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The field of paleolimnology has made tremendous progress in reconstructing past biotic and abiotic environmental conditions of aquatic ecosystems based on sediment records. This, together with the rapid development of molecular technologies, provides new opportunities for studying evolutionary processes affecting lacustrine communities over multicentennial to millennial timescales. From an evolutionary perspective, such analyses provide important insights into the chronology of past environmental conditions , the dynamics of phenotypic evolution, and species diversification. Here, we review recent advances in paleolimnological, paleogenetic, and molecular approaches and highlight how their integrative use can help us better understand the ecological and evolutionary responses of species and communities to environmental change. Paleolimnological data can help to reconstruct past environmental conditions and their changes over time in aquatic ecosystems, providing important information for inferring past ecological conditions, trends in community assembly through time, and rates and directions of evolution. New approaches to analyzing ancient sedimentary DNA, RNA, or proteins, lipid biomarkers, and stable isotopes can be combined with phenotypic analyses of (sub)fossils to test novel hypotheses about past community assembly, and evolutionary processes such as phenotypic change and adaptation, as well as phenotypic diversification and adaptive radiation. Integration of these new and classical approaches is expanding our ability to understand organism–environment interactions and evolutionary responses to environmental change. [ABSTRACT FROM AUTHOR]

Progresses in reconstructing Earth's history of biomass burning has motivated the development of a modern charcoal dataset covering the last decades through a community-based initiative called the Global Modern Charcoal Dataset (GMCD). As the frequency, intensity and spatial scale of fires are predicted to increase regionally and globally in conjunction with changing climate, anthropogenic activities and land-use patterns, there is an increasing need to further understand, calibrate and interrogate recent and past fire regimes as related to changing fire emissions and changing carbon sources and sinks. Discussions at the PAGES Global Paleofire Working Group workshop 2015, including paleoecologists, numerical modelers, statisticians, paleoclimatologists, archeologists, and anthropologists, identified an urgent need for an open, standardized, quality-controlled and globally representative dataset of modern sedimentary charcoal and other sediment-based fire proxies. This dataset fits into a gap between metrics of biomass burning indicators, current fire regimes and land cover, and carbon emissions inventories. The dataset will enable the calibration of paleofire data with other modern datasets including: data of satellite derived fire occurrence, vegetation patterns and species diversity, land cover change, and a range of sources capturing biochemical cycling. Standardized protocols are presented for collecting and analyzing sediment-based fire proxies, including charcoal, levoglucosan, black carbon, and soot. The GMCD will provide a publically-accessible repository of modern fire sediment surface samples in all terrestrial ecosystems. Sample collection and contributions to the dataset will be solicited from lacustrine, peat, marine, glacial, or other sediments, from a wide variety of ecosystems and geographic locations. [ABSTRACT FROM AUTHOR]

Fire is the most important abiotic disturbance in the interior cedar-hemlock (ICH) and Engelmann spruce–subalpine fir (ESSF) forest zone of southeastern British Columbia, Canada. Other disturbances are also important, such as defoliator and boring insect outbreaks, windthrow, diseases, and rapid mass movements. Few studies have examined the interaction between multiple types of disturbances in these forests over long timescales. Here we present high-resolution analyses of biomass burning, erosion, and vegetation assemblage changes at Sasquatch Lake (NEL02), a valley lake in the Columbia Mountains. The 531.5 cm sediment core was radiocarbon dated and provided a 7500-year stratigraphy that was used for pollen, macroscopic charcoal (>150 μm), and sedimentologic analyses. Pollen and charcoal data provided evidence of forest composition changes and fire activity. Magnetic susceptibility, loss-on-ignition, and particle size distribution analyses characterised changes in erosion into the basin. The results show that coniferous forests, with a high abundance of Pinus pollen, had established in the catchment by the beginning of the record and were subject to intermittent burning and high-energy erosive events. Tsuga heterophylla expanded by 4400 cal BP and the modern interior cedar-hemlock forests expanded throughout the lower elevations due to increased regional continentality since 4500 cal BP. High-energy erosional inputs to the lake were less frequent from 3500 to 750 cal BP and rapid mass movements may have increased in frequency during the Little Ice Age. Dendrochronological evidence in these stands suggests a mixed-severity fire regime during past ∼300 years, which has not been fully examined for charcoal-based fire event reconstruction. Here we use identified peaks as an indicator of increased biomass burning and charcoal movement in the catchment in relation to peaks in allochthonous clastic material to understand the potential relationships between biomass burning and erosion events at multiple temporal scales in the catchment. This suggests that post-fire conditions, up to several decades, were subject to increased erosion to the lake and erosion events were more common during the early Holocene. Establishment of dense ESSF and ICH forests decreased siliciclastic input to the lake throughout the mid Holocene until a recent rockslide. The high-resolution sampling of this lake sediment record provides long-term evidence of variability in the relationships between vegetation cover, fire and erosion at a catchment scale. [ABSTRACT FROM AUTHOR]

