Lake Record Research Articles

Increased aeolian activity linked to Neoglacial cooling and glacier advance in southern Greenland

Wind activity is a powerful force that shapes the landscapes of deserts, coastal areas, and regions adjacent to ice sheets, and it has significant implications for human settlement. In southern Greenland, it has been proposed that the increased wind and soil erosion observed around Norse settlements (~985–1450 CE) were caused by overgrazing by animals, which ultimately contributed to the decline of the Norse culture. Alternatively, some studies have linked the observed intensification of aeolian activity to changes in large‐scale atmospheric circulation patterns in the North Atlantic. However, the timing and impact of this increased aeolian activity in southern Greenland remain uncertain due to a lack of well‐dated records. In this study, we use a lake record and optically stimulated luminescence (OSL) dating of adjacent dunes to reconstruct the Holocene history of aeolian activity at Igaliku Kujalleq (Søndre Igaliku) in southern Greenland. Our findings indicate two periods of intensified aeolian activity over the past 10 000 years: from ~500 to 1200 CE and ~1450 CE. Importantly, the peak aeolian activity observed in the Igaliku Kujalleq records was unrelated to Norse activities and their decline. Instead, we suggest that changes in the North Atlantic atmospheric circulation pattern combined with Neoglacial glacier advances led to increased katabatic wind activity and triggered increased aeolian activity from large outwash plains.

Shallow urban lakes record industrial history over the last century: a paleolimnological study of three lochs in Greater Glasgow, Scotland, United Kingdom

Globally, freshwater ecosystems are increasingly facing anthropogenic stressors. One such stressor is urban development which not only alters land use but also increases pollutant loads to aquatic systems. Shallow freshwater lakes in urban areas are susceptible to excess nutrients and other contaminant inputs, leading to degraded water quality and ecosystem change. In this study, we applied a paleolimnological approach to investigate lake-ecosystem changes in suburban areas in response to historical anthropogenic stressors. The city of Glasgow, Scotland, is renowned as one of the major centers for the Industrial Revolution in the United Kingdom (UK), and three lakes situated in and around the city were investigated to reconstruct the historical changes surrounding the lake ecosystems. Diatom microfossils, supplemented with plant and insect macrofossils, and geochemical elements, were analyzed as indicators of chemical and ecological change in the lakes over the last 150 years. Two lakes in heavily industrialized urban catchments were found to have evident signs of eutrophication with the greatest ecological change seen in the lake with high hydrological connectivity. The third lake had a different management history due to private land ownership and did not show a clear sign of eutrophication. The study highlights the potential of paleolimnology for exploring the history of urban waterbodies. It suggests that local land-use history and degree of connectivity are important considerations in assessing the onset, degree and nature of environmental change and can result in lakes with varying types of anthropogenic stressors and variable impacts, even within the same small geographical region. This variation needs to be taken into account when designing lake-specific eutrophication management strategies.

Evaluation of repeat bathymetric surveys on water surface elevations on the Saint Clair River

The Great Lakes contain 20 percent of the world’s fresh surface water, a drinking source for 30- million people. The system is vital to manufacturing, largely due to efficient transportation of commodities and an abundance of natural resources. Understanding the water balance and predicting future water levels is important for many industries including commercial navigation, the tourist industry, hydropower and shoreline property owners, just to name a few. These predictions require an understanding of both the hydroclimate drivers across the Great Lakes as well as physical changes in the connecting channels that pass water between each lake. Since the International Upper Great Lakes Study began, the St. Clair River has been the topic of conveyance change investigations. This study tests the sensitivity of water surface elevations to small differences in bathymetric changes. Greater than 80 percent of the surveyed points had less than 0.24 m of change between any combination of survey years. Repeat bathymetric surveys collected in 2007, 2012 and 2021, along with hydrodynamic modeling, find changes in water surface elevations associated with bathymetric change are on the sub-centimeter scale. These changes are put into perspective and compared to known anthropogenic and naturally occurring conveyance changes. While these surveys represent a short duration in the observed water level record of the Great Lakes, they represent an important documentation of the geomorphic state of the St. Clair River. These changes can and should be compared to similar future surveys of the river over longer engineering and geomorphic timescales.

