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The 18 papers in this Special Issue of the Journal of Paleolimnology report new records of Holocene environmental and climate change from Arctic lake sediment. At least 15 distinct physical, chemical, and biological properties were analyzed at lakes located across the North American Arctic and subarctic, and northwestern Europe. The studies are notable for their multi-proxy approach (eight present data for at least five different proxies), and for the high quality of their geochronological control. Three of the studies analyzed sediment from more than one lake to test the influence of contrasting physiographic settings on the response of proxies to the same climate forcing. The sedimentary sequences analyzed in seven studies extend beyond 11.5 cal ka, providing evidence for pronounced climate shifts that took place during the late-glacial period. Two-thirds extend beyond 8 cal ka; many of these records were interpreted in terms of the shift in temperature and moisture that occurred during the transition from the warm early to middle Holocene to the cooler late Holocene. These records contribute to the growing network of sites that is needed to reconstruct the spatial pattern of this pronounced paleoclimate transition, and to address how ocean-atmospheric circulation changed with the mean state of climate. [ABSTRACT FROM AUTHOR]

Knowledge of paleoclimates and past climate change is important to put recent and future climate change in perspective. In the absence of well-developed methodology to reconstruct paleoprecipitation the majority of climate reconstructions focus on temperature, whereas precipitation is an equally important climate parameter. This paper explores the possibility of inferring paleoprecipitation from lake-level records by inverse hydrological modelling. Pollen spectra of a lacustrine sediment core were used to infer changes in past temperatures and lake levels during the past 14,000 years. A hydrological model that calculates lake levels using meteorological parameters and a digital terrain model were developed for the catchment area of Lake La Cocha. After calibration the model accurately simulated modern lake levels. A sensitivity analysis shows that the model results are most sensitive to temperature and precipitation. This hydrological model was subsequently used to estimate mean annual precipitation needed to reproduce the pollen-based reconstructed lake levels (inverse modelling). The lake currently discharges through the permanent Guamués River, with a modelled mean annual discharge of 3.6 m s. However, past lake levels and hydrological modelling results suggest that Lake La Cocha has been free of discharge during most of the Holocene, and after an intermittent phase only recently started discharging permanently. The uncertainty in the inferred precipitation during the discharge-free period is estimated at ~22 mm. Quasi stable lake levels seem to justify using equilibrium conditions when reconstructing precipitation. Early Holocene lake levels were ~10 m lower than modern values, implying that precipitation must have been 30-40 % less than today. [ABSTRACT FROM AUTHOR]

This paper reviews the past history of comparisons between lacustrine records of chironomid-inferred summer temperatures (CI-T) and peat bog-derived records of surface wetness (BSW), and develops a new summer temperature record for the mid-late Holocene for Northern Britain from Bigland Tarn, Cumbria. The CI-T reconstruction is well dated, and corresponds well with the only two other CI-T records for Britain. Comparisons are made with BSW records from northern Britain, which show consistent similarities over centennial to millennial timescales, demonstrating that at this resolution cooler summers equated with a wetter climate, at least during the mid- to late-Holocene. [ABSTRACT FROM AUTHOR]

Jezioro Lake is the only natural lake in southern Poland outside mountainous areas to have existed continuously since the Pleistocene. The record of environmental change in the Late Vistulian (Weichselian) and Holocene is preserved in the deposits and landforms around the lake. This paper presents the results of paleogeographical and paleoecological research that emabled us to reconstruct the history of the Jezioro Lake. At the end of the Vistulian period, the outlet of the lake was blocked by a parabolic dune moving in from the west. Limnic sedimentation was evident in the sediment core at all levels from the Holocene, with remains of Cladocera, Chironomidae larvae, and aquatic plants. The lake did not disappear at that time, although its area decreased by a factor of 12 by the end of the period. Paleobotanical research permitted the reconstruction of sequences of plant communities and changes in nutrient status and water level. An initial oligotrophic lake, as indicated by the presence of Isoëtes lacustris L., changed to a eutrophic lake, as indicated by the presence of Potamogeton natans L. and Nuphar sp., then the lake progressed to the present-day dystrophic lake that is surrounded by a swamp. The profile of organic deposits contains a record of environmental change at least since the Younger Dryas in southern Poland. [ABSTRACT FROM AUTHOR]

