21 results on '"de Vernal, Anne"'
Search Results
2. Holocene Paleoenvironmental Implications of Diatom, Non-Pollen Palynomorph, and Organic Carbon Records from the Kandalaksha Bay of the White Sea (European Arctic).
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Polyakova, Yelena, Agafonova, Elizaveta, Novichkova, Ekaterina, and de Vernal, Anne
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ACCELERATOR mass spectrometry ,HOLOCENE Epoch ,OCEAN temperature ,DIATOMS ,SEASHELLS ,WATER depth - Abstract
Variations in sea surface conditions and sea level through the Holocene in the Kandalaksha Bay, the White Sea, were reconstructed based on the study of core sediments from the outer Kandalaksha Bay, using the modern analog technique applied to dinocysts in addition to diatoms, TOC, δ
13 Corg , CaCO3 , and grain size data. The chronostratigraphy of the core sediments was defined from accelerator mass spectrometry14 C dates on mollusk shells. The results indicated an increase in water depth in the outer Kandalaksha Bay and in the central Dvina Bay until the late Holocene. From about 9.5 to 7.5 cal kyr BP, the data suggested a general trend of increasing sea surface temperatures (up to 14 °C), at least in areas with inflow of Atlantic waters. The last 2.5 kyr were characterized by increased freshwater runoff to the White Sea. [ABSTRACT FROM AUTHOR]- Published
- 2023
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3. Palynological evidence of sea-surface conditions in the Barents Sea off northeast Svalbard during the postglacial period.
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Brice, Camille, de Vernal, Anne, Ivanova, Elena, van Bellen, Simon, and Van Nieuwenhove, Nicolas
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ICE sheets , *HUMAN settlements , *WATERMARKS , *HOLOCENE Epoch , *MELTWATER , *SEA ice - Abstract
Postglacial changes in sea-surface conditions, including sea-ice cover, summer temperature, salinity, and productivity were reconstructed from the analyses of dinocyst assemblages in core S2528 collected in the northwestern Barents Sea. The results show glaciomarine-type conditions until about 11,300 ± 300 cal yr BP and limited influence of Atlantic water at the surface into the Barents Sea possibly due to the proximity of the Svalbard-Barents Sea ice sheet. This was followed by a transitional period generally characterized by cold conditions with dense sea-ice cover and low-salinity pulses likely related to episodic freshwater or meltwater discharge, which lasted until 8700 ± 700 cal yr BP. The onset of "interglacial" conditions in surface waters was marked by a major change in dinocyst assemblages, from dominant heterotrophic to dominant phototrophic taxa. Until 4100 ± 150 cal yr BP, however, sea-surface conditions remained cold, while sea-surface salinity and sea-ice cover recorded large amplitude variations. By -4000 cal yr BP optimum sea-surface temperature of up to 4°C in summer and maximum salinity of -34 psu suggest enhanced influence of Atlantic water, and productivity reached up to 150 gC/m²/yr. After 2200 ± 1300 cal yr BP, a distinct cooling trend accompanied by sea-ice spreading characterized surfacewaters. Hence, during the Holocene, with exception of an interval spanning about 4000 to 2000 cal yr BP, the northern Barents Sea experienced harsh environments, relatively low productivity, and unstable conditions probably unsuitable for human settlements. [ABSTRACT FROM AUTHOR]
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- 2022
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4. Proxy, historical, instrumental and model re-analysis climate records in the NW North Atlantic and adjacent Canada during the last 2 ka
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van Bellen, Simon, de Vernal, Anne, Allan, Estelle, Audet, René, Boucher, Étienne, Dueymes, Guillaume, Fillion, Myriam, Fréchette, Bianca, Gachon, Philippe, Garneau, Michelle, Gilson, Gaëlle, Goosse, Hugues, Hillaire-Marcel, Claude, Houde, Nicolas, Laprise, René, Ogden, Nicholas, Ouellet-Bernier, Marie-Michèle, and Tremblay, Bruno
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Holocene ,temperature ,paleo ,climate ,sea ice ,database - Abstract
Presentation atCANQUA/AMQUA 2018, Ottawa, August 11, 2018.
