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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.

A range of future climate scenarios are projected for high atmospheric CO2 concentrations, given uncertainties over future human actions as well as potential environmental and climatic feedbacks. The geological record offers an opportunity to understand climate system response to a range of forcings and feedbacks which operate over multiple temporal and spatial scales. Here, we examine a single interglacial during the late Pliocene (KM5c, ca. 3.205±0.01 Ma) when atmospheric CO2 exceeded pre-industrial concentrations, but were similar to today and to the lowest emission scenarios for this century. As orbital forcing and continental configurations were almost identical to today, we are able to focus on equilibrium climate system response to modern and near-future CO2. Using proxy data from 32 sites, we demonstrate that global mean sea-surface temperatures were warmer than pre-industrial values, by ∼2.3 ∘C for the combined proxy data (foraminifera Mg∕Ca and alkenones), or by ∼3.2–3.4 ∘C (alkenones only). Compared to the pre-industrial period, reduced meridional gradients and enhanced warming in the North Atlantic are consistently reconstructed. There is broad agreement between data and models at the global scale, with regional differences reflecting ocean circulation and/or proxy signals. An uneven distribution of proxy data in time and space does, however, add uncertainty to our anomaly calculations. The reconstructed global mean sea-surface temperature anomaly for KM5c is warmer than all but three of the PlioMIP2 model outputs, and the reconstructed North Atlantic data tend to align with the warmest KM5c model values. Our results demonstrate that even under low-CO2 emission scenarios, surface ocean warming may be expected to exceed model projections and will be accentuated in the higher latitudes.

The high-latitude oceans are key areas of carbon and heat exchange between the atmosphere and the ocean. As such, they are a focus of both modern oceanographic and palaeoclimate research. However, most palaeoclimate proxies that could provide a long-term perspective are based on calcareous organisms, such as foraminifera, that are scarce or entirely absent in deep-sea sediments south of 50∘ S in the Southern Ocean and north of 40∘ N in the North Pacific. As a result, proxies need to be developed for the opal-based organisms (e.g. diatoms) found at these high latitudes, which dominate the biogenic sediments recovered from these regions. Here we present a method for the analysis of the boron (B) content and isotopic composition (δ11B) of diatom opal. We apply it for the first time to evaluate the relationship between seawater pH, δ11B and B concentration ([B]) in the frustules of the diatom Thalassiosira weissflogii, cultured across a range of carbon dioxide partial pressure (pCO2) and pH values. In agreement with existing data, we find that the [B] of the cultured diatom frustules increases with increasing pH (Mejía et al., 2013). δ11B shows a relatively well defined negative trend with increasing pH, completely distinct from any other biomineral previously measured. This relationship not only has implications for the magnitude of the isotopic fractionation that occurs during boron incorporation into opal, but also allows us to explore the potential of the boron-based proxies for palaeo-pH and palaeo-CO2 reconstruction in high-latitude marine sediments that have, up until now, eluded study due to the lack of suitable carbonate material.

Isotopes in diatoms are increasingly used in palaeoenvironmental studies in both lacustrine and marine settings, enabling the reconstruction of a range of variables including temperature, precipitation, salinity, glacial discharge, carbon dynamics and biogeochemical cycling. This protocol details an optimised methodology for extracting diatoms for isotope analysis from sediment samples, using a range of chemical and density separation techniques that minimise sample loss and avoids the need for expensive equipment. Whilst designed for the extraction of diatoms for oxygen, silicon and carbon isotope analysis, additional stages are outlined for the analysis of other isotopes that are of increasing interest to the palaeo community (e.g., boron and zinc). The protocol also includes procedures for assessing sample purity, to ensure that analysed samples produce robust palaeoenvironmental reconstruction. Overall, the method aims to improve the quality of palaeoenvironmental research derived from isotopes in diatoms by maximising sample purity and the efficiency of the extraction process.

Sea-ice is believed to be an important control on climatic changes through the Mid-Pleistocene Transition (MPT; 0.6–1.2 Ma). However, the low resolution/short timescale of existing reconstructions prevents a full evaluation of these dynamics. Here, diatom assemblages from the Bering Sea are used to investigate sea-ice evolution on millennial timescales. We find that sea-ice was primarily controlled by ice-sheet/sea level fluctuations that modulated warm water flow into the Bering Sea. Facilitated by an amplified Walker circulation, sea-ice expansion began at ∼1.05 Ma with a step-increase during the 900 kyr event. Maximal pack ice was simultaneous with glacial maxima, suggesting sea-ice was responding to, rather than modulating ice-sheet dynamics, as proposed by the sea-ice switch hypothesis. Significant pack ice, coupled with Bering Strait closure at 0.9 Ma, indicates that brine rejection played an integral role in the glacial expansion/deglacial collapse of intermediate waters during the MPT, regulating subarctic ocean-atmospheric exchanges of CO2.

