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Lacustrine-peat sediments from the Oskino-09 borehole in Western Siberia, which span the last 7.5 cal ka BP, were sampled for pollen and plant macro-remains to better understand regional climatic changes and the position of the forest-steppe border. Analysis of palynological assemblages indicate that meadow-steppe landscapes occupied the largest area in the middle of the Holocene (7.5–4.7 cal ka BP) due to reduced effective moisture during a warm climate interval. A subsequent gradual decrease in temperatures and evaporation led to an increase in effective moisture and emergence of birch groves during 4.7–2.0 cal ka BP, with short interruptions at ca. 3.3 and 2.5 cal ka BP. The expansion of pine forests and the advance of taiga to the south were recorded at ca. 2.0 cal ka BP. There is little evidence for significant human impact on forest-steppe belt evolution, and specifically evidence for anthropogenic deforestation on the southern border of the taiga is lacking. Human activities did not start to impact forests until the emergence of semi-nomadic cattle breeding in the Iron Age. A methodological finding of this paper is that we show that the Landscape Reconstruction Algorithm (LRA) is not always reliable and often overestimates forested areas. • Forests area is overestimated by quantifying landscape assessment in forest-steppe. • Largest meadow-steppe areas were due to reduced effective moisture ca 7.5–4.7 ka BP. • Intensive spread of coniferous in Western Siberian forest-steppe ca 2.0 ka BP. • Human impact on the landscape of Western Siberian forest-steppe was not significant. [ABSTRACT FROM AUTHOR]

The 4.2 ka Event has generally been regarded as a period of decades to at most a few centuries in which comparatively dry conditions existed in the Middle East and more broadly across the mid-latitude Northern Hemisphere. This paper presents new stable-isotopic and petrographic observations from two previously-unreported U-Th-dated stalagmites from Dante Cave in northeastern Namibia. The results are most compatible with wetter conditions during the 4.2 ka Event, and wetness during the 4.2 ka Event is the only inference supported by evidence. These new results add to observations previously reported from a third Dante Cave stalagmite suggesting a comparatively wet 4.2 ka Event in which Africa's Tropical Rain Belt migrated southward and rainfall increased along the Congo Air Boundary and/or Kalahari Discontinuity. The new results support findings from three other locations in Namibia and Botswana, from at least seven other locations in the Southern Hemisphere, and at least one in southern China, that suggest a wetter rather than drier 4.2 ka Event in those regions. The pattern emerging from these sites generally agrees with recent modeling results indicating increased moisture over broad areas (but not all) of the Southern Hemisphere. This in turn suggests a 4.2 ka Event that was not a global drought but was instead a set of latitudinally-dependent responses to global-scale southward migration of the Inter-Tropical Convergence Zone (ITCZ), and thus Africa's loosely linked Tropical Rain Belt, as a result of cooling of the Northern Hemisphere, which brought drier conditions to some areas and wetter conditions to others. • Like one before, two new stalagmites indicate wet 4.2 ka Event in northeast Namibia. • Layer-bounding surfaces and stable isotope data document the wet 4.2 ka Event. • Growing body of proxy evidence from Southern Hemisphere indicates a wet 4.2 ka Event. • Independent modeling supports proxy evidence of wet Southern Hemisphere 4.2 ka Event. • Tropical Rain Belt and ITCZ migrated southward with Northern-Hemisphere cooling. [ABSTRACT FROM AUTHOR]

Abstract: Stratigraphic descriptions and radiocarbon data from eleven field locations are presented in this paper to establish a chronostratigraphic framework for offshore to nearshore deposits of Lake Bonneville. Based on key marker beds and geomorphic position, the deposits are interpreted to have accumulated during the period from the late transgressive phase, through the overflowing phase, into the regressive phase of the lake. Radiocarbon ages of sediments associated with the Provo shoreline indicate that Lake Bonneville dropped rapidly from the Provo shoreline at about 12,600 14C yr BP (15,000 cal yr B.P.). The presence of one or more sand beds in the upper part of the Provo-aged marl indicates rapid lowering of lake level or storm events at the end of the Provo episode. An accurate understanding of the timing and nature of Lake Bonneville''s climate-driven regression from the Provo shoreline is critical to correlations with records of regional and hemispheric climate change. The rapid descent of the lake from the Provo shoreline correlates with the decline of Lakes Lahontan and Estancia, and with the onset of the BØlling–AllerØd warming event. [Copyright &y& Elsevier]

Abstract: A loess–paleosol sequence and a lake sediment record from the central Hexi Corridor in the drylands of NW China show patterns of persistent millennial- to centennial-scale climate variability during the Holocene epoch, which can be well correlated with abrupt climatic events reported from the North Atlantic and the Asian monsoon-dominated regimes. Our results show that the drylands in NW China might have been regulated both by the westerlies and by the East Asian summer monsoon (EASM) in a roughly synchronous manner. It seems that cold–dry intervals in the central Hexi Corridor may generally correspond to cooling phases in high latitudes of the Northern Hemisphere, and that cold/warm–wet intervals largely correlate with relatively warm phases in northern high latitudes. A candidate mechanism involving NAO/AO and ENSO dynamics is tentatively proposed to account for this synchroneity. Climatic patterns may be spatially different in the NW China drylands in response to the changing predominant control of either the westerlies or the EASM, depending on the contrast of their relative strengths. Glacier meltwater discharges associated with alpine warming may be partly responsible, at least for the two records discussed in this paper, for such spatial heterogeneity of climatic changes during the Holocene. More work is needed to evaluate the individual roles and combined impacts of the EASM, the westerlies and alpine glacier meltwater regulation on the NW China dryland dynamics. [Copyright &y& Elsevier]