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Oxygen isotopes in biogenic silica (δ18OBSi) from lake sediments allow for quantitative reconstruction of past hydroclimate and proxy–model comparison in terrestrial environments. The signals of individual records have been attributed to different factors, such as air temperature (Tair), atmospheric circulation patterns, hydrological changes and lake evaporation. While every lake will have its own set of drivers of d18O, here we explore the extent to which regional or even global signals emerge from a series of palaeoenvironmental records. For this purpose, we have identified and compiled 71 down–core records published to date and complemented these datasets with additional lake basin parameters (e.g. lake water residence time and catchment size) to best characterize the signal properties. Records feature widely different temporal coverage and resolution ranging from decadal–scale records covering the last 150 years to records with multi–millennial scale resolution spanning glacial–interglacial cycles. Best coverage in number of records (N = 37) and datapoints (N = 2112) is available for northern hemispheric (NH) extra–tropic regions throughout the Holocene (corresponding to Marine Isotope Stage 1; MIS 1). To address the different variabilities and temporal offsets, records were brought to a common temporal resolution by binning and subsequently filtered for hydrologically open lakes with lake water residence times < 100 yrs. For mid– to high–latitude (> 45° N) lakes, we find common δ18OBSi patterns during both the Holocene and the Common Era and maxima and minima corresponding to known climate episodes such as the Holocene Thermal Maximum (HTM), Neoglacial Cooling, Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). These patterns are in line with long–term Tair changes supported by previously published climate reconstructions from other archives as well as Holocene summer insolation changes. In conclusion, oxygen isotope records from NH extratopic lake sediments feature a common climate signal at centennial (for CE) and millennial (for Holocene) time scales despite stemming from different lakes in different geographic locations and constitute a valuable proxy for past climate reconstructions.

The Grindelwald Fluctuation (1560-1630) was a cooling phase during the ‘Little Ice Age’ (c.1300-1850). Poor weather during the Fluctuation contributed to harvest failures, mass starvation and political crises across the globe. This paper examines information taken from Bristol chronicles that discuss some of the extreme weather events of the period. The entries support the notion that the Grindelwald Fluctuation featured some extraordinarily poor weather, such as great frosts, floods, severe storms, unseasonal snowfalls and droughts.

Climate may have played a critical role in early hominin evolution and dispersion, with rapid changes from humid to hyper-arid observed in East African palaeoclimate records. Many studies show linkages between these climate changes and hominin speciation and dispersion; however, few of them have focused on annual to decadal climate variability. This new study presents paleoenvironmental records (diatom assemblages and oxygen isotopes in diatom biogenic silica, d18Odiatom) from the Ol Njorowa Gorge in Kenya. The study site is located west of the African Rift Valley, from where important hominin dispersals are believed to have taken place. The study site preserves a stratigraphic record of interbedded diatomite beds spanning a key period of theorised hominin dispersals; 150,000 to 80,000 years ago. In this study, diatom assemblages and d18Odiatomrecords are used to understand past changes in moisture and precipitation patterns over East Africa as well as changes in lake water chemistry. d18Odiatom has been used in both lacustrine and oceanic settings since the early 2000s. It is however an under-utilised proxy that holds great potential, especially for diatomites from exposed lake beds where carbonate material is scarce or inexistant. The study also uses high resolution scanning XRF data from diatomite blocks to develop an age model for the diatomite beds at an annual timescale.

Rwenzori Mountains National Park, which straddles the border between the Democratic Republic of Congo and Uganda, has experienced rapid glacier loss since the beginning of the twentieth century, yet there has been little investigation of aquatic biodiversity change in the park. This study presents a paleolimnological analysis from Lake Mahoma (2990 m asl), which is situated in the bamboo-forest transition zone. Diatom and organic geochemistry data from a 39-cm-long sediment core with a basal age of c. 1715 CE were compared with new analyses of previously published data from Lakes Bujuku (3891 m asl) and Lower Kitandara (3989 m asl), in the alpine zone. Comparisons were made to determine if aquatic ecosystem changes exhibited similar inter-lake patterns over the past ~ 150 years of climate warming and glacial recession, or if only local change was apparent. The diatom flora of Lake Mahoma is acidophilous, dominated by Aulacoseira ikapoënsis since at least the mid eighteenth century. In recent decades, the obligate nitrogen-heterotroph Nitzschia palea increased in importance, concurrent with declining δ15Norg values. We suggest that these late twentieth century changes were linked to regional warming and increased thermal stratification of Lake Mahoma. Regional comparisons of the Rwenzori lakes were done using existing organic geochemistry records (total organic carbon, C/N and δ13Corg) and through diatom compositional turnover analyses, and categorisation of species into one of four diatom growth morphology traits, or guilds: tychoplanktonic, high-profile, low-profile and motile. Over the past 150 years, all three lakes showed unidirectional, compositional diatom turnover, indicating that deterministic processes had affected diatom communities. Declining turnover at each site is broadly mirrored by an increase in tychoplanktonic taxa, along with concomitant declines in high-profile diatoms at Lake Mahoma, and low-profile diatoms at Lake Bujuku, and at least for the past 60 years, at Lower Kitandara. The interplay between diatom guilds at all sites is mainly a consequence of competition for available resources. Sediment organic carbon at all sites comes from both autochthonous and allochthonous sources, the relative abundances of which are influenced by the time elapsed since lakes had glaciers in their catchment.

No formal investigations have been conducted into the efficacy or potential influence of reviewer recommendations on editorial decisions, and the impact of this on the expectations and behaviour of authors, reviewers and journal editors. This article addresses key questions about this critical aspect of the peer review submission process. We suggest several future steps which could be taken towards improving the review process and make it more transparent, better understood, and fairer for all parties.

A comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cut-off values slackened in data-sparse regions. The data derive from lake sediment (51%), marine sediment (31%), peat (11%), glacier ice (3%), and other natural archives. The database contains 1319 records, including 157 from the Southern Hemisphere. The multi-proxy database comprises paleotemperature time series based on ecological assemblages, as well as biophysical and geochemical indicators that reflect mean annual or seasonal temperatures, as encoded in the database. This database can be used to reconstruct the spatiotemporal evolution of Holocene temperature at global to regional scales, and is publicly available in Linked Paleo Data (LiPD) format. Fil: Kaufman, Darrell. Northern Arizona University.; Estados Unidos Fil: McKay, Nicholas. Northern Arizona University.; Estados Unidos Fil: Routson, Cody. Northern Arizona University.; Estados Unidos Fil: Erb, Michael. Northern Arizona University.; Estados Unidos Fil: Davis, Basil. University Of Lausanne; Suiza Fil: Heiri, Oliver. University Of Basel; Suiza Fil: Jaccard, Samuel. University Of Bern; Suiza Fil: Tierney, Jessica. University of Arizona; Estados Unidos Fil: Dätwyler, Christoph. University Of Bern; Suiza Fil: Axford, Yarrow. Northwestern University; Estados Unidos Fil: Brussel, Thomas. University of Utah; Estados Unidos Fil: Cartapanis, Olivier. University Of Bern; Suiza Fil: Chase, Brian. Universite de Montpellier; Francia Fil: Dawson, Andria. Mount Royal University; Canadá Fil: de Vernal, Anne. Université du Québec a Montreal; Canadá Fil: Engels, Stefan. University of London; Reino Unido Fil: Jonkers, Lukas. University Of Bremen; Alemania Fil: Marsicek, Jeremiah. University of Wisconsin-Madison; Estados Unidos Fil: Moffa Sánchez, Paola. University of Durham; Reino Unido Fil: Morrill, Carrie. University of Colorado; Estados Unidos Fil: Orsi, Anais. Université Paris-Saclay; Francia Fil: Rehfeld, Kira. Heidelberg University; Alemania Fil: Saunders, Krystyna. Australian Nuclear Science And Technology Organisation; Australia Fil: Sommer, Philipp. University Of Lausanne; Suiza Fil: Thomas, Elizabeth. University At Buffalo; Estados Unidos Fil: Tonello, Marcela Sandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Tóth, Mónika. Balaton Limnological Institute; Hungría Fil: Vachula, Richard. Brown University; Estados Unidos Fil: Andreev, Andrei. Alfred Wegener Institut Helmholtz Centre for Polar and Marine Research; Alemania Fil: Bertrand, Sebastien. Ghent University; Bélgica Fil: Massaferro, Julieta. Administración de Parques Nacionales. Parque Nacional "Nahuel Huapi"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

© 2020 Elsevier B.V. Southern Siberia is currently undergoing rapid warming, inducing changes in vegetation, loss of permafrost, and impacts on the hydrodynamics of lakes and rivers. Lake sediments are key archives of environmental change and contain a record of ecosystem variability, as well as providing proxy indicators of wider environmental and climatic change. Investigating how hydrological systems have responded to past shifts in climate can provide essential context for better understanding future ecosystem changes in Siberia. Oxygen isotope ratios within lacustrine records provide fundamental information on past variability in hydrological systems. Here we present a new oxygen isotope record from diatom silica (ẟ18Odiatom) at Lake Baunt (55°11′15″N, 113°01,45″E), in the southern part of eastern Siberia, and consider how the site has responded to climate changes between the Younger Dryas and Early to Mid Holocene (ca. 12.4 to 6.2 ka cal BP). Excursions in ẟ18Odiatom are influenced by air temperature and the seasonality, quantity, and source of atmospheric precipitation. These variables are a function of the strength of the Siberian High, which controls temperature, the proportion and quantity of winter versus summer precipitation, and the relative dominance of Atlantic versus Pacific air masses. A regional comparison with other Siberian ẟ18Odiatom records, from lakes Baikal and Kotokel, suggests that ẟ18Odiatom variations in southern Siberia reflect increased continentality during the Younger Dryas, delayed Early Holocene warming in the region, and substantial climate instability between ~10.5 to ~8.2 ka cal BP. Unstable conditions during the Early Holocene thermal optimum most likely reflect localised changes from glacial melting. Taking the profiles from three very different lakes together, highlight the influence of site specific factors on the individual records, and how one site is not indicative of the region as a whole. Overall, the study documents how sensitive this important region is to both internal and external forcing.

A comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cut-off values slackened in data-sparse regions. The data derive from lake sediment (51%), marine sediment (31%), peat (11%), glacier ice (3%), and other natural archives. The database contains 1319 records, including 157 from the Southern Hemisphere. The multi-proxy database comprises paleotemperature time series based on ecological assemblages, as well as biophysical and geochemical indicators that reflect mean annual or seasonal temperatures, as encoded in the database. This database can be used to reconstruct the spatiotemporal evolution of Holocene temperature at global to regional scales, and is publicly available in Linked Paleo Data (LiPD) format., Measurement(s)climateTechnology Type(s)digital curationFactor Type(s)temporal interval • geographic location • proxy typeSample Characteristic - Environmentclimate systemSample Characteristic - LocationEarth (planet) Machine-accessible metadata file describing the reported data: https://www.ncdc.noaa.gov/paleo/study/27330

Biological diversity is inextricably linked to community stability and ecosystem functioning, but our understanding of these relationships in freshwater ecosystems are largely based on short-term observational, experimental, and modelling approaches. Using a multidecadal diatom record for the past 15,800 years from Lake Baikal, we investigate how three ecosystem components – diversity, productivity, and stability – have responded to climate changes on long-timescales. In addition, we investigate how the relationships between diversity, productivity and stability have changed through time in response to these changes. We show that abrupt changes in diatom stability and diversity during the late glacial and early Holocene are part of a network of responses across southern Siberia as a result of extrinsically-forced climate instability. Productivity – diversity relationships were strongly coupled during the late glacial, which we suggest is linked to resource availability, but showed little relationship during the Holocene, perhaps due to few resources being limiting for extended periods of time. For example, periods of low diatom diversity are associated with peak palaeoproductivity, and coincide with climate disturbance events. Such strong negative relationships may reflect resources becoming limiting during palaeoproductivity, leading to monospecific diatom blooms. While species fluctuations respond rapidly to changing resources during much of the Holocene, the ecosystem function of primary production appears to be relatively resilient. Our study provides important perspectives on lake community stability and ecosystem function in relation to rapid periods of climate change.

