Monsoon Activity Research Articles

Appraising timing response of paleoenvironmental proxies to the Bond cycle in the western Mediterranean over the last 20 kyr

The timing of climate responses to the Bond cycle is investigated in the western Mediterranean. Periodicities had been previously reported in a marine sediment record from this region spanning the last 20 kyr, and registered by diverse paleoenvironmental proxies, in particular those associated with terrigenous input, redox conditions, productivity, sea surface temperature (SST) and salinity. Further cross-spectral analyses on these time series reveal leads–lags in the 1400 year climate cycle. Considering as reference a terrigenous input proxy (the K/Al ratio), all the paleoenvironmental proxies displayed time shifts varying from ca. 700 year to ca. 350 year. SST and salinity variations show a first leaded response with the inflow of cold and less salty Atlantic waters. Followed by a time lead of 525 year, progresively arid conditions with an increase of eolian dust transport to the area, given by the Zr/Al signal, are observed. The intensification of dust transport could have triggered a latest biological response, lead by 350 year, with an increase of productivity, as suggested by the Ba/Al ratio. Lastly changes in the Mediterranean thermohaline circulation, indicated by a selected redox proxy (the U/Th ratio), are observed. These results support that the oceanic response triggered the atmospheric response to the Bond cycle in the western Mediterranean. Changes in the North Atlantic Oscillation mode and in the Inter-Tropical Convergence Zone migrations with variations in the monsoon activity or Saharan winds system, are considered as main forcing mechanisms, with a complex relationship of the involved phenomena.

Timing of fluvial terrace formation and concomitant travertine deposition in the upper Sutlej River (Tirthapuri, southwestern Tibet) and paleoclimatic implications

Travertines are carbonates precipitated from hydrothermal springs and are relatively common on the Tibetan plateau and occur along tectonically active faults. The Karakoram fault system is an active strike-slip fault that extends from the Pamir into southwestern Tibet, where it controls the course of the upper Sutlej River and the occurrence of several hydrothermal springs, including the Tirthapuri hot springs. Multiple fluvial terraces that are partly capped by travertine are preserved in the Tirthapuri area. Four main fluvial terrace levels (labelled as T1 to T4 with increasing height above river) were identified and several meter-thick travertine platforms occur on the current river level as well as the T2 and T3 terraces. Sedimentological and petrographic observations suggest that the travertine platforms were deposited on active floodplains of the paleo- and modern Sutlej River, and preserved from fluvial erosion because travertine precipitation was immediately followed by vertical river-bed incision and thus terrace abandonment. Results of 230Th/U in combination with luminescence dating show that the deposition of travertine platform and river incision that led to the formation of T3 terrace (∼93 m above the Sutlej) took place at ca. 127.5 ka. The development of terrace T2 and overlying travertine platform (∼28 m above the Sutlej) occurred between ca. 10.0 and 8.8 ka. Fluvial incision has arrived at the modern level at least ca. 0.2 ka ago. Both the travertine deposition and major river incision are likely triggered by the intensified Indian summer monsoon and are linked to phases of maximum monsoon strength. During strong monsoon phases, a large quantity of moisture is transported into southwestern Tibet, activating hot springs and thus travertine precipitation, facilitating fluvial incision and stripping off sediments from the regional hill-slopes. At least over the last glacial cycle we suggest that the Tirthapuri travertine and associated fluvial incision are sensitive indicators of (peak) monsoonal activity and can thus provide valuable insights into past climate change and climate-driven landscape evolution on the southwestern Tibetan Plateau. Comparison of our findings with published data further suggests that monsoon-controlled fluvial aggradation and incision during the early Holocene is synchronous in southwestern Tibet and the adjacent sector of the Himalayan orogen (north-western Sub-to High Himalaya).

