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  • 1
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    Sediment dynamics in paired High Arctic lakes revealed from high-resolution swath bathymetry and acoustic stratigraphy surveys (2016)
    Wiley
    Details
    Publication Date: 2016-08-10
    Description: High Arctic lakes are commonly used for paleoclimatic reconstructions because they are particularly sensitive to climate variability. However, the processes leading to sediment deposition and distribution in these lakes are often poorly understood. Here, for the first time in the Canadian High Arctic, we present original data resulting from swath bathymetry and sub-bottom surveys carried out on two lakes at Cape Bounty, Melville Island. The results reveal the dynamic nature of the lakes, in which mass movements deposits and bedforms on the deltas reflect frequent slope instabilities and hyperpycnal flow activity. The analysis of the mass movement deposits reveals that small blocky debris flows/avalanches, debris flows and a slide occurred during the Holocene. These mass movements are believed to have been triggered by earthquakes and potentially by permafrost thawing along the shoreline. Altogether, these mass movement deposits cover more than 30% of the lake floors. Additionally, the river deltas on both lakes were mapped and reveal the presence of several gullies and bedforms. The presence of gullies along the delta front indicates that hyperpycnal flows generated at the river mouth can transport sediment in different trajectories downslope, resulting in a different sediment accumulation pattern and record. The dynamic nature of these two lakes suggests that further analysis on sediment transport and distribution within Arctic lakes is required in order to improve paleoclimatic reconstructions.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Global spread of hypoxia in freshwater ecosystems during the last three centuries is caused by rising local human pressure (2015)
    Wiley
    Details
    Publication Date: 2015-12-16
    Description: The spread of hypoxia is a threat to aquatic ecosystem functions and services as well as to biodiversity. However, sparse long-term monitoring of lake ecosystems has prevented reconstruction of global hypoxia dynamics while inhibiting investigations into its causes and assessing the resilience capacity of these systems. This study compiles the onset and duration of hypoxia recorded in sediments of 365 lakes worldwide since AD 1700, showing that lacustrine hypoxia started spreading before AD 1900, 70 years prior to hypoxia in coastal zones. This study also shows that the increase of human activities and nutrient release is leading to hypoxia onset. No correlations were found with changes in precipitation or temperature. There is no evidence for a post-1980s return to well-oxygenated lacustrine conditions in industrialized countries despite the implementation of restoration programs. The apparent establishment of stable hypoxic conditions prior to AD 1900 highlights the challenges of a growing nutrient demand, accompanied by increasing global nutrient emissions of our industrialized societies, and climate change. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Published by Wiley
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  • 3
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    Climate-driven ecosystem succession in the Sahara: the past 6000 years (2008)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2008-05-10
    Description: Desiccation of the Sahara since the middle Holocene has eradicated all but a few natural archives recording its transition from a "green Sahara" to the present hyperarid desert. Our continuous 6000-year paleoenvironmental reconstruction from northern Chad shows progressive drying of the regional terrestrial ecosystem in response to weakening insolation forcing of the African monsoon and abrupt hydrological change in the local aquatic ecosystem controlled by site-specific thresholds. Strong reductions in tropical trees and then Sahelian grassland cover allowed large-scale dust mobilization from 4300 calendar years before the present (cal yr B.P.). Today's desert ecosystem and regional wind regime were established around 2700 cal yr B.P. This gradual rather than abrupt termination of the African Humid Period in the eastern Sahara suggests a relatively weak biogeophysical feedback on climate.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kropelin, S -- Verschuren, D -- Lezine, A-M -- Eggermont, H -- Cocquyt, C -- Francus, P -- Cazet, J-P -- Fagot, M -- Rumes, B -- Russell, J M -- Darius, F -- Conley, D J -- Schuster, M -- von Suchodoletz, H -- Engstrom, D R -- New York, N.Y. -- Science. 2008 May 9;320(5877):765-8. doi: 10.1126/science.1154913.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Africa Research Unit, Institute of Prehistoric Archaeology, University of Cologne, Jennerstrasse 8, D-50823 Koln, Germany. s.kroe@uni-koeln.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18467583" target="_blank"〉PubMed〈/a〉
