Lake Sediment Record Research Articles

Lacustrine diatom oxygen isotopes as palaeo precipitation proxy - Holocene environmental and snowmelt variations recorded at Lake Bolshoye Shchuchye, Polar Urals, Russia

The diatom oxygen isotope composition (δ18Odiatom) from lacustrine sediments helps tracing the hydrological and climate dynamics in individual lake catchments, and is generally linked to changes in temperature and δ18Olake. Lake Bolshoye Shchuchye (67°53′N; 66°19′ E; 186 m a.s.l) is the largest and deepest freshwater reservoir in the Polar Urals, Arctic Russia. The diatom oxygen isotope interpretation is supported by modern (isotope) hydrology, local bioindicators such as chironomids, isotope mass-balance modelling and a digital elevation model of the catchment.The Bolshoye Shchuchye δ18Odiatom record generally follows a decrease in summer insolation and the northern hemisphere (NH) temperature history. However, it displays exceptional, short-term variations exceeding 5‰, especially in Mid and Late Holocene. This centennial-scale variability occurs roughly contemporaneously with and similar in frequency to Holocene NH glacier advances. However, larger Holocene glacier advances in the Lake Bolshoye Shchuchye catchment are unknown and have not left any significant imprint on the lake sediment record. As Lake Bolshoye Shchuchye is deep and voluminous, about 30–50% of its volume needs to be exchanged with isotopically different water within decades to account for these shifts in the δ18Odiatom record. A plausible source of water with light isotope composition inflow is snow, known to be transported in surplus by snow redistribution from the windward to the leeward side of the Polar Urals. Here, we propose snow melt variability and associated influx changes being the dominant mechanism responsible for the observed short-term changes in the δ18Odiatom record. This is the first time such drastic, centennial-scale hydrological changes in a catchment have been identified in Holocene lacustrine diatom oxygen isotopes, which, for Lake Bolshoye Shchuchye, are interpreted as proxy for palaeo precipitation and, on millennial timescales, for summer temperatures.

Climate and human exploitation have regulated Atlantic salmon populations in the River Spey, Scotland, over the last 2000 years

Historical salmon catch records suggest that climatic variability, and more recently human exploitation, control patterns of abundance in Atlantic salmon populations. We present the first long-term (2000-year) reconstruction of Atlantic Salmon population variations based on a Marine Derived Nutrient (MDN) lake sediment record. Our record is constructed from nitrogen isotopes (δ15N) measured from a lake sediment core, which we compare with an escapement index (EI) derived from historic net catch data on major Scottish salmon rivers. We used an isotope mixing model to demonstrate that the N isotope values are likely enriched with MDN and demonstrate that Loch Insh sediments are enriched compared with a control site (Loch Vaa) that has never had exposure to salmon. We demonstrate that current adult spawner returns are around half that of historic values prior to major human exploitation. Before the onset of widespread human exploitation and habitat degradation, large fluctuations in salmon abundance are attributed to variations in North Atlantic sea surface temperature. While our data support published reconstructions of declining Atlantic salmon stocks in Northwest European rivers over the last 1000 years, rather than point to a solely human cause, the human impact appears to be overprinted on larger-scale changes in marine habitat occurring at the transition from the warmer Medieval Climatic Anomaly (MCA) to the cooler Little Ice Age (LIA).

Past 200 kyr hydroclimate variability in the western Mediterranean and its connection to the African Humid Periods

The Iberian Peninsula is located at the intersection between the subtropical and temperate climate zones and the paleoclimate records from this region are key to elucidate the varying humidity and changing dominance of atmospheric circulation patterns in the Mediterranean-North African region in the past. Here we present a quantitative hydroclimate reconstruction for the last ca. 200 kyr from southern Iberian Peninsula based on pollen data from the Padul lake sediment record. We use the newly developed Scale-normalized Significant Zero crossing (SnSiZer) method to detect not only the statistically significant precipitation changes but also to estimate the relative magnitude of these oscillations in our reconstruction. We identify six statistically significant main humid phases, termed West Mediterranean Humid Periods (WMHP 1–6). These humid periods correlate with other West/Central Mediterranean paleohydrological records, suggesting that similar climatic factors affected different areas of the Mediterranean. In addition, the WMPHs are roughly coeval with the African Humid Periods (AHPs) during high seasonality, suggesting the same North Atlantic ocean-atmospheric dynamics and orbital forcing as main drivers of both areas. In contrast, during low seasonality periods, the West Mediterranean still appears to be affected by the westerlies and the local Mediterranean rainfall systems with moderate-to-high precipitation, whereas West Africa was characterized by droughts.

