Western Arabian Sea Research Articles

An investigation of the influence of the southern annular mode on Indian summer monsoon rainfall

ABSTRACT:The present research was aimed at identifying the influence of the southern annular mode on the Indian summer monsoon (ISM) by investigating the inter‐annual as well as seasonal variation in the southern annular mode index (SAMI) and the ISM rainfall. It is shown that each month of the ISM is influenced by the southern annular mode of different months. The association between the June SAMI and July rainfall was found to be significant as well as important. The investigation was carried out with the NCEP/NCAR reanalysis dataset. The result shows that the monsoon rainfall anomaly is significantly and negatively correlated with the SAMI. The influence of the June SAMI is estimated with sea surface temperature (SST), horizontal wind at 850 hPa pressure level, vertical wind and moisture convergence. The result shows the existence of warm sea surface at 30 ° S during high SAMI years which is surmised to control the cross‐equatorial flow during the ISM. It was also observed that the enhanced southerly flow over the south of India is divided into two parts. The major flow is observed towards the western Arabian Sea, subsequently turning clockwise and moving towards the western part of India through the north Arabian Sea. The result further shows that an intense ascending motion from the equator to 30 ° N along the western coast coincides with the low rainfall region. These conditions may lead to an enhanced divergence zone over the western and northeastern region of India which, in turn, may result in less rainfall over India.

Nature and composition of interbedded marine basaltic pumice in the ∼52–50 Ma Vastan lignite sequence, western India: Implication for Early Eocene MORB volcanism offshore Arabian Sea

The recognition of pyroclasts preserved in sedimentary environments far from its source is uncommon. We here describe occurrences of several centimetres-thick discontinuous basaltic pumice lenses occurring within the Early Eocene Vastan lignite mine sedimentary sequence, western India at two different levels – one at ∼5 m and the other at 10 m above a biostratigraphically constrained 52 Ma old marker level postdating the Deccan Volcanism. These sections have received global attention as they record mammalian and plant radiations. We infer the repetitive occurrence of pumice have been sourced from a ∼52–50 Ma MORB related to sea-floor spreading in the western Arabian Sea, most plausibly along the Carlsberg Ridge. Pyroclasts have skeletal plagioclase with horsetail morphologies ± pyroxene ± Fe–Ti oxide euhedral crystals, and typically comprise of circular polymodal (radii ≤10 to ≥30 μm), non-coalescing microvesicles (>40–60%). The pumice have undergone considerable syngenetic alteration during oceanic transport and post-burial digenesis, and are a composite mixture of Fe–Mn-rich clay and hydrated altered basaltic glass (palagonite). The Fe–Mn-rich clay is extremely low in SiO 2, Al 2 O 3, TiO 2, MgO, alkalies and REE, but very high in Fe 2 O 3, MnO, P, Ba, Sr contents, and palagonitization involved significant loss of SiO 2, Al 2 O 3, MgO and variable gain in Fe 2 O 3, TiO 2, Ni, V, Zr, Zn and REE. Bubble initiation to growth in the ascending basaltic magma (liquidus ∼1200–1250 ∘C) may have occured in ∼3 hr. Short-distance transport, non-connected vesicles, deposition in inner shelf to more confined lagoonal condition in the Early Eocene and quick burial helped preservation of the pumice in Vastan. Early Eocene Arabian Sea volcanism thus might have been an additional source to marginal sediments along the passive margin of western India.

Reconstruction of Indian summer monsoon winds and precipitation over the past 10,000 years using equatorial pacific SST proxy records