Subterranean microbial oxidation of atmospheric methane in cavernous tropical karst

Subterranean methanotrophy is a potentially important but overlooked sink for the atmospheric greenhouse gas methane (CH4). This study documents a microbial CH4 sink in tropical subterranean karst cavities in Vietnam's northern karst province where porosity, steep topography, and scarce soil and vegetation cover foster the exchange of subterranean air with the atmosphere. Our data are based on (i) surveys of CH4, carbon dioxide, and radon concentrations in the air of 11 caves, (ii) in situ mesocosm experiments in caves, as well as (iii) laboratory mesocosm measurements using sediment and rock from caves. The extent of CH4 depletion in cave air depends on the ventilation rate and the availability of moisture to provide a habitat for CH4-oxidizing bacteria, both of which are seasonally variable in northern Vietnam and in part depend on monsoonal activity. Mesocosm experiments using fresh versus sterilized rock and sediment confirmed the role of microbial methanotrophy towards uptake of CH4 from cave air. Our results also suggest that within-cave heterogeneity of environmental variables like salinity may affect rates of CH4 oxidation. We conservatively estimate that 150,000 metric tons of atmospheric CH4 are microbially oxidized annually in the ~29,000km2 of Vietnamese tropical karst, which would compensate for ~7% of Vietnam's agricultural CH4 emissions from rice farming and livestock. Future studies estimating the global fluxes of the atmospheric greenhouse gas CH4 should consider subterranean karst as a potentially important CH4 sink.

Volcanic influence on centennial to millennial Holocene Greenland temperature change

Solar variability has been hypothesized to be a major driver of North Atlantic millennial-scale climate variations through the Holocene along with orbitally induced insolation change. However, another important climate driver, volcanic forcing has generally been underestimated prior to the past 2,500 years partly owing to the lack of proper proxy temperature records. Here, we reconstruct seasonally unbiased and physically constrained Greenland Summit temperatures over the Holocene using argon and nitrogen isotopes within trapped air in a Greenland ice core (GISP2). We show that a series of volcanic eruptions through the Holocene played an important role in driving centennial to millennial-scale temperature changes in Greenland. The reconstructed Greenland temperature exhibits significant millennial correlations with K+ and Na+ ions in the GISP2 ice core (proxies for atmospheric circulation patterns), and δ18O of Oman and Chinese Dongge cave stalagmites (proxies for monsoon activity), indicating that the reconstructed temperature contains hemispheric signals. Climate model simulations forced with the volcanic forcing further suggest that a series of large volcanic eruptions induced hemispheric-wide centennial to millennial-scale variability through ocean/sea-ice feedbacks. Therefore, we conclude that volcanic activity played a critical role in driving centennial to millennial-scale Holocene temperature variability in Greenland and likely beyond.

Behavior of predicted convective clouds and precipitation in the high‐resolution Unified Model over the Indian summer monsoon region

AbstractNational Centre for Medium Range Weather Forecasting high‐resolution regional convective‐scale Unified Model with latest tropical science settings is used to evaluate vertical structure of cloud and precipitation over two prominent monsoon regions: Western Ghats (WG) and Monsoon Core Zone (MCZ). Model radar reflectivity generated using Cloud Feedback Model Intercomparison Project Observation Simulator Package along with CloudSat profiling radar reflectivity is sampled for an active synoptic situation based on a new method using Budyko's index of turbulence (BT). Regime classification based on BT‐precipitation relationship is more predominant during the active monsoon period when convective‐scale model's resolution increases from 4 km to 1.5 km. Model predicted precipitation and vertical distribution of hydrometeors are found to be generally in agreement with Global Precipitation Measurement products and BT‐based CloudSat observation, respectively. Frequency of occurrence of radar reflectivity from model implies that the low‐level clouds below freezing level is underestimated compared to the observations over both regions. In addition, high‐level clouds in the model predictions are much lesser over WG than MCZ.

Glacial-interglacial climate change on the northeastern Tibetan Plateau over the last 600 kyr

