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Climate changes on the Southwest coast of India have essential impacts on social and economic development, and the ecosystem of Southern India. Here, we present the last 2000 cal yr AD rare earth e...

The last millennium climate reconstructions are complex and limit our understanding of the mechanisms behind environmental and climate variability. We present multi-proxy centennial-scale records from the Cherai, southwest India. The last 2000 cal yr AD record suggests a complex environmental condition that prevailed at the depositional site augmenting the role of natural as well as anthropogenic agents. Increased elemental variations and indices values indicate stronger weathering, presumably wetter conditions and intense precipitation. Provenance studies suggest diverse sources and the main composition fall close to the Charnockite and Gneissic composition. Multi-proxy data suggests that a shift towards wetter climatic conditions, which occurred from 910 to 1230 cal yr AD. The core also records a shift towards the drier conditions that started around 1230 cal yr AD with a loss in vegetation diversity. The pollution load index values suggest that the overall study area falls in moderate contamination levels, which are also substantiated with the diatom data indicating human influence in the natural habitat during the deposition time. The present study reveals that the enhanced Cd and As concentration is due to strong anthropogenic influence. We compared the multi-proxy record with other continental and marine palaeoclimatic records to explore global and/or regional trends in climate variability during the last 2000 years.

Antarctic sea ice plays a vital role in global climate via its impact on ocean circulation, biological productivity and CO2 partitioning between the ocean and the atmosphere. However, very little is known about its past history, especially in the southwestern Indian sector of the Southern Ocean (SO). We here provide new quantitative records of winter sea-ice concentration (WSIC) and duration (WSID), sea-surface temperatures (SST) and productivity in sediment core SK 200/33 (55°S – 45°E) from the Permanently Open Ocean Zone over the last 156,000 years. The new records, combined with regional records, indicate that the hydrological structures migrated northward by a few degrees of latitude during all glacial periods with the Southern Antarctic Circumpolar Current Front reaching the core site, the Antarctic Polar Front located at ~46°S and the winter sea ice (WSI) probably extending to ~49°S. In contrast, hydrological fronts and WSI edge migrated poleward by a couple of degrees of latitude during the early Holocene and last interglacial. Comparison to SST and WSI records from different sectors of the SO suggests higher amplitude variations in WSI in the Atlantic sector as compared to the Indian and western Pacific sectors over the last glacial-interglacial cycle, which we attribute to the presence of the Weddell Gyre transporting far to the north the sea ice produced in the Weddell Sea. The new records also suggest a drop in productivity in the POOZ during glacial periods, probably related to greater WSI extent and reduced growing season.

This study reports the presence of Australasian microtektites in a deep-sea core (U1452) retrieved during the International Ocean Discovery Program (IODP) Expedition 354: Bengal Fan. These microtektites are found within a foraminifer-rich calcareous clay layer beneath the Matuyama-Brunhes (M–B) magnetostratigraphic boundary. The majorities are spherical and less than one millimeter in diameter. Typical splash (dumbbell, teardrop, disc etc.) and irregular-shaped forms were recovered. The most abundant microtektites are pale green in color, followed by opaque, pale brown, translucent and transparent varieties. These microtektites are characterized by various surficial attributes including pits, mounds, grooves and fractures. Geochemical analyses suggest that the major oxide compositions are very similar to Australasian tektites and microtektites reported elsewhere and also similar to the average composition of upper crustal rocks. Transparent bottle green microtektites are relatively rich in MgO and low in silica when compared to other microtektites found in U1452. Minor and trace element abundances show a wide range of distribution and individual samples show variations in their concentrations. Differences in minor and trace elements concentration are possibly due to the contamination from the impact ejecta. Other than microtektites, the presence of a possibly polymetallic exsolution structure (Widmanstatten texture), shocked minerals and unmelted and partly melted ejecta within the microtektite-bearing layer in the northern Indian Ocean provides further evidence that the Australasian microtektites might have been formed by the impact of an extraterrestrial projectile at ~0.8 Ma, somewhere in Indochina.

