Search

More than a century (1877–2011 CE) of asbestos mining activities in the Thetford Mines region have resulted in the accumulation of gigantic mineral waste piles on the banks of the Becancour River (southern Quebec, Canada). This river widens downstream from the mining sites to form a chain of lakes, successively: Stater Pond, Trout Lake, Lake William and Lake Joseph. A previous paleolimnological investigation revealed that waste erosion and transport strongly modified and polluted Trout Lake. However, questions remain about the extent of the mining contamination within the Becancour River Basin and its impacts at other spatial scales. Here, we aimed to address this lack of knowledge by analyzing the sedimentological evolution of Stater Pond, Lake William, Lake Joseph and Lake Becancour (upstream reference site). Radiometric dating (210Pb, 137Cs, 14C) and analyses of geochemical composition (ICP-AES/ICP-MS), computed tomography, magnetic susceptibility, loss-on-ignition and grain size were performed on sediment cores retrieved at these sites. In contrast to Lake Becancour, yet similar to Trout Lake, we found that Stater Pond and Lake William have received high mineral matter loads since the creation of the Lake Asbestos Mine during the 1950s. Recent lake sediments at these downstream sites were highly enriched in magnesium, chromium and nickel. Comparison of their geochemical signature with that of sedimentary source materials from within the drainage basin demonstrated that they predominantly originate from mining waste erosion. Consequently, Stater Pond and lakes Trout and William are nowadays exposed to very high sediment accumulation rates (up to 1.4 cm yr−1; 0.6 g cm−2 yr−1) and heavy metal enrichment. Evidence for contamination was also found in Lake Joseph, thereby indicating that wastes are transported and deposited over ≥25 km downstream from the former mining sites. Our study highlights the high risks and dangers associated with asbestos pollutants in aquatic ecosystems.

Nettilling Lake (Baffin Island, Nunavut) is currently the largest lake in the Canadian Arctic Archipelago. Despite its enormous size, this freshwater system remains little studied until the present-day. Existing records from southern Baffin Island indicate that in the early postglacial" period, the region was submerged by the postglacial Tyrell Sea due to isostatic depression previously exerted by the Laurentide Ice Sheet. However, these records are temporally and spatially discontinuous, relying on qualitative extrapolation. This paper presents the first quantitative reconstruction of the postglacial environmental succession of the Nettilling Lake basin based on a 8300 yr-long high resolution sedimentary record. Our multi-proxy investigation of the glacio-isostatic uplift and subsequent changes in paleosalinity and sediment sources is based on analyses of sediment fabric, elemental geochemistry (mu-XRF), diatom assemblage composition, as well as on the first diatom-based oxygen isotope record from the eastern Canadian Arctic. Results indicate that the Nettilling Lake basin experienced a relatively rapid and uniform marine invasion in the early Holocene, followed by progressive freshening until about 6000 yr BP when limnological conditions similar to those of today were established. Our findings present evidence for deglacial processes in the Foxe Basin that were initiated at least 400yrs earlier than previously thought. (C) 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.orgilicensesiby-nc-nd/4.0/).

Landscapes are changing at fast rates in subarctic regions due to recent climate warming and related permafrost thaw. As a consequence, thermokarst lakes and ponds are forming and their properties are changing rapidly. Here, we report on the interannual (2012-2014) variability of sedimentological and limnological conditions in a recently formed thermokarst pond in discontinuous permafrost terrain in Northern Quebec, and we discuss various aspects of pond sedimentation processes. Sediment samples from collecting traps and a short core were analyzed for particle size, organic matter content and geochemical composition, as well as 14 C dating of a peat sample from the core. Results reveal the preponderance of silts containing 2 to 13% organic matter and an age of 1825–1950 cal. yr. BP for the peat sample. A hypoxic hypolimnion formed in the pond during the short summers. Apparent sedimentation rates (up to 5.5 mm/d) varied in relation to local meteorological conditions and snow cover. The results also reveal major parameters associated with sediment composition, most notably dissolved oxygen in the water column, sampling depth and the year of sampling. Microplankton (20–200 μm) is likely the main source of organic matter, which represents up to 10 to 13% of sediment trap samples, considering its size matching a major grain size mode (44.9–59.0 μm). Using sedimentation rates and an estimation of long-term sediment compaction, the pond's “life span” was calculated at 370 to 600 years. This represents a baseline for the general understanding of the development of young (15–20 years) subarctic thermokarst ponds overlying impermeable soils, and provides an approximate time frame for the potential response of such systems to climate change impacts on northern landscapes.

