Search

Reconstruction of modern climate and environmental changes in east Asia using inland natural climate archives can provide valuable insights on decadal–multidecadal climate and environmental patterns that are probably related to both natural and anthropogenic forcing. Here we investigated an 89-cm-long sediment core (TH1) from Tian Lake, southeastern China, for sedimentological, physical and geochemical parameters in order to understand climate and environmental changes for the latest two centuries. 137Cs- and 210Pb-based age models show that the fine sand–coarse silt-dominated core contains ~170 years (c. AD 1842–2011) of continuous sedimentation. Sediments with fine sands, low MS values, high water content, high TOC content and a high C:N ratio from c. AD 1842 to 1897 suggest intense hydrological conditions and strong runoff in the catchment, probably because of a humid climate. From AD 1897 to 1990, sediments with very fine sand and coarse silt, high MS values, low water content and unchanged TOC and C:N ratios indicate normal hydrological conditions and in-lake algae-derived organic matter. During this interval, the chemical weathering indicators show stronger weathering conditions compared with sediments deposited during AD 1842–1897, supporting the dominance of weathered surface soil input in the earlier interval and physical erosion dominance in the later period, respectively. Since AD 1990, the continuous decrease of geochemical proxies suggests human-interacted Earth surface processes in the catchment of Tian Lake. A PCA revealed four dominant geochemical controlling factors – detrital input, trophic status, grain size and early diagenesis –, accounting for 26, 20, 18 and 16% of total variance, respectively. This study for the first time provides lacustrine geochemical evidence for the most recent two centuries of climate and environmental changes in coastal southeastern China, a region that is currently undergoing an inversion of critical zone, i.e. an overturning of its soil profile, owing to swift modernization.

Increasing interest in global climate change has led to attempts to understand and quantify the relationship between chemical weathering processes and environmental conditions, especially climate. This interest necessitates the identification of new climate proxies for the reconstruction of two important Earth surface processes: physical erosion and chemical weathering. In this study, an AMS C-14-dated 2.8-m-long sediment core, GH09B1, from Lake Gonghai in north-central China was subjected to detailed geochemical analyses to evaluate the intensity of chemical weathering conditions in the catchment. Multivariate statistical analysis of major and trace elemental data of 139 subsamples revealed that the first principal component axis PCA1 explained approximate to 53% of the variance in the assemblage of elements/oxides with significant positive correlations between PCA1 scores and the separation of mobile and soluble elements/oxides from the immobile and resistant elements/oxides, which is thus able to indicate the chemical weathering in the catchment. These results are supported by the down-core trends of other major and trace elemental ratios of chemical weathering intensity as well as by pollen data from the same core. Variations in PCA1, chemical index of alteration (CIA), Rb/Sr ratio and other oxides ratios indicate stronger chemical weathering due to a wet climate during the Medieval Warm Period (MWP). However, the MWP was interrupted by an interval of relatively weaker chemical weathering conditions from AD 940-1070. Weak chemical weathering under a dry climate occurred during the Little Ice Age (LIA), and increased chemical weathering intensity during the Current Warm Period (CWP). Our proxy records of chemical weathering over the last millennium correlate well with the available proxy records of precipitation from Gonghai Lake as well as with the speleothem oxygen isotope record from Wanxiang Cave, but do not show a significant correlation with the temperature record in N China, suggesting that the chemical weathering intensity in the study area was mainly controlled by the amount of rainfall rather than by temperature. We conclude that high resolution lacustrine sediment geochemical parameters can be used as reliable proxies for climate variations at centennial-decadal time scales.

Based on elemental geochemical data, we reconstructed the sediment provenance, surface productivity and bottom water redox conditions for the last 48 ka in the Ulleung Basin (Sea of Japan) and inferred the factors controlling them. Al2O3/TiO2 ratio and chemical index of alteration (CIA) suggest that sediment provenance changed during the glacial period (48-18 ka) compared to the deglacial (ca. 18-11 ka) and Holocene. Mass accumulation rates of total organic carbon (TOC), CaCO3, phosphorus, cadmium and excess barium reveal low paleoproductivity during low sea stand. During 18-11 ka, productivity increased due to increasing inflow of nutrient-rich water masses - the Oyashio and the East China Sea coastal water - in tandem with the rising sea level. Maximum productivity occurred during Younger Dryas and Pre-boreal periods when sea level was at �� 60 m and then gradually decreased as the Tsushima Warm Current inflow kicked off at ca. 9.3 ka, consistent with other paleoredox proxies, which reveal the presence of anoxic bottom water during ca. 12-9 ka. With the changes in paleoredox proxies and their ratios (TOC, Mo, U, Mn, C/S ratio and Uauthigenic and Mo contents), we hypothesized that the redox changes were mainly ventilation driven and were superimposed on the influence of circulation-induced productivity changes. The global climate and sea-level changes on a millennial timescale play a major role in enhancing paleoproductivity and restrict bottom water advection, subsequently driving the oxygenation of bottom water in the Ulleung Basin. Copyright # 2012 John Wiley & Sons, Ltd.

Establishing the precise timing of continental glacial dynamics and abrupt high-latitude climate events is crucial to understanding the causes of global climate change. Here we present multi-proxy records in a lake sediment core from arid Inner Mongolia (Wuliangsuhai Lake) that show two distinct glacially derived sedimentation events at � 26.2-21.8 and � 17.3-11.5k cal a BP. Fine sediments from the Last Glacial Maximum separate these glacially derived coarse sediments. Within these intervals, the occurrence of granite clasts at � 24-23.5, 17.3-17 and 15.6- 14.1k cal a BP implies either sediment discharge by meltwater as well as strong current flow in the Yellow River and/or sediment influx through hill-slope mass wasting and landsliding from the nearby Yin Mountains. Surface microfeatures of quartz grains and spot elemental analysis of black specks in these intervals, however, indicate that physical weathering is dominant and that the provenance of the rocks is probably from a glacial source. To the best of our knowledge, this is the first time glacier-derived materials have been detected in any desert lake in the Yellow River basin. The occurrence of granite clasts roughly correlates with Heinrich events in the North Atlantic, suggesting synchronous ice sheet dynamics in high- and mid-latitude regions during the Last Glacial period. Although our data provide unprecedented evidence for the influence of glacier-related processes in arid Inner Mongolia, further well- dated records are clearly needed to re-evaluate the correlative inference drawn between granite clast layers in Wuliangsuhai Lake and Heinrich events in the North Atlantic. Copyright # 2012 John Wiley & Sons, Ltd.