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- 2018
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5. Comparison of qualitative and quantitative dinoflagellate cyst approaches in reconstructing glacial-interglacial climate variability at West Iberian Margin IODP ‘Shackleton’Site U1385
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Datema, Mariska, Sangiorgi, Francesca, de Vernal, Anne, Reichart, Gert-Jan, Lourens, Lucas J., Sluijs, Appy, Marine Palynology, Marine palynology and palaeoceanography, and Stratigraphy and paleontology
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010506 paleontology ,010504 meteorology & atmospheric sciences ,Dinoflagellate cysts ,Temperature salinity diagrams ,Paleontology ,Sea surface temperature and salinity ,Shackleton Site ,Oceanography ,01 natural sciences ,Sea surface temperature ,Ice core ,Modern analogue technique ,Last glacial transition ,Climatology ,Integrated Ocean Drilling Program ,Interglacial ,Taverne ,Dinocyst ,Younger Dryas ,Glacial period ,Holocene ,Geology ,0105 earth and related environmental sciences - Abstract
Dinoflagellate cysts (dinocysts) are commonly used to reconstruct past environmental conditions at the sea surface, such as primary production, temperature and salinity. Abundances of selected dinocyst taxa are used in qualitative indices, whereas the modern analogue technique (MAT) is used for quantitative reconstructions. Qualitative indices use process-based knowledge of present-day relations between the environmental variables and the distribution of dinocysts, whereas the MAT is based on the assumption that past assemblages have modern counterparts that correspond to similar sea-surface conditions. Here we explore the potential of both approaches to reconstruct sea surface temperature (SST), production (SSP), salinity (SSS) and seasonality during the last 22 thousand years along the West Iberian Margin (WIM), at Integrated Ocean Drilling Program (IODP) Site U1385. We compare results to published paleoclimatic reconstructions. Our SST and SSS reconstructions provide the first continuous dinocyst MAT-based SST and SSS records for this area and time interval. Qualitative and quantitative dinocyst-based SST estimates from the WIM are similar and resemble previous SST estimates from dinocysts, alkenones and foraminifers from nearby sites. The surface temperature trends and millennial-scale variations largely match those from the Greenland ice core records. Quantitative MAT-based SST estimates show increased seasonality in the glacial stage resulting from strong winter cooling. Dinocyst MAT-based salinity decreases concomitantly with cooling during the Younger Dryas and Heinrich Stadial 1 (HS1), likely related to the melting of icebergs that reached the region during HS1. Our qualitative and quantitative SSP estimates show higher values in the glacial stage compared to the Holocene, which is consistent with published records and supports the usefulness of both approaches. Small differences between SST tracer records may be explained by the limited number of modern analogues from warm ocean regions in the dinocyst reference dataset for MAT, the small number of dinocysts used in the qualitative estimates, the possible effect of a parameter other than temperature that might amplify noise, and/or seasonal biases of the tracer species. In any case, the advantage of the qualitative approach is to allow reconstructions in non-analogue situations. Regression of the qualitative index versus present-day SST also allows for a quantitative reconstruction, although over a limited range of SSTs (especially towards the lower end) and with quite some uncertainty, but produces reasonable values beyond the upper limit of the MAT. The MAT reconstructs more reliable SSTs, with a much smaller error of prediction, but only up to present-day WIM values, because it is based on the assumption that past assemblages have modern counterparts that correspond to similar sea-surface conditions, which is not always valid. The advantages of the MAT approach include its quantitative nature and insights into seasonality. Hence both approaches are complementary. At Site U1385, MAT can be used for reconstructions in the colder periods (YD, HS1 and glacial stage), with a small error of prediction and the quantified index can be used to estimate SST beyond the limit of the MAT (Holocene and B-A).
- Published
- 2017
6. Natural variability of the Arctic Ocean sea ice during the present interglacial.
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de Vernal, Anne, Hillaire-Marcel, Claude, Le Duc, Cynthia, Roberge, Philippe, Brice, Camille, Matthiessen, Jens, Spielhagen, Robert F., and Stein, Ruediger
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SEA ice , *HOLOCENE Epoch , *RADIOCARBON dating , *OCEAN , *ICE - Abstract
The impact of the ongoing anthropogenic warming on the Arctic Ocean sea ice is ascertained and closely monitored. However, its long-term fate remains an open question as its natural variability on centennial to millennial timescales is not well documented. Here, we use marine sedimentary records to reconstruct Arctic sea-ice fluctuations. Cores collected along the Lomonosov Ridge that extends across the Arctic Ocean from northern Greenland to the Laptev Sea were radiocarbon dated and analyzed for their micropaleontological and palynological contents, both bearing information on the past sea-ice cover. Results demonstrate that multiyear pack ice remained a robust feature of the western and central Lomonosov Ridge and that perennial sea ice remained present throughout the present interglacial, even during the climate optimum of the middle Holocene that globally peaked ∼6,500 y ago. In contradistinction, the southeastern Lomonosov Ridge area experienced seasonally sea-ice-free conditions, at least, sporadically, until about 4,000 y ago. They were marked by relatively high phytoplanktonic productivity and organic carbon fluxes at the seafloor resulting in low biogenic carbonate preservation. These results point to contrasted west–east surface ocean conditions in the Arctic Ocean, not unlike those of the Arctic dipole linked to the recent loss of Arctic sea ice. Hence, our data suggest that seasonally ice-free conditions in the southeastern Arctic Ocean with a dominant Arctic dipolar pattern, may be a recurrent feature under “warm world” climate. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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7. Paleoceanography of northeastern Fram Strait since the last glacial maximum: Palynological evidence of large amplitude changes.
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Falardeau, Jade, de Vernal, Anne, and Spielhagen, Robert F.
