Himalayan-Tibetan Plateau Research Articles

Historical Black Carbon Reconstruction from the Lake Sediments of the Himalayan-Tibetan Plateau.

Black carbon (BC) is one of the major drivers of climate change, and its measurement in different environment is crucial for the better understanding of long-term trends in the Himalayan-Tibetan Plateau (HTP) as climate warming has intensified in the region. We present the measurement of BC concentration from six lake sediments in the HTP to reconstruct historical BC deposition since the pre-industrial era. Our results show an increasing trend of BC concurrent with increased anthropogenic emission patterns after the commencement of the industrialization era during the 1950s. Also, sedimentation rates and glacier melt strengthening influenced the total input of BC into the lake. Source identification, based on the char and soot composition of BC, suggests biomass-burning emissions as a major contributor to BC, which is further corroborated by open-fire occurrence events in the region. The increasing BC trend continues to recent years, indicating increasing BC emissions, mainly from South Asia.

Molecular characterization of organic aerosols in the Kathmandu Valley, Nepal: insights into primary and secondary sources

Abstract. Organic atmospheric aerosols in the Hindu Kush–Himalayas–Tibetan Plateau region are still poorly characterized. To better understand the chemical characteristics and sources of organic aerosols in the foothill region of the central Himalaya, the atmospheric aerosol samples were collected in Bode, a suburban site of the Kathmandu Valley (KV) over a 1-year period from April 2013 to April 2014. Various molecular tracers from specific sources of primary organic aerosols (POAs) and secondary organic aerosols (SOAs) were determined. Tracer-based estimation methods were employed to apportion contributions from each source. The concentrations of organic carbon (OC) and elemental carbon (EC) increased during winter with a maximum monthly average in January. Levoglucosan (a molecular tracer for biomass burning, BB) was observed as the dominant species among all the analyzed organic tracers and its annual average concentration was 788±685 ng m−3 (ranging from 58.8 to 3079 ng m−3). Isoprene-SOA (I-SOA) represented a high concentration among biogenic-SOA tracers. For the seasonality, anhydrosugars, phenolic compounds, resin acid, and aromatic SOA tracer showed similar seasonal variations with OC and EC while monosaccharides, sugar alcohols, and I-SOA tracers showed lower levels during winter. BB contributed a significant fraction to OC, averaging 24.9 %±10.4 % during the whole year, and up to 36.3 %±10.4 % in the post-monsoon season. On an annual average basis, anthropogenic toluene-derived secondary OC accounted for 8.8 % and biogenic secondary OC contributed 6.2 % to total OC. The annual contribution of fungal spores to OC was 3.2 % with a maximum during the monsoon season (5.9 %). For plant debris, it accounted for 1.4 % of OC during the monsoon. Therefore, OC is mainly associated with BB and other anthropogenic activity in the KV. Our findings are conducive to designing effective measures to mitigate the heavy air pollution and its impacts in the KV and surrounding area.

Flexural subsidence analysis of the Laxmi Basin, Arabian Sea and its tectonic implications

AbstractTwo-dimensional flexural backstripping and thermal modelling (assuming laterally variable stretching) is applied along regional depth-converted interpreted seismic profiles from the Laxmi Basin in the Arabian Sea. Results from reverse post-rift flexural modelling reveal considerable basin-wide subsidence in response to the crustal geodynamics during and after the last extensional phase. Unloading of the stratigraphy allows us to estimate the degree of laterally varying extension, assuming thermal subsidence and pure shear. High degrees of extension in the basin centre predict considerable water depths at the time of rift cessation, consistent with deep drilling data. We suggest that regional extension prior to Paleocene time could have fuelled variable subsidence in the Laxmi Basin but that extension is less than seen in typical oceanic lithosphere. Volcanic loading by the seamounts shortly after extension has flexed the basin and implies an effective elastic thickness (Te) at that time of ∼6 km. Reconstruction of the seamount top near sea level at the end of emplacement indicates no major transient uplift potentially linked to the Deccan mantle plume activity. Backstripping of post-rift sediments from interpreted seismic profiles supports the presence of a hyper-thinned crust underneath the Laxmi Basin, with β factors reaching >7 in the basin centre and ∼3 across much of the basin width. Computations of decompacted sediment accumulation rates in light of new results from IODP Expedition 355 show that basin sedimentation peaked during early–middle Miocene time, possibly coeval with uplift and erosion of the Himalayan–Tibetan Plateau driven by strong summer monsoon rains.

