Quaternary Climatic Changes and Landscape Evolution

2005 ◽  
Author(s):  
Jürgen Ehlers
Keyword(s):  
Climatic Change ◽  
Large Scale ◽  
Western Europe ◽  
Ice Sheets ◽  
Climatic Changes ◽  
Mountain Glaciers ◽  
Marine Deposits ◽  
The North ◽  
Terrestrial Sediments ◽  
International Geological Congress

The last 2–3 Ma have witnessed climatic changes of a scale unknown to the preceding 300 Ma. In the cold periods vegetation was reduced to a steppe, giving rise to large-scale aeolian deposition of sand and loess and river sands and gravels. In the warm stages, flora and fauna recolonized the region. Parts of Europe were repeatedly covered by mountain glaciers or continental ice sheets which brought along huge amounts of unweathered rock debris from their source areas. The ice sheets dammed rivers and redirected drainage towards the North Sea. They created a new, glacial landscape. This chapter presents an outline of the climatic history, and in particular the glacial processes involved in shaping the landscapes of western Europe. By convention, geologists generally tend to draw stratigraphical boundaries in marine deposits because they are more likely to represent continuous sedimentation and relatively consistent environments in comparison to terrestrial sediments. However, marine deposits from the period in question are relatively rarely exposed at the surface. According to a conclusion of the International Geological Congress 1948 the Tertiary/Quaternary boundary was defined as the base of the marine deposits of the Calabrian in southern Italy. In the Calabrian sediments fossils are found that reflect a very distinct climatic cooling (amongst others the foraminifer Hyalinea baltica). This climatic change roughly coincides with a reversal of the earth’s magnetic field; it is situated at the upper boundary of what is called the Olduvai Event. Consequently, it is relatively easy to identify; its age is today estimated at 1.77 Ma (Shackleton et al. 1990). However, in contrast to the older parts of the earth’s history, the significant changes within the Quaternary are not changes in faunal composition but changes in climate. For reasons of long-term climatic evolution the base of the Calabrian is not a very suitable global boundary. Its adoption excludes some of the major glaciations from the Quaternary. Therefore, in major parts of Europe another Tertiary/Quaternary boundary is in use, based on the stratigraphy of the Lower Rhine area (e.g. Zagwijn 1989). Here the most significant climatic change is already recorded as far back as the Gauss/Matuyama magnetic reversal (some 2.6 Ma ago).

scholarly journals The origin of till sequences by subglacial sediment deformation beneath mid-latitude ice sheets

1996 ◽  
Vol 22 ◽  
pp. 75-84 ◽  
Author(s):  
G. S. Boulton
Keyword(s):  
North American ◽  
Large Scale ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Glacial Cycle ◽  
Erosion And Deposition ◽  
The North ◽  
Sediment Deformation ◽  
Source Materials ◽  
The Last Glacial

A theory of erosion and deposition as a consequence of subglacial sediment deformation over beds of unlithified sediment is reviewed and applied to large-scale till sequences formed on the southern flanks of the North American and British and European ice sheets during the last glacial cycle. The distribution of till thickness, till lithology in relation to source materials and intra-till erosion surfaces along a flowline in the Michigan lobe of the North American ice sheet are shown to be compatible with the deformational theory but not with other modes of till genesis. It is then demonstrated, in the case of the British ice sheet, how the assumption of a deformational origin for tills can be used to infer time-dependent patterns of ice-sheet dynamic behaviour. By reference to an example from the Netherlands, it is argued that many till sequences interpreted as melt-out tills are more likely to have formed by subglacial sediment deformation.

Did a Beringian ice sheet once exist?

2020 ◽  
Author(s):  
Zhongshi Zhang ◽  
Qing Yan ◽  
Ran Zhang ◽  
Florence Colleoni ◽  
Gilles Ramstein ◽  
...  
Keyword(s):  
North Pacific ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Climate Modelling ◽  
Mountain Glaciers ◽  
The Past ◽  
The North ◽  
Paleoclimate Records ◽  
Glacial Landforms ◽  
The North Pacific