Exploring the interplay between the mid-latitude Westerlies and East Asian monsoon systems is crucial for revealing the mechanisms and processes behind the aridification of the central Asian interior. In this study, a high-resolution acid-dissolved Mn record of lacustrine sediments from a drilling core (SG-1) in the arid western Qaidam Basin on the northeastern Tibetan Plateau (TP) largely reveals the evolution of lake levels and climate change over the last 600kyr. The climate in the western Qaidam Basin shows distinct glacial and interglacial changes in accordance with changes in the global climate, and in North Atlantic sea surface temperatures (SSTs), indicating the teleconnection between the basin's climate and the North Atlantic in the form of the Westerlies. However, the basin's climate also correlates closely with East Asian Winter Monsoon (EAWM) activity as recorded by the grain size variations in loess-paleosol sequences on the Chinese Loess Plateau (CLP) over a glacial-interglacial timescale. Even during glacial periods, some relatively warm/humid stages accompanied by high paleolake levels in the western Qaidam Basin are generally conformable with relatively weak EAWM, whereas these warm/humid stages show a weak relation with the East Asian Summer Monsoon (EASM) and North Atlantic SSTs. These results collectively provide evidence that climate change in the western Qaidam Basin is, and was, not only controlled by the Westerlies, but also strongly influenced by the Siberian High, at least during glacial periods. The exact driving mechanism, however, needs to be explored further in future studies.

Nonstationarity in timing of extreme precipitation across China and impact of tropical cyclones

This study examines the seasonality and nonstationarity in the timing of extreme precipitation obtained by annual maximum (AM) sampling and peak-over-threshold (POT) sampling techniques using circular statistics. Daily precipitation data from 728 stations with record length of at least 55years across China were analyzed. In general, the average seasonality is subject mainly to summer season (June–July−August), which is potentially related to East Asian monsoon and Indian monsoon activities. The strength of precipitation seasonality varied across China with the highest strength being in northeast, north, and central-north China; whereas the weakest seasonality was found in southeast China. There are three seasonality types: circular uniform, reflective symmetric, and asymmetric. However, the circular uniform seasonality of extreme precipitation was not detected at stations across China. The asymmetric distribution was observed mainly in southeast China, and the reflective distribution of precipitation extremes was also identified the other regions besides the above-mentioned regions. Furthermore, a strong signal of nonstationarity in the seasonality was detected at half of the weather stations considered in the study, exhibiting a significant shift in the timing of extreme precipitation, and also significant trends in the average and strength of seasonality. Seasonal vapor flux and related delivery pathways and also tropical cyclones (TCs) are most probably the driving factors for the shifts or changes in the seasonality of extreme precipitation across China. Timing of precipitation extremes is closely related to seasonal shifts of floods and droughts and which means much for management of agricultural irrigation and water resources management. This study sheds new light on nonstationarity in timing of precipitation extremes which differs from existing ones which focused on precipitation extremes from perspective of magnitude and intensity.

Active Monsoon and Daily Rainfall in the Hill Sub Region of West Bengal – An Information Theory Approach

Active Monsoon and Daily Rainfall in the Hill Sub Region of West Bengal – An Information Theory Approach

A COMPARATIVE ANALYSIS OF CHANGING SEDIMENTATION CONDITIONS DURING THE LAST INTERGLACIAL-GLACIAL MACROCYCLE IN THE LOESS AREAS OF THE SOUTHERN EAST EUROPEAN PLAIN (THE AZOV SEA REGION) AND CENTRAL CHINA (LOESS PLATEAU)

Multi-proxy studies of loess-soil sequences in the eastern Azov Sea region (Beglitsa‑2 section) and the northwestern Loess Plateau of China (Caoxian section) let us to suggest the correlation of the main stratigraphic horizons and to provide the comparison of landscape and climatic changes in these regions during the last interglacial-glacial climatic macrocycle. It was found that the Loess Plateau was characterized by a steady accumulation of loess during both glacial and interglacial epochs, when the so-called “warm” loess was formed. In the NE Sea of Azov region, the main loess accumulation corresponded to cryoarid conditions of the glacial phases, while during the interglacials, loess accumulation became ten times slower. The average sedimentation rate of loess material calculated for Caoxian section was more than 5 times higher than the one calculated for the Beglitsa‑2 section. Late Pleistocene paleosoils in the Beglitsa‑2 section are of the steppe type and correspond to the Salyn (MIS5e), Krutitsa (MIS5c), and Bryansk (MIS3) climate phases. Morphology of the Azov paleosoils is much better expressed than that of the paleosoils at Caoxian, where only the S1SS3 semidesert paleosoil (MIS5e) can be seen directly in the section. Climatic fluctuations in the southern East European Plain within the last interglacial-glacial macrocycle had significantly greater amplitude than that in the north-west of the Loess Plateau. In the latter, cryoarid glacial conditions alternated with warm semiarid interglacial conditions. In the northwestern Loess Plateau, the main climate dynamics was associated with the hydrological regime changes under the influence of the East Asian monsoon activity, which was at its lowest during the glacial stages (drier climatic phases) and increased during the interglacial and interstadials (wetter climatic phases).