The Pingualuit Crater, located in the Ungava Peninsula (northern Quebec, Canada) is a 1.4-Ma-old impact crater hosting a ~ 245-m-deep lake. The lake has a great potential to preserve unique paleoclimatic and paleoecological sedimentary records of the last glacial/interglacial cycles in the terrestrial Canadian Arctic. In order to investigate the stratigraphy in the lake and the late Quaternary glacial history of the Pingualuit Crater, this study compiles data from three expeditions carried out in May 2007 (~ 9-m-long sediment core), in August 2010 (~ 50 km of seismic lines), and in September 2012 (high-resolution terrestrial LiDAR topography of the inner slopes). Despite the weak penetration (~ 10 m) of the 3.5-kHz subbottom profiling caused by the presence of boulders in the sedimentary column, seismic data coupled with the stratigraphy established from the sediment core enabled the identification of two glaciolacustrine units deposited during the final stages of the Laurentide Ice Sheet (LIS) retreat in the crater. Two episodes of postglacial mass wasting events were also identified on the slopes and in the deep basin of the crater. The high-resolution topography of the internal slopes of the crater generated from the LiDAR data permitted the confirmation of a paleolake level at 545 m and determination of the elevation of drainage outlets. Together with the mapping of glacial and deglacial landforms from air photographs, the LiDAR data allowed the development of a new deglaciation and drainage scenario for the Pingualuit Crater Lake and surrounding area. The model proposes three main phases of lake drainage, based on the activation of seven outlets following the retreat of the LIS front toward the southwest. Finally, as opposed to other high-latitude crater lake basins such as Lake El'gygytgyn or Laguna Potrok Aike where high-resolution paleoclimatic records were obtained owing to high sediment accumulation rates, the seismic data from the Pingualuit Crater Lake suggest extremely low sedimentation rates after the retreat of the LIS owing to the absence of tributaries.

PASADO is a multidisciplinary Potrok Aike Sediment Archive Drilling prOject, which was conducted from 2008 to 2013, focusing on the sedimentary record of the volcanic crater maar Laguna Potrok Aike (52°S, 70°W, 116 m asl) in southern Patagonia, Argentina. It represents one of the few non-glacial and extra-Andean sediment archives studied so far on the continental landmass between subtropical South America and Antarctica that covers the entire Holocene and the Late Glacial. In this study, a high-resolution diatom analysis of the Late Glacial time interval situated between 15.60 and 10.51 ka cal. BP was performed on the PASADO sediment core. This period is of particular interest as it encompasses the Antarctic Cold Reversal (ACR), as well as the Younger Dryas (YD) chronozone. To better refine the variability of environmental and climatic conditions of this Late Glacial time interval, we combined our data with those of a microsedimentological analysis conducted on the same sediments and for the same period to infer changes in lake level and water column stratification. Our study revealed that diatoms are an ideal proxy to complement microsedimentological analyses by providing important independent information on the past limnological dynamics of Laguna Potrok Aike and the paleoclimatic conditions that prevailed during the Late Glacial in the study area and allows a new way of explaining shifts in the position of Southern Hemisphere Westerly Winds (SWW) during the Late Glacial. Peaks of planktonic diatoms, particularly Cyclostephanos patagonicus, correspond to previously detected total organic carbon (TOC), Ca/Si, Ca and Mn peaks and support the hypothesis that relatively high lake levels and weaker SWW have prevailed during the Late Glacial. Moreover, a cyclic pattern, observed both in the biological and geochemical indicators, suggests at least five shifts in the position of the SWW from the beginning of the ACR to the end of the YD. The periodicity of these shifts seems to be related to Antarctic ice-sheet discharge (AID) events in the Scotia Sea that coincide with enhanced iceberg flux from the Antarctic ice-sheet. Fil: Zimmermann, Claudia. Laval University; Canadá Fil: Jouve, Guillaume. Centre Eau Terre Environnement; Canadá Fil: Pienitz, Reinhard. Laval University; Canadá Fil: Francus, Pierre. Centre Eau Terre Environnement; Canadá Fil: Maidana, Nora Irene. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentina

