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International Ocean Discovery Program (IODP) Expedition 363 recovered extended Neogene to Quaternary carbonate- and clay-rich sedimentary successions at Site U1482 (15°3.32ʹS, 120°26.10ʹE; 1466 m water depth), drilled at the southwestern edge of the Indo-Pacific Warm Pool off northwest Australia (Rosenthal et al., 2018b). Four holes were drilled with the advanced piston corer (APC) system at this site and deepened with the half-length APC (HLAPC) and extended core barrel (XCB) systems. A shipboard splice, from 0 to 451.26 m core composite depth below seafloor (CCSF), was established. After the expedition, the cores were scanned at high-resolution (1–2 cm) using an Avaatech X-ray fluorescence (XRF) core scanner. Scanning was performed along the shipboard splice with approximately 1 m overlap at the splice tie points for verification. Based on this new data set, we revised nine of the original splice tie points. The revised splice for Site U1482 now extends to 445.11 m revised CCSF and is available from the IODP Laboratory Information Management System (LIMS) database. 

We modified the original sediment splice of International Ocean Discovery Program (IODP) Expedition 353 Site U1448 over the interval 353-U1448B-48F-1, 1 cm, to 353-U1448A-56X-5, 60 cm, using new high-resolution X-ray fluorescence scanning data and linescan images. The revised splice now extends from 351.65 to 401.69 revised meters composite depth (r-mcd). We further appended the interval between 353-U1448A-53X-1, 0 cm, and 56X-5, 60 cm, thus extending the composite record down to 439.45 r-mcd. 

International Ocean Discovery Program (IODP) Expedition 353 drilled six sites in the Bay of Bengal, recovering 4280 m of sediments during 32.9 days of on-site drilling. The primary objective of Expedition 353 is to reconstruct changes in Indian monsoon circulation since the Miocene at tectonic to centennial timescales. Analysis of the sediment sections recovered will improve our understanding of how monsoonal climates respond to changes in forcing external to the Earth’s climate system (i.e., insolation) and changes in forcing internal to the Earth’s climate system, including changes in continental ice volume, greenhouse gas concentrations, sea level, and the ocean-atmosphere exchange of energy and moisture. All of these mechanisms play critical roles in current and future climate change in monsoonal regions. The primary signal targeted is the exceptionally low salinity surface waters that result, in roughly equal measure, from both direct summer monsoon precipitation above the Bay of Bengal and runoff from the numerous large river basins that drain into the Bay of Bengal. Changes in rainfall and surface ocean salinity are captured and preserved in a number of chemical, physical, isotopic, and biological components of sediments deposited in the Bay of Bengal. Expedition 353 sites are strategically located in key regions where these signals are the strongest and best preserved. 

International Ocean Discovery Program (IODP) Expedition 353 (29 November 2014–29 January 2015) drilled six sites in the Bay of Bengal, recovering 4280 m of sediments during 32.9 days of on-site drilling. Recovery averaged 97%, including coring with the advanced piston corer, half-length advanced piston corer, and extended core barrel systems. The primary objective of Expedition 353 is to reconstruct changes in Indian monsoon circulation since the Miocene at tectonic to centennial timescales. Analysis of the sediment sections recovered will improve our understanding of how monsoonal climates respond to changes in forcing external to the Earth’s climate system (i.e., insolation) and changes in forcing internal to the Earth’s climate system, including changes in continental ice volume, greenhouse gases, sea level, and the ocean-atmosphere exchange of energy and moisture. All of these mechanisms play critical roles in current and future climate change in monsoonal regions. The primary signal targeted is the exceptionally low salinity surface waters that result, in roughly equal measure, from both direct summer monsoon precipitation to the Bay of Bengal and runoff from the numerous large river basins that drain into the Bay of Bengal. Changes in rainfall and surface ocean salinity are captured and preserved in a number of chemical, physical, isotopic, and biological components of sediments deposited in the Bay of Bengal. Expedition 353 sites are strategically located in key regions where these signals are the strongest and best preserved. Salinity changes at IODP Sites U1445 and U1446 (northeast Indian margin) result from direct precipitation as well as runoff from the Ganges-Brahmaputra river complex and the many river basins of peninsular India. Salinity changes at IODP Sites U1447 and U1448 (Andaman Sea) result from direct precipitation and runoff from the Irrawaddy and Salween river basins. IODP Site U1443 (Ninetyeast Ridge) is an open-ocean site with a modern surface water salinity very near the global mean but is documented to have recorded changes in monsoonal circulation over orbital to tectonic timescales. This site serves as an anchor for establishing the extent to which the north to south (19°N to 5°N) salinity gradient changes over time. 