Holocene Temperature Variations in Semi-Arid Central Mongolia—A Chronological and Sedimentological Perspective From a 7400-year Lake Sediment Record From the Khangai Mountains

Semi-arid Mongolia is a highly sensitive region to climate changes, but the region’s Holocene paleoclimatic evolution and its underlying forcing mechanisms have been the subject of much recent debate. Here we present a continuous 7.4 ka sediment record from the high-altitude Shireet Naiman Nuur (Nuur = lake) in the central Mongolian Khangai Mountains. We extensively dated the sediments and analyzed elemental composition and bulk isotopes for lake sediment characterization. Our results show that 14C-dating of bulk organic carbon and terrestrial macrofossils provide a robust and precise chronology for the past 7.4 ± 0.3 cal ka BP at Shireet Naiman Nuur and 14C-ages are mostly in stratigraphic order. The 14C-based chronology is confirmed by paleomagnetic secular variations, which resemble the predictions of spherical harmonic geomagnetic field models. The very good chronological control makes paleomagnetic secular variation stratigraphy a powerful tool for evaluating and refining regional 14C-chronologies when compared to the record presented here. The lake sediment proxies TOC, N, log (Ca/Ti) and log (Si/Ti) reveal increased lake primary productivity and high growing season temperatures from 7.4 ± 0.3 to 4.3 ± 0.2 cal ka BP, which is likely the result of stronger summer insolation and pronounced warming. Reduced summer insolation thereafter results in decreased productivity and low growing season temperatures at Shireet Naiman Nuur from 4.3 ± 0.3 cal ka BP until present day. The globally acknowledged 4.2 ka event also appears as a pronounced cooling event at Shireet Naiman Nuur, and additional abrupt cooling events occurred during minima in total solar irradiance at ∼3.4, 2.8 and 2.4 ka BP. Low lake primary productivity and growing season temperatures are likely the result of longer ice cover periods at the high-altitude (2,429 m a.s.l.) Shireet Naiman Nuur. This leads to shorter mixing periods of the lake water which is supported by more positive δ13CTOC because of increased incorporation of dissolved HCO3− by aquatic producers during periods of longer ice cover.

Spatially calibrating polycyclic aromatic hydrocarbons (PAHs) as proxies of area burned by vegetation fires: Insights from comparisons of historical data and sedimentary PAH fluxes