In order to document long-term climate cycles and predict future climate trends for the Arctic, geological records archived in ocean sediments can help establish the link between historical and pre-historical sea-surface parameters. Dinoflagellate cysts (dinocysts) are used as proxy indicators of sea-surface parameters (temperature, salinity, sea-ice cover, primary productivity) jointly with transfer functions and a modern dinocyst reference database, to reconstruct the evolution of sea-surface conditions at decadal and millennial timescales. Here we present the surface distribution of recent dinocyst assemblages in 13 surface samples collected in four Nunatsiavut fjords (northern Labrador, Canada) along a latitudinal gradient, and their relationship with various environmental and biological parameters. Dinocyst concentrations in surface sediments increased from the inner to the outer part of each fjord and also from the northernmost to the southernmost fjords. There was also a southward increase in the species diversity with an occurrence and a dominance of cysts from autotrophic dinoflagellates. The presence of cysts of the calcareous dinoflagellate species Scrippsiella cf. S. crystallina in Anaktalak Fjord, where mining activities are underway, appears to be an indicator of human-related pollution within the fjord.

The Pingualuit Crater was formed by a meteoritic impact ca. 1.4 million years ago in northernmost Ungava (Canada). Due to its geographical position near the center of successive North American ice sheets and its favorable morphometry, the Pingualuit Crater Lake (water depth = 246 m) promises to yield a unique continuous sedimentary sequence covering several glacial/interglacial cycles in the terrestrial Canadian Arctic. In this paper, we suggest the existence of a subglacial lake at least during the Last Glacial Maximum (LGM) by hydraulic potential modeling using LGM ice-surface elevation and bed topography derived from a digital elevation model. These results support the hypothesis that the bottom sediments of the Crater Lake escaped glacial erosion and may contain a long-term continental sedimentary sequence. We also present the stratigraphy of a 9 m-long core retrieved from the deep basin of the lake as well as a multiproxy reconstruction of its deglacial and postglacial history. The base of the core is formed by very dense diamicton reflecting basal melt-out environments marking the end of subglacial conditions at the coring site. The overlying finely laminated silt are related to the onset of proglacial conditions characterized by extremely low lacustrine productivity. Infra Red Stimulated Luminescence and AMS 14C dating, as well as biostratigraphic data indicate sediment mixing between recent (e.g. Holocene) and much older (pre- to mid-Wisconsinan) material reworked by glacier activity. This process prevents the precise dating of these sediments that we interpret as being deposited just before the final deglaciation of the lake. Two finer grained and organic-rich intervals reflect the inception of lacustrine productivity resulting from the cessation of glacial meltwater inputs and ice-free periods. The lower organic interval corresponds to the early postglacial period (6850–5750 cal BP) and marks the transition between proglacial and postglacial conditions during the Holocene Thermal Maximum, while the uppermost organic-rich core section represents late Holocene sediments (∼4200–600 cal BP). The organic intervals are separated by a basin-scale erosive slide occurring around 4200 cal BP and likely related to 1) a seismic event due to the glacio-isostatic rebound following the last deglaciation or 2) slope instabilities associated with rapid discharge events of the lake.