Palaeoenvironmental changes since the last deglaciation recorded at Moon Lake on the Bashang Plateau, northern China: implications for the future sustainability of regional forests

Warming-induced ecological degradation and the continuous shrinking of lakes have been observed in the Bashang Plateau, northern China, leading to the recent demise of cultivated forests. The objective of this paper is to investigate the long-term palaeoenvironmental context of these recent changes through a multi-proxy sediment core analysis at Moon Lake to better understand forest sustainability in the future. The core chronology was determined based on seven accelerator mass spectrometry (AMS) 14C dates and covers the period from 14,000 yr BP to the present. The Moon Lake record reveals four climate stages: (1) a warm and humid period followed by a cold and arid phase corresponding to the Allerod warm period and the Younger Dryas stadial (14,000 to 11,700 yr BP), (2) a relatively warm and humid period (11,700 to 7400 yr BP), (3) a period of fluctuating dry-wet-dry changes (7400 to 4000 yr BP), and (4) a relatively arid period (4000 yr BP to present). Since 1800 yr BP, drought conditions have intensified, and significant warming and drying trends have been observed over the past 500 yr BP. This consistent warming and drying trend over the past few centuries indicate that large-scale afforestation is no longer sustainable in the Bashang region. Coupled with instrumental records of soil drying and water scarcity, our Holocene records of climate change are useful for ecological resource management and sustainable forestry planning in the region.

A Lake Record of Geomagnetic Secular Variations for the Last 23 ka From Lake Chala: Toward a Composite Directional Lake Record of the Earth's Magnetic Field for Equatorial East Africa

AbstractThe documentation and understanding of variations in the Earth's magnetic field through time is fundamental for several disciplines, but current geomagnetic models rely on datasets heavily biased toward the mid‐ and high northern latitudes. The African continent and surrounding islands and oceans are particularly underrepresented. Here, we present a new record of paleo‐secular variation (PSV) of the inclinations over the last 23 ka from Lake Chala, situated at 3°S near Mt Kilimanjaro in eastern equatorial Africa. This groundwater‐fed crater lake is characterized by a high sedimentation rate (ca. 1 cm/10 years) and a particularly well‐constrained age model based on 210Pb and 14C dating. The magnetic mineralogy of the sediments is tested with rock magnetic analyses. The Lake Chala inclination record shows four highs and lows over 20 ka and compares well with that of Lake Malawi (10°S) between 20 and 16.2 ka, and from 9.8 to 2.6 ka. This record is linked to PSV records at Lakes Victoria and Malawi using a sequence slotting technique to generate a composite PSV model for east Africa. Analyzed at best‐possible resolutions up to 200 years, the Lake Chala PSV record not only represents an important contribution to improve our understanding of local and global features of the Earth's magnetic field. It also expands the utility of paleomagnetism as a key tool for dating and correlation both for archeological sites throughout East Africa and the many volcanoes, active or dormant, of the East African Rift System.

Late Neogene and Quaternary Lacustrine History of the Great Salt Lake-Bonneville Basin