Surface sediments in the Vembanad wetland system, southwest India were analyzed for metals. Assessing the extent of metal contamination in Vembanad wetland surface sediments using individual and combined metal pollution indices shows high heterogeneity of sediment characteristics, sources, sedimentary dynamics and geochemical processes and deciphering natural to anthropogenic contribution. The metal distributions varied greatly in the northern and southern stations suggesting sediment heterogeneity. Sediment concentrations of Cd, As, Pb and Zn were high and exceeded the standard value. Enrichment factor, geoaccumulation index, modified degree of contamination and pollution load index showed that the sediments are moderate to extremely polluted in most of the northern sites. It suggests that Cd and As fell under the extreme amount of metal contamination followed by Pb and Zn which comes under strongly contaminated level. The close relationship of sedimentological and geochemical parameters could be due to the intrinsic relationship of the physico-chemical condition and provenance to the Vembanad wetland system. The main contaminated metal contribution appears to be the anthropogenic input and a small amount from the weathered rocks and sediments present in the course of the rivers. The extent of metal pollution in the Vembanad wetland system implies that the condition may impact the biota and also human health in the vicinity of the wetland.

Tropical semi-arid grasslands are a widespread and ecologically and economically important terrestrial biome. Here, we use paleoecology to understand woodland–grassland transitions across the mid- to late-Holocene period in the Banni grassland, western India. Multi proxy analyses involving palynology, phytoliths and elemental geochemistry were carried out on two sediment cores retrieved from wetlands (Chachi and Luna), to understand temporal fluctuations in vegetation, moisture availability and other environmental parameters. Based on the results, the Chachi core was divided into two major climatic phases. Phase 1 (4600–2500 cal. yr BP) was characterised by high precipitation and abundance of pollen types and phytolith morphotypes that indicate the presence of woody savanna, and mesic herbaceous taxa. Phase 2 (2500 cal. yr BP to the present) was characterised by lower precipitation, lower abundance of mesic taxa and an increase in grass phytolith abundance. However, the period from ~1000 cal. yr BP to the present was characterised by the increased abundance of leguminous taxa, dryland herbs/shrubs and a decline in grass phytolith abundance. The Luna core (~1000 cal. yr BP to the present) also showed results matching with the Chachi core for this latter period. Overall, moisture availability in the ecosystem appears to have declined since 4600 cal. yr BP, and the vegetation has responded to this. Although the balance between tree, shrub and grass elements has fluctuated, overall, the region has remained as an open ‘grass and shrub savanna’ with sparse woody vegetation throughout this period. Our study provides insights into the vegetation dynamics and environmental settings in a poorly understood tropical arid-grassland ecosystem from Asia during the mid-late-Holocene.

The present study documents the interactions between Southern Hemisphere high-latitude (Antarctica & Southern Ocean), southern Indian Ocean subtropics (Agulhas leakage) and Asian summer monsoon. The study uses SST and sea-ice reconstructions along with diatom absolute abundances and diatom biometry from two sediment cores located at the Subantarctic Front (SAF) and Antarctic Polar Front (APF) in the southwest Indian sector of the Southern Ocean. Sea-ice records suggest the presence of the mean winter sea ice limit at around the modern APF location during MIS 2 and MIS 4 and episodic and unconsolidated winter sea ice far north as ∼43°S during LGM, when the SSTs were lowest. Higher diatom productivity and larger mean sizes of F. kerguelensis and T. lentiginosa recorded at the northern core site during the glacial stages suggest a northward shift of the APF. A decrease in diatom productivity and sizes at the southern core site highlights stratified Permanent Open Ocean Zone (POOZ) surface waters in response to longer sea-ice presence during the glacial stages. The comparative study between the records of Southern Hemisphere high-latitude and Asian summer monsoon climate variability revealed that the Asian summer monsoon variability could have been more likely forced by low latitude insolation gradient changes and supported by Antarctic climate changes via meridional shifts of the fronts and sea ice. The past changes in the intensity of Asian summer monsoon along with the Southern Ocean frontal variation might have influenced the Southern Indian Ocean surface circulation by changing the Agulhas leakage intensity.