    Keywords: Africa ; Biological Evolution ; *Desert Climate ; *Ecosystem ; Fresh Water ; Geologic Sediments ; History, Ancient ; Plants ; Time ; Weather
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    PaCTS 1.0: A Crowdsourced Reporting Standard for Paleoclimate Data (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract The progress of science is tied to the standardization of measurements, instruments, and data. This is especially true in the Big Data age, where analyzing large data volumes critically hinges on the data being standardized. Accordingly, the lack of community‐sanctioned data standards in paleoclimatology has largely precluded the benefits of Big Data advances in the field. Building upon recent efforts to standardize the format and terminology of paleoclimate data, this article describes the Paleoclimate Community reporTing Standard (PaCTS), a crowdsourced reporting standard for such data. PaCTS captures which information should be included when reporting paleoclimate data, with the goal of maximizing the reuse value of paleoclimate datasets, particularly for synthesis work and comparison to climate model simulations. Initiated by the LinkedEarth project, the process to elicit a reporting standard involved an international workshop in 2016, various forms of digital community engagement over the next few years, and grassroots working groups. Participants in this process identified important properties across paleoclimate archives, in addition to the reporting of uncertainties and chronologies; they also identified archive‐specific properties and distinguished reporting standards for new vs. legacy datasets. This work shows that at least 135 respondents overwhelmingly support a drastic increase in the amount of metadata accompanying paleoclimate datasets. Since such goals are at odds with present practices, we discuss a transparent path towards implementing or revising these recommendations in the near future, using both bottom‐up and top‐down approaches.
    Print ISSN: 0883-8305
    Electronic ISSN: 2572-4525
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Holocene dynamics of the Arctic's largest ice shelf (2011)
    National Academy of Sciences
    Details
    Publication Date: 2011-10-24
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 6
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    Changes in erosion patterns during the Holocene in a currently treeless subalpine catchment inferred from lake sediment geochemistry (Lake Anterne, 2063 m a.s.l., NW French Alps): The role of climate and human activities (2011)
    Sage
    In: Holocene
    Details
    Publication Date: 2011-05-26
    Description: A high-resolution sedimentological and geochemical study was performed on a 20 m long core from the alpine Lake Anterne (2063 m a.s.l., NW French Alps) spanning the last 10 ka. Sedimentation is mainly of minerogenic origin. The organic matter quantity (TOC%) as well as its quality (hydrogen (HI) and oxygen (OI) indices) both indicate the progressive onset and subsequent stabilization of vegetation cover in the catchment from 9950 to 5550 cal. BP. During this phase, the pedogenic process of carbonate dissolution is marked by a decrease in the calcium content in the sediment record. Between 7850 and 5550 cal. BP, very low manganese concentrations suggest anoxic conditions in the bottom-water of Lake Anterne. These are caused by a relatively high organic matter (terrestrial and lacustrine) content, a low flood frequency and longer summer stratification triggered by warmer conditions. From 5550 cal. BP, a decrease in TOC, stabilization of HI and higher sedimentation rates together reflect increased erosion rates of leptosols and developed soils, probably due to a colder and wetter climate. Then, three periods of important soil destabilization are marked by an increased frequency and thickness of flood deposits during the Bronze Age and by increases in topsoil erosion relative to leptosols (HI increases) during the late Iron Age/Roman period and the Medieval periods. These periods are also characterized by higher sedimentation rates. According to palynological data, human impact (deforestation and/or pasturing activity) probably triggered these periods of increased soil erosion.