The Arctic is rapidly changing, disrupting biogeochemical cycles and the processing, delivery and sedimentation of carbon (C), in linked terrestrial-aquatic systems. In this investigation, we coupled a hydrogeomorphic assessment of catchment soils, sediments and plants with a recent lake sediment sequence to understand the source and quality of organic carbon present in three Arctic upland lake catchments on Disko Island, located just south of the Low-High Arctic transition zone. This varied permafrost landscape has exposed soils with less vegetation cover at higher altitudes, and all lakes received varying extent of glacial meltwater inputs. We provide improved isotope and biomarker source identifications for palaeolimnological studies in high latitude regions, where terrestrial vegetation is at or close to its northerly and altitudinal range limit. The poorly developed catchment soils lead to lake waters with low dissolved organic carbon (DOC) concentrations (≤ 1.5 mg L−1). Sedimentary Carbon / Nitrogen (C / N) ratios, the C isotope composition of organic matter (δ13Corg) and biomarker ratios (n-alkanes, n-alkanols, n-alkanoic acids and sterols) showed that sedimentary organic matter (OM) in these lakes is mostly derived from aquatic sources (algae and macrophytes). We used a 210 Pb dated sediment core to determine how carbon cycling in a lake-catchment system (Disko 2) had changed over recent centuries. Recent warming since the end of the Little Ice Age (LIA ~1860 AD), which accelerated after ca. 1950, led to melt of glacier ice and permafrost releasing nutrients and DOC to the lake, stimulating pronounced aquatic algal production, as shown by a > 10 fold increase in β-carotene, indicative of a major regime shift. Our findings highlight that in Arctic lakes with sparsely developed catchment vegetation and soils, recent Anthropocene warming results in pronounced changes to in-lake C processing and the deposition of more reactive, predominately autochthonous C, compared with extensively vegetated low Arctic systems.

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.

A range of future climate scenarios are projected for high atmospheric CO2 concentrations, given uncertainties over future human actions as well as potential environmental and climatic feedbacks. The geological record offers an opportunity to understand climate system response to a range of forcings and feedbacks which operate over multiple temporal and spatial scales. Here, we examine a single interglacial during the late Pliocene (KM5c, ca. 3.205 +/- 0.01 Ma) when atmospheric CO2 concentrations were higher than pre-industrial, but similar to today and to the lowest emission scenarios for this century. As orbital forcing and continental configurations were almost identical to today, we are able to focus on equilibrium climate system response to modern and near-future CO2. Using proxy data from 32 sites, we demonstrate that global mean sea-surface temperatures were warmer than pre-industrial, by ~2.3 ºC for the combined proxy data (foraminifera Mg/Ca and alkenones), or by ~3.2ºC (alkenones only). Compared to the pre-industrial, reduced meridional gradients and enhanced warming in the North Atlantic are consistently reconstructed. There is broad agreement between data and models at the global scale, with regional differences reflecting ocean circulation and/or proxy signals. An uneven distribution of proxy data in time and space does, however, add uncertainty to our anomaly calculations. The reconstructed global mean sea-surface temperature anomaly for KM5c is warmer than all but three of the PlioMIP2 model outputs, and the reconstructed North Atlantic data tend to align with the warmest KM5c model values. Our results demonstrate that even under low CO2 emission scenarios, surface ocean warming may be expected to exceed model projections, and will be accentuated in the higher latitudes.

A range of future climate scenarios are projected for high atmospheric CO2 concentrations, given uncertainties over future human actions as well as potential environmental and climatic feedbacks. The geological record offers an opportunity to understand climate system response to a range of forcings and feedbacks which operate over multiple temporal and spatial scales. Here, we examine a single interglacial during the late Pliocene (KM5c, ca. 3.205 &pm; 0.01 Ma) when atmospheric CO2 concentrations were higher than pre-industrial, but similar to today and to the lowest emission scenarios for this century. As orbital forcing and continental configurations were almost identical to today, we are able to focus on equilibrium climate system response to modern and near-future CO2. Using proxy data from 32 sites, we demonstrate that global mean sea-surface temperatures were warmer than pre-industrial, by ~ 2.3 ºC for the combined proxy data (foraminifera Mg/Ca and alkenones), or by ~ 3.2 ºC (alkenones only). Compared to the pre-industrial, reduced meridional gradients and enhanced warming in the North Atlantic are consistently reconstructed. There is broad agreement between data and models at the global scale, with regional differences reflecting ocean circulation and/or proxy signals. An uneven distribution of proxy data in time and space does, however, add uncertainty to our anomaly calculations. The reconstructed global mean sea-surface temperature anomaly for KM5c is warmer than all but three of the PlioMIP2 model outputs, and the reconstructed North Atlantic data tend to align with the warmest KM5c model values. Our results demonstrate that even under low CO2 emission scenarios, surface ocean warming may be expected to exceed model projections, and will be accentuated in the higher latitudes.