AbstractUsing a multiproxy reduced dimension methodology, we reconstruct fields of Arabian Sea summer wind stress curl and Indian monsoon rainfall anomalies since early Holocene using sea surface temperature (SST) proxies (Mg/Ca and alkenones) from 27 locations scattered across the equatorial Pacific. Reconstructions of summer wind stress curl reveal positive anomalies of ∼30% greater than present day off the coastlines of Oman and Yemen at 10 ka, suggesting enhanced ocean upwelling and an enhanced monsoon jet during this time. Positive wind stress curl anomalies in these regions continued but weakened to ∼12% greater than present day at 6 ka. Wind stress curl anomalies increased by about 8% from 6 to 4 ka but declined again until 2 ka. Positive anomalies in wind stress curl during the early to middle Holocene are consistent with greater early Holocene abundances of the upwelling indicator Globigerina bulloides in the western Arabian Sea, which accumulates most rapidly in present climates during periods of marked upwelling. Spatial rainfall reconstructions reveal the greatest difference in precipitation at 10 ka over the core monsoon region (∼20–60% greater than present day) and concurrently the greatest deficit in rainfall in North East India and on the eastern side of the Western Ghats (∼10–30% less than present day). Specifically, reconstructions for 10 ka reveal 40–60% greater rainfall than present day over northwest India. These findings advance the hypothesis that teleconnections from the equatorial Pacific contributed to, if not accounted for, greater early to middle Holocene wetness over India as recorded by various (e.g., cave, lacustrine, and discharge) paleoclimate proxies throughout the monsoon region.

Geochemical imprints of genotypic variants of Globigerina bulloides in the Arabian Sea

Planktonic foraminifera record oceanic conditions in their shell geochemistry. Many palaeoenvironmental studies have used fossil planktonic foraminifera to constrain past seawater properties by defining species based on their shell morphology. Recent genetic studies, however, have identified ecologically distinct genotypes within traditionally recognized morphospecies, signaling potential repercussions for palaeoclimate reconstructions. Here we demonstrate how the presence of Globigerina bulloides cryptic genotypes in the Arabian Sea may influence geochemical signals of living and fossil assemblages of these morphospecies. We have identified two distinct genotypes of G. bulloides with either cool water (type-II) or warm water (type-I) temperature preferences in the Western Arabian Sea. We accompany these genetic studies with analyses of Mg/Ca and stable oxygen isotope (δ18O) compositions of individual G. bulloides shells. Both Mg/Ca and δ18O values display bimodal distribution patterns. The distribution of Mg/Ca values cannot be simply explained by seawater parameters, and we attribute it to genotype-specific biological controls on the shell geochemistry. The wide range of δ18O values in the fossil assemblage also suggests that similar controls likely influence this proxy in addition to environmental parameters. However, the magnitude of this effect on the δ18O signals is not clear from our data set, and further work is needed to clarify this. We also discuss current evidence of potential genotype-specific geochemical signals in published data on G. bulloides geochemistry and other planktonic foraminiferal species. We conclude that significant caution should be taken when utilizing G. bulloides geochemistry for paleoclimate reconstruction in the regions with upwelling activity or oceanographic fronts.

Coastal Kelvin waves and dynamics of Gulf of Aden eddies

The Gulf of Aden (GA) is a small semi-enclosed oceanic region between the Red Sea and the western Arabian Sea. The GA is characterised with westward propagating cyclonic and anti-cyclonic eddies throughout the year. The genesis and propagation of these eddies into the GA have been the focus of several studies which concluded that oceanic instabilities (both barotropic and baroclinic) as well as the Rossby waves from the Arabian Sea are the responsible mechanisms for the presence and maintenance of these eddies. Using a high-resolution (~11km) reduced gravity hydrodynamic layered model with controlled lateral boundary conditions at the three sides of the GA here we show yet another factor, the coastally propagating Kelvin waves along the coastal Arabia (coasts of Oman and Yemen), is also critically important in setting up a favourable condition for the oceanic instabilities and sustenance of meso-scale eddies in the GA. These Kelvin waves at both seasonal and intra-seasonal time scales are found play an important role in the timing and amplitudes of eddies observed in the GA.

Revisiting reconstructed Indian monsoon rainfall variations during the last ∼25 ka from planktonic foraminiferal δ18O from the Eastern Arabian Sea

A careful reanalysis of recently published large body of surface seawater salinity and δ18O data indicates that the variations in the surface seawater δ18O of the Eastern Arabian Sea appear to be governed mainly by the influx of low salinity water through the Winter Monsoon Current from the relatively fresher Bay of Bengal, and transported northwards by the West India Coastal Current. Armed with this “calibration” for the present day, we revisit the south Asian summer monsoon variability during the past ∼25 ka by compiling high resolution fossil planktonic foraminiferal δ18O data from a large number of well dated sediment cores from the Eastern Arabian Sea. We clearly demonstrate that there is no evidence to believe that the south Asian summer monsoon steadily declined during the Holocene as reported in a few earlier papers from the Western Arabian Sea and speleothems from Oman. On the contrary, a majority of sediment core data corroborate the inference of a much earlier paper (Sarkar et al., 2000) of a steadily increasing monsoon rain during the Holocene. That the south Asian monsoons were driven solely by past insolation change appears invalid.

