No abstract

More than 10% of the world’s population lives in the East Asian monsoon (EAM) region, where precipitation patterns are critical to agricultural and industrial activities. However, the dominant forcing mechanisms driving spatiotemporal changes in the EAM remain unclear. We selected Holocene records tracking monsoon precipitation in the EAM region reconstructed from pollen data to explore the spatiotemporal patterns of monsoon precipitation changes. Our analysis shows a time-transgressive pattern of maximum precipitation, with earlier occurrence in the southern area and later occurrence in the northern area. The monthly insolation changes force monsoon precipitation in different parts of the EAM region through a shift in the Western Pacific Subtropical High. We conclude that low-latitude monthly insolation changes (rather than average summer insolation changes) were the main forcing mechanisms of the spatiotemporal patterns of the monsoon precipitation maximum during the Holocene.

Abstract. Global spread of hypoxia and altered mixing regimes in freshwater systems is a growing major environmental concern. Climate change and human impact are expected to increasingly deteriorate aquatic ecosystems. The study of processes and drivers of such changes in the past provides a great asset for prevention and remediation in the future. We used a multi-proxy approach combining high-resolution Hyperspectral Imaging (HSI) pigment data, with specific HPLC chlorophylls and carotenoids to examine Holocene trophic state changes and anoxia evolution in meromictic Lake Jaczno, NE Poland. A redundancy analysis RDA including pollen-inferred vegetation cover, temperature and human impacts provides insight into specific conditions and drivers of changing trophic and redox states in the lake. Anoxic and sulfidic conditions established in Lake Jaczno after initial basin infilling 9500 years ago. Until 6700 cal BP, lake trophy was relatively low, water turbidity was high, and green sulfur bacteria (GSB) were abundant within the phototrophic community, suggesting a deep oxic–anoxic boundary and weak stratification. The period between 6700–500 cal BP is characterized by constantly increasing lake production and a gradual shift from GSB to purple sulfur bacteria (PSB), suggesting a shallower oxic–anoxic boundary and pronounced stratification. Yet, the presence of spheroidene and speroidenone in the sediments indicates intermittent anoxia. After 500 cal BP, increasing human impact, deforestation and intensive agriculture promoted lake eutrophication, with a shift to PSB dominance and establishment of permanent anoxia and meromixis. Our study unambiguously documents the legacy of human impact on processes determining eutrophication and anoxia.

No abstract

No abstract

Variations in East Asian summer monsoon (EASM) precipitation impact agriculture, water resources, electricity generation, and economic development in the densely populated region of central eastern China. However, uncertainties remain in the history and driving mechanisms of precipitation changes in this region over the past two millennia. We present an 1800 yr multiproxy reconstruction of monsoon precipitation based on hydroclimate variations inferred from Lake Nvshan sediments in the Jiang-Huai region of central eastern China. We find that rainfall in the Jiang-Huai region was higher during the Little Ice Age (LIA) than during the Medieval Warm Period (MWP), and that these changes were modulated by the mean state of the tropical Pacific Ocean on centennial time scales. We infer that an El Niño–like (La Niña–like) mean state caused a strengthening and westward displacement (weakening and eastward displacement) of the Western Pacific Subtropical High (WPSH) and a weakening (strengthening) of the EASM, causing more (less) rainfall in the Jiang-Huai region during the LIA (MWP). These hydroclimate changes are likely to have been a response to changes in effective radiative forcing.

No abstract

Northern China, particularly the Yellow River Basin, which is the birth place of Chinese civilization and has been the political center throughout most of China's history, is an ideal region for studying the response of human activities to climate change. However, studies on links between climate change and variations in earlier civilization are limited due to the scarcity of macroscale monsoon precipitation records. In the present study, a ∼4,000-year record of monsoon precipitation, which represents average rainfall in large areas in northern China, was reconstructed from sediments in Northern Yellow Sea Mud (NYSM). The record shows high monsoon precipitation during ∼4,000-2,500 BP, ∼1,350-750 BP and the past ∼250 years. In general, our record of monsoon precipitation exhibits trends similar to the percentages of planted Poaceae pollen in lake sediments and the Chinese economic index, contrasting with the frequency of wars over the past 2,000 years. We postulated that, in the agricultural society of ancient China, low monsoon precipitation in northern China may be an important factor that cause reduced agricultural production, declined economy and even the occurrence of wars.