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

The development of large ice-sheets across the Northern Hemisphere during the late Pliocene and the emergence of the glacial-interglacial cycles that punctuate the Quaternary mark a significant threshold in Earth's climate history. Although a number of different mechanisms have been proposed to initiate this cooling and the onset of major Northern Hemisphere glaciation, reductions in atmospheric concentrations of CO2 likely played a key role. The emergence of a stratified (halocline) water column in the subarctic north-west Pacific Ocean at 2.73 Ma has often been interpreted as an event which would have limited oceanic ventilation of CO2 to the atmosphere, thereby helping to cool the global climate system. Here, diatom carbon isotopes (?13Cdiatom) are used to reconstruct changes in regional carbon dynamics through this interval. Results show that the development of a salinity stratification did not fundamental alter the net oceanic/atmospheric flux of CO2 in the subarctic north-west Pacific Ocean through the late Pliocene/early Quaternary. These results provide further insights into the long-term controls on global carbon cycling and the role of the subarctic Pacific Ocean in instigating global climatic changes.

It is widely held that benthic foraminifera exhibit species-specific calcification depth preferences, with their tests recording sediment pore water chemistry at that depth (i.e. stable isotope and trace metal compositions). This assumed depth-habitat-specific pore water chemistry relationship has been used to reconstruct various palaeoenvironmental parameters, such as bottom water oxygenation. However, many deep-water foraminiferal studies show wide intra-species variation in sediment living depth but relatively narrow intra-species variation in stable isotope composition. To investigate this depth-habitat–stable-isotope relationship on the shelf, we analysed depth distribution and stable isotopes of living (Rose Bengal stained) benthic foraminifera from two box cores collected on the South Georgia shelf (ranging from 250 to 300 m water depth). We provide a comprehensive taxonomic analysis of the benthic fauna, comprising 79 taxonomic groupings. The fauna shows close affinities with shelf assemblages from around Antarctica. We find live specimens of a number of calcareous species from a range of depths in the sediment column. Stable isotope ratios (δ13C and δ18O) were measured on stained specimens of three species, Astrononion echolsi, Cassidulinoides porrectus, and Buccella sp. 1, at 1 cm depth intervals within the downcore sediment sequences. In agreement with studies in deep-water settings, we find no significant intra-species variability in either δ13Cforam or δ18Oforam with sediment living depth on the South Georgia shelf. Our findings add to the growing evidence that infaunal benthic foraminiferal species calcify at a fixed depth. Given the wide range of depths at which we find living, infaunal species, we speculate that they may actually calcify predominantly at the sediment–seawater interface, where carbonate ion concentration and organic carbon availability is at a maximum.

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.

High latitude deep water upwelling has the potential to control global climate over glacial timescales through the biological pump and ocean-atmosphere CO2 exchange. However, there is currently a lack of continuous long nutrient upwelling records with which to assess this mechanism. Here we present geochemical proxy records for nutrient upwelling and glacial North Pacific Intermediate Water (GNPIW) formation in the Bering Sea over the past 850 kyr, which demonstrates that glacial periods were characterised by reduced nutrient upwelling, when global atmospheric CO2 and temperature were also lowered. We suggest that glacial expansion of sea ice in the Bering Sea, and the simultaneous expansion of low nutrient GNPIW, inhibited vertical mixing and nutrient supply across the subarctic Pacific Ocean. Our findings lend support to the suggestion that high latitude sea ice and the resultant intermediate water formation, modulated deep water upwelling and ocean-atmosphere CO2 exchange on glacial-interglacial timescales.