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GLACIAL climates , *PALEOCEANOGRAPHY , *PALYNOLOGY , *DINOFLAGELLATE cysts , *SEDIMENTS - Abstract
Sea-surface conditions in northeastern Fram Strait since the last glacial maximum (LGM) were reconstructed from cores MSM5/5-712-2 and PS2863/1–2 based on palynological assemblages, ecological preferences of dinocysts and application of the modern analog technique. Dinocyst in LGM sediments are sparse, but their assemblages reflect mild summer conditions. Given the regional context and evidence from other tracers, the dinocyst assemblages of the LGM could relate to regional fluxes of dinocysts during exceptional mild summers. From 19 to 14.7 ka, dinocyst data suggest very cold conditions with extensive sea-ice cover, while abundant reworked palynomorphs indicate intense glacial erosion. An abrupt transition at 14.7–14.5 ka was marked by a peak in summer temperatures coinciding with a rapidly deposited sediment layer related to a regional meltwater plume event in western Svalbard. From 14.7 to 12.6 ka, large seasonal temperature contrasts with mild summers and cold winters together with low salinity indicate continuous melting of the Svalbard Barents Sea ice sheet fostered by warm climate. At 12.6 ka, the regional onset of the Younger Dryas was marked by cooling and increased salinity. On a regional scale, the 12.6–12 ka interval corresponds to an important transition involving enhanced circulation of Arctic waters around Svalbard and establishment of coastal fronts along its northern and western margins. Modern-like oceanic conditions with relatively high salinity and low seasonal temperature contrast developed at about 7.6 ka. Since then, a slight cooling is observed, especially in winter. This study offers a comprehensive picture of the deglacial phases in eastern Fram Strait with unique data on the sea-surface salinity, which controls surface water stratification and plays an important role in ocean circulation. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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8. Sea surface conditions in the southern Nordic Seas during the Holocene based on dinoflagellate cyst assemblages.
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Van Nieuwenhove, Nicolas, Baumann, Astrid, Matthiessen, Jens, Bonnet, Sophie, and de Vernal, Anne
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SEA surface microlayer ,HOLOCENE Epoch ,DINOFLAGELLATE cysts ,FOSSIL dinoflagellates ,ARCHAEOLOGICAL assemblages ,OCEANOGRAPHY - Abstract
Dinoflagellate cyst (dinocyst) records from the southern Nordic Seas were compiled in order to evaluate the evolution of upper ocean conditions, on a millennial timescale and supported by a highly resolved record from the Vøring Plateau. After the transitional phase from the last deglaciation, three main phases define the Holocene. The early Holocene (>7.5 ka BP) features important numbers of cool-temperate species dominated by Nematosphaeropsis labyrinthus and Impagidinium pallidum in the west. The assemblage composition changes drastically at the transition from the early to the mid-Holocene, from when on Operculodinium centrocarpum dominates. The changeover is dated between ~6.1 and 7.5 ka BP, perhaps earlier closer to the Iceland–Scotland Ridge, and appears to be linked to the onset of a modern type of surface circulation. ‘Warmest’ assemblages occur at the Vøring Plateau shortly after the transition, when Atlantic waters also appear to have spread farthest westward. The recurrence of colder elements can be linked to cooling from ~2.4 ka BP at the Vøring Plateau and presumably earlier in the west but is difficult to date there because of the low sedimentation rates. This is a general issue in many areas of the Nordic Seas and appears to have an important effect on cyst concentrations and assemblage composition, with the possible loss of oxygenation-sensitive cysts in the older parts of the cores. Comparing dinocyst-based quantitative reconstructions with those retrieved from other plankton reveals a significantly different trend between proxies, linked to a differing autecological response to seasonal changes at their respective depth habitats. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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9. Variability in transport of terrigenous material on the shelves and the deep Arctic Ocean during the Holocene.
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Wegner, Carolyn, Bennett, Katrina E., de Vernal, Anne, Forwick, Matthias, Fritz, Michael, Heikkilä, Maija, Łącka, Magdalena, Lantuit, Hugues, Laska, Michał, Moskalik, Mateusz, O'Regan, Matt, Pawłowska, Joanna, Promińska, Agnieszka, Rachold, Volker, Vonk, Jorien E., and Werner, Kirstin
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HOLOCENE Epoch ,COASTAL changes ,TERRIGENOUS sediments ,OCEAN ,ICE sheets ,SEA ice ,ANALYSIS of river sediments ,COASTAL sediments - Abstract
Arctic coastal zones serve as a sensitive filter for terrigenous matter input onto the shelves via river discharge and coastal erosion. This material is further distributed across the Arctic by ocean currents and sea ice. The coastal regions are particularly vulnerable to changes related to recent climate change. We compiled a pan-Arctic review that looks into the changing Holocene sources, transport processes and sinks of terrigenous sediment in the Arctic Ocean. Existing palaeoceanographic studies demonstrate how climate warming and the disappearance of ice sheets during the early Holocene initiated eustatic sea-level rise that greatly modified the physiography of the Arctic Ocean. Sedimentation rates over the shelves and slopes were much greater during periods of rapid sea-level rise in the early and middle Holocene, as a result of the relative distance to the terrestrial sediment sources. However, estimates of suspended sediment delivery through major Arctic rivers do not indicate enhanced delivery during this time, which suggests enhanced rates of coastal erosion. The increased supply of terrigenous material to the outer shelves and deep Arctic Ocean in the early and middle Holocene might serve as analogous to forecast changes in the future Arctic. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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10. Long-term hydrological changes in the northeastern Gulf of Mexico (ODP-625B) during the Holocene and late Pleistocene inferred from organic-walled dinoflagellate cysts.