Many regions worldwide have experienced increasing wildfire activity in recent years and climate changes are predicted to result in more frequent and severe fires. Reconstruction of past fire activity offers paleoenvironmental context for modern and future burning. Pyrogenic polycyclic aromatic hydrocarbons (PAHs) have been increasingly used as a molecular biomarker for fire occurrence in the paleorecord and offer opportunity for nuanced reconstructions of fire characteristics. A suite of PAHs is produced during combustion, and the emission amount and assemblage is influenced by many variables including fuel type, fire temperature, and oxygen availability. Despite recent advances in understanding the controls and taphonomy of these biomass burning markers, the spatial scale of this proxy is unknown. In this paper, measurements of PAH fluxes preserved in a lake sediment archive from the Sierra Nevada, California were compared with a historical geographic information system (GIS) dataset of area burned up to 150 km distance from the lake to determine the spatial scales for which these biomarkers are reliable proxies of biomass burning. The PAH fluxes in the Swamp Lake sediments record a change in the relative anthropogenic and pyrogenic sourcing of PAHs. Anthropogenic pollution sources could explain why some PAHs (fluoranthene (Fl), pyrene (Py), benz[a]anthracene (BaA), retene (Ret), benzo[a]pyrene (BaP), dibenzo[a,h]anthracene (DA) and ideno[1,2,3-cd]pyrene (IP)) did not correlate with area burned within 150 km. This indicates that individual PAHs may have different efficacies in recording area burned and be more susceptible to masking of fire signals by pollution sources. Despite these complications, we find that the PAHs naphthalene (Na), acenaphthene (Ace), fluorene (F), and anthracene (An) are reliable local proxies of area burned (within 40 km), whereas the PAHs phenanthrene (Phe), chrysene (Ch), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), and benzo[g,h,i]perylene (Bghi) are both reliable local (within 36 km) as well as more regional (as much as 75 km for phenanthrene (Phe), chrysene (Ch), and benzo[g,h,i]perylene (Bghi) or 150 km for benzo[b]fluoranthene (BbF) and benzo[k]fluoranthene (BkF)) area burned proxies. Comparisons of PAH fluxes with charcoal accumulation rates in the same sediments suggest that pyrogenic particulate transport modulates low to mid-molecular weight PAHs via adsorption. Overall, the results show that PAH records integrate a combination of spatial signals of area burned and measurement of individual PAHs may enable cross-scale paleofire reconstructions.

A predominantly tropical influence on late Holocene hydroclimate variation in the hyperarid central Sahara.

The climate history of the Sahara desert during recent millennia is obscured by the near absence of natural climate archives, hampering insight in the relative importance of southerly (tropical) and northerly (midlatitude) weather systems at submillennial time scales. A new lake sediment record from Ounianga Serir oasis in northern Chad, spanning the Late Holocene without interruption, confirms that immediately before ca 4200 years ago, the Sahara experienced an episode of hyperaridity even more extreme than today’s desert climate. The hypersaline terminal lake which formed afterwards never desiccated during the late Holocene due to continuous inflow of fossil groundwater, yet its water balance was sensitive to temporal variation in local rainfall and lake surface evaporation. Our in-lake geochemical proxies show that, during the last 3000 years, century-scale hydroclimate variation in the central Sahara primarily tracked the intensity of the tropical West African monsoon, modulated at shorter time scales by weather patterns linked to shifts in midlatitude Atlantic Ocean circulation.

Late Holocene volcanic and human impacts on the mountain vegetation in central Sumatra, Indonesia

The Kerinci Seblat National Park (KSNP) has been a region of great significance for palynological studies featuring the combination of unique tropical vegetation, tectonics determining frequent volcanic eruptions, and a long settlement history. This palynological study aims at reconstructing ecosystem processes and is based on a long-term analysis of vegetation composition in the mountainous region of Sumatra. The research question focused on the influence of natural disturbance such as climate and volcanism, and anthropogenic impacts and fire on vegetation dynamics in the KSNP in the Sumatran highlands. A 2300-year-old lake sediment record of Danau Belibis at 2078 m asl. provides insights into the changes in vegetation composition over time in a mountainous tropical rainforest region in Jambi province. Over the entire record, Taxus was the most dominant genus. Volcanic eruptions caused continuous competition between volcanophile taxa like Casuarina and Myrica, and primary forest taxa. Settlements and agricultural activity are represented throughout the whole record. Forest clearings for wood exploitation and cultivation took place in the period from 1600 to 1000 years BP and from 600 years BP to the present. Crops were already introduced at the beginning of the record in the Kerinci highland region. The charcoal record illustrates only occasional fire events caused by natural forces. Our findings refer to the vulnerability of vegetation dynamics concerning important environmental drivers and suggest volcanic events as an important factor for environmental changes in the highlands of Sumatra.