The high latitude oceans are key areas of carbon and heat exchange between the atmosphere and the ocean. As such, they are a focus of both modern oceanographic and palaeoclimate research. However, most palaeoclimate proxies that could provide a long-term perspective are based on calcareous organisms, such as foraminifera, that are scarce or entirely absent in deep-sea sediments south of 50° latitude in the Southern Ocean and north of 40° in the North Pacific. As a result, proxies need to be developed for the opal-based organisms (e.g. diatoms) that are found at these high latitudes, and which dominate the biogenic sediments that are recovered from these regions. Here we present a method for the analysis of the boron (B) content and isotopic composition (δ11B) of diatom opal. We also apply it for the first time to evaluate the relationship between seawater pH and δ11B and B concentration ([B]) in the frustules of the diatom Thalassiosira weissflogii, cultured at a range of pCO2/pH. In agreement with existing data, we find that the [B] of the cultured diatom frustules increases with increasing pH (Mejia et al., 2013). δ11B shows a relatively well-defined negative trend with increasing pH; a completely distinct relationship from any other biomineral previously measured. This relationship not only has implications for the magnitude of the isotopic fractionation that occurs during boron incorporation into opal, but also allows us to explore the potential of the boron-based proxies for palaeo-pH and palaeo-CO2 reconstruction in high latitude marine sediments that have, up until now, eluded study due to the lack of suitable carbonate material.

The progress of science is tied to the standardization of measurements, instruments, and data. This is especially true in the Big Data age, where analyzing large data volumes critically hinges on the data being standardized. Accordingly, the lack of community-sanctioned data standards in paleoclimatology has largely precluded the benefits of Big Data advances in the field. Building upon recent efforts to standardize the format and terminology of paleoclimate data, this article describes the Paleoclimate Community reporTing Standard (PaCTS), a crowdsourced reporting standard for such data. PaCTS captures which information should be included when reporting paleoclimate data, with the goal of maximizing the reuse value of paleoclimate data sets, particularly for synthesis work and comparison to climate model simulations. Initiated by the LinkedEarth project, the process to elicit a reporting standard involved an international workshop in 2016, various forms of digital community engagement over the next few years, and grassroots working groups. Participants in this process identified important properties across paleoclimate archives, in addition to the reporting of uncertainties and chronologies; they also identified archive-specific properties and distinguished reporting standards for new versus legacy data sets. This work shows that at least 135 respondents overwhelmingly support a drastic increase in the amount of metadata accompanying paleoclimate data sets. Since such goals are at odds with present practices, we discuss a transparent path toward implementing or revising these recommendations in the near future, using both bottom-up and top-down approaches. ©2019. American Geophysical Union. All Rights Reserved., Code and data to reproduce the figures of this article are available on GitHub and released on Zenodo (doi:10.5281/zenodo.3165019). Definition of properties and recommendations are summarized here: http://wiki.linked.earth/PaCTS_v1.0 . This work was supported by the National Science Foundation through the EarthCube Program with Grant ICER‐1541029. Feedback solicitation on the standard was facilitated by the Past Global Changes (PAGES) organization. The 2016 workshop on Paleoclimate Data Standards was hosted by the World Data Service for Paleoclimatology (WDS/NOAA‐Paleo), and the participation of international attendees was made possible by a PAGES travel grant. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

The Bering Sea is one of the most biologically productive regions in the marine system and plays a key role in regulating the flow of waters to the Arctic Ocean and into the subarctic North Pacific Ocean. Cores from IODP Expedition 323 to the Bering Sea provide the first opportunity to obtain reconstructions from the region that extend back to the Pliocene. Previous research at Bowers Ridge, south Bering Sea, has revealed stable levels of siliceous productivity over the onset of major Northern Hemisphere Glaciation (NHG) (c. 2.85-2.73 Ma). However, diatom silica isotope records of oxygen (δ18Odiatom) and silicon (δ30Sidiatom) presented here demonstrate that this interval was associated with a progressive increase in the supply of silicic acid to the region, superimposed on shift to a more dynamic environment characterized by colder temperatures and increased sea ice. This concluded at 2.58 Ma with a sharp increase in diatom productivity, further increases in photic zone nutrient availability and a permanent shift to colder sea surface conditions. These transitions are suggested to reflect a gradually more intense nutrient leakage from the subarctic northwest Pacific Ocean, with increases in productivity further aided by increased sea-ice and wind-driven mixing in the Bering Sea. In suggesting a linkage in biogeochemical cycling between the south Bering Sea and subarctic Northwest Pacific Ocean, mainly via the Kamchatka Strait, this work highlights the need to consider the inter-connectivity of these two systems when future reconstructions are carried out in the region.