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Limoges, Audrey, de Vernal, Anne, and Van Nieuwenhove, Nicolas
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HYDROLOGY , *HOLOCENE Epoch , *DINOFLAGELLATE cysts , *PLEISTOCENE Epoch - Abstract
Palynological analyses are used in conjunction with oxygen isotopes and Mg/Ca ratios in foraminifers in order to document the response of dinoflagellate cysts (dinocysts) assemblages to changing climate conditions in the northeastern Gulf of Mexico over the Holocene and late Pleistocene. During MIS 6, but also during the cooler phases of MIS 5, Impagidinium species and Operculodinium centrocarpum were dominating the assemblages. By contrast, during the last interglacial (LIG) and the Holocene, assemblages were mainly composed of Spiniferites taxa and characterized by high relative abundance of Spiniferites mirabilis-hyperacanthus , Operculodinium israelianum and/or Polysphaeridium zoharyi . These two periods exhibit ~ 1-2 °C difference in temperature as inferred from Mg/Ca ratios and show significantly distinct assemblages, with higher percentages of S. mirabilis during the LIG and higher percentages of P. zoharyi during the Holocene. This likely denotes important differences in the hydrogeographical conditions (e.g. surface circulation, bathymetric configuration) between the present and last interglacial. The importance of environmental parameters other than temperature and salinity for dinocyst assemblage dynamics is furthermore illustrated. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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11. Paleoceanographic changes in the Disko Bugt area, West Greenland, during the Holocene.
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Ouellet-Bernier, Marie-Michèle, de Vernal, Anne, Hillaire-Marcel, Claude, and Moros, Matthias
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HOLOCENE paleoceanography , *DINOFLAGELLATE cysts , *FORAMINIFERA , *OCEAN temperature , *ICE sheets - Abstract
Micropaleontological analyses of a sediment core raised in Disko Bugt (West of Greenland) were undertaken in order to document paleoceanographical changes in the eastern Baffin Bay during the Holocene. The modern analogue technique (MAT) applied to dinocyst assemblages provided information on paleo-sea-surface conditions, whereas isotopic analyses of benthic foraminifers aimed at documenting the ‘deep’ water mass occupying the site. During the earlier interval recorded (~10 to ~7.3 cal. kyr BP), important discharge of ice and meltwater from the Greenland Ice Sheet (GIS) margin, notably through the Jakobshavn Isbrae, resulted in harsh conditions with a dense sea-ice cover and low temperatures, productivity, and foraminiferal abundances. Postglacial conditions settled at ~7.3 cal. kyr BP, with a sharp rise in dinocyst abundance and species diversity, which led to reconstruct increase in summer temperatures. We link this transition to the advection of West Greenland Current waters in the upper part of the water column after the reduction of meltwater inputs from GIS. Optimal temperature conditions reaching up to >10°C were finally achieved in surface waters at ~6 cal. kyr BP. Slight cooling pulses were then recorded at ~4.2–4 and ~1.5–1 cal. kyr BP, and the final optimum recorded in surface temperature from ~1 to 0.8 cal. kyr BP is associated with the ‘Medieval Warm Period’. Throughout the postglacial interval, the data suggest an opposition between sea-surface temperatures and salinity, with warmer intervals being characterized by lower salinity waters, probably as a result of the higher freshwater discharge along the ice margin and notably the Jakobshavn Isbrae. [ABSTRACT FROM PUBLISHER]
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- 2014
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12. Dinocyst-based reconstructions of sea ice cover concentration during the Holocene in the Arctic Ocean, the northern North Atlantic Ocean and its adjacent seas.
