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Edouard Bard - One of the best experts on this subject based on the ideXlab platform.
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Early Holocene Thermal Maximum recorded by branched tetraethers and pollen in Western Europe (Massif Central, France)
Quaternary Science Reviews, 2020Co-Authors: Céline Martin, Guillemette Menot, Nicolas Thouveny, Odile Peyron, Valérie Andrieu-ponel, Vincent Montade, Nina Davtian, Maurice Reille, Edouard BardAbstract:The evolution of temperatures during the Holocene is controversial, especially for the Early Holocene. The occurrence of the Holocene Thermal Maximum (HTM) during the Early Holocene has recently been reconsidered and seasonal biases have been suggested in the paleoclimatic proxies. High regional variability and a low number of reliable and continuous quantitative reconstructions compared with the oceanic realm further complicate study of the Holocene climate in the continental realm. We analyzed branched glycerol dialkyl glycerol tetraethers (brGDGTs), an organic paleothermometer, and palyno-logical signals as part of a multiproxy analysis of the sedimentary record from Lake St Front, in the Massif Central (France). Identification of a shift in brGDGT sources through the Holocene required removing terrigenous influences from the temperature signal. BrGDGT-and pollen-inferred paleotemperature reconstructions (based on the Modern Analog Technique and the Weighted Averaging Partial Least Squares method) were compared. Both showed a thermal maximum during the Early Holocene followed by a decrease of temperatures. We evaluated biases which could potentially influence the reconstructed signal. There was no evidence for a summer temperature bias either for brGDGT-derived temperatures or for pollen-derived temperatures. The Lake St Front data, in agreement with other regional records, confirm the occurrence of the HTM as a general warm period during the Early Holocene followed by mid-Holocene cooling in Western Europe and suggest that seasonal biases are not the main explanation of the Holocene conundrum d the disagreement between model simulations and proxy-based temperature reconstructions for the northern hemisphere.
Joseph M. Licciardi - One of the best experts on this subject based on the ideXlab platform.
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Surface‐melt driven Laurentide Ice Sheet retreat during the Early Holocene
Geophysical Research Letters, 2009Co-Authors: Anders E. Carlson, Allegra N. Legrande, Faron S. Anslow, Elizabeth A. Obbink, David J. Ullman, Joseph M. LicciardiAbstract:Received 21 September 2009; revised 3 November 2009; accepted 30 November 2009; published 30 December 2009. [1] To better understand mechanisms of ice-sheet decay, we investigate the surface mass balance of the Laurentide Ice Sheet (LIS) during the Early Holocene, a period of known rapid LIS retreat. We use a surface energy-mass balance model (EMBM) driven with conditions derived from an equilibrium atmosphere-ocean general circulation model 9 kilo-years ago simulation. Our EMBM indicates a net LIS surface mass balance of 0.67 ± 0.13 m yr 1 , with losses primarily due to enhanced boreal summer insolation and warmer summers. This rate of loss compared to LIS volume reconstructions suggests that surface ablation accounted for 74 ± 22% of the LIS mass loss with the remaining loss likely driven by dynamics resulting in basal sliding and calving. Thus surface melting likely played a governing role in the retreat and disappearance of this ice sheet. Citation: Carlson, A. E., F. S. Anslow, E. A. Obbink, A. N. LeGrande, D. J. Ullman, and J. M. Licciardi (2009), Surface-melt driven Laurentide Ice Sheet retreat during the Early Holocene, Geophys. Res. Lett., 36, L24502, doi:10.1029/ 2009GL040948.