Eastward shift and maintenance of Arabian Sea oxygen minimum zone: Understanding the paradox

The dominance of Oxygen Minimum Zone in the eastern part of the Arabian Sea (ASOMZ) instead of the more bio-productive and likely more oxygen consuming western part is the first part of the paradox. The sources of oxygen to the ASOMZ were evaluated through the distributions of different water masses using the extended optimum multiparameter (eOMP) analysis, whereas the sinks of oxygen were evaluated through the organic matter remineralization, using the apparent oxygen utilization (AOU). The contributions of major source waters to the Arabian Sea viz. Indian Deep water (dIDW), Indian Central water (ICW), Persian Gulf Water (PGW) and Red Sea Water (RSW) have been quantified through the eOMP analysis which shows that the PGW and RSW are significant for the eastward shift of ASOMZ instead of voluminous ICW and dIDW. The distribution of Net Primary Production (NPP) and AOU clearly suggest the transport of organic detritus from the highly productive western Arabian Sea to its eastern counterpart which adds to the eastward shifting of ASOMZ. A revised estimate of the seasonal variation of areal extent and volume occupied by ASOMZ through analysis of latest available data reveals a distinct intensification of ASOMZ by 30% and increase in its volume by 5% during the spring-summer transition. However, during this seasonal transition the productivity in the Arabian Sea shows 100% increase in mean NPP. This disparity between ASOMZ and monsoonal variation of productivity is the other part of the paradox, which has been constrained through apparent oxygen utilization, Net Primary Production along with a variation of core depths of source waters. This study reveals a subtle balance between the circulation of marginal oxygen-rich water masses from the western Arabian Sea and organic matter remineralization in the eastern Arabian Sea in different seasons that explains the maintenance of ASOMZ throughout the year.

Wind Strength Variability in the Western Arabian Sea since the Last Glacial Maximum: Southwest vs. Northeast Monsoon Modes

Wind Strength Variability in the Western Arabian Sea since the Last Glacial Maximum: Southwest vs. Northeast Monsoon Modes

Potential new production in two upwelling regions of the western Arabian Sea: Estimation and comparison

AbstractUsing satellite‐derived and in situ data, the wind‐driven potential new production (nitrate supply) for the 300 km wide coastal band in two upwelling regions of the western Arabian Sea (AS) during the southwest monsoon is estimated. The upward nitrate flux to the euphotic zone is generally based on the physical processes of coastal transport (Ekman transport and geostrophic transport) and offshore Ekman pumping. The coastal geostrophic current in the western AS influences the upwelling intensity and latitudinal distributions of nitrate supply. The Oman and Somalia upwelling regions have similar level of potential new production (nitrate supply) during the summer monsoon, while the satellite estimates of primary production off Oman are 2 times greater than those off Somalia. The much higher potential f‐ratio in the Somalia upwelling region indicates that the primary production could be limited by availability of other macronutrients (e.g., silicate). The correlation analysis of the primary production and the aerosol optical thickness shows that the Oman upwelling region displays a stronger coupling between the atmospheric deposition and the phytoplankton abundance. The high summertime dust levels in the atmosphere are suggested to contribute to the high primary production in the Oman upwelling region.