Seasonal and Intraseasonal Variability of Mesoscale Convective Systems over the South Asian Monsoon Region

Abstract Seasonal and intraseasonal differences in mesoscale convective systems (MCSs) over South Asia are examined using A-Train satellites, a ground-based lightning network, and reanalysis fields. Premonsoon (April–May) MCSs occur primarily over Bangladesh and the eastern Bay of Bengal. During the monsoon (June–September), small MCSs occur over the Meghalaya Plateau and northeast Himalayan notch, while large and connected MCSs are most widespread over the Bay of Bengal. Monsoon MCSs produce less lightning and exhibit more extensive stratiform and anvil reflectivity structures in CloudSat observations than do premonsoon MCSs. During the monsoon, Bay of Bengal and Meghalaya Plateau MCSs vary with the 30–60-day northward-propagating intraseasonal oscillation, while northeast Himalayan notch MCSs are associated with weak large-scale anomalies but locally enhanced CAPE. During intraseasonal active periods, a zone of enhanced large and connected MCSs, precipitation, and lightning extends from the northeastern Arabian Sea southeastward over India and the Bay of Bengal, flanked by suppressed anomalies. Spatial variability is observed within this enhancement zone: lightning is most enhanced where MCSs are less enhanced, and vice versa. Reanalysis composites indicate that Bay of Bengal MCSs are associated with monsoon depressions, which are frequent during active monsoon periods, while Meghalaya Plateau MCSs are most frequent at the end of break periods, as anomalous southwesterly winds strengthen moist advection toward the terrain. Over both regions, MCSs exhibit more extensive stratiform and anvil regions and less lightning when the large-scale environment is moister, and vice versa.

Asian monsoon modulation of nonsteady state diagenesis in hemipelagic marine sediments offshore of Japan

AbstractWe have identified millennial‐scale variations in magnetic mineral diagenesis from Pacific Ocean sediments offshore of Japan that we correlate with changes in organic carbon burial that were likely driven by Asian monsoon fluctuations. The correlation was determined by identifying offsets between the positions of fossil diagenetic fronts and climatically induced variations in organic carbon burial inferred from magnetic and geochemical analyses. Episodes of intense monsoon activity and attendant sediment magnetic mineral diagenesis also appear to correlate with Heinrich events, which supports the existence of climatic telecommunications between Asia and the North Atlantic region. Several lines of evidence support our conclusions: (1) fluctuations in down‐core magnetic properties and diagenetic pyrite precipitation are approximately coeval; (2) localized stratigraphic intervals with relatively stronger magnetic mineral dissolution are linked to enhanced sedimentary organic carbon contents that gave rise to nonsteady state diagenesis; (3) down‐core variations in elemental S content provide a proxy for nonsteady state diagenesis that correlate with key records of Asian monsoon variations; and (4) relict titanomagnetite that is preserved as inclusions within silicate particles, rather than secondary authigenic phases (e.g., greigite), dominates the strongly diagenetically altered sediment intervals and are protected against sulfidic dissolution. We suggest that such millennial‐scale environmental modulation of nonsteady state diagenesis (that creates a temporal diagenetic filter and relict magnetic mineral signatures) is likely to be common in organic‐rich hemipelagic sedimentary settings with rapidly varying depositional conditions. Our work also demonstrates the usefulness of magnetic mineral inclusions for recording important environmental magnetic signals.