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de Vernal, Anne, Hillaire-Marcel, Claude, Rochon, André, Fréchette, Bianca, Henry, Maryse, Solignac, Sandrine, and Bonnet, Sophie
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DINOFLAGELLATE cysts , *SEA ice , *ICE sheets , *HOLOCENE Epoch - Abstract
Abstract: Sea ice cover extent expressed in terms of mean annual concentration was reconstructed from the application of the modern analogue technique to dinocyst assemblages. The use of an updated database, which includes 1492 sites and 66 taxa, yields sea ice concentration estimates with an accuracy of ±1.1/10. Holocene reconstructions of sea ice cover were made from dinocyst counts in 35 cores of the northern North Atlantic and Arctic seas. In the Canadian Arctic, the results show high sea ice concentration (>7/10) with little variations throughout the interval. In contrast, in Arctic areas such as the Chukchi Sea and the Barents Sea, the reconstructions show large amplitude variations of sea ice cover suggesting millennial type oscillations with a pacing almost opposite in western vs. eastern Arctic. Other records show tenuous changes with some regionalism either in trends or sea ice cover variability. During the mid-Holocene, and notably at 6 ± 0.5 ka, minimum sea ice concentration is recorded in the eastern Fram Strait, northern Baffin Bay and Labrador Sea. However, this minimum cannot be extrapolated at the scale of the Arctic and circum-Arctic. The comparison of recent observations and reconstructions suggests larger variations in the Arctic sea ice cover during the last decades than throughout the Holocene. [Copyright &y& Elsevier]
- Published
- 2013
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13. Paleoceanographic changes and calcium carbonate dissolution in the central Fram Strait during the last 20ka
- Author
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Zamelczyk, Katarzyna, Rasmussen, Tine L., Husum, Katrine, Haflidason, Haflidi, de Vernal, Anne, Ravna, Erling Krogh, Hald, Morten, and Hillaire-Marcel, Claude
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PALEOCEANOGRAPHY ,CALCIUM carbonate content of seawater ,STABLE isotopes ,FORAMINIFERA ,WATER temperature ,MARINE sediments - Abstract
Abstract: A deep-sea sediment core covering the last 20ka and located between the Polar and the Arctic fronts in the marginal ice zone (MIZ) of the central Fram Strait has been investigated for changes in paleoceanography and calcium carbonate preservation. The reconstruction is based on the distribution patterns of planktic foraminifera, mean shell weight and the degree of fragmentation of their shells, stable isotopes and other geochemical and sedimentological data. The results show that the planktic foraminifera shells are poorly preserved throughout most of the record. Only the intervals comprising the early Holocene from 10.8 to ~8calka BP and the last 800yr show improved preservation of CaCO
3 . The dissolution correlated with the extent of Arctic water and the associated marginal ice zone (MIZ) and high organic productivity. Dissolution of planktic foraminifera is generally high during the late deglaciation, mid and late Holocene prior to ~800calyr BP. The abundance of small subpolar species increases in the surface sediments dating from the last century, which could be interpreted as a large and significant surface water warming. However, this apparent high-magnitude warming seems to be overestimated due to preservation changes in the youngest sediments. [Copyright &y& Elsevier]- Published
- 2012
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14. Variability of sea-surface temperature and sea-ice cover in the Fram Strait over the last two millennia
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Bonnet, Sophie, de Vernal, Anne, Hillaire-Marcel, Claude, Radi, Taoufik, and Husum, Katrine
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SEA ice , *SEDIMENTS , *WATER depth , *WATER temperature , *SEA surface microlayer , *PRINCIPAL components analysis , *DINOFLAGELLATE cysts , *HOLOCENE stratigraphic geology , *TEMPERATURE - Abstract
Abstract: A sediment core located on the West Spitzbergen margin in the Fram Strait (78°54.931′N, 6°46.005′E, water depth: 1497m) was analyzed for its dinocyst content in order to reconstruct hydroclimatic variations of the last 2500years. The relative abundance of dinocyst taxa and principal component analysis show a major transition at about 300cal. years BP. It is characterized by the disappearance of thermophilic taxa Spiniferites mirabilis-hyperacanthus and Impagidinium sphaericum and the increase of polar–subpolar taxa Impagidinium pallidum and Pentapharsodinium dalei. Sea-surface temperature (SST) estimates suggest warmer conditions than present (anomaly∼+2°C) averaging at 7°C in summer until 300cal. years BP, although cooling pulses are recorded around 1700, 1500, 1200 and 800cal. years BP. The last 300years were marked by a cooling from 7.6 to 3.5°C and sea-ice cover increasing up to 7months/yr. The results demonstrate that the Fram Strait area is sensitive to hydroclimatic variations, notably with respect to sea-ice and SSTs, which are linked to the relative strength of northward flow of North Atlantic waters to the East and southward outflow of cold and fresh waters from the Arctic Ocean. Based on our data, the warmest part of our record around 1320cal. years BP is the only interval of the last 2500years that provides a possible analogue for the modern post-AD 2000 interval, which is characterized by sea-ice free conditions. [Copyright &y& Elsevier]
- Published
- 2010
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15. Provincialism in trends and high frequency changes in the northwest North Atlantic during the Holocene
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de Vernal, Anne and Hillaire-Marcel, Claude
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DINOFLAGELLATE cysts , *SEDIMENTS , *SALINITY , *ISOTOPES - Abstract
