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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.

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.

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.