C. M. Laluraj

Nitrate records of a shallow ice core from East Antarctica: Atmospheric processes, preservation and climatic implications

High-resolution records of nitrate (NO3 −), oxygen isotope (δ 18O) and non-sea salt sulphate (nssSO4 2− ) were studied using an ice core collected from central Dronning Maud Land in East Antarctica to identify the influence of environmental variability on accumulation of NO3 − over the past 450 years. The results confirmed that multiple processes were responsible for the production and preservation of NO3 − in Antarctic ice. Correlation between NO3 − and nssSO4 2− peaks revealed that sulphate aerosols released during major volcanic eruptions might have activated the production of nitric acid, which was scavenged by ion-induced nucleation in polar ice sheets. The correlation between the nitrate and δ18 O records further suggest that enhanced NO3 − preservation in the ice occurred during periods of lower atmospheric temperature. Major shifts in the NO3 − record of the ice core presently studied and its comparison with 10Be record from a core collected from South Pole suggest that a reduction in solar activity influenced the NO3 − accumulation in Antarctica through enhanced production of odd nitrogen species.

Origin and characterisation of microparticles in an ice core from the Central Dronning Maud Land, East Antarctica

The scanning electron microscopy–energy dispersive spectroscopic (SEM–EDS) study of selected samples from an ice core collected from Central Dronning Maud Land (CDML), East Antarctica, revealed several microparticles. They are mainly siliceous and carbonaceous particles and have distinct variations in their shape and composition. The morphology and major element chemistry of the particles suggest their origin from either volcanic eruptions or continental dust. The EDS analysis revealed that the volcanic particles are enriched in silica (average SiO2 62%), compared to the continental dust particle (average SiO2 56%). We found that the tephra relating to Agung (1963) and Karkatau (1883) volcanic eruptions, as recorded, in the ice core harbored microbial cells (both coocoid and rods). The occurrence of organic and inorganic particles which bear relation to volcanic eruption and continental dust implies significant environmental changes in the recent past.

Variation of phytoplankton assemblages of Kongsfjorden in early autumn 2012: a microscopic and pigment ratio-based assessment

Phytoplankton species distribution and composition were determined by using microscopy and pigment ratios in the Kongsfjorden during early autumn 2012. Variation in sea surface temperature (SST) was minimal and matched well with satellite-derived SST. Nutrients were generally limited. Surface phytoplankton abundance ranged from 0.21u2009×u2009103 to 10.28u2009×u2009103 cellsxa0L−1. Phytoplankton abundance decreased with depth and did not show any significant correlation with chlorophyll a (chl a). Column-integrated phytoplankton cell counts (PCC) ranged from 94.3u2009×u2009106 cellsxa0m−2 (Kf4) to 13.7u2009×u2009106 cellsxa0m−2 (Kf5), while chl a was lowest at inner part of the fjord (6.3xa0mgxa0m−2) and highest towards the mouth (24.83xa0mgxa0m−2). Biomass from prymnesiophytes and raphidophytes dominated at surface and 10xa0m, respectively. The contribution of Bacillariophyceae to biomass was low. Generally, heterotrophic dinoflagellates were great in abundance (12.82xa0%) and ubiquitous in nature and were major contributors to biomass. Various chl pigments (chl b, chl c, phaeopigments (phaeo)) were measured to obtain pigment/chl a ratios to ascertain phytoplankton composition. Phaeo were observed only in inner fjord. Chl b:a ratios and microscopic observations indicated dominance of Chlorophyceae at greater depths than surface. Furthermore, microscopic observations confirmed dominance of chl c containing algae throughout the fjord. The study indicates that pigment ratios can be used as a tool for preliminary identification of major phytoplankton groups. However, under the presence of a large number of heterotrophic dinoflagellates such as Gymnodinium sp. and Gyrodinium sp., pigment signatures need to be supplemented by microscopic observations.

A geospatial analysis of Samudra Tapu and Gepang Gath glacial lakes in the Chandra Basin, Western Himalaya

Geospatial studies carried out in two major proglacial lakes of Samudra Tapu and Gepang Gath (Chandra Basin, Western Himalaya) showed substantial expansion in their area and volume over the last four decades (1971–2014). The linear and areal expansions for the lakes Samudra Tapu and Gepang Gath were 1889, 1509xa0m and 1, 0.6xa0km2, respectively. The results show that increased melting of the feeder glaciers over this period is major contributor to expand the volumes approximately 20 times of both the lakes Samudra Tapu and Gepang Gath. This expansion of lakes volume of Samudra Tapu and Gepang Gath from 3.4xa0×xa0106 to 67.7xa0×xa0106 and 1.5xa0×xa0106 to 27.5xa0×xa0106 m3, respectively, is quite significance in terms of hazards generated from glacial lake outburst floods (GLOF). This kind of climate change induced increase in the rate of glacial melting is a cause of concern, as the Himalaya Mountains may turn out to be vulnerable to natural hazards like GLOF.