Trace elements and grain size parameters of a sediment core collected from Vagamon Lake, situated at the edge of Western Ghats, were analyzed. The ascending order of average concentration of metals is showing the following order - Al > Fe > Ti > Mg > Mn > Cr > Zn > Ni > Pb > Cu > Co > As > U> Cd. The metals are not showing a good correlation with the textural parameters, which indicates the grain size is not controlling the metal distribution in the study area. The enrichment factor (EF), geo-accumulation index (Igeo), contamination factor (CF), modified degree of contamination (mCd), and pollution load index (PLI) calculated to assess anthropogenic contamination. Results showed moderately-strongly As contamination in the region. Statistical analysis, such as Principal Component Analysis and Cluster Dendrogram analysis carried out to determine possible interrelationships between the different metals and textural parameters in the Vagamon sediment core. The results indicated that As could be attributed to anthropogenic sources and may be predominantly affected by human activities. Also, the moderate pollution of the elements like Zn, Ni, Cr and Pb may be associated with both natural and anthropogenic sources. The gradual increase of this As contamination is a threat to the plants, human beings and the other biota. Present-day tourism activities, increasing constructions and usage of fertilizers-pesticides-insecticides at the Vagamon area contribute to this alarming situation.

The high abundances and high silicification levels of the diatoms Fragilariopsis kerguelensis (O'Meara) Hustedt and Thalassiosira lentiginosa (Janisch) Fryxell make them crucial silica carriers to the Southern Ocean (SO) sea-floor. However, their efficiency as silica vectors to the ocean bottom might be modulated by important variations in their sizes, from ~10 μm to ~100 μm for F. kerguelensis and ~20 μm–~120 μm for T. lentiginosa. Hence, it is important to understand the factors driving size variations of these key diatom species. Most studies on F. kerguelensis and T. lentiginosa size variations were conducted on fossil samples, back to 40,000 years before present (40 ka BP), and suggested climatically-controlled conditions in macro- and micro-nutrients, sea ice and sea-surface temperature (SST) as the main drivers. However, these studies were unable to document whether size variations were reproductive over several glacial-interglacial cycles. We present here the first record of F. kerguelensis and T. lentiginosa valve size and flux variations in core SK 200/33 from the Permanent Open Ocean Zone (POOZ) of the Indian sector over the last 161 ka BP (Marine Isotope Stage – MIS 1–6). Our results suggest that the smaller sizes and lower fluxes of F. kerguelensis and T. lentiginosa at the core site during glacial stages resulted from greater sea-ice extent, greater water column stratification, reduced SO upwelling, along with a northward shift of the Southern Hemisphere westerly winds. However, small differences in the sizes and fluxes of both species between the glacial stages (MIS 2 and 6) suggest slightly different environmental conditions between these two glacial periods. Our results also demonstrate large sizes and flux differences during Termination I as compared to Termination II. We relate this to a stronger SO upwelling, delivering higher amount of macro- and micro-nutrients to the POOZ during Termination I as compared to Termination II. Our results therefore indicate that different factors control the sizes and fluxes of these species at different time scales.

Asymmetric ventriculomegaly, interhemispheric cyst and dysgenesis of the corpus callosum (AVID) constitutes a rare imaging triad. Additional findings include subcortical and subependymal heterotopia, polymicrogyria, fused thalami, deficient falx, and hydrocephalus. The knowledge of this triad helps us to diagnose prenatally by sonography and fetal MRI. In this case report authors present MRI Imaging findings in a case of AVID syndrome in a 6year old male child presenting with history of seizures and delayed milestones.

