Charlie Rex , Richard Staff, Jaime Toney, Emma J Pearson, Alexander Francke, Megumi Saito-Kato, Takeshi Nakagawa

Glacial terminations offer a unique opportunity to examine how the East Asian Summer Monsoon (EASM) responds to rapid increases in global temperature and accompanying abrupt climatic reorganisation. Reconstructions from contrasting glacial terminations with differently evolving boundary conditions are of particular value to our understanding of deglacial EASM behaviours, e.g., Termination I (from MIS 2 to MIS 1) and Termination II (from MIS 6 to MIS 5e). However, records of EASM evolution across Termination II are substantially fewer in number than Termination I, as well as exhibiting a significant bias towards continental speleothem archives. Japan is a critically understudied, but demonstrably sensitive area of the EASM region and, during other periods, records from Japan often display unique trends not captured by continental records. Here we present a new EASM record derived from the Lake Suigetsu sediment cores, central Japan, based on compound-specific hydrogen isotope analysis of C30 n-alkanoic acids (δ2HC30acid), which constitutes the first stable isotope-based EASM record from the Japanese archipelago across Termination II. We also present lipid biomarker (n-alkane and n-alkanoic acid) concentrations and indices, which we use to reconstruct early lake formation. The catchment transitioned from a dynamic fluvial environment to a lacustrine one between 131.0 and 129.8 ka BP. The EASM strengthened from 132.5 to 130.0 ka BP (earlier than in continental China), before weakening toward 125.2 ka BP, with some evidence for submillennial-scale variability during this weakening phase; a pattern common to sites across the EASM region which are closer to the northernmost position of the monsoon front. Whilst our record displays some similar characteristics to EASM reconstructions from mainland China, our observations support the assertion that EASM behaviours during Termination II were spatially heterogeneous. Additionally, comparison of our Termination II δ2H¬C30acid record to a record of δ2H¬C30acid from Lake Suigetsu during Termination I suggests that EASM evolution during the last and penultimate deglaciations were distinct due to differently evolving climatic conditions (including the extreme decoupling of polar temperatures during Termination II). We propose that the spatial heterogeneities in EASM strength during Termination II were a result of competing influences from the Northern and Southern Hemispheres, with Japan more closely linked to the latter compared to mainland China due to its maritime location.