Variation in the seasonal response to climate change during the past 1000 years as inferred from a Maar Lake sediment record, northeast China

Variation in the seasonal response to climate change during the past 1000 years as inferred from a Maar Lake sediment record, northeast China

A multi-proxy lake-sediment record of middle through late Holocene hydroclimate change in southern British Columbia, Canada

A multi-proxy lake-sediment record of middle through late Holocene hydroclimate change in southern British Columbia, Canada

Millennial-scale periodicities associated with changes in wind ansd precipitation over the last Glacial cycle (ca. 117 ± 8.5 ka BP) recorded in sediments from Lake Kai Iwi, Northland, New Zealand

Mid-latitude Southern Hemisphere proxy records of changing environment, especially those that demonstrate past variability of the South Westerly Winds (SWW), are poorly-constrained prior to the Last Glacial Interglacial Transition (LGIT; ca. 14–11.7 ka BP) and are typically located far enough south or north that they often do not reflect both tropical and SWW signals. With this deficiency in mind, we present a ca. 117 ± 8.5 ka BP lake sediment record from Lake Kai Iwi, Northland, New Zealand (~36°S), located at a latitude that demonstrates changes in precipitation associated with both the northward expansion of the SWW belt and from tropical El Niño Southern Oscillation (ENSO) variability. We converted Lake Kai Iwi μ-XRF proxy data to even time-steps in order to apply Morelet wavelet analysis for identification of millennial-scale periodicities in the data that were likely driven by orbital forcing. The results indicate that Lake Kai Iwi records a ~1 ka periodicity possibly associated with Northern Hemisphere ice sheet dynamics; a ~2–4 ka periodicity associated with ~2.4 ka Hallstatt solar cycles, and a ~9 ka periodicity linked to CO2 outgassing from upwelling in the Southern Ocean driven by changes in intensity and position of the SWW.

Late Quaternary hydroclimate change inferred from lake sedimentary record in arid central Asia

Arid central Asia is a key region in the study of global climate change; however, the characteristics and mechanisms of regional hydroclimate changes during the late Quaternary remain poorly known. Here we present a new hydroclimate record from Lake Ebinur in arid northwestern China based on a comprehensive multiproxy analysis. The results show that Lake Ebinur formed at ~33.5 ka under relatively warm and humid conditions that continued to 26.7 ka. The following Last Glacial Maximum was cold and dry from 26.7 to 18.5 ka, most notably during the interval between 21.3 and 18.5 ka, suggesting a two‐step hydroclimate change. The moisture conditions started to improve at 15 ka and reached their highest level during the Middle Holocene (8.7–4.4 ka). A comparison of our record with other records in the Northern Hemisphere indicated that the moisture changes in central Asia followed similar variability trends to those of the east Asia monsoon region during the last glacial period, suggesting common driving forces, such as the boreal solar insolation and its associated Northern Hemisphere ice‐sheet volume. The Holocene moisture optimum in central Asia was delayed by 2000–3000 years relative to that in east Asia, which demonstrated a large influence of the remnant Northern Hemisphere ice‐sheet forcings on the mid‐latitude Asia atmospheric circulation (e.g. mid‐latitude westerlies and Siberian High) in the Early Holocene.

Alpine Glacier Reveals Ecosystem Impacts of Europe's Prosperity and Peril Over the Last Millennium

AbstractInformation about past ecosystem dynamics and human activities is stored in the ice of Colle Gnifetti glacier in the Swiss Alps. Adverse climatic intervals incurred crop failures and famines and triggered reestablishment of forest vegetation but also societal resilience through innovation. Historical documents and lake sediments record these changes at local—regional scales but often struggle to comprehensively document continental‐scale impacts on ecosystems. Here, we provide unique multiproxy evidence of broad‐scale ecosystem, land use, and climate dynamics over the past millennium from a Colle Gnifetti microfossil and oxygen isotope record. Microfossil data indicate that before 1750 CE forests and fallow land rapidly replaced crop cultivation during historically documented societal crises caused by climate shifts and epidemics. Subsequently, with technology and the introduction of more resilient crops, European societies adapted to the Little Ice Age cold period, but resource overexploitation and industrialization led to new regional to global‐scale environmental challenges.