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

Understanding the response of the climate to abrupt changes in the Earth system represents a key objective in paleoclimatology. Heinrich events in the last glacial, during which significant amounts of glacial discharge entered the North Atlantic Ocean, triggered the development of colder conditions across much of the globe. Despite widespread documentation of these events, including their occurrence and global significance, the impact of Heinrich events on the North American Cordilleran Ice Sheet and subarctic North Pacific Ocean remains relatively unconstrained. Here, records of diatom oxygen isotopes are used to show that significant amounts of glacial discharge from the Cordilleran Ice Sheet were released into the open waters of the northeast Pacific Ocean throughout the last glacial. Based on the available age model, many of these episodes and calculated changes in sea surface salinity coincide with Heinrich events. If accurate, these findings would confirm that ocean-atmospheric teleconnections linked the North Atlantic and North Pacific Oceans during intervals of abrupt change in the last glacial, as well as indicating the wider susceptibility of regional ice-sheets to global alterations in the climate system.

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).

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 stable isotope composition of benthic sponge spicule silica is a potential source of palaeoceanographic information about past deep seawater chemistry. The silicon isotope composition of spicules has been shown to relate to the silicic acid concentration of ambient water, although existing calibrations do exhibit a degree of scatter in the relationship. Less is known about how the oxygen isotope composition of sponge spicule silica relates to environmental conditions during growth. Here, we investigate the vital effects on silica, silicon and oxygen isotope composition in a carnivorous sponge, Asbestopluma sp., from the Southern Ocean. We find significant variations in silicon and oxygen isotopic composition within the specimen that are related to unusual spicule silicification. The largest variation in both isotope systems was associated with the differential distribution of an unconventional, hypersilicified spicule type (desma) along the sponge body. The absence an internal canal in the desmas suggests an unconventional silicification pattern leading to an unusually heavy isotope signature. Additional internal variability derives from a systematic offset between the peripheral skeleton of the body having systematically a higher isotopic composition than the internal skeleton. A simplified silicon isotope fractionation model, in which desmas were excluded, suggests that the lack of a system for seawater pumping in carnivorous sponges favours a low replenishment of dissolved silicon within the internal tissues, causing kinetic fractionation during silicification that impacts the isotope signature of the internal skeleton. Analysis of multiple spicules should be carried out to "average out" any artefacts in order to produce more robust downcore measurements.

In comparison to other sectors of the marine system, the palaeoceanography of the subarctic North Pacific Ocean is poorly constrained. New diatom isotope records of δ13C, δ18O, δ30Si (δ13Cdiatom, δ18Odiatom, and δ30Sidiatom) are presented alongside existing geochemical and isotope records to document changes in photic zone conditions, including nutrient supply and the efficiency of the soft-tissue biological pump, between Marine Isotope Stage (MIS) 4 and MIS 5e. Peaks in opal productivity in MIS 5b/c and MIS 5e are both associated with the breakdown of the regional halocline stratification and increased nutrient supply to the photic zone. Whereas the MIS 5e peak is associated with low rates of nutrient utilisation, the MIS 5b/c peak is associated with significantly higher rates of nutrient utilisation. Both peaks, together with other smaller increases in productivity in MIS 4 and 5a, culminate with a significant increase in freshwater input which strengthens/re-establishes the halocline and limits further upwelling of sub-surface waters to the photic zone. Whilst δ30Sidiatom and previously published records of diatom δ15N (δ15Ndiatom) (Brunelle et al., 2007, 2010) show similar trends until the latter half of MIS 5a, the records become anti-correlated after this juncture and into MIS 4, suggesting a possible change in photic zone state such as may occur with a shift to iron or silicon limitation.

The impact of climatic change along the Antarctica Peninsula has been widely debated in light of atmospheric/oceanic warming and increases in glacial melt over the past half century. Particular concern exists over the impact of these changes on marine ecosystems, not only on primary producers but also on higher trophic levels. Here we present a record detailing of the historical controls on the biogeochemical cycling of silicic acid [Si(OH)4] on the west Antarctica Peninsula margin, a region in which the modern phytoplankton environment is constrained by seasonal sea ice. We demonstrate that Si(OH)4 cycling through the Holocene alternates between being primarily regulated by sea ice or glacial discharge from the surrounding grounded ice sheet. With further climate-driven change and melting forecast for the twenty-first century, our findings document the potential for biogeochemical cycling and multi-trophic interactions along the peninsula to be increasingly regulated by glacial discharge, altering food-web interactions., Sea-ice plays a key role in regulating nutrient dynamics and primary productivity along the Antarctica Peninsula margin. Here, the authors show that over the last 13 kyr nutrient dynamics have also been regulated by glacial discharge, highlighting the potential for future changes as glaciers continue to melt.