The Great Salt Lake-Bonneville basin has contained lakes for many millions of years and has been hydrographically closed for most of its history. Lakes in the lacustrine system have ranged from saline to fresh, and from shallow to deep. Tectonics, specifically crustal extension, which began roughly 20 million years ago as part of the formation of the Basin and Range Province, is the cause of lake-basin formation. Much of the rock record of lakes from Miocene time is faulted and has been eroded and/or buried. Pliocene and Quaternary lakes are better known. For much of the past ~5 Ma the basin has probably appeared similar to today, with a shallow saline terminal lake in a dry desert surrounded by mountains. Freshwater marshes and fluvial systems existed on the basin floor during part of the past ~5 Ma, probably were caused by the lack of inflow from the upper Bear River during the Neogene Period and most of the Pleistocene Epoch (that river was diverted into the basin during the Late Pleistocene), combined with a warm and dry climate. The largest deep-lake cycles were caused by changes to a cold and wet climate, which affected the water budget of the lake system and were correlated with periods of global glaciation. Based on limited data, the total length of time deep lakes existed in the basin is thought to be less than 10% of the past ~773 ka. Lake Bonneville, the most-recent of the deep-lake cycles, was probably the deepest and largest manifestation of the lake system in the history of the basin. Named deep-lake cycles during the past ~773 ka, are Lava Creek (~620 ka), Pokes Point (~430 ka), Little Valley (~150 ka), Cutler Dam (~60 ka), and Bonneville (~30 -13 ka). Of the Quaternary deep-lake cycles, only Lake Bonneville is represented by lacustrine landforms, outcrops, and cores of offshore deposits; no landforms from older deep-lake cycles exist (some may be buried under Lake Bonneville deposits but are not visible at the surface), and pre-Bonneville lakes are represented by sediments in limited outcrops and drill holes (including a set of cores taken by A.J. Eardley in the mid 20th century). During the past ~773 ka, deep-lake cycles were correlated with changes in the total volume of global glacial ice; the available evidence indicates that prior to ~773 ka deep-lake cycles were rare.

Sedimentation rate in Lake Plescheevo in the Late Holocene

Bottom sediments of the Lake Plescheevo is a valuable lake record for the central part of the East European Plain. During this study, we analyzed the lithological characteristics of the upper 4 m of the lake sediment and calculate the sedimentation rate and mass accumulation rate of the lace sediments during last 3500 years. We established that the main part of the increase in the mass accumulation of the Lake Plescheevo bottom sediments is due to the silicate deposits associated with the introduction of terrigenous material into its water area. High values of mass accumulation rates about 3500-3000 cal BP. correspond to a stage of high fluvial activity for the East European Plain. The rapid increase in the rate of mass accumulation rate in the last few decades may be associated with the anthropogenic impact - possibly with the influence of a dam on the Vyoksa River flowing into the lake.

Mid-Holocene climate-glacier relationship inferred from landforms and relict lake sequence, Southern Zanskar ranges, NW Himalaya

The geomorphological disposition of (para/peri) glacial landforms, elemental geochemistry, and optical chronology of the relict lake sediment in the Southern Zanskar ranges, northwest Himalaya are used to understand the relationship between glacial dynamics and the lake sedimentation during the mid-Holocene climate variability. Following the Last Glacial Maxima (LGM), pulsating deposition of outwash gravels until the early Holocene overwhelmed the Zanskar valley. The obstruction of Tsarap Chu (chu = river) by alluvial fans during the mid-Holocene led to the development of Padum Lake. In the present study, cirque glacier moraines representing three minor glacial advances were mapped along with sedimentological details and dated using Optically Stimulated Luminescence (OSL) dating technique. The oldest cirque glacier advance - Padum Cirque moraine-3 (PDCm-3) is dated to 11.4 ± 0.9 ka. The succeeding advance (PDCm-2) is dated to 5.3 ± 0.6 and 4.8 ± 0.8 ka whereas, the younger cirque glacier advance (PDCm-1) remains undated. The mid to late Holocene climate variability inferred using major and trace element geochemistry of the relict Padum lake sediments supported by optical chronology indicates six centennial to millennial-scale climatic phases. The prominent warmer phases are represented by decreased mineralogical fine grain flux (low K/Ti, Fe/Si, and Al/Si) with a corresponding increased coarse grain flux (higher Ti/Al and Sr/Al ratios). These phases are dated between 5.9 and 5.5 ka (phase-I), 3.8 and 3.4 ka (phase-IV), and 2.8 and 2.5 ka (phase-VI). The increased mineralogical finer fraction (higher K/Ti, Fe/Si, and Al/Si) between 5.5 and 5.1 ka (phase-II) and 3.4 and 2.8 ka (phase-V) indicate reduced meltwater flux during cooler phases. The intervening phase-III (5.1–3.8 ka) is characterized by increased mineralogical coarse grain flux (decreasing K/Ti, Fe/Si, Al/Si) suggesting gradual warming. The oscillatory climate at millennial scale was further used to understand glacier dynamics. The PDCm-2 advance in the lake record corresponds to the first major cooling (5.5 and 5.1 ka; phase-II) and continued until ∼3.8 ka. Using geochemical data of lake record, a major recession is inferred after 3.8 ka that persisted until around 3.4 ka (phase-IV). Similarly, the undated younger cirque glacier advance (PDCm-1) is assigned to the second cooling event (3.4 and 2.8 ka; phase-V). Thereafter, the cirque glaciers receded, most likely under increasing dryness and fluctuating climate (2.8–2.5 ka, phase-VI). After ∼2.6 ka, the development of ice-wedge pseudomorphs indicates the onset of permafrost conditions that degraded after ∼2.5 ka implying an increase in air temperature. The lake sedimentation terminates with the deposition of multiple younger alluvial fan facies. The climate variability shows a close correspondence with regional climate records suggesting that marginal glacier advancements were triggered by enhanced moisture via atmospheric rivers and cooler winter temperatures. The study highlights the potential of relict lake sediment in association with para- and peri-glacial landforms to reconstruct the pattern of minor glacier responses to climate variability during the Holocene.

