Holocene Precipitation Changes Research Articles

Magnetic Fingerprints for the Paleoenvironmental Evolutions Since the Last Deglaciation: Evidence From the Northwestern South China Sea Sediments

AbstractRapid global changes since the last deglaciation can be well documented in marginal sea sediments, while isolating individual paleoenvironmental signals is still challenging. Here, we identified magnetic minerals and unmixed their variations in sediments from the northwestern South China Sea to decipher environmental variations since the last deglaciation. The variation in the hematite to goethite ratio indicates a relatively drier mid‐Holocene and a wetter early and late Holocene in the Red River catchment. The position shift and intensity variation of Western Pacific Subtropical High may account for the Holocene precipitation changes. A higher chemical weathering intensity accompanied by a relatively more fine‐grained magnetite input during the last deglaciation suggests decoupling of the Asian Summer Monsoon and chemical weathering in the catchment, which might have been caused by the shelf exposure during the deglaciation. In addition, the relative abundance of biogenic magnetite increased with the sea level and possible deep‐water temperature rise. Therefore, magnetic minerals such as hematite, goethite, detrital and biogenic magnetite are markedly potential fingerprints for continent‐ocean environmental changes.

Reconstruction of Holocene precipitation patterns and vegetation evolution in the North China Plain: Deciphering the relative influence of climate and anthropogenic forcing

In this paper, we investigate Holocene precipitation changes in northern China to improve the understanding of the East Asian summer monsoon (EASM) and provide an environmental context for the development of Chinese civilisation. Our study is based on an analysis of 260 pollen samples from Holocene lacustrine sediments at Ningjinpo in northern China, and employs the biomisation method to reconstruct regional vegetation types and vegetation changes, and to decipher their driving factors, by incorporating regional climatic data and information on human activities. Results indicate that, in the early Holocene (10,000–8100 cal yr B.P.), regional climate was dry, with annual precipitation of 470 mm. In the middle Holocene (8100–3000 cal yr B.P.), a rapid increase was observed in precipitation, reaching 580 mm. During the late Holocene (2600–600 cal yr B.P.), climate became drier again, with annual precipitation decreasing to 480 mm. Between 10,000–600 cal yr B.P., vegetation exhibited distinct successional patterns dominantly influenced by climate, transitioning from meadow-steppe to forest, and then back to meadow-steppe. After 600 cal yr B.P., vegetation succession decoupled from climate change, with human activities emerging as the primary driving force, as indicated by the substantial increase in anthropogenic pollen and charcoal concentrations. In the future, under the combined influence of global warming and intensified human activity, the implementation of scientific environmental planning measures will become increasingly important for the restoration and sustainable development of regional vegetation ecosystems.

Holocene precipitation changes in the Balikun basin based on high-resolution sporopollen quantitative reconstruction

To better understand long-term precipitation changes in arid Central Asia, reconstruction of past precipitation is critical. This paper analyzed the core sediments of Balikun lake in eastern Xinjiang. We analyzed 200 pollen samples, combined with 441 surface pollen samples and a radiocarbon chronology, using the Weighted Averaging Partial Least Sequence (WA-PLS) method, to characterize the Holocene high-resolution precipitation change process in Balikun basin. And, Combined with the vegetation types reconstructed by biome method, we discussed the landscape evolution of Balikun basin. Results show that the mean annual precipitation during the Holocene can be broken into three phases: Early Holocene (11,750–8030 cal yr B.P.), which averaged about 130 mm; Middle Holocene (8030–4420 cal yr B.P.), which averaged about 250 mm; and Late Holocene (4420–0 cal yr B.P.), which averaged about 210 mm. The vegetation changed from desert to steppe during the Holocene, and the wetlands gradually expanded, which was mainly informed by precipitation and glacial melt water.