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

Carbonates and diatoms are rarely deposited together in lake sediments in sufficient quantities for the oxygen isotope composition (δ18O) to be investigated simultaneously from both hosts. Here, δ18Ocarbonate are compared to δ18Odiatom data from the varved sediments of Nar Gölü, a closed lake in central Turkey, over the last 1710 years. Lake monitoring suggests carbonate is probably precipitated during May–June and δ18Ocarbonate is a proxy for regional water balance. Diatom activity is mainly weighted towards the spring. At times between ∼301 and 561 AD, while δ18Ocarbonate values are the highest for the entire 1710 year period, suggesting summer drought, δ18Ocorrected-diatom values are among the lowest. δ18Olakewater values estimated for the times of diatom growth and carbonate precipitation show large differences. We suggest this could be explained by increased snowmelt that formed a freshwater lid on the lake at the time of peak diatom growth. Increased snowmelt is also inferred ∼561–801 AD. From 801 AD to the present, precipitation is less winter-dominated, although increased snowmelt is inferred 921–1071 AD and in the latter part of the Little Ice Age (i.e. the mid to late 1800s AD). By combining oxygen isotope data from hosts that form in lakes at different times of the year, we show that such analyses can provide insights into palaeo-seasonality.

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.

Understanding the response of the Antarctic ice sheets during the rapid climatic change that accompanied the last deglaciation has implications for establishing the susceptibility of these regions to future 21st Century warming. A unique diatom δ18O record derived from a high-resolution deglacial seasonally laminated core section off the west Antarctic Peninsula (WAP) is presented here. By extracting and analysing single species samples from individual laminae, season-specific isotope records were separately generated to show changes in glacial discharge to the coastal margin during spring and summer months. As well as documenting significant intra-annual seasonal variability during the deglaciation, with increased discharge occurring in summer relative to spring, further intra-seasonal variations are apparent between individual taxa linked to the environment that individual diatom species live in. Whilst deglacial δ18O are typically lower than those for the Holocene, indicating glacial discharge to the core site peaked at this time, inter-annual and inter-seasonal alternations in excess of 3‰ suggest significant variability in the magnitude of these inputs. These deglacial variations in glacial discharge are considerably greater than those seen in the modern day water column and would have altered both the supply of oceanic warmth to the WAP as well as regional marine/atmospheric interactions. In constraining changes in glacial discharge over the last deglaciation, the records provide a future framework for investigating links between annually resolved records of glacial dynamics and ocean/climate variability along the WAP.

Silicon isotope geochemistry is a relatively new branch of environmental change research. Here we review the recent developments in the preparation of materials, analytical methods and applications of stable silicon isotope geochemistry in the most common types of biogenic silica currently being analysed. These materials are: diatom, radiolarian and siliceous sponges in lake and ocean sediments and plant phytoliths which are preserved in soils. Despite analyses of Si isotopes being carried out on rocks and minerals since the 1950's and the increasingly widespread use of Si isotopes since the 1990's, to date only a relatively small number of studies have applied Si isotope ratios to environmental change. In lake and ocean sediments the analysis of Si isotope ratios from biogenic materials has the potential to provide an important source of palaeoenvironmental information, especially where carbonates are not preserved. In plants and soils few studies have used Si isotopes, but important advances have recently been made in the understanding within plant fractionations. These may be useful in the application of Si isotopes in phytoliths to archaeological and palaeoenvironmental contexts. © 2009 Springer Science and Business Media BV.

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.

A method is described for the purification and extraction of diatom samples for isotope and geochemical analysis. The technique involves a micro-manipulator attached to an inverted microscope with a cellular micro-injector system used to remove contaminants or separate assemblages into single-species samples. Whilst time consuming, the advances associated with this technique, eliminating issues related to contamination and the impact of species-dependent fractionation factor/isotopic effect, allows ultra-clean as well as species and/or size specific diatom samples to be analysed in palaeoenvironmental research down to seasonal timescale resolution. By further altering the inner dimensions of the commercially available capillary tubes, (3.5–150 \(\upmu \)m) this technique can be extended for use with other microfossils including radiolaria (30 \(\upmu \)m to 1 mm), pollen (6–100 \(\upmu \)m) and phytolith samples (1–200 \(\upmu \)m).