Lake Baikal, lying in a rift zone in southeastern Siberia, is the world's oldest, deepest, and most voluminous lake that began to form over 30 million years ago. Cited as the “most outstanding example of a freshwater ecosystem” and designated a World Heritage Site in 1996 due to its high level of endemicity, the lake and its ecosystem have become increasingly threatened by both climate change and anthropogenic disturbance. Here, we present a record of nutrient cycling in the lake, derived from the silicon isotope composition of diatoms, which dominate aquatic primary productivity. Using historical records from the region, we assess the extent to which natural and anthropogenic factors have altered biogeochemical cycling in the lake over the last 2,000 y. We show that rates of nutrient supply from deep waters to the photic zone have dramatically increased since the mid-19th century in response to changing wind dynamics, reduced ice cover, and their associated impact on limnological processes in the lake. With stressors linked to untreated sewage and catchment development also now impacting the near-shore region of Lake Baikal, the resilience of the lake’s highly endemic ecosystem to ongoing and future disturbance is increasingly uncertain., Proceedings of the National Academy of Sciences of the United States of America, 117 (44), ISSN:0027-8424, ISSN:1091-6490

Over recent decades, concern has been raised regarding the management of Chrysocoma ciliata L. (Asteraceae syn. C. tenuifolia) in the eastern Lesotho Highlands. This shrub species is argued to be a Karroid invasive introduced anthropogenically within the last century. Historical botanical records in Lesotho are scarce, so the origins of this species in the region are as yet uncertain. Speculation is based on the contemporary abundance of these shrubs in overgrazed areas throughout the highlands. This study presents fossil pollen records for the eastern Lesotho Highlands which confirm the presence of this species intermittently throughout the past ~6000 cal yr BP. In so doing, this study refutes claims that the species was introduced anthropogenically within the past 100 years, and of its narrow definition as a Karoo species invasive in Lesotho. The intermittent appearance of this species in the pollen record, however, indicates that it is climate sensitive, colonising the wetlands under conditions unsuitable to other plant species. Evidence presented here calls for a re-evaluation of the categorisation of C. ciliata as an invasive in the Lesotho Highlands, and more critically, for a redevelopment of the environmental management policies which involve this species.

Southern African late Quaternary research has developed rapidly during recent decades, with an increase in the range of proxies used, the inclusion of new field sites, and increased international collaboration and skills transfer. This has enabled recent meta-studies into the synoptic drivers of palaeoenvironmental shifts across the region, and of spatial variability in climatic and environmental changes. Expanded research has also highlighted uncertainties in the understanding of southern African palaeoenvironments, and the relationships with Northern Hemisphere analogues, encouraging on-going critical debate within the discipline. Given current concerns of climate change impacts on the natural environment, the spread of invasives, increased fire frequency, and anthropogenic influences on the natural environment, palaeoenvironmental data and inferences are increasingly being utilised outside of the palaeoenvironmental discipline, providing a valuable inter-disciplinary platform for global change science ...

Constraining the continental silicon cycle is a key requirement in attempts to understand both nutrient fluxes to the ocean and linkages between silicon and carbon cycling over different time scales. Silicon isotope data of dissolved silica (δ30SiDSi) are presented here from Lake Baikal and its catchment in central Siberia. As well as being the world's oldest and voluminous lake, Lake Baikal lies within the seventh largest drainage basin in the world and exports significant amounts of freshwater into the Arctic Ocean. Data from river waters accounting for ~92% of annual river inflow to the lake suggest no seasonal alteration or anthropogenic impact on river δ30SiDSi composition. The absence of a change in δ30SiDSi within the Selenga Delta, through which 62% of riverine flow passes, suggests a net balance between biogenic uptake and dissolution in this system. A key feature of this study is the use of δ30SiDSi to examine seasonal and spatial variations in DSi utilization and export across the lake. Using an open system model against deepwater δ30SiDSi values from the lake, we estimate that 20–24% of DSi entering Lake Baikal is exported into the sediment record. While highlighting the impact that lakes may have upon the sequestration of continental DSi, mixed layer δ30SiDSi values from 2003 and 2013 show significant spatial variability in the magnitude of spring bloom nutrient utilization with lower rates in the north relative to south basin.

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 deeper understanding of long‐term forest–steppe carbon dynamics, we use a highly resolved, multiproxy, palaeolimnological 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 composition of organic matter (δ 13 CTOC). 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 sensitivity 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., 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 deeper understanding of long‐term forest–steppe carbon dynamics, we use a highly resolved, multiproxy, palaeolimnological approach, based on sediment records from Lake Baikal. Generalized additive models identify significant change points in temporal series, which we relate to abrupt sub‐Milankovitch scale events. About 1.03 Pg of C has been buried in Lake Baikal sediments since the start of the Holocene, with almost one‐quarter of budget being buried within the first few thousand years.