Relationship between pollination syndromes, pollen morphology and plant ecology in Quaternary deposits of the Cerrado

This study presents morphological descriptions and ecological information for 58 terrestrial pollen taxa and seven water-related pollen taxa from the Brazilian Cerrado, obtained from two sediment cores, Lake Feia (LFB1) and Getulio Swamp (VGE-17), encompassing the last 5000 and 15,000 cal yr BP, respectively. The relationships between the ecological and morphological traits (pollination syndrome, vegetation stratum and grain size) within each of the two depositional environments were investigated. In the LFB1 core, the pollen assemblages were dominated by arboreal pollen from closed physiognomies and lower storey trees (<10 m in height), while a combination of closed and open physiognomies was observed in the pollen assemblages from the VGE-17 core. The vast majority of the pollen taxa exhibited the entomophilous pollination syndrome, and a higher influx of entomophilous pollen was observed in both cores. Anemophilous and anemophilous/entomophilous syndromes were less well represented. Small and medium pollen grain classes were the most abundant, while the large pollen grain class was rare. The influx of small pollen grains was slightly more abundant in the lake record, while in the swamp record medium pollen grains were more abundant. Our results show that swamps and lakes differ in their representation of local versus regional pollen and in their sensitivity and responses to water-level changes. Landscape physiognomy also influences pollen dispersion: a closed physiognomy increases the local pollen signal, while a more open physiognomy results in better representation of local and regional signals.

Identifying imprints of externally derived dust and halogens in the sedimentary record of an Iberian alpine lake for the past ∼13,500 years – Lake Peixão, Serra da Estrela (Central Portugal)

Iberian lacustrine sediments are a valuable archive to document environmental changes since the last glacial termination, seen as key for anticipating future climate/environmental changes and their far-reaching implications for generations to come. Herein, multi-proxy-based indicators of a mountain lake record from Serra da Estrela were used to reconstruct atmospheric (in)fluxes and associated climatic/environmental changes over the last ∼13.5 ka. Depositions of long-range transported dust (likely from the Sahara) and halogens (primarily derived from seawater) were higher for the pre-Holocene, particularly in the late Bølling-Allerød–Younger Dryas period, compared to the Holocene. This synchronous increase could be related to a recognized dust-laden atmosphere, along with the combined effect of (i) an earlier proposed effective transport of Sahara dust for higher latitudes during cold periods and (ii) the progressive Polar Front expansion southwards, with the amplification of halogen activation reactions in lower latitudes due to greater closeness to snow/sea ice (halide-laden) surfaces. Additionally, the orographic blocking of Serra da Estrela may have played a critical role in increasing precipitation of Atlantic origin at higher altitudes, with the presence of snow prompting physical and chemical processes involving halogen species. In the Late Holocene, the dust proxy records highlighted two periods of enhanced input to Lake Peixão, the first (∼3.5–2.7 ka BP) after the end of the last African Humid Period and the second, from the 19th century onwards, agreeing with the advent of commercial agriculture, and human contribution to land degradation and dust emission in the Sahara/Sahel region. The oceanic imprints throughout the Holocene matched well with North Atlantic rapid climatic changes that, in turn, coincided with ice-rafted debris or Bond events and other records of increased storminess for the European coasts. Positive parallel peaks in halogens were found in recent times, probably connected to fire extinction by halogenated alkanes and roadway de-icing.