The Last Interglacial (LIG), corresponding to Marine Isotope Stage (MIS) 5e, provides a reference of interglacial climate variability in the absence of anthropogenic forcing. Using an expanded section of the LIG gained at Integrated Ocean Drilling Program Site U1304 in the Subarctic Atlantic, we demonstrate that the early MIS 5e was marked by oceanographic conditions conducive for high diatom production and accumulation. The appearance of diatom-dominated laminated oozes ∼3 k.y. after the beginning of MIS 5e at ca. 125 ka coincides with a shift to higher δ 30 Si diat values together with the dominance of Thalassiothrix longissima , indicative of increased nutrient availability and silicic acid utilization in surface waters. Though the Subarctic Front provided the physical conditions for high diatom production and deposition, these processes alone are insufficient to explain the high rates of siliceous productivity and the formation of diatomaceous sediments. Instead, the additional presence of an increased nutrient pool provided by Subantarctic Mode Water played the decisive role in initiating and sustaining diatom production. The high diatom productivity and the occurrence of diatomaceous sediments in the late Quaternary challenge the current hypothesis of a silica-depleted North Atlantic during the LIG.

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.

Increases in the low-field mass-specific magnetic susceptibility (χ), dropstones and the terrigenous sediment component from Ocean Drilling Program (ODP) Site 882 (~ 45°N) have been interpreted to indicate a major onset of ice-rafting to the sub-Arctic northwest Pacific Ocean during marine isotope stage (MIS) G6 (from ~ 2.75 Ma). In contrast, studies of the terrigenous content of sediments cored downwind of ODP Site 882 indicate that dust and disseminated volcanic ash deposition in the sub-Arctic Pacific increased markedly during MIS G6. To investigate the relative contribution of dust, volcanic ash and ice rafting to the Pliocene χ increase, we present new high-resolution environmental magnetic and ice-rafted debris records from ODP Sites 882 and 885. Our results demonstrate that the χ increase at both sites across MIS G6 is predominantly controlled by a previously overlooked mixture of aeolian dust and volcanic ash. Our findings call into question the reliability of χ as a proxy for ice-rafting to the North Pacific. They also highlight a previously undocumented link between iron fertilisation and biogeochemical cycling in the North Pacific at a key stage during intensification of late Pliocene northern hemisphere glaciation.

Existing techniques for measuring sediment Biogenic Silica (BSi) concentrations rely largely on conventional (Si-only) wet-alkaline digestion methods. Although results have provided detailed palaeoenvironmental information, potential errors can arise in accounting for sources of non-BSi. Here, I compare a conventional Si-only method to a Si/Al wet-alkaline digestion method, which in theory provides a more robust correction for concentrations of non-BSi. Late glacial/Holocene-aged sediment from Lake Baikal, Russia was used for the comparison. Results showed no significant difference between the two techniques, indicating that existing Si-only BSi methods are suitable for reconstructing environmental changes when levels of digested non-BSi are low to moderate.

Current studies which use the oxygen isotope composition from diatom silica (δ(18) Odiatom ) as a palaeoclimate proxy assume that the δ(18) Odiatom 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 δ(18) Odiatom values and potential misinterpretation of the palaeoclimate record are evaluated.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 δ(18) O values using step-wise fluorination and isotope ratio mass spectrometry.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 δ(18) Odiatom value was, however, lower after dissolution, but in only half the samples was this reduction outside the analytical error (2σ analytical error = 0.46‰).We have shown that dissolution can have a small negative impact on δ(18) Odiatom 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 δ(18) Odiatom values, especially when interpreting variations in these values of1‰.

Measurement of magnetic susceptibility (MS) and diffuse reflectance spectra (DRS) were used to construct environmental proxies in a 6.5 m section of the sediment core VER98-1-13 from the Academician Ridge, Lake Baikal. The interpretation of MS and DRS was supported by X-ray diffraction and microparticle voltammetry to identify the main Fe-bearing minerals. The record of the relative paleointensity of the Earth’s magnetic field was used to construct an age model showing the core interval covers the last 160 ky. The time resolution of the record was ~1 ky. The main environmental changes were recognized by a combination of DRS and MS records and compared to marine isotopic stages in addition to the diatom record from 120 to 60 ky BP so as to demonstrate the importance of these inorganic proxies as paleoenvironmental records. A dramatic climatic deterioration between 66 and 60 ky BP was probably preceded by a dry intermediate stage between 77 and 66 ky BP. The DRS-based proxies of Fe(II)/Fe(III) ratios in the mineral assemblage, MS and/or diatom records clearly reveal 1‐2 ky long environmental extremes at 110, 103, 90, 85, 77, 61, 54, 36, 27, 23, and 19 ky BP. The majority of these extremes were contemporaneous with discharges of North Atlantic and Arctic Ocean icebergs (Heinrich events) documenting a teleconnection between the North Atlantic Ocean and East Central Siberia. These sharp changes coincided with a major transition to the colder climatic stages of the last 100 ky. D 2006 Published by Elsevier B.V.