Is Himalayan-Tibetan Plateau “drying”? Historical estimations and future trends of surface soil moisture

The Himalayan-Tibetan Plateau (HTP), often known as the “Third Pole” and the “Asian Water Tower”, is the source of water resources for many Asian rivers and in turn for hundreds of millions of people living downstream. The HTP has direct impacts on the establishment and maintenance of Asian monsoon, and therefore on the climate of its surrounding areas. Besides, soil moisture plays a critical role in the hydrological cycle and is a critical link between land surface and atmosphere. Hence, soil moisture was greatly emphasized by Global Climate Observing System Programme as an Essential Climate Variable. However, little is known about soil moisture changes on the HTP from a long-term perspective. By comparing remotely sensed and modelled soil moisture datasets against in-situ observations from 100 observation stations, here we find that Noah performed better than other soil moisture datasets. In past years, soil moisture first decreased and then increased obviously. In most regions on HTP, precipitation changes can be taken as the major cause behind soil moisture variations. In future, there is persistently decreasing soil moisture trend since ~2010 with a decreasing rate of −0.044 kg/m2/10a, −0.031 kg/m2/10a and −0.0p 88 kg/m2/10a under RCP2.6, RCP4.5 and RCP8.5 scenarios, respectively, in CMIP5 (Coupled Model Intercomparision Project Phase 5). Specifically, a sudden decrease of soil moisture with a rate of −0.372 kg/m2/10a can be expected after ~2080 under RCP8.5 scenario. Amplifying terrestrial aridity due to increasing precipitation but more significant increasing potential evapotranspiration potentially results in drying HTP. Potential water deficiency for Asian rivers due to drying HTP should arouse considerable concerns.

Impact of snow-darkening by deposition of light-absorbing aerosols on snow cover in the Himalaya-Tibetan-Plateau and influence on the Asian Summer monsoon: A possible mechanism for the Blanford Hypothesis.

The impact of snow darkening by deposition of light absorbing aerosols (LAAs) on snow cover over the Himalaya-Tibetan-Plateau (HTP) and influence on the Asian summer monsoon are investigated using the NASA Goddard Earth Observing System Model Version 5 (GEOS-5). We find that during April-May-June, deposition of LAAs on snow leads to a reduction in surface albedo, initiating a sequence of feedback processes, starting with increased net surface solar radiation, rapid snowmelt in HTP and warming of the surface and upper troposphere, followed by enhanced low-level southwesterlies and increased dust loading over the Himalayas-Indo-Gangetic Plain. The warming is amplified by increased dust aerosol heating, and subsequently amplified by latent heating from enhanced precipitation over the Himalaya foothills and northern India, via the Elevated Heat Pump (EHP) effect during June-July-August. The reduced snow cover in the HTP anchors the enhanced heating over the Tibetan Plateau and its southern slopes, in conjunction with an enhancement of the Tibetan Anticyclone, and the development of an anomalous Rossby wavetrain over East Asia, leading to weakening of the subtropical westerly jet, and northward displacement and intensification of the Mei-Yu rainbelt. Our results suggest that atmosphere-land heating induced by LAAs, particularly desert dust play a fundamental role in physical processes underpinning the snow-monsoon relationship proposed by Blanford more than a century ago.