The recent continental-scale outbreak of native bark beetles in western North America is unprecedented at least since Euro-American settlement. Observational and modeling evidence suggest that warm temperatures observed during the late 20th century altered beetle population dynamics by accelerating beetle reproductive cycles leading to exponential population growth. The linkage between beetle outbreaks and climate warming has motivated efforts to reconstruct these disturbances using long-term environmental records using lake sediments. Here, we present data from across western North America in an effort to understand how beetle remains retrieved from lake sediments may be used as a proxy for reconstructing severe outbreaks and ecosystem response over centennial to millennial timescales. We (1) review existing literature related to beetle taphonomy; (2) present previously unpublished data of beetle remains in lake sediments; (3) comment on the development of a methodology to retrieve terrestrial beetle remains from lake sediments; (4) discuss potential controls on beetle carcass taphonomy into the sediment matrix; and lastly (5) speculate on the use of primary and secondary attack beetle remains as indicators of past outbreak episodes. Our synthesis suggests that the remains of primary attack beetles are rarely preserved in lake sediments, at least using small-diameter piston devices common in multi-proxy studies. Alternatively, remains of secondary attach beetles may be common but further work is required to understand how these insects can be used to aid in interpreting past forest disturbances, including bark beetle outbreaks and wildfire. A number of factors may influence whether or not bark beetle remains become entrained in the area of sediment focusing including lake water chemistry, fish predation and scavenging, and weather conditions during peak beetle emergence. [ABSTRACT FROM AUTHOR]

The Lake Victoria ecosystem is emblematic of the catastrophic effects that human activities, particularly cultural eutrophication, can have on freshwater biodiversity. However, little is known about the long-term spatial and temporal pattern of aquatic primary paleo-production (PP aq) and producer communities in Lake Victoria and how these patterns relate to past climate variability, landscape evolution, lake hydrology, mixing regimes, nutrient cycling, and biodiversity dynamics in the past 17 kyr. We use sediments from four well-dated cores along a transect from offshore to nearshore sites, and exploit XRF element scanning and hyperspectral imaging data, TC, TN, bSi, δ13C and δ15N, and sedimentary pigments to investigate paleolimnological variability and change. Our findings demonstrate that changes in PP aq and algal communities during the past 17 kyr were closely related to hydroclimatic changes, lake mixing, and nutrient availability. During the wetland phase (16.7–14.5 cal ka BP), PP aq levels remained generally low, while chromophytes and chlorophytes dominated the algal community. Following the rapid lake level rise (∼14.2 cal ka BP) during the early African Humid Period (AHP), PP aq levels steadily increased, accompanied by a shift towards cyanobacteria and chromophytes. During the Holocene, our results suggest repeated short-lived arid intervals (∼10.5, ∼9, 7.8–7.2, ∼4, and 3.2–3.0 cal ka BP) and two distinct periods of enhanced lake mixing associated with high PP aq and high diatom productivity: the first one between 11 and 9 cal ka BP, which coincided with the maximum of the AHP (high precipitation, high wind, enhanced mixing), and the second, less pronounced one, between 7 and 4 cal ka BP. Between these two periods (i.e. 9–7 cal ka BP) we observe reduced diatom productivity, relatively low PP aq , and high C/N ratios, suggesting conditions with more stable lake stratification, likely associated with reduced wind strength, and some nutrient limitation (N and P). Finally, the drier conditions around the end of the AHP (ca. 4 cal ka BP) and during the late Holocene were associated with decreasing lake mixing and increasing dominance of cyanobacteria. Given our reconstruction of PP aq over the past 17 kyr, we conclude that the levels in the 20th century are unprecedentedly high, consistent with the massive human-mediated impact on the Lake Victoria ecosystem including biodiversity loss. • Detailed reconstruction of aquatic primary production and its underlying drivers. • Primary production is linked to hydroclimatic changes, lake mixing, and nutrient availability. • The Holocene was marked by two distinct phases of increased lake mixing and higher primary production. • K and Rb/K profiles reflect hydroclimate oscillations. [ABSTRACT FROM AUTHOR]