Anthropogenic climate change has altered lake state in the Sierra Nevada (California, USA)

Climatic changes threaten freshwater resources and aquatic ecosystem health in the Sierra Nevada (California, USA), which has important consequences for millions of people and the world's fifth largest economy. However, the timing and magnitude of ecological changes driven by hydroclimate oscillations remain poorly understood in California's headwater region. Here, we develop a precisely dated, annually to decadally resolved lake sediment record of ecological change from the eastern Sierra Nevada that spans the last three millennia. Diatom paleoecology reveals a detailed history of abrupt limnologic transitions, best explained by modifications in water column stratification, mixing, and nutrient status in response to changing seasonality. Seasonally stratified conditions were registered during the Late Holocene Dry Period and the Medieval Climate Anomaly, illustrating the sensitivity of fossil diatoms to well-known periods of drought. Yet the most striking feature of the record is the uniqueness of ~1840-2016 CE: a period of singularly strong water column stratification, increased algal diversity, and reduced diatom productivity consistent with unprecedented "hot droughts." The data demonstrate that hot-dry conditions of the Industrial Era altered lake state to conditions unseen in the past ~3180years, and suggest that regional trends identified by historical monitoring began far earlier than previously recognized. Our record illustrates the profound influence of anthropogenic climate warming on high-elevation lakes and the ecosystem services they provide in the Sierra Nevada, which hold implications for water quality and availability in California.

Severe Little Ice Age drought in the midcontinental United States during the Mississippian abandonment of Cahokia

Drought has long been suspected as playing an important role in the abandonment of pre-Columbian Native American settlements across the midcontinental United States between 1350 and 1450 CE. However, high-resolution paleoclimatic reconstructions reflecting local effective moisture (the ratio of precipitation to evaporation) that are located in proximity to Mississippi period (1050–1450 CE) population centers are lacking. Here, we present a 1600-year-long decadally resolved oxygen isotope (δ18O) record from Horseshoe Lake (Collinsville, IL), an evaporatively influenced oxbow lake that is centrally located within the largest and mostly densely populated series of Mississippian settlements known as Greater Cahokia. A shift to higher δ18O in the Horseshoe Lake sediment record from 1200 to 1400 CE indicates that strongly evaporative conditions (i.e., low effective moisture) were persistent during the leadup to Cahokia’s abandonment. These results support the hypothesis that climate, and drought specifically, strongly impacted agriculturally based pre-Columbian Native American cultures in the midcontinental US and highlights the susceptibility of this region, presently a global food production center, to hydroclimate extremes.

Decoding a complex record of anthropogenic and natural impacts in the Lake of Cavazzo sediments, NE Italy

The Lake of Cavazzo is a natural, lacustrine basin in the Friuli-Venezia Giulia region (NE Italy), which occupies a fluvio-glacial suspended valley of the Tagliamento river, at the southern front of the Alpine chain. The lake formed after the melting of major glacial tongues at the end of the Last Glacial Maximum, and has been affected in recent years by natural and anthropogenic events, with economic, cultural and environmental consequences. According to local witnesses, the lake environment has changed dramatically after the 1950s, when the basin was connected to a hydroelectric power plant collecting waters from a wider catchment area, as it served as its final discharge basin.In this work, based on a densely-spaced grid of high-resolution seismic reflection profiles complemented by sediment cores, we analysed the uppermost lake stratigraphy, highlighting major changes occurring at a decadal scale. Our main purpose is to verify whether and how the lake sediments record the transition from pristine/natural to artificial conditions, as well as the effects of multiple natural impacts including the 1976–77 Friuli earthquake sequence. The results of our analysis suggest varying environmental conditions of the lake after the 1950s indicated by changing sediment mineralogy, increased deposition of allochthonous clastic sediments, and recurrent episodes of anoxic conditions at the lake's floor, likely triggered by hyperpycnal flows derived from the hydroelectric power plant discharges. We also observe that the effects of the 1976–77 seismic sequence are recorded in the lake as resedimented levels, likely due to shaking, in situ deformation, landslides, and turbidity currents. Our results stress the importance of lacustrine environments as efficient recorders of anthropogenic and natural events.

