Description: Highlights • Ba/Ca and δ18OSW records of Core SK 168 reveal distinct changes in SAM intensity. • SAM over the Irrawaddy strengthened beginning at ∼18 ka leading observed changes in the Arabian sea by ∼2–3 kyrs. • Peak monsoon strength during the mid-Holocene in the Andaman Sea consistent with model simulations. • Changes in upper ocean stratification indicate limited influence of NH insolation. Abstract The past variability of the South Asian Monsoon is mostly known from records of wind strength over the Arabian Sea while high-resolution paleorecords from regions of strong monsoon precipitation are still lacking. Here, we present records of past monsoon variability obtained from sediment core SK 168/GC-1, which was collected at the Alcock Seamount complex in the Andaman Sea. We utilize the ecological habitats of different planktic foraminiferal species to reconstruct freshwater-induced stratification based on paired Mg/Ca and δ18O analyses and to estimate seawater δ18O (δ18Osw). The difference between surface and thermocline temperatures (ΔT) and δ18Osw (Δδ18Osw) is used to investigate changes in upper ocean stratification. Additionally, Ba/Ca in G. sacculifer tests is used as a direct proxy for riverine runoff and sea surface salinity (SSS) changes related to monsoon precipitation on land. Our Δδ18Osw time series reveals that upper ocean salinity stratification did not change significantly throughout the last glacial suggesting little influence of NH insolation changes. The strongest increase in temperature gradients between the mixed layer and the thermocline is recorded for the mid-Holocene and indicate the presence of a significantly shallower thermocline. In line with previous work, the δ18Osw and Ba/Ca records demonstrate that monsoon climate during the LGM was characterized by a significantly weaker southwest monsoon circulation and strongly reduced runoff. Based on our data the South Asian Summer Monsoon (SAM) over the Irrawaddyy strengthened gradually after the LGM beginning at ∼18 ka. This is some 3 kyrs before an increase of the Ba/Ca record from the Arabian Sea and indicates that South Asian Monsoon climate dynamics are more complex than the simple N-S displacement of the ITCZ as generally described for other regions. Minimum δ18Osw values recorded during the mid-Holocene are in phase with Ba/Ca marking a stronger monsoon precipitation, which is consistent with model simulations.

Description: Environmental impact assessment studies for deep sea manganese nodule mining have been initiated in the Central Indian Ocean Basin since 1995. As a part of the first phase for collecting the benthic baseline data, echo sounding, sub-bottom profiling, seabed photography, coring and sampling have been carried out at close intervals in 5 selected areas (of 10x10 miles each). Detailed studies on topographic undulations, nodule distributions and sediment characteristics have resulted in the selection of Test and Reference Areas. A strip of 3000 200 m was disturbed with a hydraulic device, so as to cause suspension and redistribution of sediment in the near bottom waters and the impact on the seabed as well as dose to the bottom was observed. Results show that most of the disturbance is restricted to the disturbed area with some resedimentation in adjacent areas, whereas no significant mention of sediment in the bottom waters is observed. A longterm monitoring of the environmental Impact of the Benthic Disturbance has been planned in the study areas.

Description: Highlights • India is industrializing rapidly with significant releases of Pb. • Increase in anthropogenic Pb input to Indian shelf occurred over last 40 years. • Sediment leachate Pb isotopes used to assess anthropogenic Pb inputs • Sources of Pb in eastern and western shelves of India were different. • Inland coal combustion and heavy industries are major sources of Pb. India is industrializing rapidly and with this there comes higher releases of contaminants into the environment. Change in Pb deposition over the last century on the eastern (off Andhra Pradesh) and western (off Karnataka) shelves of India was investigated based on the data extracted from two sediment cores covering the past ~114 and ~145 yrs. The variations of the total Pb content, its enrichment factor, and concentrations of non-residual Pb in both the sediment cores document that there was a gradual increase in anthropogenic Pb input into the coastal sediments of India over the last century. Sediment leachates were used to monitor the increase in anthropogenic Pb input and its Pb isotope composition. The anthropogenic end member composition of the western shelf sediment location (206Pb/207Pb: 1.105; 206Pb/208Pb: 2.149) was significantly less radiogenic than the eastern shelf isotopic composition (206Pb/207Pb: 1.145; 206Pb/208Pb:2.120). A binary mixing model suggests that Pb emitted from the heavy industries (e.g., ore mining, Pb processing and smelting plants) of India has been the major source of anthropogenic Pb to the sediments of western continental shelf. In contrast, the isotopic signatures suggest that coal combustion is responsible for elevated anthropogenic Pb levels in the sediments from the eastern shelf of India.