Abstract: In the present paper, we report on micropaleontological (dinocysts) and isotopic (18O and 13C in foraminifers) analyses performed in Holocene sediments from fifteen cores raised from the central and northwest North Atlantic. Sea-surface temperature (SST), sea-surface salinity (SSS), thus potential density, and sea-ice cover are reconstructed based on dinocyst assemblages. After proper calibration, oxygen isotope data on the mesopelagic foraminifer Neogloboquadrina pachyderma left coiled (Npl) are converted into potential density values deeper in the water column, thus allowing documentation of vertical density gradients and identification of intervals favourable for winter convection to occur with formation of intermediate Labrador Sea Water (LSW). The most important findings from this study include: (1) the existence of an early-mid Holocene thermal optimum with positive anomalies up to 6 °C above present along the main SW–NE axis of the North Atlantic Current, but no significant SST maximum at most sites along eastern Canadian margins; (2) the evidence for larger than present amplitude of annual SSTs during the early Holocene, thus for a stronger seasonality; (3) minimum sea-ice cover from 11500 to 6000 cal years BP, and a slight increase of sea-ice variability, and average seasonal duration of 0.5 to 1 month per year afterwards; (4) variable SSS during the entire Holocene, suggesting changes in the routing and rates of freshwater–meltwater discharges from the Arctic and eastern Canada; (5) the setting of conditions compatible with LSW production after 8 ka only, and likely a more steady production during the late Holocene; (6) an overall trend for a potential density increase of the Labrador Sea, throughout the Holocene, matching a decreasing trend eastward, thus suggesting a progressive enhancement of the western branch of the Atlantic Meridional Overturning with respect to its northeastern route; and (7) indication of maximum production and fast dispersal of LSW in the entire North Atlantic during recent times only, as suggested by linearly-converging δ 18O-values of Npl from all sites, towards its modern relatively homogeneous composition (∼ 2.5/2.6‰). The overall picture of the Holocene North Atlantic arising from this study is that of a basin marked by a strong regionalism with large discrepancies in hydrographical trends and high frequency oscillations, at least partly controlled by freshwater–meltwater routes and rates of export from the Arctic. [Copyright &y& Elsevier]
- Published
- 2006
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16. Holocene paleoceanography of the Bay of Biscay: Evidence for west-east linkages in the North Atlantic based on dinocyst data.
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Zumaque, Jena, Eynaud, Frédérique, and de Vernal, Anne
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HOLOCENE paleoceanography , *DINOFLAGELLATE cysts , *PALYNOLOGY , *CLIMATE change - Abstract
Paleoceanographical changes during the Holocene were reconstructed from the study of core MD95-2002 situated in the northern Bay of Biscay, which is marked by the direct influence of the northeastern return branch of the North Atlantic Drift. Palynological data, sea-surface condition estimates based on dinocyst assemblages and stable isotope measurements in planktic and benthic foraminifera reveal a strong influence of freshwater/meltwaters from both the proximal European sources and the more distal Laurentide Ice Sheet, which experienced delayed deglaciation. The data also indicate the setting of a climate optimum between 7 and 5.5 ka followed by a cooling trend, which is consistent with insolation changes and other regional records of climate changes. Superimposed on the long term trends, the reconstructions of sea-surface conditions evidence large amplitude changes at centennial to millennial time-scales, with seven episodes of cooling and low salinity since 11 ka that generally match episodes of dense sea-ice cover in the Labrador Sea. The west to east transfer of the sea-ice and/or meltwater signal across the North Atlantic evidenced from core MD95-2002 points to strong linkages between western and eastern North Atlantic, probably in relation to the North Atlantic Oscillation (NAO) mode of variability. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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17. Late Quaternary sea surface conditions in the Laurentian Fan: Evidence from coccolith and dinocyst assemblages.
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Balestra, Barbara, Bertini, Adele, de Vernal, Anne, Monechi, Simonetta, and Reale, Viviana
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OCEAN temperature , *COCCOLITHS , *DINOFLAGELLATE cysts , *CLIMATE change , *HOLOCENE Epoch - Abstract
The analyses of coccoliths and dinocysts from the IMAGES core MD95-2033, collected on the Laurentian Fan (44°39.87N, 55°37.21W; water depth=1412m) in the northwest North Atlantic provide a new dataset to assess the magnitude of climatic changes during the Holocene with a millennial time resolution. Coccolith and dinocyst data were combined to reconstruct changes in past sea surface conditions. In addition, the dinocyst assemblages were used to reconstruct the sea-surface temperature (SST) and salinity (SSS) based on the modern analog technique. The distribution of the coccolith and dinocyst assemblages, suggests a succession of climatic events during the late Quaternary and early Holocene, linked to change in the influence of the Labrador Current and/or the St. Lawrence River discharge. The dinocyst assemblages recorded a thermal optimum during the mid-Holocene. In the late Holocene, coccolith concentrations show two peaks at 2.3 and 1.1ky, which coincide with the presence of species with different ecological properties, likely due to the localized influence of the Slope Water Jet (SWJ) current. The presence of this current has played a role in the development of the coccolith and dinocyst assemblages and SST fluctuations, especially in the last 2ky. Overall, the interaction between the St. Lawrence River, the SWJ, the LC, and the NAC has all controlled the SSS, SSTs, and the development of the coccolith and dinocyst assemblages, confirming a significant regionalism of the entire area. [ABSTRACT FROM AUTHOR]
- Published
- 2013
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18. A reassessment of Nd-isotopes and clay minerals as tracers of the Holocene Pacific water flux through Bering Strait.