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surface melt driven laurentide ice sheet retreat during the Early Holocene
Geophysical Research Letters, 2009Co-Authors: Anders E. Carlson, Allegra N. Legrande, Faron S. Anslow, Elizabeth A. Obbink, David J. Ullman, Joseph M. LicciardiAbstract:Received 21 September 2009; revised 3 November 2009; accepted 30 November 2009; published 30 December 2009. [1] To better understand mechanisms of ice-sheet decay, we investigate the surface mass balance of the Laurentide Ice Sheet (LIS) during the Early Holocene, a period of known rapid LIS retreat. We use a surface energy-mass balance model (EMBM) driven with conditions derived from an equilibrium atmosphere-ocean general circulation model 9 kilo-years ago simulation. Our EMBM indicates a net LIS surface mass balance of 0.67 ± 0.13 m yr 1 , with losses primarily due to enhanced boreal summer insolation and warmer summers. This rate of loss compared to LIS volume reconstructions suggests that surface ablation accounted for 74 ± 22% of the LIS mass loss with the remaining loss likely driven by dynamics resulting in basal sliding and calving. Thus surface melting likely played a governing role in the retreat and disappearance of this ice sheet. Citation: Carlson, A. E., F. S. Anslow, E. A. Obbink, A. N. LeGrande, D. J. Ullman, and J. M. Licciardi (2009), Surface-melt driven Laurentide Ice Sheet retreat during the Early Holocene, Geophys. Res. Lett., 36, L24502, doi:10.1029/ 2009GL040948.
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Rapid Early Holocene deglaciation of the Laurentide ice sheet
Nature Geoscience, 2008Co-Authors: Anders E. Carlson, Allegra N. Legrande, Delia W Oppo, Rosemarie E Came, Gavin A. Schmidt, Faron S. Anslow, Joseph M. Licciardi, Elizabeth A. ObbinkAbstract:The demise of the Laurentide ice sheet during the Early Holocene epoch is the most recent and best constrained disappearance of a large ice sheet in the Northern Hemisphere, and thus allows an assessment of rates of ice-sheet decay as well as attendant contributions to sea level rise. Here, we use terrestrial and marine records of the deglaciation to identify two periods of rapid melting during the final demise of the Laurentide ice sheet, when melting ice contributed about 1.3 and 0.7cm of sea level rise per year, respectively. Our simulations with a fully coupled ocean‐atmosphere model suggest that increased ablation due to enhanced Early Holocene boreal summer insolation was the predominant cause of Laurentide ice-sheet retreat. Although the surface radiative forcing in boreal summer during the Early Holocene is twice as large as the greenhouse-gas forcing expected by the year 2100, the associated increase in summer surface air temperatures is very similar. We conclude that our geologic evidence for a rapid retreat of the Laurentide ice sheet may therefore describe a prehistoric precedent for mass balance changes of the Greenland ice sheet over the coming century.
Ole Bennike - One of the best experts on this subject based on the ideXlab platform.
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Early Holocene insect and plant remains from Jameson Land, East Greenland
Boreas, 2008Co-Authors: Jens Böcher, Ole BennikeAbstract:Fluvial and deltaic sediments from Jameson Land in East Greenland contain the first record of the leaf beetle Phratora of. polaris, not presently found in Greenland; the ground beetle Bembidion grapii, north of this species' present northern range limit; and the true bug Nysius gruenlandieus. In addition, there is a rather diverse flora. All of these records are in sediments of Early Holocene age. We suggest that most of these animals and plants immigrated to East Greenland in the Early Holocene by long-distance chance dispersal, mostly from northwest Europe. The environment was physiognomically similar to that of today, but Salix aretica and Cassiope tetragonu that are important dwarf shrubs today had not yet immigrated.
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Late Glacial and Early Holocene records of Stratiotes aloides L. from northwestern Europe
Review of Palaeobotany and Palynology, 1999Co-Authors: Ole Bennike, Wim Z. HoekAbstract:Early Holocene finds of the freshwater plant Stratiotes aloides L. (water soldier) are reported from southern Sweden and the southwestern Baltic Sea for the first time. However, the species has previously been reported from Late Glacial deposits from Poland and The Netherlands, and from Early Holocene deposits from Finland. Thus the species was an Early immigrant to northwestern Europe after the last glacial maximum.
Anders E. Carlson - One of the best experts on this subject based on the ideXlab platform.