Performance of the CMIP5 models in the simulation of the Himalaya-Tibetan Plateau monsoon

In this paper, the performance of 28 CMIP5 models in simulating the climate of the Himalaya-Tibetan Plateau (HTP) for the recent past (1975–2005) is evaluated using the observations from the Asian Precipitation Highly-Resolved Observational Data Integration Towards Evaluation (APHRODITE). Many models realistically simulate the spatial distribution of surface air temperature (Tas) and precipitation with pattern correlation as high as 0.8; however, they possess severe biases in their magnitude. The biases in Tas appear to be associated with the biases in the surface elevation. All the models capture the observed phase of the annual cycle of the Tas but underestimate the amplitude. For precipitation, the phase is captured by most models (except few), but the amplitude is overestimated in all models. In the mid-intensity precipitation range (10–80 mm day−1), most of the models overestimate the probability of occurrence and show large intermodel differences. Most of the models fail to simulate the spatial distribution of the trend in Tas and precipitation. As compared to many individual models, the biases are noted to reduce when using multimodel means (MMMs); however, the MMMs also failed to capture the observed trends in both Tas and precipitation. Many models still struggle to capture the large-scale phenomena, such as the location and intensity of upper-level Asian anticyclone and middle troposphere temperature maximum over the HTP, which have large implications on the HTP as well as the Indian summer monsoon. The results show that none of the models capture all features of the HTP monsoon, and hence, further improvement in the parameterization schemes and resolution is required to gain more confidence in the projection of HTP climate using these models.

Evaluation of Remotely Sensed and Reanalysis Soil Moisture Against In Situ Observations on the Himalayan‐Tibetan Plateau

AbstractThis study collected soil moisture (SM) observations from 100 in situ observations and compared them with widely used SM estimations, derived from the Essential Climate Variables, European Reanalysis (ERA)‐Interim, the Modern‐Era Retrospective analysis for Research and Applications, and Noah at spatial resolutions of 0.25° × 0.25°, 0.5° × 0.5°, and 1° × 1° during unfreezing and freezing periods. Results indicate that all estimations except ERA can depict the SM changes on the Himalayan‐Tibetan Plateau (HTP) well to some extent and Noah performs the best as a whole. In the Ngari region, however, SM estimations substantially overestimate SM observations. In the Naqu region, except ERA, SM estimations overestimate the SM amount during freezing periods but underestimate the SM amount during unfreezing periods. In Maqu, except ERA, SM estimations can characterize SM variations with substantial underestimation of SM during unfreezing periods, however, slight underestimation of SM during freezing periods. In space, the Modern‐Era Retrospective analysis for Research and Applications and Noah can evaluate the spatial distribution of SM better. The SM changes across most parts of the HTP are heavily influenced by precipitation changes. In addition, these changes in the western flank of the HTP are the combined result of snow and glacial melting and precipitation. Except in the western and northern regions, SM during unfreezing periods is usually higher than during freezing periods. Besides, evaluations can better describe SM changes at medium and large spatial scales than at small spatial scales. This study provides important basis for the selection of proper remote sensing and reanalysis SM data sets for the analysis of SM on the HTP.

Changes in Tibetan Plateau latitude as an important factor for understanding East Asian climate since the Eocene: A modeling study

Previous climate modeling studies suggest that the surface uplift of the Himalaya–Tibetan plateau (TP) is a crucial parameter for the onset and intensification of the East Asian monsoon during the Cenozoic. Most of these studies have only considered the Himalaya–TP in its present location between ∼26°N and ∼40°N despite numerous recent geophysical studies that reconstruct the Himalaya–TP 10° or more of latitude to the south during the early Paleogene. We have designed a series of climate simulations to explore the sensitivity of East Asian climate to the latitude of the Himalaya–TP. Our simulations suggest that the East Asian climate strongly depends on the latitude of the Himalaya–TP. Surface uplift of a proto-Himalaya–TP in the subtropics intensifies aridity throughout inland Asia north of ∼40°N and enhances precipitation over East Asia. In contrast, the rise of a proto-Himalaya–TP in the tropics only slightly intensifies aridity in inland Asia north of ∼40°N, and slightly increases precipitation in East Asia. Importantly, this climate sensitivity to the latitudinal position of the Himalaya–TP is non-linear, particularly for precipitation across East Asia. The simulated precipitation patterns across East Asia are significantly different between our scenarios in which a proto-plateau is situated between ∼11°N and ∼25°N and between ∼20°N and ∼33°N, but they are similar when the plateau translates northward from between ∼20°N and ∼33°N to its modern position. Our simulations, when interpreted in the context of climate proxy data from Central Asia, support geophysically-based paleogeographic reconstructions in which the southern margin of a modern-elevation proto-Himalaya–TP was located at ∼20°N or further north in the Eocene.