Holocene precipitation changes in northeastern China from CCSM3 transient climate simulations

To date, climate records have mainly shown three different trends of Holocene precipitation evolution in northeastern (NE) China, and the underlying mechanisms remain unclear. Here, we use model results from Holocene transient climate simulations conducted by the Community Climate System Model version 3 to investigate the evolution of precipitation in NE China and the associated mechanisms. The model results indicate that precipitation changes within NE China show obvious spatial discrepancies. In particular, the annual precipitation maximum occurs in the early Holocene for the western subregion, while it occurs in the mid-late Holocene for the eastern subregion. These results show two different trends of Holocene precipitation within NE China capturing the large-scale precipitation changes appearing in climate records. These spatial features are closely related to the gradual weakening of the East Asian summer monsoon during the Holocene and are mainly attributed to the combined effects of orbital forcing and the ice sheet. Changes in orbital parameters play a major role in the decreased precipitation in the western subregion, while changes in the ice sheet contribute more to the increased precipitation in the eastern subregion. The observed model-data discrepancy partly relates to the low horizontal resolution employed and the physical processes and parameterizations of the model used.

Variability of East Asian summer monsoon precipitation during the Holocene and possible forcing mechanisms

Projecting how the East Asian summer monsoon (EASM) rainfall will change with global warming is essential for human sustainability. Reconstructing Holocene climate can provide critical insight into its forcing and future variability. However, quantitative reconstructions of Holocene summer precipitation are lacking for tropical and subtropical China, which is the core region of the EASM influence. Here we present high-resolution annual and summer rainfall reconstructions covering the whole Holocene based on the pollen record at Xinjie site from the lower Yangtze region. Summer rainfall was less seasonal and ~ 30% higher than modern values at ~ 10–6 cal kyr BP and gradually declined thereafter, which broadly followed the Northern Hemisphere summer insolation. Over the last two millennia, however, the summer rainfall has deviated from the downward trend of summer insolation. We argue that greenhouse gas forcing might have offset summer insolation forcing and contributed to the late Holocene rainfall anomaly, which is supported by the TraCE-21 ka transient simulation. Besides, tropical sea-surface temperatures could modulate summer rainfall by affecting evaporation of seawater. The rainfall pattern concurs with stalagmite and other proxy records from southern China but differs from mid-Holocene rainfall maximum recorded in arid/semiarid northern China. Summer rainfall in northern China was strongly suppressed by high-northern-latitude ice volume forcing during the early Holocene in spite of high summer insolation. In addition, the El Nino/Southern Oscillation might be responsible for droughts of northern China and floods of southern China during the late Holocene. Furthermore, quantitative rainfall reconstructions indicate that the Paleoclimate Modeling Intercomparison Project (PMIP) simulations underestimate the magnitude of Holocene precipitation changes. Our results highlight the spatial and temporal variability of the Holocene EASM precipitation and potential forcing mechanisms, which are very helpful for calibration of paleoclimate models and prediction of future precipitation changes in East Asia in the scenario of global warming.

Impact of mid- to late Holocene precipitation changes on vegetation across lowland tropical South America: a paleo-data synthesis

AbstractA multi-proxy paleo-data synthesis of 110 sites is presented, exploring the impact of mid- to late Holocene precipitation changes upon vegetation across Southern Hemisphere tropical South America. We show that the most significant vegetation changes occurred in southwest Amazonia and southeast Brazil, regions reliant on precipitation derived from the South American summer monsoon (SASM). A drier mid-Holocene in these regions, linked to a weaker SASM, favored more open vegetation (savannah/grasslands) than present, while increased late-Holocene precipitation drove expansion of humid forests (e.g., evergreen tropical forest in southwest Amazonia,Araucariaforests in southeast Brazil). The tropical forests of central, western and eastern Amazonia remained largely intact throughout this 6000-year period. Northeastern Brazil’s climate is “antiphased” with the rest of tropical South America, but a lack of paleo-data limits our understanding of how vegetation responded to a wetter (drier) mid-(late) Holocene. From this paleo-data perspective, we conclude that ecotonal forests already close to their climatic thresholds are most vulnerable to predicted future drought, but the forest biome in the core of Amazonia is likely to be more resilient. Of greater concern are widespread deforestation and uncontrolled anthropogenic burning, which will decrease ecosystem resilience, making them more vulnerable than they might be without current anthropogenic pressures.