Differences in the Climatological Characteristics of Precipitation between Active and Break Spells of the Indian Summer Monsoon

Abstract Climatological characteristics of precipitation during the active and break spells of the monsoon are studied using 15 years of TRMM measurements. The spatial variation of rain fraction suggests that most of the seasonal rainfall occurs in spells of active monsoon over India, except for the zones along the east coast. The broader reflectivity distribution at higher altitudes and larger average storm height during active spells indicate the high prevalence of deep systems during this spell. The spatial distribution of the occurrence and fraction of different types of rain exhibits large variability from land to ocean and between the spells. The higher occurrence and fraction of stratiform rain during the active spell, particularly over the core monsoon zone, is due to the prevalence of organized mesoscale systems with large stratiform portions. The break spells are characterized by higher occurrence of shallow rain and larger fraction of convective rain. While an evening peak is observed over land during the break spell, the phase of the diurnal cycle exhibits large spatial variability during the active spell. The rainfall peaks from late night to midnight in southeastern India and in the morning near the foothills of the Himalayas during the active spell. The diurnal and semidiurnal components together explain more than 90% of total variance over many of the zones during both spells. The observed differences in precipitation between the spells are discussed in light of the differences in synoptic- and mesoscale mechanisms responsible for the production of precipitation.

Hematology hurdles – Infusion of biologics in cynomolgus monkeys

A multi-proxy reconstruction of a sediment core from the Tatos basin in the Mauritian lowlands reveals a dynamic environmental history during the last 8000 years. Under influence of sea level rise, the basin progressed from a wetland to a shallow lake between 8000 and 2500 cal yr BP and it slowly changed back into a wetland after sea level reached its highest position at around 2500 cal yr BP. The groundwater level in the basin was strongly affected by sea level rise and precipitation-forced runoff through the porous volcanic bedrock.Millennial-scale precipitation changes in the Mauritian lowlands were derived from the pollen records of semi-dry forest and palm woodland. Salinity and environmental reconstructions based on diatoms, ostracods, stable isotopes and sediment composition showed numerous decadal and centennial droughts and wet events. Mauritius experienced wet conditions between ∼8000 and ∼6800 cal yr BP, followed by decreasing humidity from 6800 to 6000 cal yr BP. Dry conditions persisted until ∼1200 cal yr BP, after which wetter conditions have prevailed as recorded from Mauritian lowland and upland records. Climate dynamics reflects northern hemisphere monsoon activity and suggest that Mauritian rainfall and the Indian and Asian summer monsoons are linked, as both receive moisture from the southern equatorial Indian Ocean.The anti-phased relationship of climate dynamics between the Mauritian lowlands and western tropical Australia during the middle Holocene is interpreted as a prolonged configuration of a negative mode of the Indian Ocean Dipole (IOD). A negative IOD-like state is supported by decreased Asian summer monsoon rainfall, higher Austral-Indonesian summer monsoon rainfall and lower temperatures in the Kilimanjaro record. Conversely, repeated decadal-scale wet events in the Mauritian lowlands occurring every ∼350 years reflect short positive IOD-like events.The onset of ENSO climate variability followed an anomalously strong negative IOD-like event and shifted teleconnections from the tropical Indian Ocean to the Pacific Ocean. A shift in ENSO activity around ∼2600 cal yr BP signifies the decoupling of ENSO from the Atlantic ITCZ. Subsequently, the influence of ENSO on climate in the western Indian Ocean is indicated by increased storm frequency and drought events after 2660 cal yr BP in Mauritius and reduced monsoon activity in the western and eastern Indian Ocean.

On the relationship between Indian Ocean Dipole events and the precipitation of Pakistan

This study investigated the relationship between the Indian Ocean Dipole (IOD) and the precipitation of Pakistan using data for the period of 1958–2010. The long-term evolution of the IOD index did not show interannual patterns similar to those of the annual precipitation of Pakistan. No linkage between the co-occurring trends of the IOD and the precipitation was traced during the period of investigation. The correlation between the IOD and the precipitation of Pakistan indicated a noteworthy impact over the monsoonal regions, especially the coastal area and the western region of Pakistan, which showed a significant positive correlation between the IOD index and annual and summer precipitation. A significant positive relationship was also revealed between the precipitation of the Balochistan Plateau and the IOD index for the summer monsoon season. No connection was observed between the IOD and the precipitation of the northern regions and the upper Indus Plain of Pakistan. Positive phases of the IOD have been noted to occur along with surplus precipitation during active monsoon conditions. The southeasterly wind moves from the Arabian Sea and transports additional moisture from the Arabian Sea to the coastal and southwestern parts of Pakistan during positive phases of the IOD.