Characteristics of monsoon inversions over the Arabian Sea observed by satellite sounder and reanalysis data sets

Abstract. Monsoon inversion (MI) over the Arabian Sea (AS) is one of the important characteristics associated with the monsoon activity over Indian region during summer monsoon season. In the present study, we have used 5 years (2009–2013) of temperature and water vapour measurement data obtained from satellite sounder instrument, an Infrared Atmospheric Sounding Interferometer (IASI) onboard MetOp satellite, in addition to ERA-Interim data, to study their characteristics. The lower atmospheric data over the AS have been examined first to identify the areas where MIs are predominant and occur with higher strength. Based on this information, a detailed study has been made to investigate their characteristics separately in the eastern AS (EAS) and western AS (WAS) to examine their contrasting features. The initiation and dissipation times of MIs, their percentage occurrence, strength, etc., has been examined using the huge database. The relation with monsoon activity (rainfall) over Indian region during normal and poor monsoon years is also studied. WAS ΔT values are ∼ 2 K less than those over the EAS, ΔT being the temperature difference between 950 and 850 hPa. A much larger contrast between the WAS and EAS in ΔT is noticed in ERA-Interim data set vis-à-vis those observed by satellites. The possibility of detecting MI from another parameter, refractivity N, obtained directly from another satellite constellation of GPS Radio Occultation (RO) (COSMIC), has also been examined. MI detected from IASI and Atmospheric Infrared Sounder (AIRS) onboard the NOAA satellite have been compared to see how far the two data sets can be combined to study the MI characteristics. We suggest MI could also be included as one of the semipermanent features of southwest monsoon along with the presently accepted six parameters.

Decadal changes of the Western Arabian sea ecosystem

Historical data from oceanographic expeditions and remotely sensed data on outgoing longwave radiation, temperature, wind speed and ocean color in the western Arabian Sea (1950–2010) were used to investigate decadal trends in the physical and biochemical properties of the upper 300 m. 72 % of the 29,043 vertical profiles retrieved originated from USA and UK expeditions. Increasing outgoing longwave radiation, surface air temperatures and sea surface temperature were identified on decadal timescales. These were well correlated with decreasing wind speeds associated with a reduced Siberian High atmospheric anomaly. Shoaling of the oxycline and nitracline was observed as well as acidification of the upper 300 m. These physical and chemical changes were accompanied by declining chlorophyll-a concentrations, vertical macrofaunal habitat compression, declining sardine landings and an increase of fish kill incidents along the Omani coast.

A Study on the Lower Tropospheric Thermal Inversion Over the Arabian Sea Using Radiosonde and IASI Data

Over the temperature inversion regions, tropospheric temperature increases with height and clouds are unable to grow vertically. Over the western Arabian Sea, thermal inversion (TI) is seen at the lower troposphere during the Indian summer monsoon season of June to September. Characteristics of this TI are studied using radiosonde data collected over two stations viz., Muscat (23.5°N; 58.5°E) and Salalah (17.0°N; 54.1°E), located close to the TI region and compared with satellite data. Results suggest that the inversion pattern is highly variable on day-to-day basis over Muscat but is nearly constant over Salalah. Three distinct inversion patterns are identified over Muscat. They are: Type-1: temperature increases with height from surface to about 900 hPa and decreases thereafter; Type-2: temperature decreases with height in a shallow region close to the surface followed by an increase up to about 900 hPa and decreases thereafter; and Type-3: multiple inversions up to about 850 hPa. Salalah always showed type-2 inversion with peak temperature around 950 hPa. Statistics of the occurrence of different inversion types are computed for Muscat and Salalah. This paper also evaluates the ability of Infrared Atmospheric Sounding Interferometer (IASI) onboard MetOP satellite in identifying the TI over the Arabian Sea. IASI data are able to capture type-1 and type-2 inversions over Muscat but is unable to capture the type-3 inversions due to its coarser vertical resolution. IASI data are also unable to capture the sharp inversion over Salalah for the same reason.

Records of <i>Chelidoperca maculicauda</i> and <i>C. occipitalis</i> (Serranidae) from the Arabian Sea, with Comments on Diagnostic Characters

Eight specimens of Chelidoperca maculicauda Bineesh and Akhilesh, 2013 from the Gulf of Aden and five of C. occipitalis Kotthaus, 1973 from the Gulf of Oman represent the first records of those species from the respective localities, and suggest a wide distribution of both along the Arabian Sea coast. Chelidoperca maculicauda was previously recorded only from its type locality on the southwest coast of India, and C. occipitalis, only from the west coast of India, Pakistan, and Socotra Island (Yemen; type locality), western Arabian Sea. The two are compared with all currently known congeners and their diagnostic characters are reviewed.

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.