Precipitation characteristics over the steep slope of the Himalayas in rainy season observed by TRMM PR and VIRS

Characteristics of the precipitation in rainy season over the steep Himalayas and adjacent regions, including four selected sectors of the flat Gangetic Plains (FGP), foothills of the Himalayas (FHH), the steep slope of the southern Himalayas (SSSH), and the Himalayan–Tibetan Plateau tableland (HTPT), are investigated using collocated satellite datasets from the TRMM PR and VIRS at pixel level during May–August of 1998–2012. Results indicate that the rain frequency increases significantly from the FGP via FHH to the lower elevations of the SSSH (~ 2.5 km), then decreases as the elevation further increases up to the HTPT, and reaches the minimum over the HTPT. Along with such spatial variation of the rain frequency, mean rain rates (RRs) are the heaviest over the FGP (4 mm h−1) and the FHH (5.5 mm h−1), medium over the SSSH (2–4 mm h−1), and the weakest over the HTPT (less than 2 mm h−1). More than 60% of precipitation over the FGP, FHH, and HTPT is produced by ice-phase topped clouds, while more than 70% over the SSSH is from mixed-phase topped clouds. Analysis suggests that the highest rain frequency over the SSSH in rainy season may be caused by a strong upward motion over the SSSH as warm moist air monsoon flow interacting with the terrain of the Himalayas, while the heaviest RR over the FHH may result from low-level convergence where the air flow is blocked by the SSSH. The elevation and relief effects have linear relationships with precipitation over the south sub-region of the SSSH, which indicates that both effects play important roles on precipitation over complex plateau topography.

Stable isotopes reveal southward growth of the Himalayan-Tibetan Plateau since the Paleocene

Original stable isotope compositions of carbonates representing conditions in the latest Oligocene-early Miocene Kailas and Qiabulin areas, both in southern Tibet, record Oligocene-Miocene paleoelevations of the Gangdese arc and the Himalayan orogen, and provide constraints on the formation of the Himalayan-Tibetan Plateau. Oxygen isotope compositions of bivalve shell, paleosol, and lacustrine carbonates indicate the preservation of unaltered isotopic signals of paleometeoric waters in the Kailas and Qiabulin areas, whereas the oxygen isotopic compositions of Liuqu Eocene paleosols were likely altered by paleometeoric waters. Paleoelevation estimates using oxygen isotopes indicate the Kailas area was at ~4.9km during ~20–19Ma and the Qiabulin Basin was at ~2.0km during 24–21Ma, but rose rapidly to ~4.1km between 21 and 19Ma. These results suggest a steep south-facing flank on the proto-Tibetan highland prior to the onset of the India-Asia collision. The Himalayan orogen began to be built against the pre-existed high (~4.5km) Gangdese Mountains in the early Eocene and obtained elevations close to those of the present by the early Miocene. We propose that the southernmost Tibetan Plateau and Himalayan orogen are the expression of an early Eocene to early Miocene southward migration of the locus of deformation. Early stage uplift is linked to the crustal thickening in the early Eocene, but the dramatic elevation gain in the early Miocene may have been caused by Indian slab rollback, break-off and coeval renewed underthrusting, behind which late Miocene to present east-west crustal extension took place.

