Detailed reconstruction of Indian summer monsoons is necessary to better understand the late Quaternary climate history of the Bay of Bengal and Indian peninsula. We established a chronostratigraphy for a sediment core from Hole 19B in the western Bay of Bengal, extending to approximately 80 kyr BP and examined major and trace element compositions and clay mineral components of the sediments. Higher δ¹⁸O values, lower TiO₂ contents, and weaker weathering in the sediment source area during marine isotope stages (MIS) 2 and 4 compared to MIS 1, 3, and 5 are explained by increased Indian summer monsoonal precipitation and river discharge around the western Bay of Bengal. Clay mineral and chemical components indicate a felsic sediment source, suggesting the Precambrian gneissic complex of the eastern Indian peninsula as the dominant sediment source at this site since 80 kyr. Trace element ratios (Cr/Th, Th/Sc, Th/Co, La/Cr, and Eu/Eu*) indicate increased sediment contributions from mafic rocks during MIS 2 and 4. We interpret these results as reflecting the changing influences of the eastern and western branches of the Indian summer monsoon and a greater decrease in rainfall in the eastern and northeastern parts of the Indian peninsula than in the western part during MIS 2 and 4.

Matsushima Bay was less affected by the 2011 Tohoku Earthquake Tsunami than other Pacific coastal areas of northeast Japan because of the sheltering effects of islands in the bay mouth. To understand the recovery from the 2011 tsunami of benthic environments in Matsushima Bay, we conducted surveys of the geochemical properties of surface sediments over 5 years following the earthquake and compared them to sedimentary data before the earthquake. Before the tsunami, the mud fraction (<63‐μm size) proportion of the surface sediments varied over a wide range, whereas after the tsunami, the mud content range was relatively narrow. During 2012–2015, the mud content was linearly correlated with the total organic carbon (TOC) content, but the slope of the relationship differed from that before the tsunami. The tightly coupled mud‐TOC relationship and the almost constant C/N ratios in the surface sediments suggest that the bay sediments were resuspended and transported by the tsunami. In addition, loss of some organic matter sources in the bay may partly account for the uniform C/N ratios. By 2016, the slope of the mud‐TOC relationship was almost the same as the pretsunami value, but the C/N ratios remained constant. These results suggest that ecosystems and biogeochemical cycles in the bay had not yet fully recovered their pretsunami state. Trace element compositions of core samples indicated that sediment sources were little changed by the tsunami, probably because islands in the mouth of the bay reduced sediment transport into the bay from distant sources.