Scientific ocean drilling (Deep Sea Drilling Project [DSDP], Ocean Drilling Program [ODP], and Integrated Ocean Drilling Program) has never taken place in the Bay of Bengal north of 9°N. Thus, the core region of summer monsoon precipitation has never been investigated. DSDP Leg 22 (1974) and ODP Leg 121 (1989) drilled the southernmost region (5°–9°N), capturing the distal end of the summer monsoon influence. India’s partnership in the International Ocean Discovery Program (IODP) provides an opportunity to investigate this key northern region. IODP Expedition 353 seeks to recover Upper Cretaceous–Holocene sediment sections that record erosion and runoff signals from river input to the Bay of Bengal as well as the resulting north–south surface water salinity gradient. Analysis of sediment sections from the Mahanadi Basin (northeast Indian margin), the Nicobar-Andaman Basin (Andaman Sea), and the northern Ninetyeast Ridge (southern Bay of Bengal) will be used to understand the physical mechanisms underlying changes in monsoonal precipitation, erosion, and run-off across timescales from millennial through tectonic. These sites will provide crucial new information within which to interpret differences among existing results from previous monsoon-themed drilling expeditions in the Arabian Sea (ODP Leg 117), the South China Sea (ODP Leg 184), and the Sea of Japan (Integrated Ocean Drilling Program Expedition 346). These goals directly address challenges in the “Climate and Ocean Change” theme of the IODP Science Plan. 

Structure and paleogeographic history of the northern Ninetyeast Ridge International Ocean Discovery Program (IODP) Site U1443 is located ~100 m southeast of Ocean Drilling Program (ODP) Leg 121 Site 758 on the crest of the Ninetyeast Ridge and is a redrill of Site 758 (Figure F1). The Ninetyeast Ridge represents the trace of the Kerguelen/Ninetyeast hotspot prior to middle Eocene rifting (Shipboard Scientific Party, 1989a). As a result of northward movement, Site U1443 moved from temperate southern latitudes during the Campanian, to ~5°S near the Oligocene/Miocene boundary, and to its present location of 5°N in the southernmost Bay of Bengal. The site has been within 10° of the Equator for the past 35 My (Shipboard Scientific Party, 1989a). The ridge-top location has prevented the deposition of sedimentary sequences typically associated with fan transport processes. 

International Ocean Discovery Program (IODP) Site U1446 is located in the Mahanadi offshore basin on the eastern margin of India (Figure F1). This sedimentary basin extends both onshore and offshore and was formed during the Late Jurassic rifting of Gondwana (Sastri et al., 1981; Subrahmanyam et al., 2008). Today, the Mahanadi River basin (19°21′ to 23°35′N, 80°30′ to 86°50′E; ~1.42 × 105 km2) drains a catchment composed of late Archaean and early Proterozoic granite batholiths and gneisses from the Eastern Ghats (~56%); Gondwana-age limestones, shales, and sandstones (~39%); and recent alluvium (~5%) (Mazumdar et al., 2015; Rickers et al., 2001), including one of the richest mineral belts on the Indian subcontinent. This mineralization results in higher concentrations of trace metals such as Fe, Cu, Zn, and Pb in suspended river sediments compared to other rivers in peninsular India (Chakrapani and Subramanian, 1990b). Kaolinite, chlorite, quartz, dolomite, and minor montmorillonite and illite are characteristic components of suspended sediments discharged by the Mahanadi River into the Bay of Bengal (Subramanian, 1980; Chakrapani and Subramanian, 1990b). 