Rieden tephra layers in the Dottinger Maar lake sediments: Implications for the dating of the Holsteinian interglacial and Elsterian glacial

This study reconstructs the tephrochronology of the infilled Dottinger Maar lake (Eifel, Germany) by analysing the mineralogical composition of tephra layers in lake sediments from the Middle Pleistocene. Three sediment cores document deposits from the Rieden Volcanic Complex. Four distinct tephra layers were identified as the Rieden-leucite-phonolite tuff 1, 3, and 4, and the Weibern-leucite-phonolite tuff 1, which were previously dated by 40Ar/39Ar and indicate a volcanic active phase between 390 and 440 ka before present. In addition, the cores reveal an interglacial section with a typical Holsteinian vegetation succession superimposing Elsterian dust deposits. Annual layer counts, tephrochronology, and high-resolution Corg(chlorins) data were used to align the Dottinger Maar sediments to the EPICA ice core stratigraphy and to link it to Marine Isotope Stages 11 and 12. A comparison of clastic (aeolian) sediments in the Dottinger Maar lake record with the Antarctic EPICA dust stack displays thicker annual layer deposits during higher dust accumulation rates. Based on these lines of evidence, the Dottinger lake sediments date back to 385–457 ka before present.

Spatial analysis of paleoclimate variations based on proxy records in the south-central Andes (18°- 35° S) from 32 to 4 ka

The long-term climate dynamics of the central Andes are part of an ongoing international research effort to reconstruct past climatic variations and sensitivity to different regional and global drivers during the last 50,000 years. The large number of diverse records, however, makes it difficult to compare results without an integrated spatial analysis that considers the nature of the record and whether they are integrating environmental conditions across a large basin (i.e., a lake record) or at a very local scale (such as a rodent midden). We compiled 92 records from the southern sector of the central Andes (SCA, 18°-35°S). Recalibrated records were further compared by converting the original author's interpretation into a scale of relative moisture anomalies (compared to the present) that ranges from −2 (very dry) to very wet (+2). Moisture anomaly maps were generated for intervals at 4, 6, 9.5, 14, 17, 21 and 32 ka BP (103 calibrated 14C years before present) using records within a 5% age uncertainty. Our compilations show a surprising degree of agreement in the extent and magnitude of past climate changes during late Pleistocene, but less spatial agreement during the Holocene. The TRACE21 transient climate model shows similar results, with better agreement during the Pleistocene compared to the Holocene. Our analyses not only reveal discrepancies between proxy record interpretations at sites from the same region but show which regions in the SCA require more study.

A recent Cannabis pollen increase on the Iberian Pyrenees

The continuous, varved and absolutely dated sedimentary record of Lake Montcortès (Iberian Pyrenees) has provided evidence for a distinct and characteristic 20th century (1980s) increase in Cannabis pollen (20C) that persists today. This event was coeval with the geographical shift of the hemp production center in the Iberian Peninsula from east to northeast (where Lake Montcortès lies), which was accompanied by a significant production increase. This increasing trend was fostered by the renewed interest of the paper industry in hemp and was promoted by the onset of European Union subsidies to hemp cultivation. Illegal cannabis crops could have also contributed to the Cannabis pollen increase, but sound evidence is still lacking. These preliminary conclusions should be reinforced by increasing the resolution of the current palynological record and modeling the dispersal of Cannabis pollen around the Montcortès region. More similar high-resolution records are needed to verify the geographical extent of the 20C event. Additionally, Lake Montcortès varved sediments are proposed as a suitable candidate to characterize the onset of the “Anthropocene” epoch (mid-20th century), as currently defined by the Anthropocene Working Group.