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Song, Tengfei, Hillaire-Marcel, Claude, de Vernal, Anne, Liu, Yanguang, Wang, Weiguo, and Huang, Yuanhui
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NEODYMIUM isotopes , *CLAY minerals , *HOLOCENE Epoch , *MERIDIONAL overturning circulation , *STRAITS , *OCEAN circulation , *RIVER channels , *SEA ice - Abstract
The flux of low-salinity Pacific water (PW) through Bering Strait (BS) weights on the freshwater budget of the Arctic Ocean, which, in turn, impacts the Atlantic Meridional Overturning Circulation (AMOC). Through time, this PW flux has been tightly controlled by the bathymetry of the Strait (~50 m water depth at present), thus by sea-level (SL) changes, as documented in several papers based on a large array of sedimentological and geochemical tracers. The present study aimed at reassessing the robustness of these tracers of the PW-flux, based on five surface samples collected along a south–north transect from BS to the Chukchi Plateau, within the bathymetric range of the PW-mass dispersal. We also estimated their variation in relation to the post-glacial SL-rise in a sedimentary core (ARC4-R09), from the Chukchi shelf, spanning the last ~10 cal kyr. Potential indicators of PW-flux include sortable silt, clay minerals, and the particulate and exchangeable Nd-isotope composition of specific grain-size fractions. The results indicate that ɛNd-values in leachates, and to a lesser extent, the smectite abundance, both relating to volcanic rocks of the Bering Sea, are sensitive indicators of the PW-flux, whereas sortable silts and other clay minerals relative abundances are also influenced by other processes (e.g., west–east shelf currents, sea-ice rafting). The modern distributions of ɛNd-value and smectite abundance illustrate mixing between two endmembers: i) a northern Bering Sea endmember, characterized by ~14% of smectite (vs all clay minerals) and a ɛNd-value of the exchangeable fraction of ~ −2; ii) a Chukchi Sea endmember, characterized by ~8% of smectite and a ɛNd-value ranging from −7 to −8. The Holocene sedimentary record from the study core indicates a progressive increase in Bering Sea supplies through time, linked to an enhanced inflow of PW, which we associate with the deepening of the Strait due to the rising SL. Following a major reorganization of the Arctic Ocean circulation at ~8 cal kyr BP, a steady increase in PW flux prevailed until ~4 cal kyr BP. A tenuous but continuous positive trend towards modern εNd values followed during the late Holocene. The middle Holocene steep increase of warm, low salinity PW-flux through BS, led to important changes in the Arctic Ocean, in particular of its salinity budget. Assuming that the BS bathymetry is the main parameter governing the PW-flux towards the Arctic Ocean, a first-order estimate of PW-flux under a higher than modern SL can be made using the SL-elevation-ɛNd relationship of the major middle Holocene shift. • Assessment of the reliability of clay minerals and Nd-isotopes as tracers of PW-fluxes through Bering Strait. • Recording of Holocene PW-fluxes through Bering Strait by exchangeable ɛNd-values in a gravity core from the Chukchi Shelf. • Estimation of past changes in PW-fluxes towards the Arctic in relation with SL changes. [ABSTRACT FROM AUTHOR]
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- 2022
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19. North Atlantic-Fennoscandian Holocene climate trends and mechanisms.
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Sejrup, Hans Petter, Seppä, Heikki, McKay, Nicholas P., Kaufman, Darrell S., Geirsdóttir, Áslaug, de Vernal, Anne, Renssen, Hans, Husum, Katrine, Jennings, Anne, and Andrews, John T.
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HOLOCENE Epoch , *CLIMATE change , *MULTIPLE correspondence analysis (Statistics) , *OCEAN temperature , *RELIEF models - Abstract
To investigate the mechanisms behind Holocene regional climate trends from north of 58°N in the North Atlantic-Fennoscandian region Principal Component Analysis (PCA) was performed and a temperature anomaly stack produced from 81 proxy derived summer temperature time series from 74 sites. The PC results show distinctly different trends for near-surface versus surface temperatures, demonstrating the importance of handling these separately. The first PC of weighted sea surface summer temperature time series and continental time series explains 45 ± 8% of the variance, where the uncertainty is the standard deviation of the distribution of variance explained across the 1000 age-uncertain ensemble members. PC1 has a relatively uniform expression over the whole region, closely following the summer insolation at 65°N. The second PC explains 22 ± 4% of the variance and shows a non-uniform expression, with loadings in opposite directions in the northern and southeastern parts of the region. Comparing the PC time series with model runs and with the timing of the demise of the Laurentide Ice Sheet (LIS), suggest that this pattern reflects both topographic and albedo effects of the LIS as well as release of meltwater into the North Atlantic and Arctic Oceans. Comparing the stack of gridded records with published global stacks reveals an unusual Holocene temperature development in the North Atlantic-Fennoscandian region most likely resulting from the location relative to the decaying LIS. [ABSTRACT FROM AUTHOR]
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- 2016
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20. Holocene climate change in Arctic Canada and Greenland.