Spatial variability of Holocene changes in the annual precipitation pattern: a model-data synthesis for the Asian monsoon region

This study provides a detailed analysis of the mid-Holocene to present-day precipitation change in the Asian monsoon region. We compare for the first time results of high resolution climate model simulations with a standardised set of mid-Holocene moisture reconstructions. Changes in the simulated summer monsoon characteristics (onset, withdrawal, length and associated rainfall) and the mechanisms causing the Holocene precipitation changes are investigated. According to the model, most parts of the Indian subcontinent received more precipitation (up to 5 mm/day) at mid-Holocene than at present-day. This is related to a stronger Indian summer monsoon accompanied by an intensified vertically integrated moisture flux convergence. The East Asian monsoon region exhibits local inhomogeneities in the simulated annual precipitation signal. The sign of this signal depends on the balance of decreased pre-monsoon and increased monsoon precipitation at mid-Holocene compared to present-day. Hence, rainfall changes in the East Asian monsoon domain are not solely associated with modifications in the summer monsoon circulation but also depend on changes in the mid-latitudinal westerly wind system that dominates the circulation during the pre-monsoon season. The proxy-based climate reconstructions confirm the regional dissimilarities in the annual precipitation signal and agree well with the model results. Our results highlight the importance of including the pre-monsoon season in climate studies of the Asian monsoon system and point out the complex response of this system to the Holocene insolation forcing. The comparison with a coarse climate model simulation reveals that this complex response can only be resolved in high resolution simulations.

Late Holocene changes in precipitation in northwest Tasmania and their potential links to shifts in the Southern Hemisphere westerly winds

Accurate projections of future climate changes in regions susceptible to drought depend on a good understanding of past climate changes and the processes driving them. In the absence of longer term instrumental data, paleoclimate data are needed. In this study we develop a precipitation reconstruction for Rebecca Lagoon (41°11′S, 144°41′E), northwest Tasmania. First, the relationship between scanning reflectance spectroscopy measurements of sediment cores in the visible spectrum (380–730nm) and instrumental precipitation record (1912–2009) was used to develop a model to reconstruct precipitation back in time. Results showed that the ratio of reflectance between 660 and 670nm (i.e., reflectance at 660nm/reflectance at 670nm; a measure of pigment diagenesis) was significantly related to annual precipitation. A calibration model was developed (R=−0.56, pauto<0.001, RMSEP=43.0mm yr−1, 5year triangular filtered data, calibration period 1912–2009). Second, this calibration-in-time model was used to reconstruct late Holocene precipitation changes over the last ~3000years. This showed relatively dry conditions from ca. 3100–2800cal yr BP, wet conditions from ca. 2800–2400cal yr BP, dry conditions from ca. 2400–2000calyr BP, and variable conditions after this. Relatively wet conditions occurred from ca. 500cal yr BP to the late AD 1800s (ca. 50cal. yr BP). The precipitation reconstruction indicates that conditions were relatively dry for the 20th century compared to the last ~3000years. In particular, the dry period measured in recent decades is one of the most intense in at least the last 500years. As precipitation in this region is primarily driven by the Southern Hemisphere westerly winds, these changes are discussed in terms of shifts in westerly wind strength and/or position.

Quantitative reconstruction of Holocene precipitation changes in southern Patagonia

Holocene variations in annual precipitation ( P ann) were reconstructed from pollen data from southern Argentinian Patagonia using a transfer function developed based on a weighted-averaging partial least squares (WA-PLS) regression. The pollen–climate calibration model consisted of 112 surface soil samples and 59 pollen types from the main vegetation units, and modern precipitation values obtained from a global climate database. The performance ( r 2 = 0.517; RMSEP = 126 mm) of the model was comparable or slightly lower than in other comparable pollen–climate models. Fossil pollen data were obtained from a sediment core from Cerro Frias site (50°24'S, 72°42'W) located at the forest-steppe ecotone. Reconstructed P ann values of about 200 mm suggest dry conditions during the Pleistocene–Holocene transition (12,500–10,500 cal yr BP). P ann values were about 300–350 mm from 10,500 to 8000 cal yr BP and increased to 400–500 mm between 8000 and 1000 cal yr BP. An abrupt decrease in P ann at about 1000 cal yr BP was associated with a Nothofagus decline. The reconstructed P ann suggests a weakening and southward shift of the westerlies during the early Holocene and intensification, with no major latitudinal shifts, during the mid-Holocene at high latitudes in southern Patagonia.