Global Cooling Events of the Late Holocene Preserved in the Coastal Sediments in the Southern Far East of Russia

Abstract

Comprehensive study of the lagoon terrace section at the apex of Amur Bay has made it possible to identify sharp short-term cooling events at 4450, 2870–2510, 1740–1200, and 680–150 cal BP that are compared to cold events in many regions around the world. The reconstructions are based on the results of diatom, botanical, and palynological analyses. The age–depth model is generated by the Bacon program using radiocarbon dating and tephrostratigraphy. Tephra B-Tm from the caldera-forming eruption of Baitoushan volcano was found in the section. The section selected as a natural archive has its own specifics. In contrast to the mountainous areas and river basins, where the climate became dry 3320–3050 years ago due to a sharp decrease in the intensity of the summer monsoon, coastal lacustrine–boggy sequences developed in constantly waterlogged conditions. This made it possible to identify short-term dry events that correlate well with the global climatic rhythm caused by the decrease in solar radiation. The decrease in moisture was closely related to the influence of the ocean: the intensity of tropical cyclogenesis. The shallowing of the lagoon during the decline of the low-amplitude transgression, intensified by the weakening of the summer monsoon, led to a change from terrigenous to organogenic sedimentation at about 3460 years ago. The cooling event 2870–2510 years ago had the most complex structure with sharp changes in moisture. Change in the course of bog-forming processes around 1740 years ago associated with the activation of floods, which caused periodic flooding of the peat deposits in the vast estuary zone of the Razdolnaya River, led to the disappearance of the tree layer and the development of a grass bog. In general, the regional conditions were dry until the Medieval Warm Period. The response of the landscapes to cooling is identified: the role of broadleaved species in the forest vegetation of the low mountains decreased, and the participation of plants preferring less inundated habitats in the development of local landscapes increased. The Little Ice Age is the exception of the cold events, which was wet and characterized by frequent floods. The meridional transport of moist air masses from the ocean to the continent became more active during that time.