Ammonium (NH4+) accumulation and variability in Antarctic ice cores possess signals of various biological, anthropogenic, and atmospheric processes. However, the use of NH4+ variability in Antarctic ice cores for paleoclimate reconstructions is not well established. Addressing this, we have utilized, published NH4+ ice core records from the Dronning Maud Land (DML), Antarctica to assess the sources of NH4+, its transport, major forcing factors, and their mechanism in controlling the variability of ammonium signals in coastal ice cores. The first principle component (PC1) derived from PC analysis of NH4+ data comprises ∼43% of total variability and also depicts a significant spatial correlation with the NSIDC Sea ice concentration (SIC) variability in the Weddell Sea region of the Southern Ocean. In addition, the PC1 shows strong 2–9 year periodicities related to El Niño Southern Oscillation along with two major decadal to centennial periodicities of ∼40 and 100 years. The control of sea ice fluctuations and related oceanic processes (ENSO) provide evidence of the marine sources and influence of ocean-related processes as a major controlling factor for the NH4+ variability in DML ice cores. The cumulative accumulation of the NH4+ produced from enhanced biological decomposition, and unutilized ammonium during nitrification under high SIC conditions are possible mechanisms for the increased supply. The correlation of ERA5 surface air temperatures with Nino3.4 suggests that during El Niño conditions, the air temperatures significantly dropped in the Weddell Sea sector, fostering the high SIC conditions. The findings of this study regarding the role of the SIC in the ammonium variability in Antarctic ice cores would help us better interpret the paleo NH4+ records and their applications to deduce the paleoclimate conditions in coastal Antarctic regions.

Coastal lakes in Antarctica receive an enormous amount of ions and trace elements (TEs) during the austral summer. Some of these TEs and ions are utilised as essential nutrients in primary productivity. In the present study, selected dissolved TEs (Ba, Mn, Cu, Co, Cd, Mo and U) along with dissolved organic carbon (DOC) and Chlorophyll-a were studied in ten coastal lakes of the Larsemann Hills, East Antarctica to decipher their (TEs) sources, understand geochemical behaviour and assess their role on nutrient dynamics. Dissolved concentrations of these TEs are in sub-nanomolar range; almost an order of magnitude lower than the average seawater and global river concentrations. Sea-salt spray and chemical weathering in the catchments of these lakes are dominant sources for these TEs and ions. Though most of the Antarctic lakes have been reported for their oligotrophic character, however, a significant amount of DOC and Chlorophyll-a, and occurrence of algal mats in some of the LH lakes indicate seasonal (austral summer) productivity with the availability of sunlight and nutrients. Our investigation reveals that phosphate (PO43−) and Mo act as limiting nutrients because of their lower concentrations in the water column. Dissolved Cu plays an important role in bacterial-induced organic matter decompositions and release of organic carbon to lake water. We also found Ba excess (non-terrigenous) in the lake and catchment sediments varying from 26 to 63%. The higher Baexcess in the catchment sediments could be due to significant removal of dissolved Ba during the solute transport and later supplied to these lakes. The geochemical data sets presented in this study were found at a natural background level and therefore, would be useful for comparison with other global aquatic environments. Findings of the present study improve our understanding about the biogeochemical cycling of trace elements and their critical role in oligotrophic lakes of Antarctica.

Dissolved major ions, Sr concentrations and Sr-87/Sr-86 ratios of 10 coastal lakes from the Larsemann Hills, East Antarctica have been studied to constrain their solute sources, transport and glacial weathering patterns in their catchments. In absence of perennial river/streams, lakes serve as only reliable archive to study land surface processes in these low-temperature regions. The lake water chemistry is mostly Na-Cl type and it does not show any significant depth variations. Sr isotope compositions of these lakes vary from 0.7110 to 0.7211 with an average value of 0.7145, which is higher than modern seawater value. In addition to oceanic sources, major ions and Sr isotopic data show appreciable amount of solute supply from chemical weathering of silicate rocks in lake catchments and dissolution of Ca-Mg rich salts produced during the freezing of seawaters. The role of sulphide oxidation and carbonate weathering are found to be minimal on lake hydro-chemistry in this part of Antarctica. Inverse model calculations using this chemical dataset provide first-order estimates of dissolved cations and Sr; they are mostly derived from oceanic (seawater + snow) sources (cations approximately 76%) and (Sr approximately 92%) with minimal supplies from weathering of silicates (cations approximately 15%); (Sr approximately 2%) and Ca-rich minerals (cations approximately 9%); (Sr approximately 7%). The silicate weathering rate and its corresponding atmospheric CO2 consumption rate estimates for Scandrett lake catchment (3.6 +/- 0.3 tons/km(2)/year and 0.5 x 10(5) moles/km(2)/year), are lower than that of reported values for the average global river basins (5.4 tons/km(2)/year and 0.9 x 10(5) tons/km(2)/year) respectively. The present study provides a comprehensive report of chemical weathering intensity and its role in atmospheric CO2 consumption in low-temperature pristine environment of Antarctica. These estimates underscore the importance of Antarctica weathering on atmospheric CO2 budget, particularly during the past warmer periods when the large area was exposed and available for intense chemical weathering.

The chapter aims to revise the capabilities of a water balance modelling approach to be applied on climate-related or practical studies of lakes located in specific conditions of Antarctica. The seasonal water balance equation (WBaL) of a lake was suggested for the lakes located in the vicinity of the Antarctic scientific stations: Bellinshausen, Progress and Maitri. First, the methods and models used to evaluate the income and outcome terms of the WBaL from minimal observational datasets are considered. Then the historical observations available on the lakes Kitezh, Priyadarshini, Stepped, Nella, Progress and Reid are described based on the technical reports of the Finnish, Indian and Russian Antarctic research programmes and from open source publications. Finally, practical recommendations on improving temporal hydrological network are formulated to give a simple solution for the seasonal water balance studies of the Lake Priyadarshini.