1. We explored controls of algal taxon richness (hereafter richness) in complex and hydrologically dynamic flood-pulsed wetlands by comparing results from independent studies in two globally important subtropical wetlands: the Okavango Delta (Botswana) and the Florida Everglades (U.S.A.). In both wetlands, the flood pulse hydrology is regulated by distinct wet and dry seasons, and creates floodplain landscapes with heterogeneous habitats; algal growth is limited by phosphorus (P); and water uses threaten ecosystem function. To inform future comparisons of algal richness and distribution patterns, we assessed the role of hydrology and P as key controls of richness, and identified indicator taxa of desiccation disturbance and P scarcity in these wetlands under increasing hydrological, nutrient, and habitat changes. 2. We used the intermediate disturbance hypothesis, and the species-energy theory to explain algal richness patterns, and the competitive, stress-tolerant, ruderal (CSR) framework to classify indicator taxa. We collected algal samples, environmental data and information expected to influence community structure (water depth, relative depth change, P concentrations, hydroperiod and habitat type) over several years at sites representing a broad range of environmental characteristics. To account for sample size differences, we estimated algal richness by determining the asymptote of taxon accumulation curves. Using multiple regression analysis, we assessed if and how water depth, depth change, P, hydroperiod, and habitat type influence richness within each wetland. We then compared the strength of the relationships between these controlling features and richness between wetlands. Using indicator species analysis on relative abundance data, we classified C, S and R indicator taxa associated with shorter/longer hydroperiod, and lower/higher P concentrations. 3. In either wetland, we did not observe the negative unimodal relationship between site-specific richness and water depth change that was expected following the intermediate disturbance hypothesis. It is possible that this relationship exists at more highly resolved temporal scales than the semi-annual to annual scales hypothesised here. However, as nutrient flows and algal habitats depend on these wetlands' flood pulse, maintaining the Okavango's natural pulse, and increasing freshwater flow in the Everglades would help protect these wetlands' algal diversity. Chlorophyta richness (Okavango), and total, Bacillariophyta, Chlorophyta and cyanobacteria richness (Everglades) increased with higher P concentrations, as per species-energy theory. In the Okavango, we classified 6 C and 49 R indicator taxa (e.g. many planktonic Chlorophyta), and in the Everglades, 15 C, 1 S and 9 R taxa (e.g. benthic Bacillariophyta and planktonic/benthic Chlorophyta), and one stress- and disturbance-tolerant cyanobacterium species. 4. Our results offer baseline information for future comparisons of richness, and abundance of C, S and R indicator taxa in subtropical wetlands; this can be used to quantify how algal communities may respond to potential changes in hydrology and P due to water diversion, anthropogenic nutrient loads, and climate change. Examining microhabitat heterogeneity, nitrogen and light availability, and grazing pressure in such wetlands would further illuminate patch-scale controls of richness and life-history strategy distribution in algal communities.

Copyright © 2019, Springer Nature. The attached document is the authors’ final accepted/submitted version of the journal article. You are advised to consult the publisher’s version if you wish to cite from it.

During the latter stages of the Holocene, and prior to anthropogenic global warming, the Earth underwent a period of cooling called the neoglacial. The neoglacial is associated with declining summer insolation and changes to Earth's surface albedo. Although impacts varied globally, in China the neoglacial was generally associated with a cooler climate and an attenuated Asian summer monsoon. Few studies in central China, however, have explored the impact of neoglacial cooling on freshwater diversity, especially in alpine regions. Here we take a palaeolimnological approach to characterise multi-decadal variability in diatom community composition, ecological guilds, and compositional turnover over the past 3500 years from the alpine Yuhuang Chi lake on Mount Taibai in the Qinling mountains. Diatoms in the high-profile guild dominate much of the record from 3500 to 615 cal BP, which suggests that few nutrients in the lake were limiting overall, and disturbance and herbivory were likely low. After 615 cal BP, low-profile and planktic guild diatoms increase, suggesting greater turbulence in the lake, alongside a decline in available nutrients. Diatom turnover highlights periods in the lake history when deterministic processes structured diatom communities. For example, an abrupt decline in turnover is coincident with the shift from high- to low-profile diatoms at 615 cal BP, and this is likely due to the onset of the Little Ice Age in the region. We suggest that Yuhuang Chi lake became more shallow during peak regional aridity, which led to the short-lived community restructuring observed in the record.

For years, publication in a peer-reviewed scientific journal has served as the official announcement that a piece of research has entered the accepted body of scientific knowledge. However, chances are good that the data, method innovations, and preliminary conclusions contained in a scientific paper have been circulating among the researchers’ colleagues for a year or more before the paper is officially published. By the time a journal issue goes to the printing press, the research may have made significant progress beyond what the published papers document. Preprints—published, non-peer-reviewed scholarly papers that often precede publication in a peer-reviewed journal—have been a part of science since at least the 1960s [Cobb, 2017]. ArXiv, arguably the most prominent preprint system, has served the physics, mathematics, and computer science communities for more than 25 years.

The eastern Lesotho Highlands experience climate patterns distinct from those of surrounding lower altitude regions, representing a niche environment with a unique biodiversity, leading to well-adapted but restricted vegetation. This study explores changes in the Holocene composition of diatoms and pollen at southern Africa’s highest altitude wetland (Mafadi: 3390 m a.s.l.). The palaeoenvironmental record for Mafadi Wetland indicates fluctuations between cold, wet conditions, prevalent between ~8140 and 7580 cal. yr BP and between ~5500 and 1100 cal. yr BP, and warmer, drier periods between ~7520 and 6680 cal. yr BP and between ~6160 and 5700 cal. yr BP. Marked climatic variability is noted from ~1100 cal. yr BP with colder conditions at ~150 kyr BP. Notably, the first of these cold periods occurs soon after the Northern Hemisphere 8.2 kyr event, while a second period of notably cold conditions occurs around 1100 cal. yr BP. Variability exists between the moisture reconstructions presented in this study and those from adjacent lower altitude sites, which is hypothesised to reflect variations in the strength and extent of the Westerlies throughout the Holocene.

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.

Rationale Current studies which use the oxygen isotope composition from diatom silica (δ18Odiatom) as a palaeoclimate proxy assume that the δ18Odiatom value reflects the isotopic composition of the water in which the diatom formed. However, diatoms dissolve post mortem, preferentially losing less silicified structures in the water column and during/after burial into sediments. The impact of dissolution on δ18Odiatom values and potential misinterpretation of the palaeoclimate record are evaluated. Methods Diatom frustules covering a range of ages (6 samples from the Miocene to the Holocene), environments and species were exposed to a weak alkaline solution for 48 days at two temperatures (20 °C and 4 °C), mimicking natural dissolution post mucilage removal. Following treatment, dissolution was assessed using scanning electron microscope images and a qualitative diatom dissolution index. The diatoms were subsequently analysed for their δ18O values using step-wise fluorination and isotope ratio mass spectrometry. Results Variable levels of diatom dissolution were observed between the six samples; in all cases higher temperatures resulted in more frustule degradation. Dissolution was most evident in younger samples, probably as a result of the more porous nature of the silica. The degree of diatom dissolution does not directly equate to changes in the isotope ratios; the δ18Odiatom value was, however, lower after dissolution, but in only half the samples was this reduction outside the analytical error (2σ analytical error = 0.46‰). Conclusions We have shown that dissolution can have a small negative impact on δ18Odiatom values, causing reductions of up to 0.59‰ beyond analytical error (0.46‰) at natural environmental temperatures. These findings need to be considered in palaeoenvironmental reconstructions using δ18Odiatom values, especially when interpreting variations in these values of