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Briner, Jason P., McKay, Nicholas P., Axford, Yarrow, Bennike, Ole, Bradley, Raymond S., de Vernal, Anne, Fisher, David, Francus, Pierre, Fréchette, Bianca, Gajewski, Konrad, Jennings, Anne, Kaufman, Darrell S., Miller, Gifford, Rouston, Cody, and Wagner, Bernd
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HOLOCENE Epoch , *SPATIO-temporal variation , *CLIMATE change - Abstract
This synthesis paper summarizes published proxy climate evidence showing the spatial and temporal pattern of climate change through the Holocene in Arctic Canada and Greenland. Our synthesis includes 47 records from a recently published database of highly resolved Holocene paleoclimate time series from the Arctic (Sundqvist et al., 2014). We analyze the temperature histories represented by the database and compare them with paleoclimate and environmental information from 54 additional published records, mostly from datasets that did not fit the selection criteria for the Arctic Holocene database. Combined, we review evidence from a variety of proxy archives including glaciers (ice cores and glacial geomorphology), lake sediments, peat sequences, and coastal and deep-marine sediments. The temperature-sensitive records indicate more consistent and earlier Holocene warmth in the north and east, and a more diffuse and later Holocene thermal maximum in the south and west. Principal components analysis reveals two dominant Holocene trends, one with early Holocene warmth followed by cooling in the middle Holocene, the other with a broader period of warmth in the middle Holocene followed by cooling in the late Holocene. The temperature decrease from the warmest to the coolest portions of the Holocene is 3.0 ± 1.0 °C on average (n = 11 sites). The Greenland Ice Sheet retracted to its minimum extent between 5 and 3 ka, consistent with many sites from around Greenland depicting a switch from warm to cool conditions around that time. The spatial pattern of temperature change through the Holocene was likely driven by the decrease in northern latitude summer insolation through the Holocene, the varied influence of waning ice sheets in the early Holocene, and the variable influx of Atlantic Water into the study region. [ABSTRACT FROM AUTHOR]
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- 2016
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21. Surface and sub-surface multi-proxy reconstruction of middle to late Holocene palaeoceanographic changes in Disko Bugt, West Greenland.
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Moros, Matthias, Lloyd, Jeremy M., Perner, Kerstin, Krawczyk, Diana, Blanz, Thomas, de Vernal, Anne, Ouellet-Bernier, Marie-Michele, Kuijpers, Antoon, Jennings, Anne E., Witkowski, Andrzej, Schneider, Ralph, and Jansen, Eystein
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HOLOCENE Epoch , *PALEOCEANOGRAPHY , *OCEAN temperature , *MELTWATER , *SEA ice - Abstract
We present new surface water proxy records of meltwater production (alkenone derived), relative sea surface temperature (diatom, alkenones) and sea ice (diatoms) changes from the Disko Bugt area off central West Greenland. We combine these new surface water reconstructions with published proxy records (benthic foraminifera - bottom water proxy; dinocyst assemblages – surface water proxy), along with atmospheric temperature from Greenland ice core and Greenland lake records. This multi-proxy approach allows us to reconstruct centennial scale middle to late Holocene palaeoenvironmental evolution of Disko Bugt and the Western Greenland coastal region with more detail than previously available. Combining surface and bottom water proxies identifies the coupling between ocean circulation (West Greenland Current conditions), the atmosphere and the Greenland Ice Sheet. Centennial to millennial scale changes in the wider North Atlantic region were accompanied by variations in the West Greenland Current (WGC). During periods of relatively warm WGC, increased surface air temperature over western Greenland led to ice sheet retreat and significant meltwater flux. In contrast, during periods of cold WGC, atmospheric cooling resulted in glacier advances. We also identify potential linkages between the palaeoceanography of the Disko Bugt region and key changes in the history of human occupation. Cooler oceanographic conditions at 3.5 ka BP support the view that the Saqqaq culture left Disko Bugt due to deteriorating climatic conditions. The cause of the disappearance of the Dorset culture is unclear, but the new data presented here indicate that it may be linked to a significant increase in meltwater flux, which caused cold and unstable coastal conditions at ca. 2 ka BP. The subsequent settlement of the Norse occurred at the same time as climatic amelioration during the Medieval Climate Anomaly and their disappearance may be related to harsher conditions at the beginning of the Little Ice Age. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
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