Geochemical data obtained from X-ray fluorescence, physical properties, total organic and inorganic carbon content (TOC/TIC), and diatom analysis from a 6.61-m-long sedimentary sequence near the modern northern shore of Lake Zirahuen (101° 44′ W, 19° 26′ N, 2000 m asl) provide a reconstruction of lacustrine sedimentation during the last approximately 17 cal kyr BP. A time scale is based on ten AMS C dates and by tephra layers from Jorullo (AD 1759-1764) and Paricutin (AD 1943-1952) volcanoes. The multiproxy analyses presented in this study reveal abrupt changes in environmental and climatic conditions. The results are compared to the paleo-record from nearby Lake Patzcuaro. Dry conditions and low lake level are inferred in the late Pleistocene until ca. 15 cal kyr BP, followed by a slight but sustained increase in lake level, as well as a higher productivity, peaking at ca. 12.1 cal kyr BP. This interpretation is consistent with several regional climatic reconstructions in central Mexico, but it is in opposition to record from Lake Patzcuaro. A sediment hiatus bracketed between 12.1 and 7.2 cal kyr BP suggests a drop in lake level in response to a dry early Holocene. A deeper, more eutrophic and turbid lake is recorded after 7.2 cal kyr BP. Lake level at the coring site during the mid Holocene is considered the highest for the past 17 cal kyr BP. The emplacement of the La Magueyera lava flows (LMLF), dated by thermoluminiscence at 6560 ± 950 year, may have reduced basin volume and contributed to the relative deepening of the lake after 7.2 cal kyr BP. The late Holocene (after 3.9 cal kyr BP) climate is characterized by high instability. Extensive erosion, lower lake levels, dry conditions and pulses of high sediment influx due to high rainfall are inferred for this time. Further decrease in lake level and increased erosion are recorded after ca. AD 1050, at the peak of Purepechas occupation (AD 1300-1521), and until the eighteenth century. Few lacustrine records extend back to the late Pleistocene-early Holocene in central Mexico; this paper contributes to the understanding of late Pleistocene-Holocene paleoclimates in this region. [ABSTRACT FROM AUTHOR]

Lake Elsinore is the largest natural lake in Southern California. As such, the lake provides a unique opportunity to investigate terrestrial climate on timescales otherwise underrepresented in the region’s terrestrial environment. In November 2003, three ∼10 m drill cores were extracted from the depocenter region of Lake Elsinore. These drill cores, spanning the past 9,500–11,200 calendar years, represent the first complete Holocene record of terrestrial climate from Southern California. In this paper, we focus on two adjacent, depocenter cores (LEGC03-2 and LEGC03-3), which have been correlated to develop a single composite core. Twenty-two AMS 14C dates on bulk organic matter and one cross-correlated exotic pollen age constitute the composite core’s age control. Several methods of analysis, including mass magnetic susceptibility, % total organic matter, % total carbonate, % HCl-extractable Al, and total inorganic P are used to infer climate for the past 9,500 calendar years in Southern California. Together, these data indicate a wet early Holocene followed by a long-term drying trend. Recent lake-level reconstructions from Owens Lake and Tulare Lake support our contention for a wetter-than-today early Holocene. Lacustrine sediments from the Mojave Desert also support our conclusions. We suggest that over the duration of the Holocene changing summer/winter insolation alters the region’s long-term hydrologic balance through its modulation of atmospheric circulation and its associated storm tracks. Minimum early Holocene winter insolation and maximum summer insolation act together to increase the region’s total annual precipitation by increasing the frequency of winter storms as well as enhancing the magnitude and spatial extent of the North American monsoon, the frequency of land-falling tropical cyclones in Southern California, and regional convective storms, respectively. Gradual decreases in summer insolation and increases in winter insolation produce the opposite effect with maximum drying in the late Holocene. [ABSTRACT FROM AUTHOR]

Tanypodinae usually form an important component in subfossil Chironomidae assemblages but can be difficult to identify beyond subfamily level due to fragmentation of subfossil material. However, generic identification of most subfossil specimens can be achieved by reference to the arrangement of cephalic setae. This paper presents the first identification guide to Holarctic Tanypodinae genera based on the cephalic setae. A total of 33 genera is described and illustrated, of which 9 were previously undescribed, and 26 descriptions are based on new material. A total of 42 species is illustrated to show intrageneric and intraspecific variation. Improved taxonomic resolution will enhance the performance of chironomid-environmental variable inference models and chironomid biostratigraphy. [ABSTRACT FROM AUTHOR]

This paper reports a first estimate of the Holocene lake sediment carbon pool in Alberta, Canada. The organic matter content of lake sediment does not appear to depend strongly on lake size or other limnological parameters, allowing a simple first estimate in which we assume all Alberta lake sediment to have the same organic matter content. Alberta lake sediments sequester about 15 g C m-2 yr-1, for a provincial total of 0.23 Tg C yr-1, or 2.3 Pg C over the Holocene. Alberta lakes may represent as much as 1/1700 of total global, annual permanent carbon sequestration. [ABSTRACT FROM AUTHOR]

