 of the Coupled Model Intercomparison Project (CMIP6), are implemented by the First Institute of Oceanography Earth System Model version 2 (FIO-ESM v2.0), following the GMMIP protocols. Evaluation of global mean surface air temperature from 1870 to 2014 and climatological precipitation (1979–2014) in tier-1 shows that the atmosphere model of FIO-ESM v2.0 can reproduce the basic observed atmospheric features. In tier-2, the internal variability is captured by the coupled model, with the SST restoring to the model climatology plus the observed anomalies in the tropical Pacific and North Atlantic. Simulation of the Northern Hemisphere summer monsoon circulation is significantly improved by the SST restoration in the North Atlantic. In tier-3, five orographic perturbation experiments are conducted covering the period 1979–2014 by modifying the surface elevation or vertical heating in the prescribed region. In particular, the strength of the South Asian summer monsoon is reduced by removing the topography or thermal forcing above 500 m over the Asian continent. Monthly and daily simulated outputs of FIO-ESM v2.0 are provided through the Earth System Grid Federation (ESGF) node to contribute to a better understanding of the global monsoon system.

Future Changes of Summer Monsoon Characteristics and Evaporative Demand Over Asia in CMIP6 Simulations

AbstractFuture greenhouse warming is expected to influence the characteristics of global monsoon systems. However, large regional uncertainties still remain. Here we use 16 Coupled Model Intercomparison Project Phase 6 (CMIP6) models to determine how the length of the summer rainy season and precipitation extremes over the Asian summer monsoon domain will change in response to greenhouse warming. Over East Asia the models simulate on average on the earlier onset and later retreat; whereas over India, the retreat will occur later. The model simulations also show an intensification of extreme rainfall events, as well as an increase of seasonal drought conditions. These results demonstrate the high volatility of the Asian summer monsoon systems and further highlight the need for improved water management strategies in this densely populated part of the world.

CAS FGOALS-f3-L Model Datasets for CMIP6 GMMIP Tier-1 and Tier-3 Experiments

The Chinese Academy of Sciences (CAS) Flexible Global Ocean–Atmosphere–Land System (FGOALS-f3-L) model datasets prepared for the sixth phase of the Coupled Model Intercomparison Project (CMIP6) Global Monsoons Model Intercomparison Project (GMMIP) Tier-1 and Tier-3 experiments are introduced in this paper, and the model descriptions, experimental design and model outputs are demonstrated. There are three simulations in Tier-1, with different initial states, and five simulations in Tier-3, with different topographies or surface thermal status. Specifically, Tier-3 contains four orographic perturbation experiments that remove the Tibetan–Iranian Plateau, East African and Arabian Peninsula highlands, Sierra Madre, and Andes, and one thermal perturbation experiment that removes the surface sensible heating over the Tibetan–Iranian Plateau and surrounding regions at altitudes above 500 m. These datasets will contribute to CMIP6’s value as a benchmark to evaluate the importance of long-term and short-term trends of the sea surface temperature in monsoon circulations and precipitation, and to a better understanding of the orographic impact on the global monsoon system over highlands.

A modified seasonal cycle during MIS31 super-interglacial favors stronger interannual ENSO and monsoon variability

Abstract. It has long been recognized that the amplitude of the seasonal cycle can substantially modify climate features in distinct timescales. This study evaluates the impact of the enhanced seasonality characteristic of the Marine Isotope Stage 31 (MIS31) on the El Niño–Southern Oscillation (ENSO). Based upon coupled climate simulations driven by present-day (CTR) and MIS31 boundary conditions, we demonstrate that the CTR simulation shows a significant concentration of power in the 3–7-year band and on the multidecadal timescale between 15 and 30 years. However, the MIS31 simulation shows drastically modified temporal variability of the ENSO, with stronger power spectrum at interannual timescales but the absence of decadal periodicity. Increased meridional gradient of sea surface temperature (SST) and wind stress in the Northern Hemisphere subtropics are revealed to be the primary candidates responsible for changes in the equatorial variability. The oceanic response to the MIS31 ENSO extends to the extratropics, and fits nicely with SST anomalies delivered by paleoreconstructions. The implementation of the MIS31 conditions results in a distinct global monsoon system and its link to the ENSO in respect to current conditions. In particular, the Indian monsoon intensified but no correlation with ENSO is found in the MIS31 climate, diverging from conditions delivered by our current climate in which this monsoon is significantly correlated with the NIÑO34 index. This indicates that monsoonal precipitation for this interglacial is more closely connected to hemispherical features than to the tropical–extratropical climate interaction.