Biogeochemistry of iron in the Arabian Sea

AbstractThe Arabian Sea is a productive basin where seasonal upwelling and convective mixing result in high surface nutrient concentrations and widespread algal blooms. The factors controlling primary productivity in the Arabian Sea are of interest because the region contains an intense oxygen minimum zone (OMZ) that is a major sink for nitrate in the ocean. A survey of iron (Fe) distribution and redox chemistry was carried out in 2007 to assess its role in Arabian Sea biogeochemistry, including an investigation of the biological response to Fe additions. Results show that Fe is strongly enriched in the eastern Arabian Sea, associated with the OMZ. Much of the Fe within the OMZ is present as Fe(II), which enhances the residence time and accumulation of Fe. In contrast, Fe concentrations are lower in the western Arabian Sea, separated from the Fe‐rich OMZ by a water mass boundary. Consequently, low surface values are associated with monsoon‐driven upwelling off the Omani coast. Incubations revealed that primary production during the southwest monsoon was strongly limited by Fe over much of the study area. Incubation of surface waters with Fe resulted in rapid growth of Phaeocystis and up to sixfold increase in chlorophyll. This is the first demonstration of Fe limitation in the Arabian Sea, and the first high resolution zonal survey of dissolved Fe and Fe(II) across the basin. Our findings suggest that models developed to predict the response of the Arabian Sea biogeochemistry to global warming need to consider effects on Fe inputs.

Implications of scaled δ15N fractionation for community predator-prey body mass ratio estimates in size-structured food webs.

Nitrogen stable isotope ratios (δ(15) N) may be used to estimate community-level relationships between trophic level (TL) and body size in size-structured food webs and hence the mean predator to prey body mass ratio (PPMR). In turn, PPMR is used to estimate mean food chain length, trophic transfer efficiency and rates of change in abundance with body mass (usually reported as slopes of size spectra) and to calibrate and validate food web models. When estimating TL, researchers had assumed that fractionation of δ(15) N (Δδ(15) N) did not change with TL. However, a recent meta-analysis indicated that this assumption was not as well supported by data as the assumption that Δδ(15) N scales negatively with the δ(15) N of prey. We collated existing fish community δ(15) N-body size data for the Northeast Atlantic and tropical Western Arabian Sea with new data from the Northeast Pacific. These data were used to estimate TL-body mass relationships and PPMR under constant and scaled Δδ(15) N assumptions, and to assess how the scaled Δδ(15) N assumption affects our understanding of the structure of these food webs. Adoption of the scaled Δδ(15) N approach markedly reduces the previously reported differences in TL at body mass among fish communities from different regions. With scaled Δδ(15) N, TL-body mass relationships became more positive and PPMR fell. Results implied that realized prey size in these size-structured fish communities are less variable than previously assumed and food chains potentially longer. The adoption of generic PPMR estimates for calibration and validation of size-based fish community models is better supported than hitherto assumed, but predicted slopes of community size spectra are more sensitive to a given change or error in realized PPMR when PPMR is small.

Mesoscale and intraseasonal air–sea CO2 exchanges in the western Arabian Sea during boreal summer

Intraseasonal variability, considered a coupled phenomenon, typically occurs in the 20-to-90 day-band and is seen in several of the air–sea interaction parameters over the Indian Ocean. The corresponding variability in the air–sea CO2 exchanges and oceanic pCO2 are not widely studied. In this study, we focus on the boreal summer season to find that there is a strong air–sea interaction of carbon cycle over the Somali region of the western Arabian Sea where the intraseasonal variability during this season is clearly evident in the intense variability in winds, the strength of the upwelling and the evolution of meso-scale eddies. The oceanic pCO2 variability in this intraseasonal band over the Somali region is also remarkably consistent with the other variables and is found to be driven by sea surface temperatures (SST) albeit with a counteracting but relatively minor influence from the dynamics of dissolved inorganic carbon (DIC). The 20-to-90 day-band in pCO2 accounts for about 40% of the monthly mean variability of the sea-to-air CO2 fluxes of this region in boreal summer. Ocean dynamic control on the atmospheric wind response at these mesoscales has been reported before and this study demonstrates that the ocean dynamics also control the seawater pCO2 and the air–sea CO2 fluxes in this region. Other regions with similar meso-scale dynamics must be analyzed for processes that determine air–sea CO2 exchanges and to determine whether the mesoscale fluxes contribute to the low-frequency CO2 fluxes. The role of the intraseasonal variability in atmospheric pCO2 in this exchange is not quantified here due to the lack of data at such high resolutions and needs to be considered in further observational and modeling efforts.