The paper involves detailed geochemical and mineralogical analysis of lacustrine sediments from a 95 cm core profile collected in the closed lake basin of the Laguna de Gallocanta, central Iberian Chain. The environmental and depositional changes are confirmed by: (1) variations in concentrations of SiO2, CaO and P2O5, (2) Fe2O3:MnO-ratios, (3) ς(CaO,MgO):SiO2-ratio, (4) statistical relationship of silica and phosphate content to metallic oxide content, (5) the Mg:Ca-ratio of protodolomites in relation to the position of the diffraction angle of dolomite's major diffraction peak (dol100, and (6) changes in mineralogical composition. Three sedimentary units were identifyed and characterized by their mineralogical and geochemical composition. The deposition of the underlying strata (section 1) occurred under sub-arid conditions. The environment changed to sub-humid conditions during deposition of the sediments in section 2 (post Middle Ages). Increasing aridity influenced the accumulation of the upper sediments (section 3). It is also proven that mineralogical analyses of lacustrine sediments allows mostly conclusions on the limnic environments during deposition. In contrast to this, geochemical features of lacustrine sediments indicate weathering and soil forming processes during deposition and the overall geomorphological system. [ABSTRACT FROM AUTHOR]

A 27.15-m-long core from Lake Chapala, west-central Mexico (1520 masl) possesses a continuous 15,000-year record of sediment accumulation with abundant diatoms, pollen, charcoal particles, and organic and inorganic carbon. Analyses of multiple sediment variables revealed the lake was deep, dominated by Stephanodiscus niagarae, and was surrounded by temperate forests of Pinus, Quercus, and Alnus in the late Pleistocene (14,700–12,760 cal yr BP). During the Pleistocene-Holocene transition (12,760–9660 cal yr BP), the lake level dropped and a temperate forest of Pinus and Quercus occupied the watershed and was persistently affected by fire. During the earliest Holocene, Quercus nearly disappeared and Pinus, relatively abundant, declined abruptly. Pollen of dry forests became more common, indicating the onset of drier conditions in the region. During the interval from 7500 to 6500 cal yr BP, more humid climate conditions prevailed and abundant Surirella spp. diatom valves were well preserved. Sediments of the time also contain Stephanodiscus niagarae and Ulnaria acus, suggesting deep-water conditions. Between 6500 and 2000 cal yr BP, the lake experienced higher conductivity and longer water residence times. The Pinus and Quercus forests began to be replaced by open vegetation, with Asteraceae and Poaceae dominating the pollen spectrum. Lake level fluctuated, but overall declined. Between the interval of ca. 2 ky to 0.5 cal yr BP basin conditions remained relatively wet. During the last ~ 0.5 kyr BP to present day, the lake level declined and ionic concentration increased, as inferred from representation of planktonic and benthic saline diatom taxa and TIC increases. Numerous micro-tephras are common in this interval; additionally, frequent fires favored the dominance of Poaceae. Paleolimnological records suggest that after the Last Glacial Maximum, Chapala and other lakes of west-central Mexico maintained relatively high water levels. Some records from the region showed evidence of increased humidity beginning ca. 8200 cal yr BP, a consequence of strength intensification in North American Monsoon, associated with ENSO variability and/or tropical cyclones. The record from the last 0.5 cal yr BP in Lake Chapala is similar to records from other lakes in Central Mexico, as it displays a trend toward drier conditions with a more variable precipitation regime. [ABSTRACT FROM AUTHOR]

Lake sediments are important archives of past climate variability and lake responses to climate. In order to accurately infer past climates, it is necessary to understand, and account for, the ecological processes that affect the record of indicators preserved in lake sediment. This is particularly the case with respect to the concentration of carbon and nitrogen (TOC, TN, and calculated C:N), and the stable isotope composition of organic matter preserved in lake sediments. These are common, yet ambiguous, tracers of environmental change. Ideally, palaeoenvironmental reconstructions using the concentration and isotope composition of organic matter should be grounded in a detailed understanding of the sources of the organic material. This study documents the history and evolution of Blue Lake, an environmentally and culturally important oligotrophic, groundwater window lake on North Stradbroke Island, Queensland, Australia. We utilise organic matter δ13C, TOC, TN, and C:N from a 2.4 m sediment core with a basal age of 7.5 cal kyr BP, to investigate changing organic matter sources as a measure of the climate sensitivity of Blue Lake. This interpretation is supported by data from contemporary algae, aquatic and terrestrial plants, and catchment soils. We show that lake nutrient dynamics drove an increase in algal biomass at 4.2 cal kyr BP. This change coincides with a widely documented intensification of the El Niño-Southern Oscillation, which we infer to have influenced lake nutrient concentrations by reducing groundwater throughflow. Climatic changes resulted in marked changes in lake primary productivity, despite relatively little turnover of the lake diatom flora and catchment vegetation. This suggests that south-east Queensland dune lakes are sensitive to climate changes and helps to refine past and future palaeoclimate research using sediments from these lakes. It also indicates that increased nutrient concentrations in Blue Lake may result from projected changes in 21st Century climate. [ABSTRACT FROM AUTHOR]