Understanding Himalayan erosion and the significance of the Nicobar Fan

A holistic view of the Bengal–Nicobar Fan system requires sampling the full sedimentary section of the Nicobar Fan, which was achieved for the first time by International Ocean Discovery Program (IODP) Expedition 362 west of North Sumatra. We identified a distinct rise in sediment accumulation rate (SAR) beginning ∼9.5 Ma and reaching 250–350 m/Myr in the 9.5–2 Ma interval, which equal or far exceed rates on the Bengal Fan at similar latitudes. This marked rise in SAR and a constant Himalayan-derived provenance necessitates a major restructuring of sediment routing in the Bengal–Nicobar submarine fan. This coincides with the inversion of the Eastern Himalayan Shillong Plateau and encroachment of the west-propagating Indo–Burmese wedge, which reduced continental accommodation space and increased sediment supply directly to the fan. Our results challenge a commonly held view that changes in sediment flux seen in the Bengal–Nicobar submarine fan were caused by discrete tectonic or climatic events acting on the Himalayan–Tibetan Plateau. Instead, an interplay of tectonic and climatic processes caused the fan system to develop by punctuated changes rather than gradual progradation.

Monsoonal upwelling in the western Arabian Sea since the middle Miocene

Research Article| July 01, 2017 Monsoonal upwelling in the western Arabian Sea since the middle Miocene Guangsheng Zhuang; Guangsheng Zhuang 1Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA Search for other works by this author on: GSW Google Scholar Mark Pagani; Mark Pagani 2Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520, USA Search for other works by this author on: GSW Google Scholar Yi Ge Zhang Yi Ge Zhang 3Department of Oceanography, Texas A&M University, College Station, Texas 77843, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Guangsheng Zhuang 1Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA Mark Pagani 2Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520, USA Yi Ge Zhang 3Department of Oceanography, Texas A&M University, College Station, Texas 77843, USA Publisher: Geological Society of America Received: 01 Feb 2017 Revision Received: 21 Mar 2017 Accepted: 21 Mar 2017 First Online: 28 Jun 2017 Online Issn: 1943-2682 Print Issn: 0091-7613 © 2017 Geological Society of America Geology (2017) 45 (7): 655–658. https://doi.org/10.1130/G39013.1 Article history Received: 01 Feb 2017 Revision Received: 21 Mar 2017 Accepted: 21 Mar 2017 First Online: 28 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Guangsheng Zhuang, Mark Pagani, Yi Ge Zhang; Monsoonal upwelling in the western Arabian Sea since the middle Miocene. Geology 2017;; 45 (7): 655–658. doi: https://doi.org/10.1130/G39013.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The Asian monsoon has long been argued to be a product of the Himalaya–Tibetan Plateau, and simulation experiments have confirmed the key role of the Himalaya–Tibetan Plateau in transforming regional atmospheric and oceanic circulations. However, temporal constraints on the strengthening of the Asian monsoon inferred from foraminifer isotopic and faunal data and terrestrial climatic and ecological records are inconsistent with each other, which has obscured the tectonic-climatic linkage. In particular, discriminating the post-middle Miocene global cooling from the monsoon upwelling cooling is critical, but poorly understood due to the lack of adequate constraints for monsoonal upwelling. Here we present new middle to late Miocene biomarker-based reconstructions of sea-surface temperature (SST) for the western Arabian Sea. Our new SSTs capture a long-term ocean cooling since ca. 14.8 Ma and a major drop in SST in the period 11–10 Ma after which the SSTs reached similar values as the Holocene. The new SST record is consistent with planktonic foraminifer, siliceous biota, and geochemical tracer studies, suggestive of ocean cooling and high productivity associated with monsoonal upwelling. The 11–10 Ma ocean cooling is not clearly expressed in other tropical oceans, indicating that the ocean cooling in the western Arabian Sea is not a simple reflection of global cooling. We interpret the 11–10 Ma ocean cooling as representing the establishment of monsoonal upwelling in the western Arabian Sea, triggered by strong cyclonic activities as a result of the Neogene outward expansion of the Himalaya–Tibetan Plateau. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The influence of Cretaceous paleolatitude variation of the Tethyan Himalaya on the India-Asia collision pattern

