An array of lake sediment proxies including paleobotanic, geochemical, and historical records has been used to determine former environments of Bugbee Pond, a small, mesotrophic pond in northeastern ...Minnesota. Much research has been produced on the history of climate and vegetation change of the region, yet we have little information on the impact of human settlement. This well-dated, high resolution, multi-proxy record is important for its length and concentration on the historic period. The lake itself became established by ~7000 years ago. Pollen evidence suggests a transition between the regional Prairie Period to the Great Lakes mixed conifer – hardwood forest was established in the region at this time. XRF data suggest dry basin accumulation early in the record after ~7000 cal yr BP, but lake levels substantially increased by ~5600 cal yr BP, during a regionwide climatic transition to more humid conditions. Birch and boreal conifers increased after about 3800 cal yr BP; further increases in boreal conifers occurred by ~2000 cal yr BP. Anthropogenic vegetation changes during the Historic period, beginning in the late 19th century, is well represented by forest clearance of white pine (Pinus strobus), followed by increases in early successional species and an increased sediment accumulation rate due to land clearance. Establishment of farming communities locally are shown by occurrence of corn (Zea mays) and oat (Avena sativa) pollen, and pasturing and grazing are documented by Rumex, Fabaceae and Poaceae pollen, as well as coprophilous fungi, such as Sordaria. The increase and subsequent decline in Pb and S concentrations in the uppermost sediments are mirrored by historically documented, nearby industrial activities.
Lake Van sediment cores from the Ahlat Ridge and Northern Basin drill sites of the ICDP project PALEOVAN contain a wealth of information about past environmental processes. The sedimentary sequence ...was dated using climatostratigraphic alignment, varve chronology, tephrostratigraphy, argon–argon single-crystal dating, radiocarbon dating, magnetostratigraphy, and cosmogenic nuclides. Based on the lithostratigraphic framework, the different age constraints are compiled and a robust and precise chronology of the 600,000 year-old Lake Van record is constructed. Proxy records of total organic carbon content and sediment color, together with the calcium/potassium-ratios and arboreal pollen percentages of the 166-m-long event-corrected Ahlat Ridge record, mimic the Greenland isotope stratotype (NGRIP). Therefore, the proxy records are systematically aligned to the onsets of interstadials reflected in the NGRIP and synthesized Greenland ice-core stratigraphy. The chronology is constructed using 49 age control points derived from visual synchronization with the Greenland ice-core stratigraphy using the GICC05 timescale, an absolutely-dated speleothem timescale (e.g., Hulu, Sanbao, Linzhu cave) and the Epica Dome C timescale. In addition, the uppermost part of the sequence is complemented with four ages from Holocene varve chronology and three calibrated radiocarbon ages. Furthermore, nine argon–argon ages and a comparison of the relative paleointensity record of the magnetic field with reference curve PISO-1500 confirm the accuracy of the age model. Also the identification of the Laschamp event via measurements of 10Be in the sediment confirms the presented age model. The chronology of the Ahlat Ridge record is transferred to the 79-m-long event-corrected composite record from the Northern Basin and supplemented by additional radiocarbon dating on organic marco-remains. The basal age of the Northern Basin record is estimated at ∼90 ka. The variations of the time series of total organic carbon content, the Ca/K ratio, and the arboreal pollen percentages illustrate that the presented chronology links ice-marine-terrestrial stratigraphies and that the paleoclimate data are suited for reconstructions and modeling of the Quaternary and Pleistocene climate evolution in the Near East at millennial timescales. Furthermore, the chronology of the last 250 ka can be used to test other dating techniques.
•Long lacustrine drill cores were dated using a suite of age constraints.•A robust chronology of the 600,000 year-old Lake Van record is constructed.•Proxy records are aligned to the NGRIP/GLT syn ice-core stratigraphy.•Ar/Ar ages, 14C, relative paleointensity and 10Be confirm the age model.
A well-dated suite of Lake Van climate-proxy data covering the last 360 ka documents environmental changes over 4 glacial/interglacial cycles in Eastern Anatolia, Turkey. The picture of cold and dry ...glacials and warm and wet interglacials emerging from pollen, organic carbon, authigenic carbonate content, elemental profiling by XRF and lithological analyses is inconsistent with classical interpretation of oxygen isotopic composition of carbonates pointing to a more complex pattern in Lake Van region. Detailed analysis of glacial terminations allows for the constraining of a depositional model explaining different patterns observed in all the proxies. We hypothesize that variations in relative contribution of rainfall, snowmelt and glacier meltwater recharging the basin have a very important role for all sedimentary processes in Lake Van. Lake level of glacial Lake Van, predominantly fed by snowmelt, was low, the water column was oxic, and carbonates precipitating in the epilimnion recorded the light isotopic signature of inflow. During terminations, increasing rainfall and significant supply of mountain glaciers' meltwater contributed to lake level rise. Increased rainfall enhanced density gradients in the water column, and hindered mixing leading to development of bottom-water anoxia. Carbonates precipitating during terminations show large fluctuations in their isotopic composition. Full interglacial conditions in Lake Van are characterized by high or slowly falling lake level. Rainfall and snowmelt feed the lake but due to re-established mixing, the isotopic composition of authigenic carbonates is heavier and closer to that of evaporation-influenced lake water than that of runoff representing snowmelt and atmospheric precipitation.