We present a multiproxy paleoclimate record using leaf wax hydrogen isotopes (δH) and varve thickness from Arctic proglacial lake sediments. We also provide one of the first evaluations of the utility of δH as a paleoclimate proxy in Arctic proglacial lakes. We compare varve thickness and δH at sub-decadal resolution from 1948 to 2004 AD, and at sub-centennial resolution from 1450 to 2004 AD. Varve thickness and δH both contain large interannual variability and are anti-correlated during the late twentieth century, suggesting that both proxies respond rapidly, but by different mechanisms, to catchment-scale forcings. At longer time scales, varve thickness exhibits a strong response to Little Ice Age cooling (1661-1827 AD in this record) but does not show evidence for twentieth century warming recorded throughout the Arctic. δH does record regional-scale temperature changes, with more H-depleted values during the Little Ice Age and an abrupt change to more H-enriched values in the twentieth century. This corresponds well with a recent Arctic-wide temperature reconstruction in which the seventeenth century is the coldest interval, and the twentieth century is the warmest interval. Our results suggest that δH is a promising proxy that can be applied at high resolution in proglacial Arctic lakes. [ABSTRACT FROM AUTHOR]

Sub-bottom profiling was conducted at eight sub-basins within the lower French River area, Ontario, to investigate deposits preserved within the ancient North Bay outlet. Ten cores were collected that targeted the four depositional acoustic facies identified in the sub-bottom profiling records. The rhythmically laminated/bedded glaciolacustrine deposits of facies I are interpreted to have aggraded within glacial Lake Algonquin and its associated recessional lakes that persisted between 13,000 and 11,300 cal BP (~11,100 and 9,900 BP). The majority of the facies II, III and IV lacustrine deposits accumulated between about 9,500 cal BP (~8,500 BP) and the mid-Holocene, based on radiocarbon-dated organic materials. These deposits represent sedimentation within a 'large' lake during the late portion of the Mattawa-Stanley phase, and the Nipissing transgression, Nipissing Great Lakes and post-Nipissing recession phases of lake levels. Two sets of organic-rich sand beds are preserved within facies II deposits and reveal that the large lake lacustrine depositional environment was interrupted during the late Mattawa-Stanley phase between 9,500-9,300 and 9,000-8,400 cal BP (~8,500-8,300 and ~8,000-7,600 BP), when the water surface of Lake Hough fell below the outlet threshold and the lake basin became hydrologically closed. Pre-9,500 cal BP (~8,500 BP), the early and middle portions of the Mattawa-Stanley phase were dominated by erosion, as reflected by an unconformity at the base of facies II that occurs widely in the sub-basins and the general lack of preserved deposits for these intervals in the cores. This erosion is attributed to wave action and fluvial scouring within the outlet mouth during the early and mid-Stanley-Hough low stages and relates specifically to the period when the flowing portion of the North Bay outlet was situated over the lower French River area. This study reveals that the majority of the post-glacial deposits accumulated after the outlet threshold had shifted permanently eastwards and the lower French River area was inundated under the multiple phases of the large lake occupying the Nipissing Lowlands and Georgian-Huron basins, extending well into the mid-Holocene. The occurrence of deposits marking two closed-basin intervals during the late Stanley-Hough stage are well preserved locally within the lacustrine depositional sequence, but identifying earlier closed-basin intervals from the French River stratigraphy is hindered by the lack of preserved pre-9,500 cal BP (~8,500 BP) post-glacial deposits. [ABSTRACT FROM AUTHOR]

We measured stable isotopes (δ18O and δ13C) in Sphagnum cellulose that was extracted from a long peat core drilled in the ombrotrophic Mohos peat bog, Ciomadul Mountain, Romania. The 10-m-long peat profile spans the period from 11,800 cal yr BP to present. The δ18O and δ13C data indicate there were several cooling events and warm periods in the area of the Mohos peat bog during the Holocene. The 8.2-ka cold event, however, was not detected using δ18O and δ13C values. Response of the peat bog to changing environmental conditions was inferred using data on organic matter accumulation, independent of the stable isotope results. All cool periods during the Holocene, whether of short or long duration, were identified as times of reduced organic matter accumulation rate. Similarly, dry periods were also correlated with reduced accumulation rates of organic matter. [ABSTRACT FROM AUTHOR]