Holocene climatic vicissitudes and sea level changes in the south western coast of India: Appraisal of stable isotopes and palynology

The southern Kerala coast in SW India has experienced dramatic changes in climate and sea level during Holocene. These changes are apparently well preserved in the sedimentary archives of the estuarine basins that are entrenched on the uplifted Neogene deposits. Here we report the sedimentary processes, palaeoclimate and sea level records decoded from two borehole cores – Puthenthuruthu and Munrothuruthu borehole cores – retrieved respectively from the marine and fluvial ends of the second largest estuarine basin in SW India, the Ashtamudi estuary, using sedimentology, palynology and stable isotopes as the major proxies. The heavy rainfall event at the latter half of Early Holocene (6117 ± 101 BP) is reflected well in the isotopic signatures of the Puthenthuruthu borehole core. The higher level of lighter isotopes of oxygen and carbon at 10–15 m below ground level is a clear indication of freshwater influx from the hinterland due to intensified monsoon activity. This, in turn, was responsible for the development of Bay Head Delta in the fluvial end of the estuary during Early–Middle Holocene period. Palynological contents below the level indicate a facies change as freshwater and terrestrial elements dominate over marine contents. Further, the occurrence of desmids shows the marine facies is being gradually replaced by freshwater to continental facies. This was followed by the deposition of littoral sands as Flood Tide Islands within the estuarine basin. The palynological investigations of sediments with radiocarbon age of 4350 ± 90 BP in the Munrothuruthu borehole core show a dry phase with high saline depositional environment in the beginning which is followed by influx of freshwater as indicated by the higher content of lighter isotopes of carbon and oxygen in the calcareous nodules (algal pisolites) embedded in the sediments. The occurrence of pteridophytic spores and a few pollen of Cullenia in the palynological preparations in the upper half of the silt and clay dominated intervening layers reiterate this view.

CCN concentrations and BC warming influenced by maritime ship emitted aerosol plumes over southern Bay of Bengal.

Significant quantities of carbon soot aerosols are emitted into pristine parts of the atmosphere by marine shipping. Soot impacts the radiative balance of the Earth-atmosphere system by absorbing solar-terrestrial radiation and modifies the microphysical properties of clouds. Here we examined the impact of black carbon (BC) on net warming during monsoon season over southern Bay-of-Bengal, using surface and satellite measurements of aerosol plumes from shipping. Shipping plumes had enhanced the BC concentrations by a factor of four around the shipping lane and exerted a strong positive influence on net warming. Compiling all the data, we show that BC atmospheric heating rates for relatively-clean and polluted-shipping corridor locations to be 0.06 and 0.16 K/day respectively within the surface layer. Emissions from maritime ships had directly heated the lower troposphere by two-and-half times and created a gradient of around 0.1 K/day on either side of the shipping corridor. Furthermore, we show that ship emitted aerosol plumes were responsible for increase in the concentration of cloud condensation nuclei (CCN) by an order of magnitude that of clean air. The effects seen here may have significant impact on the monsoonal activity over Bay-of-Bengal and implications for climate change mitigation strategies.

Entropy analysis of stable isotopes in precipitation: tracing the monsoon systems in China.

Due to the complexity of monsoon systems and random behaviors of isotope tracers, conventional methods are not adequate for uncovering detailed information about monsoon activities from typically limited precipitation isotope data. We developed a new approach based on the entropy theory to analyze such data with a focus on the monsoon systems in China, dealing with the complexity of these systems and data deficiency. Using precipitation isotope data from 42 selected stations in and around China within the GNIP network, we computed entropies associated with D and 18O. These entropies were found to relate linearly to each other with a proportionality factor close to unity. The spatial variations of the D and 18O entropy in the study area revealed the origins, extents and pathways of the Chinese monsoon systems, as well as their interactions. While further investigation is needed at a greater (global) scale, this study has demonstrated how the entropy theory enables an in-depth analysis of precipitation isotope data to trace the pathway and determine the range of a monsoon system.

