The microbial community in eutrophic freshwater sediment was investigated from a 67-cm-deep sediment core collected from the Daechung Reservoir in South Korea, where cyanobacterial blooms have occurred annually for the past 30 years. The majority of core sediments were characterized by dark-grayish, fine-grained mud with abundant gas-escaped and thinly laminated layers. Intervals of summer and winter seasons were represented by periodic peaks of geochemical profiles of parameters such as grain size and relative carbon mass ratios to various nutrients such as nitrogen, sulfur, and phosphorus. In bacteria, Proteobacteria (66.6%) was the most prevalent phylum, followed by Chloroflexi (8.9%), Bacteroidetes (5.1%), and Spirochaetes (2.6%). Archaea were also abundant, representing approximately half of the total prokaryotes in the sediments. Notably, three Bacteria (Sulfuricurvum, Sideroxydans, and Gallionella) and one Archaea (Thermoplasmata) accounted for 43.4% and 38.4% of the total bacteria and archaea, respectively, implying that iron and sulfur oxidizing microorganisms dominate in this eutrophic freshwater sediment. These results indicate that 1) eutrophic freshwater lakes in monsoon climates undergo a stratified sedimentary process with seasonal and annual variations in geochemical and microbial profiles, and 2) the microbial oxidative metabolism of iron and sulfur is notably active in sediments from a eutrophic lake.

We present a multiproxy record of Sr‐Nd isotopes and major and trace elements for clay‐sized (<2 μm) siliciclastic sediment fractions from the International Ocean Discovery Program Site U1456 in the eastern Arabian Sea to extract reliable chemical indicators not influenced by the grain‐size effect, quantitatively estimate detrital provenance, and constrain silicate weathering/erosion in response to the Indian summer monsoon over orbital timescales. A provenance analysis of fine‐grained siliciclastic sediments indicates a two end‐member mixture from the Indus River (20–90%) and rivers draining the Deccan Traps (10–80%). A prominent increase in terrigenous input from the Indus River occurred at ~0.5 Ma, probably resulting from an intensive erosional event in the Himalayan region. Moreover, α^Al_K at Site U1456, which is calculated as Al/K ratio of the study sample versus Al/K ratio of the upper continental crust, can be generally used to reflect the chemical weathering intensity in the source regions. During most interglacial and even certain glacial periods, the Indian summer monsoon reinforcement is closely coupled with enhanced continental chemical weathering and physical erosion. Wavelet and spectral analyses of the α^Al_K record display strong 125‐, 35‐, 29‐, and 23‐kyr periodicities since 1.2 Ma with significant ~100‐kyr cycles established at the end of the Mid‐Pleistocene Transition (~0.7 Ma), suggesting forcing mechanisms linked with both Northern and Southern Hemispheric processes. Significant fluctuations observed in silicate weathering/erosion during ~1.2–0.7 Ma indicate an enhancement of the Indian summer monsoon with increased variability in association with the Mid‐Pleistocene Transition.