Identifying when, where, and how India and Asia collided is a prerequisite to better understand the evolution of the Himalayan-Tibetan Plateau. Whereas with essentially the same published paleomagnetic data, a large range of different India-Asia collision models have been proposed in the literature. Based upon the premise of a northwards-moving Indian plate during the Cretaceous times, we analyze the significant variations in relative paleolatitude produced by a nearly 90° counterclockwise (CCW) rotation of the plate itself during the Cretaceous. Interestingly, recent studies proposed a dual-collision process with a Greater India basin or post-Neo-Tethyan ocean for the India-Asia collision, mainly in the light of divergent Cretaceous paleolatitude differences of the Tethyan Himalaya between the observed values and expected ones computed from the apparent polar wander path of the Indian plate. However, we find that these varied paleolatitude differences are mainly resulted from a nearly 90° CCW rotation of a rigid/quasi-rigid Greater Indian plate during the Cretaceous. On the other hand, when the Indian craton and Tethyan Himalaya moved as two individual blocks rather than a united rigid/quasi-rigid Greater Indian plate before the India-Asia collision, current available Cretaceous paleomagnetic data permit only multiple paleogeographic solutions for the tectonic relationship between the Indian plate and the Tethyan Himalayan terrane. We therefore argue that the tectonic relationship between the Indian plate and the Tethyan Himalayan terrane cannot be uniquely constrained by current paleomagnetic data in the absence of sufficient geological evidence, and the so-called Greater India basin model is just one of the ideal scenarios.

Characteristics of cloud cluster over the steep southern slopes of the Himalayas observed by CloudSat

ABSRACTA cloud cluster (CC) dataset is presented using CloudSat Cloud Profile Radar (CPR) observations from June to August, between 2006 and 2010. The CCs were defined by grouping contiguous cloud pixels using a defined criteria, including reflectivity, ‘cloud mask’, and topographic information. The characteristics of identified CCs were then analysed. Based on the complex topography of the southern Himalayas, four adjacent regions were selected, including the flat Gangetic Plains (FGP), the foothills of the Himalayas (FHH), the steep slope of the southern Himalayas (SSSH), and the Himalayan‐Tibetan Plateau (HTPT). The characteristics of the CCs in the four regions were different, and the distribution of the cloud‐top height gradually changed from bimodal (3 and 15 km) over the FGP and FHH, to unimodal (7–9 km) over the HTPT. From the plain to the Plateau, the average cloud‐top height and cloud‐base height increased after an initial decrease. The maximum reflectivity increased from −6 (plain) to 2 dBZ (slope areas), and then decreased to −2 dBZ (Plateau), which suggests that the CCs may produce precipitation on the slope. Maximum CCs occurred over the FHH. The characteristics of the CCs also showed semidiurnal variation, which may have been affected by the variation of the monsoon and the circulation over the mountain valley. According to the physical principles of the cloud‐type definitions from ISCCP, high‐level cirrus, deep convective CCs, and mid‐ to low‐level CCs were categorized. As the elevation increased, the cloud‐top height of the mid‐ to low‐level CCs also significantly increased to 8 km, whereas the cloud‐top height of the high‐level cirrus clouds decreased. Our results suggest that the different characteristics of CCs may be caused by a strong upward motion interacting with the terrain of the Himalayas.

A Phylogenetic Perspective on Biogeographical Divergence of the Flora in Yunnan, Southwestern China

In recent years, an increasing number of studies incorporated biogeography with phylogenetic analyses to reveal the origin and evolutionary history of specific floras. In this study, we constructed the mega-phylogeny of the floras of three representative regions across Yunnan, southwestern China. We analyzed the phylogenetic structure and beta diversity based on the presence/absence of species (genus or family) data to investigate the phylogenetic patterns of regional floras. We found conspicuous divergence at the genus and species level in the pattern of phylogenetic structures, which most likely related to historical biogeography. The flora of southern Yunnan was shaped by the strike-slip extrusion of Indochina and the regional climatic stability, while the flora of northwestern Yunnan was shaped by the uplift of the Himalaya-Tibetan Plateau and the oscillations of the glacial-interglacial periods. The flora of central Yunnan had nearly equal proportions of the northern and southern floras that may be derived from a common Tertiary tropical or subtropical flora. Geological events fit well with the floristic and phylogenetic patterns across Yunnan. This study highlighted the importance of linking phylogenetic analyses to biogeographic interpretations to improve our understanding of the origin, evolution and divergence of regional floras.