Freshwater aquaculture is an important source of protein worldwide. Over-exploitation of fisheries can, however, add severely to pressures on ecosystem functioning and services. In Southeast Asia, aquaculture in freshwater lakes contributes significantly to the economy and to reductions in poverty and nutritional insecurity. However, overstocking and excessive feeding of fish can lead to a degradation of affected water bodies, manifest as eutrophication, toxic algal blooms, losses of biodiversity and amenity, anoxia and, in extreme cases, collapse of fisheries. Projected increased warming and storminess associated with global climate change are likely to magnify existing problems. Matching levels of aquaculture production with ecological carrying capacity is therefore likely to become increasingly challenging, requiring levels of data and understanding that are rarely available, a problem that is impossible to rectify in the short term using standard limnological approaches. This paper reviews the development of freshwater aquaculture in the Philippines, associated environmental impacts, and relevant environmental regulations and regulatory bodies. The potential role of palaeolimnology, a science that is relatively under-utilised in the tropics generally and in tropical Asia in particular, in complementing extant datasets, including monitoring records, is highlighted through reference to a preliminary study at Lake Mohicap. Lake Mohicap currently supports aquaculture and is one of a cluster of seven volcanic crater lakes on Luzon, the largest of the archipelago of islands forming the Philippines.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Limnological reconstructions of primary productivity have demonstrated its response over Quaternary timescales to drivers such as climate change, landscape evolution and lake ontogeny. In particular, sediments from Lake Baikal, Siberia, provide a valuable uninterrupted and continuous sequence of biogenic silica (BSi) records, which document orbital and sub-orbital frequencies of regional climate change. We here extend these records via the application of stable isotope analysis of silica in diatom opal (δ30Sidiatom) from sediments covering the Last Interglacial cycle (Marine Isotope Stage [MIS] 5e; c. 130 to 115 ka BP) as a means to test the hypothesis that it was more productive than the Holocene. δ30Sidiatom data for the Last Interglacial range between +1.29 and +1.78‰, with highest values between c. 127 to 124 ka BP (+1.57 to +1.78‰). Results show that diatom dissolved silicon (DSi) utilisation, was significantly higher (p = 0.001) during MIS 5e than the current interglacial, which reflects increased diatom productivity over this time (concomitant with high diatom biovolume accumulation rates [BVAR] and warmer pollen-inferred vegetation reconstructions). Diatom BVAR are used, in tandem with δ30Sidiatom data, to model DSi supply to Lake Baikal surface waters, which shows that highest delivery was between c. 123 to 120 ka BP (reaching peak supply at c. 120 ka BP). When constrained by sedimentary mineralogical archives of catchment weathering indices (e.g. the Hydrolysis Index), data highlight the small degree of weathering intensity and therefore representation that catchment-weathering DSi sources had, over the duration of MIS 5e. Changes to DSi supply are therefore attributed to variations in within-lake conditions (e.g. turbulent mixing) over the period, where periods of both high productivity and modelled-DSi supply (e.g. strong convective mixing) account for the decreasing trend in δ30Sidiatom compositions (after c. 124 ka BP).

Persistent organic pollutants (POPs) and polycyclic aromatic hydrocarbons (PAHs) have previously been detected in the surface sediments, water, and endemic organisms of Lake Baikal, a UNESCO World Heritage Site. The Selenga River is the primary source of freshwater to Lake Baikal, and transports pollutants accumulating in the Selenga River basin to the lake. Sources of POPs and PAHs in the Selenga River basin grew through the 20th century. In the present study, temporal changes in the concentrations of PAHs and POPs were reconstructed from two lakes in the Selenga River basin over the past 150 years using paleolimnological techniques. Increased concentrations in PAHs and PCBs were recorded initially in the 1930s. The 1940s-1980s was the period of greatest exposure to organic contamination, and concentrations of dichlorodiphenyltrichloroethane (DDT), polychlorinated biphenyls (PCBs), hexachlorocyclohexanes (HCHs) and many PAHs peaked between the 1960s and 1980s in the two lakes. Declines in concentrations and fluxes were recorded for most PAHs and POPs in the 1980s and 1990s. Temporal trends in concentrations of total and individual compounds/congeners of PAH, PCBs, and polybrominated diphenyl ethers (PBDEs) indicate the contribution of both local and regional sources of contamination in the 20th and 21st centuries. Temporal variations in contaminants can be linked to economic and industrial growth in the former USSR after World War II and the economic decline of Russia in the late-1980s and early-1990s, as well as global trends in industrialization and development during the mid-20th century.

Climate models currently provide conflicting predictions of future climate change across Central Asia. With concern over the potential for a change in water availability to impact communities and ecosystems across the region, an understanding of historical trends in precipitation is required to aid model development and assess the vulnerability of the region to future changes in the hydroclimate. Here we present a record from Lake Baikal, located in the southern Siberian region of central Asia close to the Mongolian border, which demonstrates a relationship between the oxygen isotope composition of diatom silica (?18Odiatom) and precipitation to the region over the 20th and 21st Century. From this, we suggest that annual rates of precipitation in recent times are at their lowest for the past 10,000 years and identify significant long-term variations in precipitation throughout the early to late Holocene interval. Based on comparisons to other regional records, these trends are suggested to reflect conditions across the wider Central Asian region around Lake Baikal and highlight the potential for further changes in precipitation with future climate change.