Diatom responses to warming, heavy rains and human impact in a Mediterranean lake since the preindustrial period

In the Mediterranean region, annual mean air temperature will continue to increase during the 21st century, while seasonal precipitation is expected to decrease and extreme events to be more frequent. Human-induced climate change will severely impact aquatic ecosystems. A subdecadal stratigraphic diatom record of Lake Montcortès (central Pyrenees) was investigated, focusing on the potential responses of diatoms to anthropogenic warming and catchment alteration. The study includes the end of the Little Ice Age (LIA), the transition to the industrial and postindustrial eras, and the recent global warming and its current acceleration. Sediment samples were treated and diatoms taxonomically identified. Relationships between diatom taxa abundances and climatic (temperature and precipitation) and environmental (land use, soil erosion, and eutrophication) variables were investigated using multivariate statistical methods. The results indicate that, from ca. 1716 to 1971 CE, the diatom community was dominated by Cyclotella cyclopuncta and showed small perturbations, despite the pressure of important stressors such as strong cooling episodes, droughts and an intense use of the lake for hemp retting during the 18th and 19th centuries. However, during the 20th century, other centric species gained relevance, and from the 1970s on, Cyclotella ocellata competed with C. cyclopuncta for dominance. These changes coincided with pulse-like disturbances in the form of extreme rainfall events along with the gradual 20th century increase in global temperature. These perturbations affected the planktonic diatom community and led to instability dynamics. The benthic diatom community did not reflect any comparable shifts under the effect of the same climatic and environmental variables. Because heavy rainfall episodes are likely to intensify with current climate change in the Mediterranean region, their importance as stressors of planktonic primary producers should be taken into account as potential disrupters of biogeochemical cycles and trophic networks of lakes and ponds.

Holocene environmental changes inferred from an oxbow lake in a Mauritia palm swamp (aguajal) in the Madre de Dios region, southeastern Peru

Mauritia peatland palm swamps (locally called aguajales) are typical ecosystems in Madre de Dios River floodplains in southeastern Peru. We investigated a sediment core from an oxbow lake in Los Amigos Aguajal to reconstruct paleoclimatic changes, vegetation dynamics on a regional scale, and human impact using multi-proxy analysis. The results show that the oxbow lake was part of Madre de Dios River's active meandering system and cut off at ca. 1760 cal yr BP. X-Ray Fluorescence results combined with stratigraphy suggest that since the cutting off, the recorded climate was humid until 540 cal yr BP excepting a shortly drier period of 640–610 cal yr BP, but after 540 cal yr BP the climate became less wet until the present. Pollen results show a stable terra firme forest composed primarily by Moraceae/Urticaceae throughout the record. The dense aguajal surrounding the oxbow lake developed from 1240 cal yr BP until the present, but canopy was more open during 780–180 cal yr BP. Hedyosmum became consecutively abundant since 270 cal yr BP until the present. Charcoal analysis indicated almost no human activity in the study area throughout the record. Comparison of the oxbow lake record and the previously studied palm swamp record both from Los Amigos Aguajal shows that: (1) main environmental changes in the palm swamp may correspond to moisture changes; (2) vegetation composition and dynamics on local aguajal and more regional scales are similar, except for the missing period of marsh in the oxbow lake. Furthermore, the oxbow lake record shows less wet conditions during the Little Ice Age and relatively wet in the Medieval Climate Anomaly, which is contrary to many records from the Peruvian Andes. This might be related to elevational differences (lowland vs. mountain) and/or non-climate factors and will need further investigation.

Environmental shifts in and around Lake Pannon during the Tortonian Thermal Maximum based on a multi-proxy record from the Vienna Basin (Austria, Late Miocene, Tortonian)