•Lake Van climate-proxy data document changes in Turkey for the last 360 ka.•Switch from snowmelt-fed to rainfall-fed runoff control the δ18O of carbonates.•Most Lake Van data imply dry glacial/wet interglacial conditions in Eastern Mediterranean.•But oxygen isotopes show a more complex pattern.
Fossil long-chain alkenones have been used for several decades to reconstruct past ocean surface water temperatures and gained recent interest as a paleotemperature proxy for continental lake ...settings. However, factors besides temperature can affect alkenone distributions in haptophyte algae, and alkenone compositions can differ between haptophyte species. Alkenone-biosynthesizing haptophyte algae are genetically much more diverse in lakes than in the marine realm, and species-level variations in alkenone compositions could have implications for alkenone paleothermometry. Here, we performed a paired analysis of alkenone distributions and haptophyte species compositions using ancient DNA in up to 270 ka-old sediments of Lake Van in Turkey to reveal a possible species-effect on fossil alkenone distributions and paleotemperature estimates. The same predominant haptophyte in Lake Van today prevailed also since the last ∼100 ka. However, a calibration of alkenone paleotemperature especially in the oldest analyzed intervals is complicated due to a more complex haptophyte species composition predominated by a haptophyte (LVHap_6), which is phylogenetically different from sequences recovered from currently existing lakes including Lake Van and from haptophyte species existing in culture. The predominance of LVHap_6 coincided with the presence of alkenone MeC38:3 and relatively high MeC37:3/4 (2.4) and MeC38:4/5 ratios (3.0). Uk37 index values in the sediment core over the last 270 ka reflect relative changes in past temperature and are additionally linked to haptophyte species composition. A sustained period of high salinity, as indicated by pore-water salinity measurements, could potentially have triggered the succession of haptophytes as sources of alkenones in Lake Van.
•Alkenone analyses in a record from Eastern Anatolia covering the past 270 ka.•New insight into the influence of haptophyte species on alkenone distribution.•Semi-quantitative link between Uk37 index and past temperatures in Lake Van.
Lake Chalco lies south of the Basin of Mexico and has been the subject of studies related to Late Quaternary climate variability. In 2016, the International Continental Scientific Drilling Program ...“MexiDrill Project” recovered a 520-m sediment record from Lake Chalco. Magnetic susceptibility measurements revealed substantial changes in sediment physical properties between 343 and 285 m depth, suggesting changes in composition associated with fluctuations in the depositional environment. We targeted sediments in the 343–285 m interval for high-resolution facies analysis, to develop a model of Lake Chalco formation. We identified three facies associations, using sediment composition, texture, mineralogy and micro-morphological characteristics: (1) detrital facies, consisting of laminated silt, massive sand, stratified silty sand, clast-supported gravel and matrix-supported gravel; (2) biogenic facies, which include diatom ooze and bivalve coquina; and (3) volcaniclastic facies, represented by clast-supported pumice deposits. We propose that formation of Lake Chalco occurred in four stages, which we identified by changes in sediment characteristics. The first stage was an alluvial delta environment, in which debris and hyper-concentrated flows were the main sediment transport agents. The second was characterized by turbulent flows in a fluvial deltaic environment, which alternated with laminar flows associated with floodplains. The third stage was a time of fluvio-lacustrine transition in the basin, with formation of the previously identified Paleo-Chalco-I Lake, in response to wet conditions. During the fourth stage, a deep eutrophic lake formed (Paleo-Chalco-II), with an origin that appears to have been related to regional volcanism. Our working age-depth model indicates establishment of the lake at ca. 400 ± 46 ka. This paper presents the only available record of the transition from alluvial to lacustrine sedimentation of Lake Chalco. Our results allow us to establish (1) how the lake was formed and what the phases of its development were, (2) how a major volcanic event altered and transformed the lacustrine sedimentation, and (3) which climatic conditions dominated during the lake formation. The age for the onset of the lacustrine sedimentation in Chalco is for the first time constrained to around 400 ka. This enables to expand our knowledge of the climate for a time for which there is no information from terrestrial records of tropical North America.
In closed-basin lakes, sediment porewater salinity can potentially be used as a conservative tracer to reconstruct past fluctuations in lake level. However, until now, porewater salinity profiles did ...not allow quantitative estimates of past lake-level changes because, in contrast to the oceans, significant salinity changes (e.g., local concentration minima and maxima) had never been observed in lacustrine sediments. Here we show that the salinity measured in the sediment pore water of Lake Van (Turkey) allows straightforward reconstruction of two major transgressions and a major regression that occurred during the last 250 ka. We observed strong changes in the vertical salinity profiles of the pore water of the uppermost 100 m of the sediments in Lake Van. As the salinity balance of Lake Van is almost at steady-state, these salinity changes indicate major lake-level changes in the past. In line with previous studies on lake terraces and with seismic and sedimentological surveys, we identify two major transgressions of up to +105 m with respect to the current lake level at about 135 ka BP and 248 ka BP starting at the onset of the two previous interglacials (MIS5e and MIS7), and a major regression of about -200 m at about 30 ka BP during the last ice age.