The main scientific objective of International Ocean Discovery Program (IODP) Expedition 353 was to analyze the variability of precipitation and runoff in the Bay of Bengal on suborbital to orbital timescales. To achieve this objective, site locations were selected according to their proximity to the main sources of freshwater feeding the northern Bay of Bengal, including the Mahanadi River and the Ganges-Brahmaputra river complex, and the Andaman Sea, including the Irrawaddy and Salween river systems. 

International Ocean Discovery Program (IODP) Expedition 353 (29 November 2014–29 January 2015) drilled six sites in the Bay of Bengal, recovering 4280 m of sediments during 32.9 days of on-site drilling. Recovery averaged 97%, including coring with the advanced piston corer, half-length advanced piston corer, and extended core barrel systems. The primary objective of Expedition 353 is to reconstruct changes in Indian monsoon circulation since the Miocene at tectonic to centennial timescales. Analysis of the sediment sections recovered will improve our understanding of how monsoonal climates respond to changes in forcing external to the Earth’s climate system (i.e., insolation) and changes in forcing internal to the Earth’s climate system, including changes in continental ice volume, greenhouse gas concentrations, sea level, and the ocean-atmosphere exchange of energy and moisture. All of these mechanisms play critical roles in current and future climate change in monsoonal regions. The primary signal targeted is the exceptionally low salinity surface waters that result, in roughly equal measure, from both direct summer monsoon precipitation above the Bay of Bengal and runoff from the numerous large river basins that drain into the Bay of Bengal. Changes in rainfall and surface ocean salinity are captured and preserved in a number of chemical, physical, isotopic, and biological components of sediments deposited in the Bay of Bengal. Expedition 353 sites are strategically located in key regions where these signals are the strongest and best preserved. Salinity changes at IODP Sites U1445 and U1446 (northeast Indian margin) result from direct precipitation as well as runoff from the Ganges-Brahmaputra river complex and the many river basins of peninsular India. Salinity changes at IODP Sites U1447 and U1448 (Andaman Sea) result from direct precipitation and runoff from the Irrawaddy and Salween river basins. IODP Site U1443 (Ninetyeast Ridge) is an open-ocean site with modern surface water salinity very near to the global mean but is documented to have recorded changes in monsoonal circulation over orbital to tectonic timescales. This site serves as an anchor for establishing the extent to which the north to south (19°N to 5°N) salinity gradient changes over time. 

International Ocean Discovery Program (IODP) Site U1445 is located near the southern end of the Mahanadi basin, on the eastern margin of India (Figure F1). This sedimentary basin extends both onshore and offshore and was formed during the late Jurassic rifting of Gondwana (Sastri et al., 1981; Subrahmanyam et al., 2008). Today, the Mahanadi River basin (19°21′ to 23°35′N, 80°30′ to 86°50′E; ~1.42 × 105 km2) drains a catchment composed of late Archaean and early Proterozoic granite batholiths and gneisses from the Eastern Ghats (~56%); Gondwana-age limestones, shales, and sandstones (~39%); and recent alluvium (~5%) (Mazumdar et al., 2015; Rickers et al., 2001), including one of the richest mineral belts on the Indian subcontinent. This mineralization results in higher concentrations of trace metals such as Fe, Cu, Zn, and Pb in suspended river sediments compared to other rivers in peninsular India (Chakrapani and Subramanian, 1990b). Kaolinite, chlorite, quartz, dolomite, and minor montmorillonite and illite are characteristic components of suspended sediments discharged by the Mahanadi River into the Bay of Bengal (Subramanian, 1980; Chakrapani and Subramanian, 1990b).