Composite development and stratigraphy of the Onepoto maar lake sediment sequence (Auckland Volcanic Field, New Zealand)

Abstract. The accurate and precise reconstruction of Quaternary climate as well as the events that punctuate it is an important driver of the study of lake sediment archives. However, until recently lake sediment-based palaeoclimate reconstructions have largely concentrated on Northern Hemisphere lake sequences due to a scarcity of continuous and high-resolution lake sediment sequences from the Southern Hemisphere, especially from the southern mid-latitudes. In this context, the deep maar lakes of the Auckland Volcanic Field of northern New Zealand are significant as several contain continuous and well-laminated sediment sequences. Onepoto Basin potentially contains the longest temporal lake sediment record from the Auckland Volcanic Field (AVF), spanning from Marine Isotope Stage 6e (MIS 6e) to the early Holocene when lacustrine sedimentation was terminated by marine breach of the south-western crater tuff ring associated with post-glacial sea-level rise. The Onepoto record consists of two new, overlapping cores spanning ca. 73 m combined with archive material in a complete composite stratigraphy. Tephrochronology and 14C dating provide the fundamental chronological framework for the core, with magnetic relative palaeo-intensity variability downcore, and meteoric 10Be influx into the palaeolake to refine the chronology. The µ-XRF (micro X-ray fluorescence) downcore variability for the entirety of the lake sediment sequence has been established with measurement of a range of proxies for climate currently underway. This work will produce the first continuous record of the last 200 kyr of palaeoclimate from northern New Zealand to date.

Effects of Pleistocene to Holocene seismicity on the landforms and fluvial-lacustrine sequences of the Ixtlahuaca paleobasin, and their possible relation with the Acambay graben: Implications for the seismic hazard assessment of central Mexico

We mapped Plio-Pleistocene lake deposits in the Ixtlahuaca paleobasin in Central Mexico, located 51 km south of the Acambay Graben and 69 km west of Mexico City. Within the Acambay basin, Pleistocene to Holocene lake sediments record primary and secondary environmental effects of strong local earthquakes as a consequence of Quaternary activity of the major normal border faults. Likewise, the Ixtlahuaca paleobasin has been controlled mainly by the Quaternary evolution of the Perales and Ixtlahuaca faults, even if there is no record of local historical earthquakes, and therefore the area has not been considered as potentially seismic. However, the application of the ESI 2007 Scale to deformation structures as effects of seismic events on the geological-natural environment in the Tierras Blancas - San Bartolo Lanzados basins and San Pedro El Alto, within the Acambay graben, and its comparison with seismites identified in the Ixtlahuaca paleobasin, show that past earthquakes similar to the Mw 6.5 to 7 surface faulting events generated by the main faults of the Acambay graben have also occurred in the Ixtlahuaca area.

Impacts of Norse settlement on terrestrial and aquatic ecosystems in Southwest Iceland

Norse colonization of North Atlantic islands in the 1st millennium of the Common Era led to drastic prehistoric environmental changes in these previously “pristine” landscapes. In Iceland, Norse settlement is associated with a rapid decline in birch trees and heightened soil erosion, yet the timing of Norse exploration in the North Atlantic coincided with large climate changes that also influenced Icelandic environments. To date, there are few records that disentangle climatic and human impacts on terrestrial ecosystems, and there has been very little work on the impacts of Norse arrival on Iceland’s aquatic ecosystems. Here we use a high-resolution lake-sediment record from Vestra Gislholtsvatn (VGHV), southwest Iceland to investigate these processes during the last 2,000 years. Norse arrival (c. 870 CE) in Iceland is followed by a rapid increase in sedimentation rate and a transition in leaf wax n-alkanes indicating a decrease in trees and expansion of grasses. This transition coincides with limnological changes, including increased primary productivity (i.e. C17 n-alkane and biogenic opal fluxes) and shifts in the haptophyte algal community. Many of these changes are still apparent today. Comparisons with a new winter-spring alkenone temperature reconstruction from VGHV and marine sea surface temperature records show little to no correlation between terrestrial and aquatic ecological changes and climate at this time. Similarly, volcanic eruptions recorded in VGHV are not associated with any long-term environmental changes. Rather, the VGHV record suggests that human settlement had a lasting impact on the catchment area of VGHV and changes within the lake ecosystem.