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Surface‐melt driven Laurentide Ice Sheet retreat during the Early Holocene
Geophysical Research Letters, 2009Co-Authors: Anders E. Carlson, Allegra N. Legrande, Faron S. Anslow, Elizabeth A. Obbink, David J. Ullman, Joseph M. LicciardiAbstract:Received 21 September 2009; revised 3 November 2009; accepted 30 November 2009; published 30 December 2009. [1] To better understand mechanisms of ice-sheet decay, we investigate the surface mass balance of the Laurentide Ice Sheet (LIS) during the Early Holocene, a period of known rapid LIS retreat. We use a surface energy-mass balance model (EMBM) driven with conditions derived from an equilibrium atmosphere-ocean general circulation model 9 kilo-years ago simulation. Our EMBM indicates a net LIS surface mass balance of 0.67 ± 0.13 m yr 1 , with losses primarily due to enhanced boreal summer insolation and warmer summers. This rate of loss compared to LIS volume reconstructions suggests that surface ablation accounted for 74 ± 22% of the LIS mass loss with the remaining loss likely driven by dynamics resulting in basal sliding and calving. Thus surface melting likely played a governing role in the retreat and disappearance of this ice sheet. Citation: Carlson, A. E., F. S. Anslow, E. A. Obbink, A. N. LeGrande, D. J. Ullman, and J. M. Licciardi (2009), Surface-melt driven Laurentide Ice Sheet retreat during the Early Holocene, Geophys. Res. Lett., 36, L24502, doi:10.1029/ 2009GL040948.
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surface melt driven laurentide ice sheet retreat during the Early Holocene
Geophysical Research Letters, 2009Co-Authors: Anders E. Carlson, Allegra N. Legrande, Faron S. Anslow, Elizabeth A. Obbink, David J. Ullman, Joseph M. LicciardiAbstract:Received 21 September 2009; revised 3 November 2009; accepted 30 November 2009; published 30 December 2009. [1] To better understand mechanisms of ice-sheet decay, we investigate the surface mass balance of the Laurentide Ice Sheet (LIS) during the Early Holocene, a period of known rapid LIS retreat. We use a surface energy-mass balance model (EMBM) driven with conditions derived from an equilibrium atmosphere-ocean general circulation model 9 kilo-years ago simulation. Our EMBM indicates a net LIS surface mass balance of 0.67 ± 0.13 m yr 1 , with losses primarily due to enhanced boreal summer insolation and warmer summers. This rate of loss compared to LIS volume reconstructions suggests that surface ablation accounted for 74 ± 22% of the LIS mass loss with the remaining loss likely driven by dynamics resulting in basal sliding and calving. Thus surface melting likely played a governing role in the retreat and disappearance of this ice sheet. Citation: Carlson, A. E., F. S. Anslow, E. A. Obbink, A. N. LeGrande, D. J. Ullman, and J. M. Licciardi (2009), Surface-melt driven Laurentide Ice Sheet retreat during the Early Holocene, Geophys. Res. Lett., 36, L24502, doi:10.1029/ 2009GL040948.
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Rapid Early Holocene deglaciation of the Laurentide ice sheet
Nature Geoscience, 2008Co-Authors: Anders E. Carlson, Allegra N. Legrande, Delia W Oppo, Rosemarie E Came, Gavin A. Schmidt, Faron S. Anslow, Joseph M. Licciardi, Elizabeth A. ObbinkAbstract:The demise of the Laurentide ice sheet during the Early Holocene epoch is the most recent and best constrained disappearance of a large ice sheet in the Northern Hemisphere, and thus allows an assessment of rates of ice-sheet decay as well as attendant contributions to sea level rise. Here, we use terrestrial and marine records of the deglaciation to identify two periods of rapid melting during the final demise of the Laurentide ice sheet, when melting ice contributed about 1.3 and 0.7cm of sea level rise per year, respectively. Our simulations with a fully coupled ocean‐atmosphere model suggest that increased ablation due to enhanced Early Holocene boreal summer insolation was the predominant cause of Laurentide ice-sheet retreat. Although the surface radiative forcing in boreal summer during the Early Holocene is twice as large as the greenhouse-gas forcing expected by the year 2100, the associated increase in summer surface air temperatures is very similar. We conclude that our geologic evidence for a rapid retreat of the Laurentide ice sheet may therefore describe a prehistoric precedent for mass balance changes of the Greenland ice sheet over the coming century.
Hilary H. Birks - One of the best experts on this subject based on the ideXlab platform.
