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Lake Sihailongwan in Jilin province, NE China, provides the first continuous and almost entirely seasonally laminated sediment record on the East Asian mainland comprising the complete Holocene, the Late-glacial period, and large parts of the Last Glacial. Sediment and palynological proxy data provide a finely resolved regional environmental history of the East Asian monsoon. A varve-based chronology (shl-vc2) has been established for the last 65,000 years and allows a detailed comparison with other long regional and global palaeoclimate records. Vegetation density of the study area depends, on the long run, on precessionally forced insolation changes, with superimposed millennial-scale variability during the last Glacial. Periodic increase of organic carbon content and thermophilous tree species like Ulmus and Fraxinus and contemporary decrease of shrub Alnus precisely mirror millennial-scale climatic variations primarily known from Greenland ice-cores as Dansgaard-Oeschger cycles, as well as Late-glacial period climate changes. Percentages of trees & shrubs pollen and in particular lake productivity-related data reveal substantial differences between interstadial intensities, with those between 50 and 60 ka BP being more pronounced than the following ones. (C) 2018 Elsevier Ltd. All rights reserved.

The forest–steppe ecotone in southern Siberia is highly sensitive to climate change; global warming is expected to push the ecotone northwards, at the same time resulting in degradation of the underlying permafrost. To gain a dee- per understanding of long-term forest–steppe carbon dynamics, we use a highly resolved, multiproxy, palaeolimno- logical approach, based on sediment records from Lake Baikal. We reconstruct proxies that are relevant to understanding carbon dynamics including carbon mass accumulation rates (CMAR; g C m 2 yr 1 ) and isotope com- position of organic matter (d 13 C TOC ). Forest–steppe dynamics were reconstructed using pollen, and diatom records provided measures of primary production from near- and off-shore communities. We used a generalized additive model (GAM) to identify significant change points in temporal series, and by applying generalized linear least- squares regression modelling to components of the multiproxy data, we address (1) What factors influence carbon dynamics during early Holocene warming and late Holocene cooling? (2) How did carbon dynamics respond to abrupt sub-Milankovitch scale events? and (3) What is the Holocene carbon storage budget for Lake Baikal. CMAR values range between 2.8 and 12.5 g C m 2 yr 1 . Peak burial rates (and greatest variability) occurred during the early Holocene, associated with melting permafrost and retreating glaciers, while lowest burial rates occurred during the neoglacial. Significant shifts in carbon dynamics at 10.3, 4.1 and 2.8 kyr BP provide compelling evidence for the sensi- tivity of the region to sub-Milankovitch drivers of climate change. We estimate that 1.03 Pg C was buried in Lake Baikal sediments during the Holocene, almost one-quarter of which was buried during the early Holocene alone. Combined, our results highlight the importance of understanding the close linkages between carbon cycling and hydrological processes, not just temperatures, in southern Siberian environments.

Last Interglacial variability is commonly used as an analogue for variability in a future, warmer world. Pervasive cycles are increasingly apparent in Last Interglacial archives, although studies in continental regions are under-represented. Here we provide a new isotopic record of diatom silica (δ18Odiatom) spanning c. 127.5–115 ka BP from Lake Baikal in central Asia. Peak rain-fed discharge occurred c. 125.4 ka BP, shortly after July insolation maximum and initiation of Siberian soil development. Between 127 and 119.7 ka BP there are six marked fluctuations in δ18Odiatom values, with a pacing of approximately 1.26 ± 0.3 ka, similar to fluctuations of within lake productivity. Fluctuations in δ18Odiatom values show good agreement with patterns in Atlantic meridional overturning circulation (AMOC), supporting hypothesis of strong teleconnections via the Westerlies between the North Atlantic and central Asia. Two periods of low δ18Odiatom values are especially notable. The earliest between c. 126.5 and 126 ka BP is concurrent with the final stages of the Heinrich 11. The second between 120.5 and 119.7 ka BP is also concurrent with an increase in ice-rafted debris in the North Atlantic. Aquatic productivity in Lake Baikal increased between 119.7 and 117.4 ka BP before declining to the top of the record (115 ka BP) concomitant with a shift to predominately cool steppe catchment vegetation. However, isotopic composition of discharge into Lake Baikal provides evidence for strong penetration of Westerlies into central Asia during the latter stages of the Last Interglacial. Variability in δ18Odiatom values was compared between the Last Interglacial and the Holocene. Millennial-scale variability was significantly more stable during the Last Interglacial, possibly linked to diminished influence of freshwater discharge on AMOC during periods of higher, global mean temperatures.

