Northeastern Indian Ocean paleoceanography and Indian monsoon variability reconstructed from Miocene sediment archives (IODP Expedition 353) | Late Neogene sediment archives at the margins of the Bay of Bengal and Andaman Sea (IODP Expedition 353, iMonsoon) record Indian Ocean intermediate- and deep-water circulation and Indian Monsoon variability in unprecedented resolution. Site U1443 (2925 m water depth), drilled on the crest of the Ninetyeast Ridge at the southern end of the Bay of Bengal, provided the first high-resolution deep-water record extending back to 17 Ma. Benthic foraminiferal isotope records in combination with micropaleontological and geochemical dissolution indices based on X-ray fluorescence (XRF) scanner derived elemental data track the abrupt onset and development of the Miocene Climatic Optimum with eccentricity-paced transient carbonate dissolution events coinciding with warmer phases, followed by major expansion of the East Antarctic ice sheet. We relate intense carbonate dissolution episodes between ~13.2 and ~8.5 Ma to changes in the intensity of chemical weathering and riverine input of calcium and carbonate ions into the ocean reservoir linked to latitudinal shifts of the monsoonal rainbelt. Recovery from the “Carbonate Crash” in the tropical eastern Indian Ocean was coupled to a marked increase in biological productivity, associated with strengthening of monsoonal winds and upper ocean mixing. At Sites U1447 (1392 m water depth) and U1448 (1098 m water depth) in the Andaman Sea, orbitally tuned, high-resolution benthic isotope records and XRF scanner derived elemental data, combined with mixed layer temperature/salinity reconstructions from paired stable isotope and Mg/Ca records closely track changes in the intensity of the Indian summer monsoon rainfall after ~10 Ma. Major changes in the response of the Indian Monsoon to orbital forcing towards an obliquity driven glacial-interglacial mode between ~7 and ~5.5 Ma were associated with intense, pulsed cooling of surface and intermediate waters and changes in the amount and composition of the monsoonal discharge from the Asian continent into the Andaman Sea.
Kuhnt, Wolfgang | Holbourn, Ann, | Janika, Jöhnck, | Lübbers, Julia | Kochhann, Karlos | Andersen, Nils | Bolton, C. T.
[sde] environmental sciences
AGU Chapman Conference 2020
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