Basement tectonics and flexural subsidence along western continental margin of India

The Paleocene-recent post-rift subsidence history recorded in the Mumbai Offshore Basin off western continental margin of India is examined. Results obtained through 2-D flexural backstripping modelling of new seismic data reveal considerable thermo-tectonic subsidence over last ca. 56 Myr. Reverse post-rift subsidence modelling with variable β stretching factor predicts residual topography of ca. 2000 m to the west of Shelf Margin Basin and fails to restore late Paleocene horizon and the underlying igneous basement to the sea level. This potentially implies that: (1) either the igneous basement formed during the late Cretaceous was emplaced under open marine environs; or (2) a laterally varying cumulative subsidence occurred within Mumbai Offshore Basin (MOB) during ca. 68 to ca. 56 Ma. Pre-depositional topographic variations at ca. 56 Ma across the basin could be attributed to the extensional processes such as varied lower crustal underplating along Western Continental Margin of India (WCMI). Investigations about basement tectonics after unroofing of sediments since late Paleocene from this region support a transitional and heavily stretched nature of crust with high to very high β factors. Computations of past sediment accumulation rates show that the basin sedimentation peaked during late Miocene concurrently with uplift of Himalayan–Tibetan Plateau and intensification of Indian monsoon system. Results from basin subsidence modelling presented here may have significant implications for further studies attempting to explore tectono–climatic interactions in Asia.

Sources of black carbon to the Himalayan-Tibetan Plateau glaciers.

Combustion-derived black carbon (BC) aerosols accelerate glacier melting in the Himalayas and in Tibet (the Third Pole (TP)), thereby limiting the sustainable freshwater supplies for billions of people. However, the sources of BC reaching the TP remain uncertain, hindering both process understanding and efficient mitigation. Here we present the source-diagnostic Δ14C/δ13C compositions of BC isolated from aerosol and snowpit samples in the TP. For the Himalayas, we found equal contributions from fossil fuel (46±11%) and biomass (54±11%) combustion, consistent with BC source fingerprints from the Indo-Gangetic Plain, whereas BC in the remote northern TP predominantly derives from fossil fuel combustion (66±16%), consistent with Chinese sources. The fossil fuel contributions to BC in the snowpits of the inner TP are lower (30±10%), implying contributions from internal Tibetan sources (for example, yak dung combustion). Constraints on BC sources facilitate improved modelling of climatic patterns, hydrological effects and provide guidance for effective mitigation actions.

Impact of springtime Himalayan–Tibetan Plateau snowpack on the onset of the Indian summer monsoon in coupled seasonal forecasts

The springtime snowpack over the Himalayan–Tibetan Plateau (HTP) region and Eurasia has long been suggested to be an influential factor on the onset of the Indian summer monsoon. To assess the impact of realistic initialization of springtime snow over HTP on the onset of the Indian summer monsoon, we examine a suite of coupled ocean–atmosphere 4-month ensemble reforecasts made at the European Centre for Medium-Range Weather Forecasts, using their Seasonal Forecasting System 4. The reforecasts were initialized on 1 April every year for the period 1981–2010. In these seasonal reforecasts, the snow is initialized “realistically” with ERA-Interim/Land Reanalysis. In addition, we carried out an additional set of forecasts, identical in all aspects except that initial conditions for snow-related land surface variables over the HTP region are randomized. We show that high snow depth over HTP influences the meridional tropospheric temperature gradient reversal that marks the monsoon onset. Composite difference based on a normalized HTP snow index reveal that, in high snow years, (1) the onset is delayed by about 8 days, and (2) negative precipitation anomalies and warm surface conditions prevail over India. We show that about half of this delay can be attributed to the realistic initialization of snow over the HTP region. We further demonstrate that high April snow depths over HTP are not uniquely influenced by El Nino-Southern Oscillation, the Indian Ocean Dipole or the North Atlantic Oscillation.