The automation of fossil pollen analysis promises many advantages in handling large numbers of samples with less resource allocation. However, automation is often obstructed by the high abundance of organic and minerogenic non-pollen debris in fossil pollen samples. We used a Convolutional Neural Network-based approach to detect pollen-like objects in digital images of prepared microscopic slides for fossil pollen analysis and subsequently classified them into nine pollen classes and the marker spore Lycopodium. We trained the object detection and the classification model independently with a newly developed dataset of annotated images of fossil pollen grains. The object detection model achieved average recall rates of 89.8 % and 75.5 % for pollen classes and Lycopodium , respectively. The classification model correctly categorizes fossil pollen images with >95 % accuracy. We applied the assembled pipeline to Late Glacial pollen samples using class-dependent thresholds to discriminate true pollen from non-pollen objects and compared automated count data for nine pollen types with manual pollen counts. For the selected pollen types, our results demonstrate the feasibility to replicate major fossil pollen changes with automated counts, even when the automated pipeline was applied to pollen samples from a different site than used to train the models. High correlations (r = 0.97) between the first two axes of Principal Component Analyses (PCA) calculated based on automated and manual counts and high correlation (r = 0.93) indicated by a Procrustes rotation analysis of the PCA results demonstrate that the two procedures reconstructed similar pollen patterns. While our automated approach is not yet able to achieve the taxonomic resolution of manual counts by expert analysts and is limited to selected pollen types, it provides a "proof of principle" that automated analyses can be applied to complex fossil pollen samples and to develop downcore stratigraphies. Automated analyses may with time lead to reliable pollen records. For instance, our pipeline can be further improved by adding more pollen classes, increasing the dataset of annotated images of fossil pollen grains, expanding the training data to rare pollen types, refining taxonomic resolution (e.g., separation of Betula nana -type or Pinus -types), and incorporating more challenging pollen types (e.g., Juniperus), to expand its application beyond reconstructing temporal changes in a few selected pollen types. • Automated object detection and classification for fossil pollen sediment samples. • Late Glacial pollen patterns captured by automated counting methods. • Automated counting proved robust despite the presences of debris and taphonomy. • Use of class-dependent thresholds increases precision of automated counting methods. [ABSTRACT FROM AUTHOR]

Black carbon emitted from incomplete combustion of biomass and fossil fuel burning is an important aerosol; however, available long-term black carbon data are limited to remote polar and high-alpine ice cores from few geographic regions. Black carbon records from lake sediments fill geographic gaps but such records are still scarce, particularly in the Southern Hemisphere. We applied a new incandescence-based methodology to develop Holocene refractory black carbon (rBC) records from four lake-sediment archives in New Zealand and compare these with macroscopic charcoal records. Our rBC records suggest periods with substantial rBC deposition during the Holocene before human arrival in the 13th century reflecting long-range transport and possibly local wetland fires. With Polynesian settlement, rBC deposition increased on the South Island in agreement with macroscopic charcoal records, and it is this period of burning that is proposed as the source of rBC increases evident in Antarctic ice cores. However, sites on the North Island show no contemporaneous rBC increase suggesting regional differences in biomass burning patterns between the North and South islands. None of the New Zealand records show an increase in rBC from fossil fuel sources during the Industrial Era post-1850 CE. • Refractory black carbon (rBC) links lake sediment and ice core fire record. • New Zealand lake-sediment rBC suggests fire activity before human arrival. • Regional patterns of past rBC differ between the South and North Island. • rBC from the South Island contributed to Antarctic rBC increase. • New Zealand lake sediments show no rBC signal from fossil fuel sources. [ABSTRACT FROM AUTHOR]

Fire regimes differ across tropical and subtropical biomes depending on multiple parameters whose interactions and levels of importance are poorly understood, particularly at multidecadal and longer time scales. In the catchment of Lake Victoria, savanna, rainforest, and Afromontane vegetation have interspersed over the last 17,000 years, which may have influenced the fire regime and vice versa. However, climate and humans are most often the primary drivers of fire regime changes, and analysing their respective roles is critical for understanding current and future fire regimes. Besides a handful of radiocarbon dates on grassy charcoal, the timescales of published studies of Lake Victoria sediment chronologies rely mostly on dates of bulk sediment, and chronological disagreements persist, mainly due to variation between estimations of the 14C reservoir effect. Here, we provide independent 14C chronologies for three Late Glacial and Holocene lacustrine sediment cores from various water depths and compare them with the biostratigraphy to establish a new chronological framework. We present the first continuous sedimentary charcoal records from Lake Victoria; these suggest that fire activity varied substantially during the past 17,000 years. Our new pollen records reveal the long-term vegetation dynamics. The available evidence suggests that before human impact increased during the Iron Age (ca. 2400 yr BP), biomass burning was linked to climate and vegetation reorganizations, such as warming, drying, and the expansion of rainforests and savannas. Our results imply that climate can trigger substantial fire regime changes and that vegetation responses to climate change can co-determine the fire regime. For instance, biomass burning decreased significantly when the rainforest expanded in response to increasing temperatures and moisture availability. Such insights into the long-term linkages between climate, vegetation, and the fire regime may help to refine ecosystem management and conservation strategies in a changing global climate. • Three age–depth models provide a highly reliable chronology of Lake Victoria. • A regional desiccation phase might have occurred from ca. 18,500 until 15,500 cal yr BP. • The savanna biome persisted until the onset of the Holocene. • During the AHP forest species expanded and fire activity declined steadily. • Long-term variations of 1–2 °C may drive biome reorganizations in the LV basin. [ABSTRACT FROM AUTHOR]