The Makgadikgadi–Okavango–Zambezi basin (MOZB) is a structural depression in the south-western branch of the East African Rift System of the northern and middle Kalahari, central southern Africa. In the present day, the mainly dry subbasins of the MOZB are part of a long-lived lacustrine system that has likely existed since Early Pleistocene and from which an extant freshwater fish radiation emerged seeding all major river systems of southern Africa. During hydrologically favourable periods the subbasins were connected as a single mega-lake termed Lake Palaeo-Makgadikgadi. Previous geomorphological studies and OSL dates have provided evidence for repeated mega-lake periods since approximately 300 ka. The environmental and climatic implications of such large scale late Quaternary lake-level fluctuations are controversial, with the duration of mega-lake phases poorly constrained. Here, we present the first evidence for a Marine Isotope Stage (MIS) 5 mega-lake period (about 935–940 m a.s.l.) reconstructed from a diatom-rich, 30-cm-thick lacustrine sediment section, exposed close to a palaeo-shoreline of the Makgadikgadi Basin. Based upon the environmental setting and in comparison with sedimentation rates of other similar lake environments, we tentatively estimated that the highstand lasted approximately 1 ka during MIS 5d–b. The 30-cm section was sampled in 0.5-cm steps. Diatom species diversity ranges from 19 to 30 through the section. The dominant species are Pseudostaurosira brevistriata, Rhopalodia gibberula, Cyclotella meneghiniana and Epithemia sorex. The total of 60 sediment samples provide us with a record at decadal to bi-decadal resolution. Based on diatom assemblages and their oxygen isotope composition (δ18O) we infer an alkaline and mostly oligohaline lake with shallow water conditions prevailing in MIS 5, and is potentially analogous to a Heinrich event. The climate over southern Africa during MIS 5 has been considered very arid but the hydromorphological context of our sediment section indicates that we captured a mega-lake period providing evidence that short-term excursions to significantly higher humidity existed. A hydrologically more favourable environment during MIS 5 than formerly presumed is in line with the early human occupation of the Kalahari.

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 consider whether the Anthropocene is recorded in the isotope geochemistry of the atmosphere, sediments, plants and ice cores, and the time frame during which any changes are recorded, presenting examples from the literature. Carbon and nitrogen isotope ratios have become more depleted since the 19th century, with the rate of change accelerating after ~ad 1950, linked to increased emissions from fossil fuel consumption and increased production of fertiliser. Lead isotope ratios demonstrate human pollution histories several millennia into the past, while sulphur isotopes can be used to trace the sources of acid rain. Radioisotopes have been detectable across the planet since the 1950s because of atmospheric nuclear bomb tests and can be used as a stratigraphic marker. We find there is isotopic evidence of widespread human impact on the global environment, but different isotopes have registered changes at different times and at different rates.

The Boteti palaeo-estuary in northern Botswana is located where the endoreic Boteti river, an overflow from the regional Okavango river system, enters the Makgadikgadi pans. The present work considers diagenetic silica and calcium carbonate dominated transformations. The aims are to help identify precursor conditions for the origin of microcrystalline silcrete–calcrete intergrade deposits while developing insight into pene-contemporaneous silica and calcite matrix formation. General precursor conditions require the presence of cyclical endoreic freshwater inflow into a saline pan. The pan should be deep enough to sustain a permanent watertable under climatic conditions sufficient to cause carbonate fractionation within the groundwater. Freshwater inflow into a saline pan drives the geochemistry of the system (from freshwater to saline, from neutral to high pH). The geochemistry is controlled by the periodicity of inflow relative to salinity levels of phreatic groundwater in the receptor saline pan. The source of most silica and localized CaCO3 is derived from the dissolution and precipitation of micro-fossils, while more general CaCO3 enrichment stems from saline pan based carbonate fractionation. Diagenetic change leads to colloidal then more consolidated bSiO2/CaO aggregate formation (amorphous silica) followed by transformations into opaline silica over time. Irregular zones of siliceous sediment forming in otherwise calcareous deposits may relate to the irregular occurrence of biogenic silica in the source sediments, inferring a source for local silica mobilization in intergrade deposits. The distribution of calcareous micro-fossils may have a similar converse effect. Diagenetic evidence from an intergrade deposit with a low SiO2/CaO ratio suggests that transformation occurred more into the pan, while an intergrade deposit with a high SiO2/CaO ratio more likely formed closer to a land margin and was frequently inundated by freshwater. Pene-contemporaneous silcrete–calcrete intergrade formation under the above conditions may take place where dissolved silica crystallizes out in the vicinity of calcite crystals due to local decreases in pH. The continuing consolidation of bSiO2/CaO aggregates may be facilitated by the presence of increasing amounts of calcite. It appears that CaCO3 may act as a catalyst leading to pene-contemporaneous bSiO2/CaO aggregate formation. However the processes involved require further work. Copyright © 2013 John Wiley & Sons, Ltd.

[This corrects the article DOI: 10.1371/journal.pone.0208765.].

Tipping points – where systems shift radically and potentially irreversibly into a different state – have received considerable attention in ecology. Although there is convincing evidence that human drivers can cause regime shifts at local and regional scales, the increasingly invoked concept of planetary scale tipping points in the terrestrial biosphere remains unconfirmed. By evaluating potential mechanisms and drivers, we conclude that spatial heterogeneity in drivers and responses, and lack of strong continental interconnectivity, probably induce relatively smooth changes at the global scale, without an expectation of marked tipping patterns. This implies that identifying critical points along global continua of drivers might be unfeasible and that characterizing global biotic change with single aggregates is inapt.

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.

A palaeolimnological study of Lake Khall was undertaken to reconstruct impacts from five thousand years of climate change and human activity in the Ol'khon region of Lake Baikal. Taiga biome dominated regional landscapes, although significant compositional turnover occurred due to the expansion of eurythermic and drought resistant Scots pine. Climate during the mid-Holocene was wetter than the present, and Lake Khall was fresh, with abundant molluscs. By 4.4 cal ka BP, sedimentary geochemistry indicated a gradual change in lake water chemistry with an increase in lake salinity up to the present day, most likely controlled by groundwater influences. Vegetation turnover rate was highest between 2.75 and 2.48 cal ka BP, with the onset of drier, more continental climate, which resulted in an influx of aeolian particles to the lake. This abrupt shift was coincident with ice rafted debris event (IRD-2) in North Atlantic sediments and an attenuation of the East Asian summer monsoon. A second arid period occurred shortly afterwards (2.12–1.87 cal ka BP) which resulted in the decline in ostracod numbers, especially Candona sp. A rather more quiescent, warmer period followed, between 1.9 and 0.7 cal ka BP, with very little change in vegetation composition, and low amounts of detrital transfer from catchment to the lake. Peak reconstructed temperatures (and low amounts of annual precipitation) were concurrent with the Medieval Climate Anomaly. Between 0.77 and 0.45 cal ka BP, climate in the Ol'khon region became colder and wetter, although Lake Khall did not become fresher. Cold, wet conditions are seen at other sites around Lake Baikal, and therefore represent a regional response to the period concurrent with the Little Ice Age and IRD-0. After AD 1845 the region warms, and Pediastrum appears in the lake in high abundances for the first time. This increase is ascribed to nutrient enrichment in the lake, linked to the rapid increase in regional pastoral farming.

