Characteristics and driving mechanisms of early Holocene weakened monsoon events: Evidence from northern Bohai Bay, China

Abstract

The characteristics and driving mechanisms of early Holocene extreme climatic events can provide a basis for the prediction and assessment of such events under ongoing global warming. Coastal areas, with their unique geographical location and fragile ecological environment, are highly sensitive to climate change, making the study of extreme climatic events in these regions potentially providing a different understanding of the processes and mechanisms involved. We studied the Holocene sediments of core BXZK04 from northern Bohai Bay, China, combining 9 AMS ¹⁴C dates with high-resolution analyses of pollen, algal remains, and grain size, together with modern pollen databases, to quantitatively reconstruct mean annual precipitation. Our principal findings are: (1) The climate in northern Bohai Bay during 10,900–8600 cal yr BP showed a gradual trend towards increased humidity, with fluctuations. We propose that long-term climate change in the study area was dominated by Northern Hemisphere insolation and regional sea-level changes. (2) Two significant weak monsoon events occurred in the study area, during 9600–9300 cal yr BP and 9060–8950 cal yr BP, corresponding to the 9.4 ka and 8.9 ka climatic events, respectively. During these events, forest vegetation decreased, herbaceous vegetation expanded, and there was a significant reduction in monsoon precipitation (a decrease of ∼200 mm). These events may have been controlled by the weakening of solar activity and reduced Atlantic Meridional Overturning Circulation (AMOC) caused by freshwater influx to the North Atlantic, leading to the southward shift of the Intertropical Convergence Zone (ITCZ) and more frequent El Niño events.