The absence of datable macrofossils in six sediment cores recovered from northern Ungava (Canada) lakes constituted a major challenge for the establishment of reliable lacustrine chronologies for the Holocene. Consequently, AMS radiocarbon dating of humic acids was used to assess age–depth in the cores. The reliability of the radiocarbon results near some of the core tops was evaluated through 210 Pb dating. The offset of sediment radiocarbon ages with their most probable time of formation and deposition in the lakes was found to be in the order of about 1000 years for recently deposited sediments. However, the basal dates in one core covering the entire postglacial period yielded a remarkable fit with previously established dates performed on marine shells at the maximum marine limit. Hence, the aim of this study was to describe how the two dating methods can be combined to address some of the problems paleolimnologists face when trying to assign ages to high-latitude lake sediment records. Suggestions are made for improving the quality of age–depth models developed in future studies for northernmost Quebec and other comparable regions where paleolimnologists must deal with the combined challenges of very slow sediment accumulation rates in lakes, an extreme paucity of datable material and the sequestration of old carbon in the watersheds.

Sediments from Effingham Inlet, Vancouver Island, British Columbia hold a valuable high-resolution Holocene record of paleoclimatic and paleoceanographic conditions in the northeast Pacific Ocean. Accurate interpretation of this record requires that the depositional environment be well understood. In order to assess deposition within the fjord over the last 1500 years, two cores, a Soutar box core and a Kasten core, were analyzed for fossil diatoms, and biogeochemical properties. The cores contain varved sequences intercalated with homogeneous mud layers and a seismite. We show that homogeneous mud units related to periods of bottom water renewal are geochemically distinct from the seismite and that these bottom renewal events are favored when brackish rather than marine surface water conditions are present. The seismite, deposited in AD 1946, has lower opal and higher organic carbon concentrations and higher organic carbon: nitrogen ratios reflecting greater terrestrial material input. In contrast, homogeneous mud units are marked by a lower organic C/N and more isotopically heavy δ 13 C values, suggesting a stronger marine influence. Major metals and trace element data also confirm that the source material of these units differs from that of the AD 1946 seismite. Fossil diatom assemblages within the homogeneous mud units are characterized by a decreased abundance of typical marine spring bloom taxa ( Skeletonema costatum , Chaetoceros spp., Thalassiosira spp.) coupled with an increased abundance of the brackish-water taxon Cyclotella choctawhatcheeana . Reduced surface salinity enhances stratification of the water column which, in turn, favors an intensified two-layer estuarine exchange across the shallow sills and associated bottom water renewal. The homogeneous mud units are produced through transport of sediment into the fjord coupled with a reworking of the upper layers of the sediment column. Therefore, these units represent a recorder of past changes in regional oceanography and climate.

To better understand past aquatic ecosystems and their development, a 99-cm sediment core was extracted from a shrub- tundra lake in northern Quebec. Fossil chironomids, diatoms and pollen were analysed at 1.0-cm intervals. Several inference models based on chironomids and diatoms were used to reconstruct lake water conditions (surface water temperature, dissolved organic carbon (DOC), alkalinity, and water colour) for the last 6700 cal. yr. Reconstructed water temperatures varied between 10.3 and 17.6 8C, with a cooling trend since at least 1500 cal. yr BP. DOC concentrations increased with the establishment of terrestrial vegetation in the lake's catchment and decreased with the onset of the late Holocene cooling trend. Lake water alkalinity was higher during the lake's early history and decreased throughout its postglacial development, whereas water colour remained at fairly low levels throughout the entire record. Our results suggest that aquatic organisms directly influenced by temperature (chironomids) reacted most rapidly to climatic changes, whereas terrestrial vegetation (pollen) reacted with a slight lag. The vegetation succession in the catchment had subsequent impacts on the composition of runoff waters, and hence on other aquatic organisms (diatoms). D 2004 Elsevier B.V. All rights reserved.