Oxygen isotope analyses of different size fractions of Pliocene diatoms (δ18Odiatom) from the Bering Sea show no evidence of an isotope offset and support the use of bulk diatom species samples for palaeoceanographic reconstructions. Additional samples containing concentrations of sponge spicules produce δ18O values several per mille (‰) lower than δ18Odiatom with a calculated mean offset of 3.9‰ ± 1.5. This difference is significantly greater than modern-day variations in water δ18O through the regional water column. Despite the potential for oxygen isotope disequilibrium within δ18Osponge, there appears to be some similarity between δ18Osponge and a global stacked benthic δ18Oforam record. This highlights the potential for δ18Osponge in palaeoenvironmental research at sites where carbonates are not readily preserved.

The causes for rising temperatures along the Antarctic Peninsula during the late Holocene have been debated, particularly in light of instrumental records of warming over the past decades1. Suggested mechanisms range from upwelling of warm deep waters onto the continental shelf in response to variations in the westerly winds2, to an influence of El Nino–Southern Oscillation on sea surface temperatures3. Here, we present a record of Holocene glacial ice discharge, derived from the oxygen isotope composition of marine diatoms from Palmer Deep along the west Antarctic Peninsula continental margin. We assess atmospheric versus oceanic influences on glacial discharge at this location, using analyses of diatom geochemistry to reconstruct atmospherically forced glacial ice discharge and diatom assemblage4 ecology to investigate the oceanic environment. We show that two processes of atmospheric forcing—an increasing occurrence of La Nina events5 and rising levels of summer insolation—had a stronger influence during the late Holocene than oceanic processes driven by southern westerly winds and upwelling of upper Circumpolar Deepwater. Given that the evolution of El Nino–Southern Oscillation under global warming is uncertain6, its future impacts on the climatically sensitive system of the Antarctic Peninsula Ice Sheet remain to be established.

In 2003 sediment core Lz1024 was drilled at Lake El'gygytgyn, far east Russian Arctic, in an area of the Northern Hemisphere which has not been glaciated for the last 3.6 Ma. Biogenic silica was used for analysing the oxygen isotope composition (δ18Odiatom) in the upper 13 m long section dating back about 250 ka with samples dominated by one taxa in the Cyclotella ocellata). Downcore variations in δ18O values show that glacial-interglacial cycles are present throughout the core and δ18Odiatom-values are mainly controlled by δ18Oprecipitation. Changes reflect the Holocene Thermal Maximum, the Last Glacial Maximum (LGM) and the interglacial periods corresponding to MIS 5.5 and MIS 7 with a peak-to-peak amplitude between LGM and MIS 5.5 of Δ18O = 5.3‰. This corresponds to a mean annual air temperature difference of about 9 °C. Our record is the first continuous δ18Odiatom record from an Arctic lake sediment core directly responding to precipitation and dating back more than 250 ka and correlates well with the stacked marine δ18O LR04 (r = 0.58) and δD EPICA Dome-C record (r = 0.69). With δ18O results indicating strong links to both marine and ice-core records, records from Lake El'gygytgyn can be used to further investigate the sensitivity of the Arctic climate to both past and future global climatic changes.

The development of a rapid and non-destructive method to assess levels of purity in samples of biogenic silica prior to geochemical/isotope analysis remains a key objective in improving both the quality and use of such data in environmental and palaeoclimatic research. Here a Fourier Transform Infrared Spectroscopy (FTIR) mass-balance method is demonstrated for calculating levels of contamination in cleaned sediment core diatom samples from Lake Baikal Russia. Following the selection of end-members representative of diatoms and contaminants in the analysed samples, a mass-balance model is generated to simulate the expected FTIR spectra for a given level of contamination. By fitting the sample FTIR spectra to the modelled FTIR spectra and calculating the Euclidean distance, the optimum “best-fit” model and level of contamination is obtained. When compared to X-ray Fluorescence (XRF), FTIR method results portray the main changes in sample contamination through the core sequence, permitting its use in instances where other, destructive, techniques are not appropriate. The ability to analyses samples of