Features of the Formation of Lakes in the Cryogenic Regions of the Upper Kolyma, Northeast Siberia

Long-term observations of the evolution of the Elikchan lakes (Kolyma Upland, Maimandzha Mountains), which form a "chain" that stretches across the flat watershed separating the Upper Kolyma and the Sea of Okhotsk drainages, make it possible to determine how slope, thermokarst processes, and ecology affected landscape changes within this area. Clastic material coming from the slopes of the Maimandzha Mountains formed dams, which created large lakes within the Okhotsk basin (Elikchan-4 Lake, Elikchan-3 Lake). The origin of the lakes belonging to the Kolyma basin is the result of active thermokarst processes associated with the thawing of ice wedges, the development of bogs, the confluence of small lakes and the formation of new larger reservoirs. Such thermokarst processes were some of the main factors in the origin of Elikchan-1 Lake. The continuous palynological record and radiocarbon dating of the Elikchan-1 Lake sediments reflect the successive changes of biocenoses, which correspond to the general pattern of the evolution of the vegetation cover in the Upper Kolyma basin and in Northern Priokhotye. This record shows a change in plant communities over at least the past 9 000 years with a climatic optimum at ca. 8 000 - 6 100 years ago. Comprehensive analysis of Elikchan-1 Lake also emphasizes the significant discrepancies between the boundaries of Holocene subdivisions in the Far Eastern region and the European chrono-stratigraphy for the Holocene. Attempts to resolve the problems of Far East stratigraphy by comparison to the traditional divisions for Europe are a serious mistake. Moreover, a complete analogy of the Far Eastern subdivisions of the Holocene with the European chronological standard should not be expected, just as it is inappropriate to use the УEuropeanФ terminology in the Far Eastern reconstructions. The influences of the primary factors that determine the Holocene events in the Far East sharply differ from those of Europe, including the specific features of the regional climates as they respond to global forcing factors, diversity of the vegetation cover, and variations in the timing of changes in the biocenoses. Given such differences, it is quite natural that equating the Holocene divisions between the two regions is unacceptable. Radiocarbon dating at the base of the Elikchan-1 Lake sedimentary column indicates that the site was originally a peat bog in the Early Holocene with subsequent lake formation. Comparison of radiocarbon dates from the Elikchan-1 peat with other peat deposits in the region suggests that the Early Holocene was a time of active formation and fairly widespread development of peat bogs in the mountainous regions of the Kolyma and Northern Priokhotye.

Using a lake sediment record to infer the long-term history of cyanobacteria and the recent rise of an anatoxin producing Dolichospermum sp.

Lakes that experience recurrent toxic cyanobacterial harmful algae blooms (cyanoHABS) are often subject to cultural eutrophication, where landscape development and upland activities increase the nutrient inputs to the water column and fuel cyanoHABS. Few studies have focused on the response of a lake to nutrient inputs for which the natural geomorphic setting predisposes a nutrient-rich water column to already support abundant cyanobacteria. Here, we present a sediment core record from a lake surrounded by parkland that experiences recurrent cyanoHABs which produce dangerous levels of the neurotoxin, anatoxin-a, impacting the recreational use of the lake and park. Using photoautotrophic pigments in the sediment record, we establish cyanobacteria have long been part of the diverse and abundant phytoplankton community within the lake. Despite this long record, shotgun metagenome and other DNA analyses of the sediment record suggest that the current anatoxin-a producer Dolichospermum sp. WA102 only emerged to dominate the cyanobacterial community in the mid-1990s. A period of lakeshore farming that finished in the 1950s-1960s and possibly the stocking of rainbow trout fry (1970–2016) coincide with a progressive shift in primary production, together with a change in bacterial communities. Based on the history of the lake and contemporary ecology of Dolichospermum, we propose that the legacy of nutrient inputs and changes in nutrient cycling within the lake has encouraged the development of an ecosystem where the toxin producing Dolichospermum sp WA102 is highly competitive. Understanding the historical presence of cyanobacteria in the lake provides a context for current-day management strategies of cyanoHABs.