A high-resolution (∼every 20 y) pollen and charcoal record from Erlongwan maar lake (EML) documents the vegetation history and fire activity of the Long Gang region (northeast China) over the past millennium. The age–depth model is based on 137Cs, 210Pb measurements, and one calibrated 14C-AMS date at the base of the core. For much of the record, vegetation was dominated by a mixed conifer-hardwood forest. Pollen and charcoal concentrations reveal considerable variability during the past 1000 years. Between 980 and 1500 AD both pollen and charcoal reached maximum concentrations (∼1100 AD and 1300 AD respectively). The high pollen concentration was indicative of prevailing moist conditions during the period commonly referred to as the Medieval Climatic Anomaly (MCA). The high concentration of charcoal indicated high frequency and intensity of wildfire during the MCA, probably linked to high biomass productivity and less snow in winter. Between 1500 and 1850 AD both pollen and charcoal concentrations were low, indicative of colder winters with higher snowfall, relative drier summers and less intensive wildfire, coincidence with the cold period commonly known as the Little Ice Age (LIA). During 1900–1950 AD year, the highest relative abundance of Artemisia and the lowest abundance of Pinus together with high concentration of charcoal indicated strong human activity. The pollen data are in broad agreement with a previous study from an adjacent lake, indicating regional rather than localized human impact.

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.

The first δ30Sidiatom data from lacustrine sediment traps are presented from Lake Baikal, Siberia. Data are compared with March surface water (upper 180 m) δ30SiDSi compositions for which a mean value of +2.28‰ ± 0.09 (95 % confidence) is derived. This value acts as the pre-diatom bloom baseline silicic acid isotopic composition of waters (δ30SiDSi initial). Open traps were deployed along the depth of the Lake Baikal south basin water column between 2012 and 2013. Diatom assemblages display a dominance ( > 85 %) of the spring/summer bloom species Synedra acus var radians, so that δ30Sidiatom compositions reflect predominantly spring/summer bloom utilisation. Diatoms were isolated from open traps and, in addition, from 3-monthly (sequencing) traps (May, July and August 2012) for δ30Sidiatom analyses. Mean δ30Sidiatom values for open traps are +1.23‰ ± 0.06 (at 95 % confidence and MSWD of 2.9, n = 10). Total dry mass sediment fluxes are highest in June 2012, which we attribute to the initial export of the dominant spring diatom bloom. We therefore argue that May δ30Sidiatom signatures (+0.67‰ ± 0.06, 2σ) when compared with mean upper water δ30SiDSi initial (e.g. pre-bloom) signatures can be used to provide a snapshot estimation of diatom uptake fractionation factors (ϵuptake) in Lake Baikal. A ϵuptake estimation of −1.61 ‰ is therefore derived, although we emphasise that synchronous monthly δ30SiDSi and δ30Sidiatom data would be needed to provide more robust estimations and therefore more rigorously test this, particularly when taking into consideration any progressive enrichment of the DSi pool as blooms persist. The near-constant δ30Sidiatom composition in open traps demonstrates the full preservation of the signal through the water column and thereby justifies the use and application of the technique in biogeochemical and palaeoenvironmental research. Data are finally compared with lake sediment core samples, collected from the south basin. Values of +1.30‰ ± 0.08 (2σ) and +1.43‰ ± 0.13 (2σ) were derived for cores BAIK13-1C (0.6–0.8 cm core depth) and at BAIK13-4F (0.2–0.4 cm core depth) respectively. Trap data highlight the absence of a fractionation factor associated with diatom dissolution (ϵdissolution) (particularly as Synedra acus var radians, the dominant taxa in the traps, is very susceptible to dissolution) down the water column and in the lake surface sediments, thus validating the application of δ30Sidiatom analyses in Lake Baikal and other freshwater systems, in palaeoreconstructions.

Boreal ecosystems are highly vulnerable to climate change, and severe ecological impacts in the near future are virtually certain to occur. We undertook a multiproxy study on an alpine lake (ESM-1) at the modern tree-line in boreal, southern Siberia. Steppe and tundra biomes were extensive in eastern Sayan landscapes during the early Holocene. Boreal forest quickly expanded by 9.1 ka BP, and dominated the landscape until c 0.7 ka BP, when the greatest period of compositional turnover occurred. At this time, alpine meadow landscape expanded and Picea obovata colonised new habitats along river valleys and lake shorelines, because of prevailing cool, moist conditions. During the early Holocene, chironomid assemblages were dominated by cold stenotherms. Diatoms for much of the Holocene were dominated by alkaliphilous, fragilarioid taxa, up until 0.2 ka BP, when epiphytic species expanded, indicative of increased habitat availability. C/N mass ratios ranged between 9.5 and 13.5 (11.1–15.8 C/N atomic ratios), indicative of algal communities dominating organic matter contributions to bottom sediments with small, persistent contributions from vascular plants. However, δ13C values increased steadily from −34.9‰ during the early Holocene (9.3 ka BP) to −24.8‰ by 0.6 ka BP. This large shift in magnitude may be due to a number of factors, including increasing within-lake productivity, increasing disequilibrium between the isotopic balance of the lake with the atmosphere as the lake became isotopically ‘mature’, and declining soil respiration linked to small, but distinct retreat in forest biomes. The influence of climatic variables on landscape vegetation was assessed using redundancy analysis (RDA), a linear, direct ordination technique. Changes in July insolation at 60 °N significantly explained over one-fifth of the variation in species composition, while changes in estimates of northern hemisphere temperature and ice-rafted debris events in the North Atlantic were also significant, but considerably less important. The potential importance of climate and biome development (tundra, steppe, cold deciduous forest and taiga) on different trophic levels (i.e. chironomid and diatom communities) in lake ESM-1 was also assessed using RDA. Climate predictors had a more significant influence on Holocene chironomid assemblages, especially July insolation at 60 °N, estimates of regional precipitation and estimates of northern hemisphere temperature, while only the development of the taiga biome had a significant impact on these primary consumers. Diatom communities also had a small, but significant influence on Holocene chironomid populations, perhaps linked to variation in faunal feeding strategies. In contrast, climatic and biome predictors explained similar amounts of variation in the Holocene diatom assemblage (approximately 20% each), while chironomids themselves as predictors explained just under 7% of diatom variation. Lake acidity was inferred using a diatom inference model. Results suggest that after deglaciation, the lake did not undergo a process of gradual acidification, most likely due to the presence of continuous permafrost and low levels of precipitation, preventing base cations and dissolved organic carbon entering the lake (except for the period between 1.7 and 0.7 ka BP). We conclude that lakes in continental, boreal regions undergo different models of lake ontogeny than oceanic boreal regions. Unlike other regions discussed, climate is a more important driver of ecosystem change than catchment changes. We also demonstrate that the start of the period coincident with the onset of the Little Ice Age resulted in important thresholds crossed in catchment vegetation and aquatic communities.