The Multiscale Global Monsoon System: Research and Prediction Challenges in Weather and Climate

The Multiscale Global Monsoon System: Research and Prediction Challenges in Weather and Climate

Decoupled early Holocene summer temperature and monsoon precipitation in southwest China

Proxy-based reconstructions of Holocene temperature show that both the timing and magnitude of the thermal maximum varied substantially across different regions. Given the ‘Holocene temperature conundrum’, it is becoming increasingly important to reconstruct seasonal temperature variations. As a major component of the global monsoon system, the Indian summer monsoon (ISM) transports moisture and heat from the tropical oceans to higher latitudes and thus it has substantial socioeconomic implications for its regions of influences. We developed a well-dated, pollen-based summer temperature record (mean July; MJT) for the last 14,000 years from Xingyun Lake in southwest China, where the climate is dominated by the ISM. MJT decreased during the Younger Dryas, increased slowly to high values during 8000–5500 yr BP, and decreased thereafter. The MJT record differs from that inferred using carbonate oxygen isotopes (δ18O) from the same sediment core. The latter record reflects variations in monsoon precipitation, with highest precipitation during the early Holocene (11,000–6500 yr BP). We propose that summer temperature and precipitation in southwest China were decoupled during the early Holocene. Both MJT and monsoon precipitation decreased after the middle Holocene, tracking the trend in boreal summer insolation. We suggest that greater cloud cover, associated with high precipitation and generated by a strong summer monsoon, may have depressed early Holocene temperatures that would otherwise be driven by greater summer insolation. Melting ice sheets in high-latitude regions and high concentrations of atmospheric aerosols during the early Holocene may also have contributed, in part, to the relatively cool summer temperatures.

High-resolution mid-Holocene Indian Summer Monsoon recorded in a stalagmite from the Kotumsar Cave, Central India

The Indian Summer Monsoon (ISM), a significant part of the global monsoon system, is driven by several climate forcing parameters. With the growing pace of global climate change scenario, there is need to focus on generating more high-resolution records of past monsoon. The ISM reconstructions from Core Monsoon Zone (CMZ) of India, which represents all-India Summer Monsoon Rainfall, are useful for a better understanding of its past variability. Such reconstructions from the CMZ are rather sparse and require detailed study based on various climate proxies. Here, we focus on the reconstruction of ISM variability during the mid-Holocene, based on stalagmite oxygen isotope ratios from the Kotumsar cave, Central India. We show that with decreasing insolation, monsoon started declining at the beginning of the mid-Holocene from 8.5 to 6.5 ka BP, which is also observed in the previous ISM reconstructions with coarser resolutions. However, a gradual increase in the rainfall is observed from 6.5 to 5.6 ka BP, a feature which is also noted in the East Asian Monsoon reconstruction from the Dongge cave. Our record mainly emphasizes on the occurrence of several abrupt weak monsoon events throughout the mid-Holocene. The occurrence of 8.2 and 5.9 ka abrupt weak monsoon events suggest that ISM variability is tightly bound to North-Atlantic Oscillation (NAO). We also demonstrate that ISM during the mid-Holocene was partly sensitive to El-Nino Southern Oscillation (ENSO), and displayed an inverse relationship.