The Neogene Lake Pannon was the largest lake that ever existed in Europe. It attained its greatest extent during the Tortonian Thermal Maximum. For the first time, results from a detailed lake record documenting about 85 kyr of Late Miocene time in a continuously recovered, 60-m-long, clay-rich core of Lake Pannon are reported. This record includes the transition from the lake's maximum transgression into its highstand at around 10.4 Ma. The environmental development of Lake Pannon during its maximum extent is interpreted based on integrated paleontological, sedimentological, mineralogical and geochemical data. The maximum extent coincided with stable sedimentation of clay, little influx from the hinterland, low surface productivity and severe bottom-water anoxia. The clay mineralogy of the lower part of the core points to prevailing chemical weathering based on the illite/smectite ratios. Distinct Fe, Mn and Ba enrichments are interpreted to have formed close to sulfate-methane transition zones during the maximum flooding. The highstand phase was marked by rapid environmental shifts with frequent phases of well‑oxygenated bottom waters. These phases are reflected by rich benthic communities including stenohaline tunicates. The increased input of detritic kaolinite suggests a shift towards physical weathering and higher precipitation coinciding with a shift in the provenance of clay minerals.Increasing amounts of nutrients stimulated surface water productivity and nannoplankton blooms. Despite the offshore position of the core at ∼8 km from the mountainous ranges of the Alps, strong fluvial input is reflected from 32.5 to 30.3 m by coarser sediment and the occurrence of terrestrial and freshwater molluscs. The Rhenodanubian Flysch Unit was the main source of the siliciclastics of the core and was drained by the Paleo-Wien river. Drainage from the Calcareous Alps was limited to an exceptionally strong fluvial event and related deposits, which documents the presence of a second river in the southwest, which might represent the Paleo-Liesing.The dominance of smectite throughout the core suggests a temperate climate with distinct seasonality during the Tortonian Thermal Maximum. In view of the autochthonous ascidian sclerites in three samples, and assuming generally similar ecological requirements for both Pannonian and modern tunicates, we conclude a polyhaline salinity for Lake Pannon around 10.4 Ma.

Late glacial and Holocene climate in the Kunlun Pass region (northern Tibetan Plateau) inferred from a multi-proxy lake record

Holocene environmental and climate change on the Tibetan Plateau is intensively studied and discussed with the aim to better understand the factors controlling the hydrology of individual river catchments and especially the availability of water which is of utmost significance for the communities downstream in times of rapid climate change. Thus, a late glacial and Holocene sediment record from Lake Heihai in the Kunlun-Pass region was investigated using ostracod and geochemical analyses. Cold and dry conditions were inferred between ca. 12.9 and 12.3 cal ka BP and higher temperatures before and afterwards. The cold spell probably corresponds to the Younger Dryas (YD) event in the North Atlantic region. Warmer and wetter conditions with highest lake levels and decreased lake-water salinity were recorded from ca. 10.8 to 7.0 cal ka BP when the summer monsoon was strengthened. The cold 8.2 cal ka BP event is not significantly recorded in the region probably due to the predominance of the summer monsoon over the westerlies. A declined lake level and increased lake-water salinity as the result of cold and dry conditions are inferred from ca. 7.0 to 4.5 cal ka BP when the strengthening of the mid-latitude westerly circulation probably triggered glacier advances in the catchment. An even lower lake level existed during cold conditions with glacier advances from ca. 4.5 to 1.2 cal ka BP. The level of Lake Heihai rose again after ca. 1.2 cal ka BP due to warmer conditions, causing the retreat of glaciers and higher runoff. Our record from the Kunlun Pass region provides further evidence for the catchment-specific response of hydrographical systems which are partly controlled by glaciers as major water sources.

Climatic and hydrological variations on the southwestern Tibetan Plateau during the last 30,000 years inferred from a sediment core of Lake Zabuye

Climate change on the Tibetan Plateau (TP) is governed by the mid-latitude westerlies and Indian summer monsoon (ISM). However, the past hydrological changes on the TP induced by interactions between the westerlies and the ISM remain unclear. A sediment core from Lake Zabuye on the southwestern TP was analyzed to reconstruct climatic and hydrological variability over the last 30 kyr. Stable isotopic compositions (δ13C and δ18O) of authigenic carbonate act as an indicator of hydrological status for closed-basin lakes on the TP. Four major climatic and hydrological stages were identified: (1) last glacial maximum (29.8–18.9 cal kyr BP), the influence of the westerlies dominated, and a cold-wet climate prevailed; (2) last deglaciation (18.9–11.8 cal kyr BP), the influence of the westerlies receded, and a general trend of decreased wetness was interrupted by two pronounced glacial meltwater events recorded at 17.2 and 15.2 cal kyr BP, respectively; (3) early and middle Holocene (11.8–3.8 cal kyr BP), the Holocene climate optimum was attained and sustained under the dominance of ISM circulation; (4) late Holocene (from 3.8 cal kyr BP to the present), the ISM collapsed during the middle to late Holocene, and a hypersaline lacustrine environment was ultimately formed, as inferred from mirabilite deposition and isotopic signals. Our lake record demonstrates an anti-phase relationships between the westerlies and the ISM on the glacial-interglacial timescale over the southwestern TP. We suggest that both North Atlantic climate and tropical ocean temperature are major drivers of climatic variations on the TP.

