Ecosystem Responses to Abrupt Climatic and Environmental Change in Southern Siberia during the Late Quaternary

The Late Quaternary documents climatic changes over a number of timescales. These are well studied in many regions, including Northern Europe, but much less so in some critical areas. One such region is continental southern Siberia, which is highly sensitive to modern climate changes. Palaeoenvironmental reconstructions are essential to provide context for these changes, and to examine regional sensitivity to climate forcing, however studies in Siberia are limited and good records of the last 30 ka BP, an important period for studying climatic changes, are rare. This thesis reconstructs the palaeoenvironment of Lake Baunt (55°11’15” N, 113°01’45” E), a site situated at the southern limits of Siberian permafrost, over the Late Quaternary (~30-6 ka BP). The reconstruction is based on a high-resolution diatom study from a record with excellent preservation, combined with organic geochemistry, and 18Odiatom/ 13Cdiatom, for the LGIT and Early Holocene, and supporting data, integrated through Bayesian age modelling. Baunt records the LGM, Heinrich events 1 and 2, the Lateglacial Interstadial, Younger Dryas, and Holocene fluctuations, shown through changes in ecosystem productivity, carbon cycling and hydrology. This highlights Baunt’s sensitivity to extrinsic climate forcing. Internal forcing’s have also been important factors, with local glacier melt influencing the record. Comparisons to regional and key Northern Hemisphere sites, along with climate models, has added to the understanding of the expression of these events in Southern Siberia. In particular, this work has shown that there is a complex response to Heinrich events, and also confirms suggestions of a link between AMOC and Siberian climate in the Early Holocene. This work highlights the sensitivity of southern Siberia to past climatic forcing and shows the need for more work in both this lake, and other sites within the region, to further understanding of how palaeoclimatic change influences regions remote from oceanic influences

Disentangling the environmental signals recorded in Holocene calcite varves based on modern lake observations and annual sedimentary processes in Diss Mere, England

© 2023, The Author(s), under exclusive licence to Springer Nature B.V. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1007/s10933-023-00282-zDiss Mere is a small natural lake located in the centre of the town Diss in Norfolk (England). The lake, which has been exposed to different stressors including climate variability and changing land use, has significant recreational, historical and environmental value. The Diss Mere sediments are annually-laminated for most of the Holocene (2.1–10.3 ka BP), which allows the study of the lake evolution and its response to changing environmental conditions at an exceptionally high resolution. As with many mid-latitude, alkaline lakes, Diss Mere’s sediments are formed of biogenic-calcite varves. We have conducted a 3.5-year lake-monitoring survey including sediment trapping to identify the main drivers and seasonal processes contributing to lake sedimentation. Our results demonstrate that the modern lake is still producing seasonally-differentiated sediments today, however, are unable to be preserved as varves due to the permanent oxygenation of the lake bottom through gradual lake shallowing. Seasonal sediment fluxes follow a general pattern of (i) an early spring-diatom bloom; (ii) spring precipitation of medium-coarse calcite grains; (iii) summer precipitation of smaller endogenic calcite grains; and (iv) an autumn algal bloom and endogenic calcite precipitation intermixed with benthic diatoms and micrite. Whilst calcite precipitates throughout the whole year, peaks are observed in the epilimnion during the summer. This study shows that a modern analogue approach can be applied to the varves revealing their potential for environmental and climate reconstruction and highlights the significance of monitoring surveys for modern analogue approaches to palaeolimnological research.Peer reviewe

Middle Pleistocene environments, landscapes and tephrostratigraphy of the Armenian Highlands: evidence from Bird Farm 1, Hrazdan Valley

The significance of the southern Caucasus in understanding Pleistocene hominin expansions is well established. However, the palaeoenvironments in which Palaeolithic occupation of the region took place are presently poorly defined. The Hrazdan river valley, Armenian Highlands, contains a rich Palaeolithic record alongside Middle Pleistocene volcanic, fluvial and lacustrine strata, and thus offer exciting potential for palaeoenvironmental reconstruction. We present the first results of sedimentological, geochemical, tephrostratigraphical and biological (diatoms) study of the sequence of Bird Farm 1, located in the central part of the valley. These data show six phases of landscape development during the interval 440–200 ka. The sequence represents the first quantitative Pleistocene diatom record from the Armenian Highlands and the southern Caucasus, and indicates the persistence of a deep, stratified lacustrine system, with evidence for changing lake productivity that is tentatively linked to climate. Furthermore, major element chemical characterization of visible and crypto-tephra horizons in the sequence enables the first stages of the development of a regional tephrostratigraphy. Together, the evidence from Bird Farm 1 demonstrates the importance of lacustrine archives in the region for palaeoenvironmental reconstruction and highlights the potential for linkages between archives on both a local and regional scale