Past environmental changes based on diatom relative abundances have been inferred from the maar Lake Erlongwan in northeast China. The limnology of Lake Erlongwan is affected by the strongly seasonal regional climate. The composition of diatom assemblages, in turn, responds to changes in the seasonal duration of ice cover in winter, water-column turnover in spring and autumn, and thermal stratification in summer. Statistical analysis of the sedimentary diatom assemblages reveals three significant stratigraphic zones over the past 1000 yr. The highest abundance of the planktonic speciesDiscostellaspecies occurs between AD 1050 and 1400 and suggests an annual ice-free period of long duration and well-developed summer stratification of the water column. This planktonic diatom peak between ca. AD 1150 and 1200 suggests that this period was the warmest over the past 1000 yr. The interval between AD 1400 and 1800 is marked by a decline in planktonic diatoms and suggests shorter duration of the ice-free season, weaker water stratification and possibly generally cold conditions. After AD 1800 relative abundances of planktonic diatoms, includingPuncticulata praetermissaandAsterionella formosa, increase again, which indicates lengthening of the duration of the annual ice-free period and a stronger overturn of the water column. All these data imply that the pattern of the seasons is different between the MWP and the 20th century.

1. Flood-pulsed wetlands make vital contributions to local and global biodiversity. However, the patterns and controls of spatial and temporal variation in aquatic biodiversity in flood-pulsed wetlands are not well understood. We analysed the relationship between variation in hydrological regime and the patterns of aquatic biodiversity in a large pristine flood-pulsed wetland, the Okavango Delta, Botswana. 2. Surveys of water chemistry, diatoms and macroinvertebrates were conducted over the seasonal phases of the flood pulse. Hydrological variables of flood frequency and hydroperiod class were collated from 16 years of satellite images. Multivariate regression trees and generalised least squares regression were used to determine the chief controls of community composition and taxon richness. 3. Hydroperiod class, phase of the flood and conductivity explained 32% and 43% of the variation in diatom and invertebrate taxon richness, respectively. There was a negative relationship between hydroperiod class and invertebrate taxon richness on the rising, peak and receding flood, whereas at low flood there was no significant relationship. Multivariate regression tree analysis revealed hydroperiod class, phase of the flood and conductivity as the dominant forces shaping invertebrate and diatom community composition. 4. Seasonal and spatial variation in hydrological conditions are the principal drivers of variation in aquatic biodiversity in flood-pulsed wetlands. In pristine flood-pulsed wetlands, increased productivity caused by the arrival of the flood waters appears to override disturbance and connectivity in shaping taxon richness and community composition. Thus, these data suggest that the maintenance of a rich mosaic of habitats covering a broad range of hydroperiod is the key to preserving aquatic biodiversity and natural ecosystem function in flood-pulsed wetlands.

The East Asian winter monsoon (EAWM) not only plays an important role within the Asian climate system, but also carries cold air from the high northern latitudes across the Equator to the Southern Hemisphere, acting as a link between the polar and tropical climate systems. However, past changes of the EAWM have not been clearly established so far due to the lack of suitable proxy records. Here, we at first establish an index of the EAWM by comparing the results of a sediment trap experiment and 100year sedimentary record from Huguang Maar Lake (HML) with modern records of the EAWM, Siberian High (SH) and Arctic Oscillation (AO). Secondly, we present a continuous record of the strength of the EAWM for the past 14,500 years based on sedimentary diatom assemblages in HML. The record is derived from fluctuations in the relative abundance of two planktonic diatom species. The link with the EAWM intensity is through high wind speeds inducing turbulent mixing, which stimulates the productivity of the meroplanktonic species Aulacoseira granulata. The diatom record of the past 14,500 years shows that the EAWM shifted from strong to weak from the early to late Holocene. This linked to both changes in winter temperature at high-latitudes and in El Nino conditions in the tropics. Our record shows that the EAWM and East Asian summer monsoon (EASM) as recorded in stalagmites, were in-phase instead of anti-correlated on orbital time scales during the Holocene. On a millennial time scales, the EAWM was anti-phase with the EASM during the Last GlacialeHolocene transition. However, during the early emiddle Holocene the relationship between the EAWM and EASM shows spatial variations. In northern China, the records show significant anti-phase, but in southern China the anti-phase was not observed. During the late Holocene, we did not find any clear relationship between the EAWM and EASM. We also explored the link between the EAWM and the Australian summer monsoon (ASM). Anti-phase of the ASM with summer insolation in the Southern Hemisphere is an enigmatic exception that cannot be explained by the classic theory of insolation. During early Holocene the EAWM was in-phase with the Australian summer monsoon (ASM), which provides the first direct evidence to support the hypothesis that the intensity of the EAWM affected, at least in part, the strength of the ASM.

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.