Ocean upwelling and intense monsoonal activity based on late Miocene diatom assemblages from Neil Island, Andaman and Nicobar Islands, India

The late Miocene (Tortonian) diatoms in 21 outcrop samples from Neil Island, Andaman and Nicobar Islands were investigated with eighty two planktonic and benthic taxa belonging to 35 genera. Principal Component Analysis reveals the existence of two distinct groups; samples dominated by Thalassionema nitzschioides and Thalassiothrix longissima, belong to one group and the other group is dominated by Actinocyclus ellipticus, Azpeitia nodulifera, Coscinodiscus asteromphalus and C. radiatus. Five palaeoecological zones have been proposed with the help of CONISS cluster analysis according to the dominance of diatom taxa. To ascertain high resolution palaeoecological zones SHEBI analysis was carried out, which reveals seven zones. The studied outcrop is also characterised by the late Miocene marker radiolarians of RN8 and RN9 zones. The overall analysis indicates a strong monsoonal system; however there are evidences of relatively weaker intermittent monsoonal activity. The diatom planktonic/benthic ratio shows evidence of minor sea level fluctuations during that period. The dominance of the upwelling diatom taxon Thalassionema nitzschioides confirms the strong monsoonal activity during the late Miocene in the study area.

Long-Term Variability of the Wind Field over the Indian Ocean Based on ERA-Interim Reanalysis

A detailed study of long-term variability of winds using 30 years of data from the European Centre for Medium-range Weather Forecasts global reanalysis (ERA-Interim) over the Indian Ocean has been carried out by partitioning the Indian Ocean into six zones based on local wind extrema. The trend of mean annual wind speed averaged over each zone shows a significant increase in the equatorial region, the Southern Ocean, and the southern part of the trade winds. This indicates that the Southern Ocean winds and the southeast trade winds are becoming stronger. However, the trend for the Bay of Bengal is negative, which might be caused by a weakening of the monsoon winds and northeast trade winds. Maximum interannual variability occurs in the Arabian Sea due to monsoon activity; a minimum is observed in the subtropical region because of the divergence of winds. Wind speed variations in all zones are weakly correlated with the Dipole Mode Index (DMI). However, the equatorial Indian Ocean, the southern part of the trade winds, and subtropical zones show a relatively strong positive correlation with the Southern Oscillation Index (SOI), indicating that the SOI has a zonal influence on wind speed in the Indian Ocean. Monsoon winds have a decreasing trend in the northern Indian Ocean, indicating monsoon weakening, and an increasing trend in the equatorial region because of enhancement of the westerlies. The negative trend observed during the non-monsoon period could be a result of weakening of the northeast trade winds over the past few decades. The mean flux of kinetic energy of wind (FKEW) reaches a minimum of about 100 W m−2 in the equatorial region and a maximum of about 1500 W m−2 in the Southern Ocean. The seasonal variability of FKEW is large, about 1600 W m−2, along the coast of Somalia in the northern Indian Ocean. The maximum monthly variability of the FKEW field averaged over each zone occurs during boreal summer. During the onset and withdrawal of monsoon, FKEW is as low as 50 W m−2. The Southern Ocean has a large variation of about 1280 W m−2 because of strong westerlies throughout the year.

The Indo-Pacific Warm Pool: critical to world oceanography and world climate

The Indo-Pacific Warm Pool holds a unique place on the globe. It is a large area [>30 × 106 km2] that is characterised by permanent surface temperature >28 °C and is therefore called the ‘heat engine’ of the globe. High convective clouds which can reach altitudes up to 15 km generate much latent heat in the process of convection and this area is therefore called the ‘steam engine’ of the world. Seasonal and contrasting monsoonal activity over the region is the cause for a broad seasonal change of surface salinities, and since the area lies along the path of the Great Ocean Conveyor Belt, it is coined the ‘dilution’ basin due to the high incidence of tropical rain and, away from the equator, tropical cyclones contribute to a significant drop in sea water salinity. Discussion about what may happen in the future of the Warm Pool under global warming is presented together with a description of the Warm Pool during the past, such as the Last Glacial Maximum when sea levels had dropped by ~125 m. A call for urgent monitoring of the IPWP area is justified on the grounds of the significance of this area for global oceanographic and climatological processes, but also because of the concerned threats to human population living there.