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We present bulk organic carbon isotopic composition (δ13C), total organic carbon (TOC) content, and total organic carbon to total nitrogen (C/N) ratio along with major and trace element geochemistry of an AMS radiocarbon-dated Holocene sediment core collected from Chilika Lagoon, India. The data are used to understand changes in the organic matter (OM) sources and the strength of the Indian summer monsoon (ISM). Our results indicate that during early to middle Holocene (10.4–4.9 ka), terrestrial (23–65%) and macrophyte (24–32%) sources were significant contributors to the sediment OM; marine component contributed ≤23%. An abrupt shift in the OM sources was observed at ~4.0 ka, marked by a significant decrease in OM contributions from the terrestrial (5%) and macrophyte (14%) end-members, and an increase in the marine end-member source (70%) into the lagoon. The period from ~4.0 to 2.1 ka recorded the lowest and highest contribution from the terrestrial (5–11%) and marine (50–70%) sources, respectively. This was followed by a gradual increase in the terrestrial and decrease in the marine contribution to 21% and 25% till the present, respectively. During this period, phytoplankton became the major source (31–40%) of OM to the lagoon. This period also experienced increasing anthropogenic activities in the catchment. In this study, proxy records show a strong ISM during early Holocene (10.4–9.0 ka), which was followed by a gradual weakening until 4.9 ka. At ~4.0 ka, an abrupt and pronounced weakening of ISM occurred that was followed by an amelioration of ISM precipitation towards 1.1 ka. Later, the ISM gradually weakened to the present-day condition. Overall, Chilika Lagoon core records exhibit that changes in the Northern Hemisphere summer insolation regulate the long-term trend of ISM during the Holocene. [ABSTRACT FROM AUTHOR]

The distribution and fractionation of heavy metals in the sediment cores from five locations and their impacts on ecological health of Chilika lagoon were investigated. The heavy metals Cu, Zn, Pb, Cd, Co, Ni, Mn and Fe were determined in the cores. In general the average concentration of heavy metals in different cores are found in the following order Fe > Mn > Cu > Pb > Zn > Ni > Co > Cd. The cores (C1, C3 and C5) collected near the major fishing villages and jetties have higher metal concentration when compared with cores collected from relatively pristine regions. Correlations between the trace metals and Organic Carbon (OC), Total Nitrogen (TN), Total Phosphorus (TP) and silty clay fraction, suggests that these elements and grain size play a role in controlling the abundance of heavy metals in the sediments. Metals like Pb, Cu, Zn are positively correlated to OC, TN and TP and grain size. Significant enrichment for Pb (EF = 5–20) and moderately significant enrichments for Cu (EF = 2–5) is observed in almost all the cores. Co and Ni are moderately enriched in cores C1 and C2. Extremely severe enrichment for Cd (EF > 40) is observed in core C1. Runoff from the agricultural fields, untreated sewage discharge and boat traffic are the major heavy metal sources. Roadway runoff, fuel discharge and atmospheric deposition are the dominant source of elevated Pb levels. The fractionation profiles of metals in different cores found them to be associated mostly with residual phase followed by Fe-Mn oxides and organic bound metals. Risk Assessment Code (RAC) reveals significant pollution by Mn in almost all the cores, whereas Pb, Cu and Zn are also present in bioavailable form to some extent in the sediments. In general, Fe-Mn oxides and organic bound metal fraction phases would contribute metals accumulation into the food-chain (i.e plant and fishery resources) consumed by the population create human health hazards. [ABSTRACT FROM AUTHOR]

Abstract: The palynological studies of a sediment core collected from the northeastern region of the Chilka Lagoon, reveal the history of mangrove vegetation during the last 4165 yrs BP The Chilka Lagoon (a Ramsar Site) is one of the ecologically and socio-economically important wetlands situated in the humid tropical climatic zone along the east coast of India. The palynological results indicate that the mangrove vegetation was well developed between 4165 and 2549 yrs BP, indicating warm and humid climatic conditions; though, they show a degrading trend in the latter phase of this period. After 2549 yrs BP, mangroves again flourished in the area and persisted until 2246 yrs BP, as a result of relative stability of sea-level. The mangroves disappeared since 2246 yrs BP, as inferred from the marked increase of midland taxa, indicating drier conditions. Along with climatic factors, anthropogenic activities have also accelerated the degradation of mangroves in the study site. The present study provides an understanding of mangrove ecosystem in the past and such investigations could also be useful for the regeneration of the mangroves in the region. [Copyright &y& Elsevier]

Abstract: A 17-year-long δ13C and δ18O record from a scleractinian coral (Porites spp.) of Bangaram island (Lakshadweep Archipelago) is based on a nearly-monthly sample interval. This live coral head of Porites spp. was recovered from the lagoon of Bangaram (Lakshadweep) island at ∼20m water-depth. The skeletal δ13C and δ18O values varied approximately in phase and exhibit a positive relationship with each other. High-density (monsoon) bands are characterized by enriched δ18O values and low-density (non-monsoon) bands by depleted δ18O values. Coral δ13C and δ18O primarily reflects local oceanographic and climatic variability. The high-density bands were formed during the southwest monsoon (June–September) because of increased turbidity and cloud cover, whereas low-density bands were deposited during the non-monsoon months (October–May). Temporal changes in coral-derived sea surface temperature (SST) show a good agreement with instrumental SST record. The δ18O values in monsoon and non-monsoon bands are mainly due to the sea surface temperature (SST) changes, controlled by monsoon-induced upwelling and insolation changes. Coral-derived SST values clearly show warming events during summer 1993 and 1998. Spectral analysis of δ18O data reveals a teleconnection between the local SST and tropical Pacific climate variability. Enriched δ18O values for the monsoon months of 1984, 1985, 1993 and 1997 are probably indicative of cooler surface water due to the stronger upwelling at the studied location. Generally higher δ13C values correlate with enriched δ18O values of the monsoon bands. This increase in δ13C during the southwest monsoon months is attributed to a decrease in endosymbiotic photosynthesis. Alternatively, an increase in biological production, due to monsoon-induced upwelling, may have resulted in the δ13C enrichment of dissolved inorganic carbon (DIC) in surface waters. However, other possibilities, such as higher δ13C values due to coral mass-spawning events during monsoon times cannot be ruled out. A progressive decrease of ∼0.5‰ in δ13C from 1985 to 2001 may be due to the changes in photosynthesis and/or changing food habits from autotrophy to heterotrophy as the coral grew in size. [Copyright &y& Elsevier]