Reconstruction of palaeoproductivity from Southern Ocean is crucial for understanding the functioning of the Southern Ocean biological pump in the past. High resolution records of multi-proxy parameters (calcium carbonate, opal, total organic carbon biogenic barium and planktonic carbon isotope ratios (δ 13 C)) were investigated in two well-dated sediment cores (SK200/22a and SK200/27) from the Indian sector of Southern Ocean situated to the north and south of Antarctic Polar front (APF), respectively. The palaeoproductivity records extending ~95 ka BP (SK200/22a) and 75 ka BP (SK200/27) revealed inverse relationships between the calcite and opal productivity, indicating the influence of shifting nutrient regimes. At core SK200/22a, reduced calcite productivity during marine isotope stage (MIS) 2, 4, and part of MIS 3 suggest an equatorward migration of the frontal regimes during glacial intervals. Compared to this, the region south of the APF (core SK200/27) was characterized by the near absence of calcite content during the last glacial period and increased opal productivity during MIS 1 and MIS 3, supporting a southward migration of APF during warmer intervals. Ba (bio) records exhibit good correlation with opal records in both the cores and also correlate with that of calcite record at SK200/22a, indicating that Ba is influenced by the combined opal and calcite productivity. The enhanced opal productivity during the glacial periods north of the APF is attributed to the northward shifting of oceanic fronts and associated transfer of nutrients. Diatom productivity records of SK200/22a reveal significant similarities with the dust records from the Antarctic and Southern Ocean, but showed no significant relationships with the diatom record of SK200/27. It is proposed that the dust-derived Fe input had apparently influenced the palaeoproductivity north of the modern APF, but had a minor influence on opal productivity south of the APF. Comparison with the ice core climate records from Antarctica and Greenland revealed that bioproductivity peaks in the study region are nearly synchronous with the millennial Antarctic warming events. Remarkably, the calcite and opal productivity records at SK200/22a responded differently to the Antarctic warming events, with opal productivity lagging behind the calcite productivity peaks by ~1–2 ka.

Rare earth element (REE) geochemistry of sediments from Vembanad Coastal Wetland, southwest India, shows that light rare earth elements (LREEs) are the more abundant compared to middle rare earth element (MREE) and heavy rare earth element (HREE). We suggest that the textural parameters and the biochemical processes lead to the REE variation in this coastal wetland environment. Variations in the REE abundance are mainly controlled by the source materials deposited by riverine input. REE records in sediments showed spatial heterogeneity due to the influence of the physico-chemical conditions like, sedimentological conditions, salinity and depositional flux of the sediments along the wetland. Enriched values observed along the northern and southern stations are due to the increased riverine input. The REE ratios and enrichment factor values suggest that the abundance is in the order of LREE > MREE > HREE. Positive Eu anomaly is linked to the source sediments brought down from the catchment areas of the Periyar River and Muvattupuzha River. However, Ce anomaly suggests no significant variation in the oxidation condition at the sites of deposition.

Multiple proxy studies on sediment core SK 200/22a from the sub-Antarctic sector of the Indian Ocean revealed millennial-scale fluctuations in terrigenous input during the last 63,000 years. The marine isotope stages 1 (MIS 1) and MIS 3 are characterized by generally low concentrations of magnetic minerals, being dominated by fine-grained magnetite and titano-magnetite. Within the chronological constraints, periods of enhanced terrigenous input and calcite productivity over the last 63,000 years are nearly synchronous with the warming events recorded in Antarctic ice cores. An equatorward shift of the westerly wind system in association with a strengthening of the Antarctic Circumpolar Current (ACC) system may have promoted wind-induced shallow-water erosion around oceanic islands, leading to enhanced terrigenous input to the core site. Major ice-rafted debris events at 13–23, 25–30, 45–48 and 55–58 ka BP are asynchronous with δ18O and carbonate productivity records. This out-of-phase relation suggests that ice-sheet dynamics and ACC intensity were the primary factors influencing ice rafting and terrigenous input to the Indian sector of the Southern Ocean, with only limited support from sea-surface warming.

Ice rafted debris (IRD) records were studied in two sediment cores (SK200/22a and SK200/27) from the sub-Antarctic and Polar frontal regime of the Indian sector of Southern Ocean for their distribution and provenance during the last 22,000 years. The IRD fraction consists of quartz and lithic grains, with the lithic grains dominated by volcaniclastic materials. IRD content was high at marine isotope stage 2 but decreased dramatically to near absence at the Termination 1 and the Holocene. The concentration of IRD at glacial section of the core SK200/27 was nearly twice that of SK200/22a. Moreover, IRD were more abundant at the last glacial maxima (LGM) in SK200/27 with its peak abundance proceeding by nearly two millennia than at SK200/22a. It appears that an intensification of Antarctic glaciation combined with a northward migration of the Polar Front during LGM promoted high IRD flux at SK200/27 and subsequent deglacial warming have influenced the IRD supply at SK200/22a. Quartz and lithic grains may have derived from two different sources, the former transported from the Antarctic mainland, while the latter from the islands of volcanic origin from Southern Ocean. Sea-ice, influenced by the Antarctic Circumpolar Current is suggested to be a dominant mechanism for the distribution of lithic IRD in the region.