Carbon isotope ratio (δ13Corg) values of organic matter in lake sediments are commonly used to reconstruct environmental change, but the factors which influence change are varied and complex. Here we report δ13C values for sediments from Erlongwan maar lake in northeast China. In this record, changes in δ13C cannot be explained by simple changes in aquatic productivity. Instead, values were likely influenced by differences in the ratio between planktonic and benthic algae, as indicated by the remains of diatoms. This is because the variation of δ13Corg in algae from different habitats is controlled by the thickness of the diffusive boundary layer, which is dependent on the turbulence of the water. Compared with benthic algae, which grow in relatively still water, pelagic algae are exposed to greater water movement. This is known to dramatically reduce the thickness of the boundary layer and was found to cause even more severe δ13C depletion. In Erlongwan maar lake, low values were linked to the dominance of planktonic diatoms during the period commonly known as the Medieval Warm Period. Values gradually increased with the onset of the Little Ice Age, which we interpret as being driven by an increase in the proportion of benthic taxa, due to effect of the colder climate. The increase in planktonic diatoms at the end of the Little Ice Age, linked to higher temperature and a reduction in ice cover, resulted in a further decline in δ13Corg.

Lake Xiaolongwan is a closed maar lake located in the Long Gang Volcanic Field, northeast China. Core XLW2 was collected in 2007 from the central region of the lake and provides a palaeoecological reconstruction over the past ca. 130 years (dated using radiometric methods: 210Pb and 137Cs). Diatom floristic changes and catchment productivity (carbon isotope ratios) were analysed within the core. Indicators of atmospheric pollution (XRF and SCP inventories) were also measured. Results show a marked transition from a dominant benthic assemblage to a planktonic one (increasing P:B ratios) starting after ca. 1940 AD, becoming most prominent after ca. 1980 AD (P:B > 1). Most notable floristic changes result from the increase in the planktonic species Discostella woltereckii. These changes are concomitant with increased temperature trends from the region and reconstructed temperature anomalies of the Northern Hemisphere. SCP concentrations and flux rates also increase after ca. 1950 AD, with highest values seen at ca. 1980 AD after which values decline. Normalised elemental geochemistry (e.g. Pb/Ti) also show marked changes after ca. 1970 AD, most likely derived from atmospheric deposition of Pb. The recent increase in D. woltereckii precedes anthropogenic contamination (Pb/Ti) at the site and persists after the decline in SCP concentrations. This suggests that the recent increases are driven by increased mean annual temperature trends. These temperature trends may be manifested as changes in ice cover persistence, a longer growing season and/or increased DOC at Lake Xiaolongwan: conditions for which planktonic species have a more competitive advantage.

We present a new palaeoenvironmental record of hydrological variability in Lake Baikal, based on re-modelled δ18Odiatom values of diatom silica (δ18Omodelled), where the residual contaminants are identified and compensated for using electron optical imaging and whole-sample geochemistry. δ18Omodelled interpretations are based on the balance between rivers with high δ18O values and rivers with low δ18O values. Isotopic variability is related to latitudinal differences in precipitation which feed these rivers. The δ18Omodelled record suggests that rather moist conditions prevailed in the Lake Baikal region during the latter stages of the Younger Dryas. Throughout the Holocene, episodes of low δ18Omodelled values are, in general, in good agreement with increases in percentage haematite-stained grains in North Atlantic sediments (indicative of ice-rafted debris events). Rivers with southerly catchments dominate fluvial input especially between c. 3.3 and 2 cal ka BP, concurrent with high precipitation in the Lake Baikal region.