Multi-centennial scale SST and Indian summer monsoon precipitation variability since the mid-Holocene and its nonlinear response to solar activity

Indian Summer Monsoon (ISM) shows a weak correlation with solar variability in the 20th century. However, such climatological observations on solar activity–monsoon relationship are very short and hence uncertain. A few paleomonsoon records also exhibit prominent correspondence with solar activity during early Holocene and beyond. But despite the strong recent solar minima (e.g. Maunder, Spörer, Oort, Wolf), their correlation with monsoon precipitation is weak and inconclusive. Additionally, many of the earlier studies have been from the western Arabian Sea that provides records of the ISM wind intensity instead of the ISM precipitation. We present here mid-Holocene to recent sea surface temperature (SST) reconstructed from Mg/Ca measurements of planktic foraminifera ( Globigerinoides ruber; white, sensu stricto) on a centennial-scale resolution from the southeastern Arabian. These measurements are used to correct the oxygen isotope ratios of G. ruber to reconstruct salinity related to monsoon runoff in this region more precisely than hitherto. The long-term trend indicates that the ISM precipitation has declined since the mid-Holocene similar to the solar activity. On shorter multi-centennial timescale, we show that the ISM precipitation declined concurrently with the recent periods of strong solar minima, but lagged by a couple of hundred years beyond 1300 yr BP toward the mid-Holocene – confirmed statistically using wavelet analysis. This nonstationary phase relationship between the ISM and the solar activity indicates the possible influence of the tropical coupled ocean–atmosphere phenomenon.

Moisture variability over the Indo-Pacific region and its influence on the Indian summer monsoon rainfall

The Indo-Pacific Ocean (i.e. region between 30°E and 150°E) has been experiencing a warming since the 1950s. At the same time, the large-scale summer monsoon rainfall over India and the moisture over the East Africa/Arabian Sea are both decreasing. In this study, we intend to investigate how the decrease of moisture over the East Africa/Arabian Sea is related to the Indo-Pacific Ocean warming and how this could affect the variability of the Indian summer monsoon rainfall. We performed the analysis for the period 1951–2012 based on observed precipitation, sea surface temperature and atmospheric reanalysis products and we verified the robustness of the result by comparing different datasets. The decreasing trend of moisture over the East Africa/Arabian Sea coincides with an increasing trend of moisture over the western Pacific region. This is accompanied by the strengthening (weakening) of the upward motion over the western Pacific (East Africa/Arabian Sea) that, consequently, contributes to modulate the western Pacific-Indian Ocean Walker circulation. At the same time, the low-level westerlies are weakening over the peninsular India, thus contributing to the reduction of moisture transport towards India. Therefore, rainfall has decreased over the Western Ghats and central-east India. Contrary to previous decades, since 2003 moisture over the East Africa/Arabian Sea started to increase and this is accompanied by the strengthening of convection due to increased warming of sea surface temperature over the western Arabian Sea. Despite this moisture increase over the Arabian Sea, we found that moisture transport is still weakening over the Indian landmass in the very recent decade and this has been contributing to the decreased precipitation over the northeast India and southern part of the Western Ghats.

Use of the Boron partition coefficient ‘<i>K</i><i><sub>D</sub></i>' and B/Ca from planktonic foraminifera in the estimation of past seawater pCO<sub>2</sub>

We assess the usefulness of the empirical boron partition coefficient, KD and B/Ca measured from planktonic foraminifera in estimation of pCO2 using three different relationships between KD and temperature derived from various studies. Two sediment cores spanning the last 22 kyr were utilised, one from the intense CO2 source region of the Western Arabian Sea (WAS) and another from the Eastern Arabian Sea (EAS). The sea-air difference in pCO2 at these sites shows results contrary to the present day scenario. Moreover the reconstructions using the three KD relationships lead to assorted results which suggests that the KD approach may not be suitable in paleo-pCO2 reconstructions.