    Print ISSN: 0959-6836
    Electronic ISSN: 1477-0911
    Topics: Geography , Geosciences
    Published by Sage
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  • 7
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    Holocene dynamics of the Arctic's largest ice shelf [Environmental Sciences] (2011)
    National Academy of Sciences
    Details
    Publication Date: 2011-11-23
    Description: Ice shelves in the Arctic lost more than 90% of their total surface area during the 20th century and are continuing to disintegrate rapidly. The significance of these changes, however, is obscured by the poorly constrained ontogeny of Arctic ice shelves. Here we use the sedimentary record behind the largest remaining ice shelf in the Arctic, the Ward Hunt Ice Shelf (Ellesmere Island, Canada), to establish a long-term context in which to evaluate recent ice-shelf deterioration. Multiproxy analysis of sediment cores revealed pronounced biological and geochemical changes in Disraeli Fiord in response to the formation of the Ward Hunt Ice Shelf and its fluctuations through time. Our results show that the ice shelf was absent during the early Holocene and formed 4,000 years ago in response to climate cooling. Paleoecological data then indicate that the Ward Hunt Ice Shelf remained stable for almost three millennia before a major fracturing event that occurred ∼1,400 years ago. After reformation ∼800 years ago, freshwater was a constant feature of Disraeli Fiord until the catastrophic drainage of its epishelf lake in the early 21st century.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 8
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    Microfacies and microstructures of subglacial and deglacial sediments from the Pingualuit Crater Lake (Ungava Peninsula, Canada) (2014)
    National Research Council Canada (NRC)
    Details
    Publication Date: 2014-12-24
    Description: The Pingualuit Crater (Ungava Peninsula, Canada) hosts a freshwater basin in which a subglacial lake subsisted under the Laurentide Ice Sheet during the last glacial period. Microfacies and microstructures of a 9 m long sediment core are presented to discuss the depositional environment of deformed glacigenic and postglacial sequences deposited in the deep basin of the lake. Five distinct lithofacies are characterized. The range of glacial microstructures observed in the lower facies (Facies IV) reveals that high stress level occurred outside the crater during the formation of this diamicton released by the ablation of debris-rich basal glacier ice in an ice contact subglacial–proglacial lacustrine environment. The overlying subaqueous and glacigenic sediment gravity flow (Facies IIIb) is associated with a temporary absence of ice cover over the coring site, and likely results from the efflux plume and the associated suspension sedimentation produced during the retreat of the ice margin. Then, the finely laminated (〈1–2 mm) and normally graded meltout silts (Facies IIIa) containing dropstones and load cast features suggest underflows in an unstable ice marginal lacustrine environment hydrologically separated from the retreating glacier but containing floating glacial ice blocks. Microstructures within occasional diamictic layers indicate sudden meltout deposits from these drifting ice blocks. The above finer-grained sediments (Facies Ib) lack typical glacial microstructures, marking the onset of postglacial organic sedimentation. These postglacial sediments are affected by post-depositional deformations due to an overlying rotational slide (Facies II) that may have perturbed the associated environmental record.
    Print ISSN: 0008-4077
    Electronic ISSN: 1480-3313
    Topics: Geosciences
    Published by National Research Council Canada (NRC)
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  • 9
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    Palaeoenvironmental history of the last six centuries in the Nettilling Lake area (Baffin Island, Canada): A multi-proxy analysis (2016)
    Sage
    In: Holocene
    Details
    Publication Date: 2016-10-08
    Description: The Baffin Island region in the eastern Canadian Arctic has recently experienced a rapid warming, possibly unprecedented in millennia. To investigate the response of freshwater environments to this warming and place it in a secular perspective, we analyzed a 90-cm-long sediment core from Nettilling Lake, the largest lake of the Canadian Arctic Archipelago. The core was taken from a part of the lake basin that receives meltwater and sediment inputs from the nearby Penny Ice Cap. The core time scale, established using 137 Cs and palaeomagnetic techniques, spans an estimated 600 years. A multi-proxy approach was used to document changes in the physical, chemical, and biological properties of the sediments. We found evidence for a relatively warm period (mid/late 15th century to mid/late 16th century) during the early part of the ‘Little Ice Age’ (LIA), characterized by high sedimentation rates and laminations. This was followed by colder, drier, and windier conditions corresponding to the coldest phase of LIA and coinciding with the latest and most extensive period of regional ice cap expansion (early 16th to late 19th centuries). A rapid warming occurred at the beginning of the 20th century. Variations in titanium (Ti) content in the core, a proxy for detrital sediment inputs, showed good agreement with reconstructed secular variations in summer melt rates on Penny Ice Cap between the mid-14th century and the present-day, providing supporting evidence for a climatic–hydrological connection between the ice cap and Nettilling Lake.
    Print ISSN: 0959-6836
    Electronic ISSN: 1477-0911
    Topics: Geography , Geosciences
    Published by Sage
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  • 10
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    Impacts of point sources of nutrients on lakes [Environmental Sciences] (2016)
    National Academy of Sciences
    Details
    Publication Date: 2016-11-09
    Description: Enhanced phosphorus (P) export from land into streams and lakes is a primary factor driving the expansion of deep-water hypoxia in lakes during the Anthropocene. However, the interplay of regional scale environmental stressors and the lack of long-term instrumental data often impede analyses attempting to associate changes in land cover...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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