Wind regime changes in the Euro-Atlantic region driven by Late-Holocene Grand Solar Minima

Understanding atmospheric response to radiative forcing, including the intensity and distribution of wind patterns is critical as this might have important implications in the coming decades. Long-term episodes of reduced solar activity (i.e. Grand Solar Minima, GSM) have triggered rapid climate change in the past, recorded in proxy-based records, including varved sediments from Meerfelder Maar, Germany, where the Homeric GSM (~2800 years ago) was studied. This study reconstructs windy conditions during the same GSM from Diss Mere, another varved record in England, to support the solar-wind linkage in the North Atlantic-European region. We use diatoms as proxies for windiness and support the palaeolimnological and palaeoclimate interpretation with a multi-proxy chironomids and pollen) evidence. The diatom assemblage documents a shift from Pantocsekiella ocellata dominance to Stephanodiscus parvus and Lindavia comta, indicating a shift to more turbulent waters from ~2767 ± 28, linked to increased windiness. This shift is synchronous with changes in 14C production, linked to solar activity changes during the GSM. Both proxy records reflect a rapid and synchronous atmospheric response (i.e. stronger winds) at the onset and during the GSM in the North Atlantic and continental Europe. In order to test whether this solar-wind linkage is consistent during other GSMs and to understand the underlying climate dynamics, we analyse the wind response to solar forcing at the two study sites during the Little Ice Age, a period that includes several GSMs. For this, we have used a reconstruction based on a 1200-year-long simulation with an isotope-enabled climate model. Our study suggests that wind anomalies in the North Atlantic-European sector may relate to an anomalous atmospheric circulation in response to long-term solar forcing leading to north-easterlies modulated by the East Atlantic pattern

Wind regime changes in the Euro-Atlantic region driven by late-Holocene Grand Solar Minima

© 2022 Springer Nature Switzerland AG. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1007/s00382-022-06388-wUnderstanding atmospheric response to radiative forcing, including the intensity and distribution of wind patterns is critical as this might have important implications in the coming decades. Long-term episodes of reduced solar activity (i.e. Grand Solar Minima, GSM) have triggered rapid climate change in the past, recorded in proxy-based records, including varved sediments from Meerfelder Maar, Germany, where the Homeric GSM (~ 2800 years ago) was studied. This study reconstructs windy conditions during the same GSM from Diss Mere, another varved record in England, to support the solar-wind linkage in the North Atlantic-European region. We use diatoms as proxies for windiness and support the palaeolimnological and palaeoclimate interpretation with a multi-proxy approach, including sedimentological, geochemical, and biological (chironomids and pollen) evidence. The diatom assemblage documents a shift from Pantocsekiella ocellata dominance to Stephanodiscus parvus and Lindavia comta, indicating a shift to more turbulent waters from ~ 2767 ± 28, linked to increased windiness. This shift is synchronous with changes in 14C production, linked to solar activity changes during the GSM. Both proxy records reflect a rapid and synchronous atmospheric response (i.e. stronger winds) at the onset and during the GSM in the North Atlantic and continental Europe. In order to test whether this solar-wind linkage is consistent during other GSMs and to understand the underlying climate dynamics, we analyse the wind response to solar forcing at the two study sites during the Little Ice Age, a period that includes several GSMs. For this, we have used a reconstruction based on a 1200-year-long simulation with an isotope-enabled climate model. Our study suggests that wind anomalies in the North Atlantic-European sector may relate to an anomalous atmospheric circulation in response to long-term solar forcing leading to north-easterlies modulated by the East Atlantic pattern.Peer reviewe

Tephrochronology and the extended intimate (integration of ice-core, marine and terrestrial records) event stratigraphy 8–128 ka b2k

The comparison of palaeoclimate records on their own independent timescales is central to the work of the INTIMATE (INTegrating Ice core, MArine and TErrestrial records) network. For the North Atlantic region, an event stratigraphy has been established from the high-precision Greenland ice-core records and the integrated GICC05 chronology. This stratotype provides a palaeoclimate signal to which the timing and nature of palaeoenvironmental change recorded in marine and terrestrial archives can be compared. To facilitate this wider comparison, without assuming synchroneity of climatic change/proxy response, INTIMATE has also focussed on the development of tools to achieve this. In particular the use of time-parallel marker horizons e.g. tephra layers (volcanic ash). Coupled with the recent temporal extension of the Greenland stratotype, as part of this special issue, we present an updated INTIMATE event stratigraphy highlighting key tephra horizons used for correlation across Europe and the North Atlantic. We discuss the advantages of such an approach, and the key challenges for the further integration of terrestrial palaeoenvironmental records with those from ice cores and the marine realm

A global compilation of diatom silica oxygen isotope records from lake sediment – trends, and implications for climate reconstruction

International audienceOxygen 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 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