Evolution of the South Asian monsoon wind system since the late Middle Miocene

Abstract The evolution and timing of the inception of the South Asian monsoon (SAM) has been one of the most debated climatic mysteries amongst climate workers. The Himalaya–Tibetan plateau (HTP) complex has been implicated as the main driver for SAM circulation. However, there are intense debates as to whether there was a critical elevation of the HTP complex that drove the SAM and at what time such a critical elevation was attained. Also, the role of the HTP complex in driving the SAM has been questioned in recent climate model studies. The model simulation suggests a major intensification of the SAM as early as ~ 30 Ma, whereas marine records from the Arabian Sea indicate a major strengthening of the South Asian summer or southwest monsoon winds between 10 and 8 Ma. The continental vegetation, on the other hand, captured a major transition from C 3 to C 4 type during 8–7 Ma but whether this change was local or global and whether this transition was driven by monsoonal precipitation is not unanimously accepted. Our new record from Ocean Drilling Program holes located off the Oman margin and on the Owen Ridge, western Arabian Sea shows appearance of monsoon wind proxy planktic foraminifer Globigerina bulloides , a significant increase in total organic carbon, and a negative shift in stable carbon isotope record of benthic foraminifera at ~ 12.9 Ma. These proxies indicate that present day South Asian monsoon wind system began to develop during the late Middle Miocene (~ 12.9 Ma) and summer monsoon was in its full strength in the late Miocene (~ 7 Ma). From 11 to 7 Ma, the summer monsoon was weaker when winter monsoon was stronger.

Origin and evolution of Petrocosmea (Gesneriaceae) inferred from both DNA sequence and novel findings in morphology with a test of morphology-based hypotheses.

BackgroundPetrocosmea Oliver (Gesneriaceae) currently comprises 38 species with four non-nominate varieties, nearly all of which have been described solely from herbarium specimens. However, the dried specimens have obscured the full range of extremely diverse morphological variation that exists in the genus and has resulted in a poor subgeneric classification system that does not reflect the evolutionary history of this group. It is important to develop innovative methods to find new morphological traits and reexamine and reevaluate the traditionally used morphological data based on new hypothesis. In addition, Petrocosmea is a mid-sized genus but exhibits extreme diverse floral variants. This makes the genus of particular interest in addressing the question whether there are any key factors that is specifically associated with their evolution and diversification.ResultsHere we present the first phylogenetic analyses of the genus based on dense taxonomic sampling and multiple genes combined with a comprehensive morphological investigation. Maximum-parsimony, maximum likelihood and Bayesian analyses of molecular data from two nuclear DNA and six cpDNA regions support the monophyly of Petrocosmea and recover five major clades within the genus, which is strongly corroborated by the reconstruction of ancestral states for twelve new morphological characters directly observed from living material. Ancestral area reconstruction shows that its most common ancestor was likely located east and southeast of the Himalaya-Tibetan plateau. The origin of Petrocosmea from a potentially Raphiocarpus-like ancestor might have involved a series of morphological modifications from caulescent to acaulescent habit as well as from a tetrandrous flower with a long corolla-tube to a diandrous flower with a short corolla-tube, also evident in the vestigial caulescent habit and transitional floral form in clade A that is sister to the remainder of the genus. Among the five clades in Petrocosmea, the patterns of floral morphological differentiation are consistent with discontinuous lineage-associated morphotypes as a repeated adaptive response to alternative environments.ConclusionOur results suggest that the lineage-specific morphological differentiations reflected in the upper lip, a functional organ for insect pollination, are likely adaptive responses to pollinator shifts. We further recognize that the floral morphological diversification in Petrocosmea involves several evolutionary phenomena, i.e. evolutionary successive specialization, reversals, parallel evolution, and convergent evolution, which are probably associated with adaptation to pollination against the background of heterogeneous abiotic and biotic environments in the eastern wing regions of Himalaya-Tibetan plateau.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0540-3) contains supplementary material, which is available to authorized users.