Export fluxes of geochemical solutes in the meltwater stream of Sutri Dhaka Glacier, Chandra basin, Western Himalaya

The hydrochemistry of meltwater from the Sutri Dhaka Glacier, Western Himalaya, has been studied to understand the influence of the factors controlling the weathering processes of the glaciers during the peak ablation period. The high solar irradiance prompted intense melting, which has raised the stream flow of the glacier. The meltwater has been observed as slightly alkaline (mean pH 8.2) and contains the major anions (HCO3−xa0>xa0SO42−xa0>xa0NO3−xa0>xa0Cl−) and cations (Ca2+xa0>xa0Mg2+xa0>xa0K+xa0>xa0Na+xa0>xa0NH4+) with Ca2+ (78.5%) and HCO3− (74.5%) as the dominant species. The piper diagram indicates the category of stream meltwater as Ca2+-HCO3− type. In addition, it is evident from the Gibbs diagram that the interaction between the meltwater and bedrock controls the ionic concentrations of the glacial meltwater. The high ratio value (~xa00.75) of HCO3−/(HCO3−xa0+xa0SO42−) indicates that the carbonate weathering is dominant. Fe and Al followed by Mn, Sr, and Ti are the most dominant trace elements present in the meltwater. The significant negative correlation exhibited by the major ions and Sr with the discharge is recommended for the enrichment of these solutes during the lean discharge periods. However, the insignificant correlation of Fe, Al, Mn, and Ti with discharge suggests their physicochemical control. The principal component analysis (PCA) carried has highlighted three dominant composites, i.e., the water-rock interaction, atmospheric dust inputs, and physicochemical changes in the meltwater. Hence, the present study elucidates the export of geochemical solutes from Sutri Dhaka Glacier and factors governing the water chemistry, which helps in the better understanding of hydrochemical processes of the Himalayan glaciers and substantial improvement of our understanding about the glacio-hydrological environments and their response in the scenario of global warming.

Twentieth-century sea ice variability in the Weddell Sea and its effect on moisture transport: Evidence from a coastal East Antarctic ice core record

High-resolution study of deuterium excess (d-excess), sea salt sodium (ss-Na+), and methane sulfonic acid (MSA) in an ice core from coastal Dronning Maud Land (cDML), East Antarctica, revealed the history of moisture transport and sea ice extent (SIE) during the last century. Backward wind trajectories show that air parcels were mainly derived from the Weddell Sea region. The d-excess profile shows a dramatic shift from an average value of 8‰ during 1905–1920 to −1‰ during ~1940 and thereafter positive excursion during 1940–1980. The dramatic shift during 1920–1940 has been attributed to the reduced moisture supply from low/mid-latitude to Antarctica associated with shifting of Southern Annular Mode (SAM) from positive to negative mode. The ss-Na+ flux profile shows systematic positive excursion during 1940–1980 which coincide with that of the d-excess profile. The MSA flux shows a negative excursion during 1950–1965, overlapping with the period of positive excursions in ss-Na+ and d-excess profiles. The concomitant increase of ss-Na+ and d-excess values and positive excursions during 1940–1980 indicate higher SIE. Based on significant correlation between the Na+ flux and satellite-derived winter SIE record of the Weddell Sea, ~10% increase in SIE is estimated compared to its average value of the last century. The power spectrum analysis of d-excess and ss-Na+ flux shows a significant periodicity at ~3.5u2009years, exactly matching with that of the winter SIE in the Weddell Sea. Wavelet analysis of SAM index and Southern Oscillation Index (SOI) shows the highest common power in 4 to 8 year band, overlapping with the periods of higher SIE and opposite phase in 10 to 16 year band, overlapping with the periods of higher d-excess. This study highlights the role of SAM and its teleconnection to El Niño Southern Oscillations (ENSO) in controlling sea ice and moisture source variability in annual to decadal scale in the coastal regions of Antarctica.

Antarctic Climate Variability During the Past Few Centuries Based on Ice Core Records from Coastal Dronning Maud Land and Its Implications on the Recent Warming

Instrumental and proxy records have revealed that the Antarctic climate system experienced remarkable changes in the past. In order to reconstruct the recent Antarctic climate change during the past centuries with annual to seasonal resolution and to understand its spatial variability, two well-dated ice cores (IND-22/B4 – 62 m and IND-25/B5 – 65 m) from the coastal Dronning Maud Land region of East Antarctica were studied for stable oxygen and hydrogen isotope ratio variability. Of these, the IND-25/B5 provided high-resolution records of the past 100 years (1905–2005) and the IND-22/B4 core represented the past ~470 years (1530–2002) of climate change. The considerable variations in δ18O records on an interannual to decadal scale seems to be associated with changes in low and mid latitude climatic modes like the Southern Annular Mode (SAM) and El Nino Southern Oscillation (ENSO). The extended records of IND-22/B4 exhibited relatively more negative δ18O values during periods of reduced solar activity like the Dalton and Maunder Minima, indicating manifestations of solar activity on Antarctic climate. The estimated surface air temperatures using the δ18O profiles of two ice cores revealed a significant warming by 0.6–1°C per century, with greatly enhanced warming during the past several decades (~0.4°C per decade). Complimentary to the recent findings, it is proposed that the coastal areas of Dronning Maud Land are experiencing significant warming in the recent centuries and further support for a detailed evaluation on actual rates of Antarctic warming through a combination of instrumental and proxy records.