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The eastern Lesotho Highlands host an array of periglacial and glacial geomorphic features. Their analysis has provided past climate interpretations predominantly for cold periods, yet no multi-proxy temporally continuous palaeoenvironmental records exist. This study presents a palaeoenvironmental reconstruction based on sedimentary characteristics, fossil pollen and diatoms from an alpine wetland located in the Sekhokong Mountain Range. The record commences in the late Pleistocene with a wet period from ∼16 450 to 14 440 cal a BP, interrupted by dry conditions from ∼16 350 to 15 870 cal a BP. From ∼14 150 to 8560 cal a BP, drier conditions are inferred, slowly transitioning to warmer, wetter conditions. Warmer, dry conditions are inferred for ∼8560–7430 cal a BP, followed by cold, wet conditions from ∼7280 to 6560 cal a BP. A dry, warmer period occurs from ∼6560 to 3640 cal a BP indicated by pollen, diatom and sedimentary records, followed by cool, wet conditions from ∼3400 to 1200 cal a BP. The period from ∼1110 cal a BP to the present is characterized by progressive drying. Pronounced cold events are detected from the diatom record. Moisture records appear relatively specific to the topographic setting of Sekhokong near the Great Escarpment edge, probably driven by orographically constrained synoptic controls.

Analysis of the oxygen isotope composition (δ18O) of diatom silica is a commonly used tool for palaeoclimate reconstruction that recent studies have demonstrated may be complicated by the presence of non-diatom detrital material. Such contamination can mask any true climate-driven signal, leading to spurious results. Analysis of the 2.6-Ma Barsemoi diatomites from the East African Rift Valley highlights the presence of both tephra and clay in purified samples. Here we present a new method for assessing the relative contribution and geochemical composition of contamination components where sedimentary samples may be affected by more than one type of contamination. This approach shows that the incorporation of analytical techniques, such as X-ray fluorescence spectrometry, coupled with statistical modelling, can be used to develop a three end-member model to successfully resolve climate-driven changes in δ18Odiatom. Mass-balance corrections made to δ18Odiatom data demonstrate the importance of adopting quantitative geochemical analysis in tandem with the δ18O analysis of biogenic silica, to obtain accurate and meaningful results for palaeoclimate reconstruction.

We present a new palaeoenvironmental record of hydrological variability in Lake Baikal, based on re-modelled delta O-18(diatom) values of diatom silica (delta O-18(modelled)), where the residual contaminants are identified and compensated for using electron optical imaging and whole-sample geochemistry. delta O-18(modelled) interpretations are based on the balance between rivers with high delta O-18 values and rivers with low delta O-18 values. Isotopic variability is related to latitudinal differences in precipitation which feed these rivers. The delta O-18(modelled) 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 delta O-18(modelled) 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. Copyright (C) 2011 John Wiley & Sons, Ltd.

In this paper we reconstruct hydrological variability in Lake Baikal during Marine Isotope Stage 11 (MIS 11) (427-362 ka BP) from oxygen isotope analysis of diatom silica. Highest d 18 Odiatom values are found during MIS 11.3, highlighting the dominance of hydrological input from rivers flowing into the south and central basins of Lake Baikal, especially the Selenga River. Hydrological input from south basin rivers dominated for over 30 ka. However, there is evidence from both biogenic silica and d 18 Odiatom records for an abrupt cooling event at ca. 390 ka BP. Stadial conditions at this time are coincident with an iceberg discharge event into the North Atlantic. The decline in d 18 Odiatom values suggests increasing proportion of hydrological input from rivers to the north of Lake Baikal, due to greater influence of winter precipitation and snow-melt. After a period of interstadial conditions during the early stages of MIS 11.1, biogenic silica and d 18 Odiatom values decline, mirroring the slow growth in Northern Hemisphere ice sheets. Despite rigorous cleaning procedures, palaeoclimatic inferences need to be treated with caution due to contamination of the d 18 Odiatom record; during stadial and glacial periods, contamination of the d 18 Odiatom record is even more significant. # Natural Environment Research Council (NERC) copyright 2008. Reproduced with the permission of NERC. Published by John Wiley & Sons, Ltd.

The oxygen isotope composition of diatom silica (δ18Odiatom) provides valuable information for palaeoclimate studies where carbonate proxies are either rare or absent in many lakes and ocean sediments. Unfortunately, mineral and rock fragments found alongside diatoms in most sediments can be problematic as the method used will liberate oxygen from all components within the sediment, producing both high-frequency noise and low-frequency excursions that can resemble climate signals. Removal of mineral contamination to date has largely relied upon the combination of chemical leaching and physical separation techniques (e.g. sieving, density). This combination can be inefficient and often significant proportions of contaminants are present in the 'purified' diatom sample. Using electron optical imaging and whole-rock geochemistry on previously 'purified' diatom samples, a mass balance approach has been developed whereby the types and proportions of residual contaminants are identified. By integrating this information with measured oxygen isotope ratios of the contaminants, it is then possible to remove contamination effects from the δ18Odiatom record. Contamination effects relating to carbonates, tephra and silt are modelled for cores from Lake Tilo (Ethiopia) and Lake Baikal (Siberia). In both lakes the new modelled δ18Odiatom curves show less high-frequency noise, thus enabling better resolution of low-frequency climate signals. © Natural Environment Research Council (NERC) copyright 2008. Reproduced with the permission of NERC. Published by John Wiley and Sons, Ltd.