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Using species attributes to characterize late‐glacial and Early‐Holocene environments at Kråkenes, western Norway
Journal of Vegetation Science, 2019Co-Authors: Vivian A. Felde, Hilary H. BirksAbstract:AIM: We aim to use species attributes such as distributions and indicator values to reconstruct past biomes, environment, and temperatures from detailed plant‐macrofossil data covering the late glacial to the Early Holocene (ca. 14–9 ka). LOCATION: Krakenes, western Norway. METHODS: We applied attributes for present‐day geographical distribution, optimal July and January temperatures, and Ellenberg indicator values for plants in the macrofossil data‐set. We used assemblage weighted means (AWM) to reconstruct past biomes, changes in light (L), nitrogen (N), moisture (F), and soil reaction (R), and temperatures. We compared the temperature reconstructions with previous chironomid‐inferred temperatures. RESULTS: After the start of the Holocene around 11.5 ka, the Arctic‐montane biome, which was stable during the late‐glacial period, shifted successively into the Boreo‐arctic montane, Wide‐boreal, Boreo‐montane, Boreo‐temperate, and Wide‐temperate biomes by ca. 9.0 ka. Circumpolar and Eurasian floristic elements characteristic of the late‐glacial decreased and the Eurosiberian element became prominent. Light demand (L), soil moisture (F), nitrogen (N), and soil reaction (R) show different, but complementary responses. Light‐demanding plants decreased with time. Soil moisture was relatively stable until it increased during organic soil development during the Early Holocene. Soil nitrogen increased during the Early Holocene. Soil reaction (pH) decreased during the Allerod, but increased during the Younger Dryas. It decreased markedly after the start of the Holocene, reaching low but stable levels in the Early Holocene. Mean July and January temperatures show similar patterns to the chironomid‐inferred mean July temperature trends at Krakenes, but chironomids show larger fluctuations and interesting differences in timing. CONCLUSION: Assigning attributes to macrofossil species is a useful new approach in palaeoecology. It can demonstrate changes in biomes, ecological conditions, and temperatures. The late‐glacial to Early‐Holocene transition may form an analogue for changes observed in the modern arctic and in mountains, with melting glaciers, permafrost thaw, and shrub encroachment into tundra.
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Diatom responses to late-glacial and Early-Holocene environmental changes at Kråkenes, western Norway
Journal of Paleolimnology, 2000Co-Authors: E.g. Bradshaw, V. J. Jones, H.j.b. Birks, Hilary H. BirksAbstract:A stratigraphic diatom sequence is presented for the period from 13,870-9,170 cal BP from Kråkenes Lake, western Norway. Changes in species assemblages are discussed with reference to the changing environmental conditions in the Allerød, Younger Dryas, and the Early Holocene and to the development of the aquatic ecosystem. The site is sensitive to acidification, and diatom-based transfer functions are applied to estimate the past pH status. The combination of rapid sediment accumulation together with an excellent calibrated radiocarbon chronology means that the rate of inferred pH change and associated increase in [H^+] can be assessed and compared with recent, anthropogenically acidified situations. The Allerød diatom assemblages are dominated by benthic taxa particularly Fragilaria species, indicating an unproductive, alkaline, turbid, and immature system. Diatoms are absent in the Early part of the Younger Dryas, but subsequently a sparse planktonic flora develops reflecting decreased turbidity and/or increased nutrient supply. A clear sequence of diatom assemblages is seen in the Early Holocene. A short-lived peak of Stephanodiscus species indicating a period of increased nutrient availability occurred at ca. 11,500 cal BP. Throughout the Early Holocene, acid-tolerant species increasingly replaced less acidophilous, circumneutral taxa. The lake became slightly more acid during the Allerød, but this was statistically insignificant in a trend test involving regression of pH or [H^+] in relation to age. Diatom-inferred pH declined rapidly during the Early Holocene period investigated (9,175-11,525 cal BP) with a statistically significant overall rate of 0.024 pH units per 100 yrs. This consisted of an older (ca. 11,525-10,255 cal BP) phase, where pH fell more rapidly at up to 0.095 pH units per 100 yrs; and a younger phase after ca. 10,500 cal BP where the pH fall was extremely slow (0.008 pH units per 100 yrs) and was not statistically significant.In the Allerød a combination of low catchment productivity together with disturbance, weathering, and minerogenic inwash ensured that the base-cation status remained relatively high. In the Holocene the catchment soils stabilised and base cations were sequestered by terrestrial vegetation and soil. This resulted in reduced base-cation leaching and this, together with the production of organic acids caused the lake to acidify, reaching an equilibrium by ca. 10,000 cal BP.