Lake Van is the fourth largest terminal lake in the world (38.5°N, 43°E, volume 607 km3, area 3570 km2, maximum water depth 460 m), extending for 130 km WSW–ENE on the eastern Anatolian high plateau, ...Turkey. The sedimentary record of Lake Van, partly laminated, obtains a long and continuous continental sequence that covers multiple interglacial–glacial cycles. Promoted by the potential of the sedimentary sequence for reconstructing the paleoecological and paleoclimate development of the Near East, a deep drilling operation was carried out in 2010 supported by the International Continental Scientific Drilling Program (ICDP). The 219 m long continental pollen record presented here is based on a well-dated composite profile drilled on the so-called Ahlat Ridge in water depth of 360 m encompassing the last 600,000 years. It is the longest continuous continental pollen record of the Quaternary in the entire Near East and central Asia obtained to date. The glacial–interglacial cycles and pronounced interstadials are clearly reflected in the vegetation development based on millennial-scale time resolution. In general, the glacial/stadial vegetation is characterized by dwarf-shrub steppe and desert steppe, whereas the climax vegetation of past interglacials can be described as oak steppe-forest similar to the present interglacial in this sensitive semi-arid region between the Black, Caspian, and Mediterranean Seas. By comparing the Lake Van pollen record with other western Asian and southern European long continental pollen sequences as well as marine and ice-core records, the regional variability of the climate signals is also discussed.
•Lake Van record is the longest Quaternary paleoclimate archive in the Near East.•It documents multiple glacial–interglacial cycles encompassing the last 600 ka.•The pollen data reflect high-amplitude climate shifts.•The results are compared with continental, marine and ice-core records.
We here estimate past temperature and hydroclimate variations in eastern Anatolia for marine isotope stages 4 to 1 (MIS4 to MIS1) respectively using branched glycerol dialkyl glycerol tetraethers ...(brGDGTs) and the hydrogen isotopic composition of n-C29 leaf-wax n-alkanes (δ2Hwax) stored in the sedimentary record of Lake Van (Turkey). Our millennial-scale lipid biomarker records reflect warm and wet conditions during interstadials/interglacials and colder and dryer periods with increased evapotranspiration and aridity during stadials/glacials. The degree of methylation of the 5-methyl brGDGTs (MBT´5me) indicates increasing mean annual air temperatures (MAT) during stadial/interstadial transitions, that characterize Dansgaard-Oeschger events, and during the last glacial termination.
Based on the effects of changes in precipitation amount on apparent enrichment factors between the δ2H of the C29n-alkanes and δ2H of precipitation, a total increase in annual precipitation of about 200 mm during transitions from stadials to interstadials, and of 300–350 mm during glacial-interglacial transitions can be determined, in line with previous paleoclimate reconstructions for the Eastern Mediterranean.
High sterol concentrations in sediments deposited during warm and humid interstadials reflect increases in lake level, vegetation density and algal blooms, whereas lower values of the branched versus isoprenoid tetraethers ratio (BIT) likely reflects the increased niche of Thaumarchaeota resulting from enhanced windiness and mixing of the water column during colder periods. This quantitative hydroclimate reconstruction from Lake Van (Turkey), as it is optimally situated to respond to North Atlantic climate change via changes in the large-scale wind fields shed light into millennial-scale global climate variability.
•70 kyr-long reconstruction of millennial-scale climate variability from Lake Van.•BrGDGTs and hydrogen isotope data obtained from long-chain n-alkanes were used.•BrGDGTs show that MAT fluctuates during global climate transitions.•δ2H of fatty acids and plant wax alkanes indicate warm/humid and cold/dry conditions.•Algal blooms occurred during periods of warmer climate and increased humidity.
Millennial to orbital-scale rainfall changes in the Mediterranean region and corresponding variations in vegetation patterns were the result of large-scale atmospheric reorganizations. In spite of ...recent efforts to reconstruct this variability using a range of proxy archives, the underlying physical mechanisms have remained elusive. Through the analysis of a new high-resolution sedimentary section from Lake Van (Turkey) along with climate modeling experiments, we identify massive droughts in the Eastern Mediterranean for the past four glacial cycles, which have a pervasive link with known intervals of enhanced North Atlantic glacial iceberg calving, weaker Atlantic Meridional Overturning Circulation and Dansgaard-Oeschger cold conditions. On orbital timescales, the topographic effect of large Northern Hemisphere ice sheets and periods with minimum insolation seasonality further exacerbated drought intensities by suppressing both summer and winter precipitation.
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•Eastern Mediterranean climate reconstruction of Dansgaard-Oeschger variability over 360 k.•Lake Van multi-proxy hydroclimate index correlates well with transient LOVECLIM simulations.•Droughts in the EM for the past three glacial cycles show a pervasive link with DO stadials.•North Atlantic stadials generate anticyclonic circulation anomaly over EM.•NH ice sheets exacerbated large-scale glacial drying in the EM.
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