Maritime controls on coastal East Asian climate during the Holocene: evidence from the sediments of Lake Motosu, Japan.

Abstract

The East Asian Summer Monsoon controls the timing and amount of rainfall for around a third of the world’s population. An understanding of past changes in monsoon strength is crucial for placing current events in context and characterising future climate risk. Despite numerous studies focusing on the East Asian Summer Monsoon, debates remain surrounding the timing, spatial patterns, and drivers of Holocene monsoon variability. This thesis presents a well-dated, 8000-year lacustrine sedimentary sequence recovered from Lake Motosu, central Japan. Variations in the amount and isotopic composition of carbon and nitrogen in bulk organic matter suggest strong monsoon conditions between 8-6 ka, with sedimentation after 3 ka influenced by local volcanic activity. This record is then used to increase the spatial coverage of a multi-proxy synthesis of 18 hydroclimate records from East Asia. Two peaks in monsoon strength are identified centred on ~6.5 ka and ~4.5 ka. Spatial heterogeneity in this analysis suggests that sites in coastal East Asia are more sensitive to changes in Pacific Ocean conditions than sites in continental Asia. This record has the potential to improve understanding of the drivers of monsoon variability through the Holocene in this socially and economically important region.