Paleoeconomy more than demography determined prehistoric human impact in Arctic Norway.

Population size has increasingly been taken as the driver of past human environmental impact worldwide, and particularly in the Arctic. However, sedimentary ancient DNA (sedaDNA), pollen and archaeological data show that over the last 12,000 years, paleoeconomy and culture determined human impacts on the terrestrial ecology of Arctic Norway. The large Mortensnes site complex (Ceavccageađgi, 70°N) has yielded the most comprehensive multiproxy record in the Arctic to date. The site saw occupation from the Pioneer period (c. 10,000cal. years BP) with more intensive use from c. 4,200 to 2,000cal. years BP and after 1,600cal. years BP. Here, we combine on-site environmental archaeology with a near-site lake record of plant and animal sedaDNA. The rich animal sedaDNA data (42 taxa) and on-site faunal analyses reveal switches in human dietary composition from early-Holocene fish+marine mammals, to mixed marine+reindeer, then finally to marine+reindeer+domesticates (sheep, cattle, pigs), with highest reindeer concentrations in the last millennium. Archaeological evidence suggests these changes are not directly driven by climate or variation in population densities at the site or in the region, but rather are the result of changing socio-economic activities and culture, probably reflecting settlers' origins. This large settlement only had discernable effects on its hinterland in the last 3,600 years (grazing) and more markedly in the last 1,000 years through reindeer keeping/herding and, possibly domestic stock. Near-site sedaDNA can be linked to and validate the faunal record from archaeological excavations, demonstrating that environmental impacts can be assessed at a landscape scale.

Stable carbon isotope values of syndepositional carbonate spherules and micrite record spatial and temporal changes in photosynthesis intensity.

Marine and lacustrine carbonate minerals preserve carbon cycle information, and their stable carbon isotope values (δ13C) are frequently used to infer and reconstruct paleoenvironmental changes. However, multiple processes can influence the δ13C values of bulk carbonates, confounding the interpretation of these values in terms of conditions at the time of mineral precipitation. Co‐existing carbonate forms may represent different environmental conditions, yet few studies have analyzed δ13C values of syndepositional carbonate grains of varying morphologies to investigate their origins. Here, we combine stable isotope analyses, metagenomics, and geochemical modeling to interpret δ13C values of syndepositional carbonate spherules (>500 μm) and fine‐grained micrite (<63 μm) from a ~1600‐year‐long sediment record of a hypersaline lake located on the coral atoll of Kiritimati, Republic of Kiribati (1.9°N, 157.4°W). Petrographic, mineralogic, and stable isotope results suggest that both carbonate fractions precipitate in situ with minor diagenetic alterations. The δ13C values of spherules are high compared to the syndepositional micrite and cannot be explained by mineral differences or external perturbations, suggesting a role for local biological processes. We use geochemical modeling to test the hypothesis that the spherules form in the surface microbial mat during peak diurnal photosynthesis when the δ13C value of dissolved inorganic carbon is elevated. In contrast, we hypothesize that the micrite may precipitate more continuously in the water as well as in sub‐surface, heterotrophic layers of the microbial mat. Both metagenome and geochemical model results support a critical role for photosynthesis in influencing carbonate δ13C values. The down‐core spherule–micrite offset in δ13C values also aligns with total organic carbon values, suggesting that the difference in the δ13C values of spherules and micrite may be a more robust, inorganic indicator of variability in productivity and local biological processes through time than the δ13C values of individual carbonate forms.