Twenty-nine surface sediment samples from Effingham Inlet, a small fjord on the west coast of Vancouver Island, British Columbia, were analyzed for diatoms. This fjord has been selected for paleoceanographic investigation due to the presence of laminated sediments resulting from the dysoxic to anoxic bottom water conditions in the inner and outer basins of the inlet. Distributional patterns of the diatom microflora reflected proximity to littoral regions, phytoplankton production, and marine influence from outside the fjord. Principal components and cluster analyses of the microflora established four diatom assemblages with a clear separation between the inner and outer basin diatom floras. Inner basin stations were characterized by elevated absolute abundance with assemblages dominated by spring–early summer bloom taxa including Skeletonema costatum, Thalassiosira nordenskioeldii, and Thalassiosira pacifica. Chaetoceros spp. resting spores were abundant throughout Effingham Inlet, with the exception of the stations closest to the fjord head. Stations located in the outer basin and towards the fjord mouth had relatively lower absolute abundance yet showed a higher relative and absolute abundance of Thalassionema nitzschioides, Rhizosolenia setigera, Coscinodiscus radiatus, Ditylum brightwellii, Odontella longicruris, and Paralia sulcata in relation to the inner basin. Many of these latter taxa are often associated with late summer and autumn conditions in fjords along coastal British Columbia. Oceanographic data for Effingham Inlet suggest that increased offshore penetration is more likely to occur from summer to early fall, with a more restricted offshore influence in the inner basin. Diatom surface sediment assemblages in Effingham Inlet appear to reflect incursions of offshore waters into the fjord. Absolute abundance estimates and the preservation of lightly silicified taxa suggest excellent preservation of fossil material in the sediments of the predominantly anoxic inner basin. Preservation in the outer basin is reduced, reflecting more frequent recharge by oxygenated waters spilling over the outer sill into the basin. Our findings suggest the inner basin should be an optimal site for reconstruction of diatom production, with records from the outer basin providing more consistent information about offshore influence and coastal upwelling conditions over the Holocene. Estimates of diatom abundance within the inner basin sediment may serve as a good proxy of production, although proxy tracers of bottom water conditions and sedimentological analyses must be coupled to the diatom record to ensure depositional conditions were not influencing valve preservation or abundance. Our results suggest that fjords can serve as good environments for paleoceanographic reconstructions of both inshore and offshore conditions although careful site selection and understanding of processes affecting the microfossil record are essential.

Surface sediment diatom assemblages in depth profiles along the southeastern Beaufort Sea coasts (Canada) were analysed to describe the relationship between species distribution and water depth of deposition. The 74 coastal stations sampled were distributed in several sedimentary environments, from salt marshes to the inner shelf. The relationship between diatom species distribution and water depth was examined using canonical correspondence analysis (CCA) and partial CCA. The water depth accounted for 9.7% of the variance in the data set. The diatom/water-depth relationship is believed to be controlled by the shoreface circulation which results in a shift in the relative abundance of the epipsammon, epipelon, and plankton along the water depth gradient. Upper shoreface assemblages are dominated mainly by epipelic species and a few number of epipsammic taxa, whereas deeper environments are dominated by planktonic species. A transfer function was derived using weighted averaging regression and calibration to reconstruct the water depth of deposition over the coastal interval from mean sea level to a maximum of 14 m depth on the coastal shelf of the southeastern Beaufort Sea. The transfer function allows relative sea level to be predicted from fossil diatom assemblages with a root mean square error of 1.43 m. This model is likely to produce reliable water depth inferences along the southeastern Beaufort Sea coasts and in other shallow sandy microtidal environments dominated by low energy waves and influenced by freshwater discharge. The transfer function was used to provide quantitative paleodepth inferences for late Holocene sediments from the Atkinson Point area based on fossil diatom assemblages.

In this paper we conduct an empirical test of a published equation which relates lake surface area and maximum lake depth to the presence or absence of laminated lake sediments. A 297 lake dataset from New York State and six regions in Canada, representing a number of biogeoclimatic zones, is employed. The results suggest that deeper lakes are more likely to contain laminated lake sediments than are shallower lakes. The percentage of lakes incorrectly predicted to contain laminated sediments (false positives) and that incorrectly predicted to contain massive sediments (false negatives), was much higher than that found in the study in which the original equation was developed. Its low predictive ability suggests, therefore, that in addition to lake morphometry, many other factors affect the formation and preservation of laminated sediments.