<p>Did a Beringian ice sheet once exist? This question was hotly debated decades ago until compelling evidence for an ice-free Wrangel Island excluded the possibility of an ice sheet forming over NE Siberia-Beringia during the Last Glacial Maximum (LGM). Today, it is widely believed that during most Northern Hemisphere glaciations only the Laurentide-Eurasian ice sheets across North America and Northwest Eurasia became expansive, while Northeast Siberia-Beringia remained ice-sheet-free. However, recent recognition of glacial landforms and deposits on Northeast Siberia-Beringia and off the Siberian continental shelf has triggered a new round of debate.These local glacial features, though often interpreted as local activities of ice domes on continental shelves and mountain glaciers on continents,   could be explained as an ice sheet over NE Siberia-Beringia. Only based on the direct glacial evidence, the debate can not be resolved. Here, we combine climate and ice sheet modelling with well-dated paleoclimate records from the mid-to-high latitude North Pacific to readdress the debate. Our simulations show that the paleoclimate records are not reconcilable with the established concept of Laurentide-Eurasia-only ice sheets. On the contrary, a Beringian ice sheet over Northeast Siberia-Beringia causes feedbacks between atmosphere and ocean, the result of which well explains the climate records from around the North Pacific during the past four glacial-interglacial cycles. Our ice-climate modelling and synthesis of paleoclimate records from around the North Pacific argue that the Beringian ice sheet waxed and waned rapidly in the past four glacial-interglacial cycles and accounted for ~10-25 m ice-equivalent sea-level change during its peak glacials. The simulated Beringian ice sheet agrees reasonably with the direct glacial and climate evidence from Northeast Siberia-Beringia, and reconciles the paleoclimate records from around the North Pacific. With the Beringian ice sheet involved, the pattern of past NH ice sheet evolution is more complex than previously thought, in particular prior to the LGM.</p>

scholarly journals Quaternary palaeoceanography and palaeogeography in northern Denmark: a review of results from the Skagen cores

1996 ◽  
Vol 43 ◽  
pp. 22-31
Author(s):  
Karen Luise Knudsen ◽  
Keld Conradsen ◽  
, Susanne Heier Nielsen ◽  
Marit-Solveig Seidenkrantz
Keyword(s):  
North Atlantic ◽  
Late Quaternary ◽  
Climatic Changes ◽  
Last Interglacial ◽  
North Atlantic Region ◽  
Atlantic Region ◽  
Radiocarbon Dates ◽  
Marine Deposits ◽  
The North ◽  
Late Weichselian

Palaeoenvironmental reconstructions from the Skagen record contribute to the understanding of Late Quatemary climatic changes and variations in the oceanographic circulation pattem in the entire North Atlantic region. The Skagen cores penetrated c. 192 m of Quatemary sediments comprising two marine Late Quaternary records: A 7 m marine unit (185.3-178.3 m) comprised the entire last interglacial, including its lower and upper transitions (Late Saalian-Eemian-Early Weichselian), while the upper 132 m of marine deposits covered the last about 15,000 years from the Late Weichselian through the Holocene, including the Pleistocene-Holocene transition. Results from the study of lithology, foraminifera, stable isotope measurements and radiocarbon dates are reviewed while emphasizing the most important contributions to the general understanding of the North Atlantic Quatemary history

Younger Dryas research and its implications for understanding abrupt climatic change

1997 ◽  
Vol 21 (2) ◽  
pp. 230-249 ◽  
Author(s):  
David E. Anderson
Keyword(s):  
Climatic Change ◽  
North Atlantic ◽  
Large Scale ◽  
Thermohaline Circulation ◽  
Younger Dryas ◽  
Theoretical Understanding ◽  
The North ◽  
Consequent Reduction ◽  
The North Atlantic ◽  
Abrupt Climatic Change

The Younger Dryas refers to the final phase of cold, glacial conditions preceding the abrupt climatic warming at the beginning of the Holocene. The existence of the Younger Dryas in Europe has been known for most of this century, although recent research suggests that the Younger Dryas cooling may have been global. Estimates of the timing of the event have also improved in recent years, showing that both the onset and termination of the Younger Dryas were abrupt, occurring within decades. The Younger Dryas has been linked with a large-scale shift of the North Atlantic thermohaline circulation (THC) to a near glacial mode with a consequent reduction in northward heat transport. This shift in the THC may have been triggered by a discharge of Laurentide ice, combined with meltwater inputs from several locations around the North Atlantic. Further study of the events leading up to the Younger Dryas is necessary for improving theoretical understanding of abrupt climatic change, and for evaluating GCM models which seek to simulate the response of the THC to freshwater forcing. With predicted increases in freshwater input to the North Atlantic resulting from increases in atmospheric CO2, a future shift in the THC is a possibility. Predicting the magnitude and climatic consequences of such an event depends upon further study of the Younger Dryas and of other abrupt palaeoclimatic changes which involved the THC.

scholarly journals The origin of till sequences by subglacial sediment deformation beneath mid-latitude ice sheets

1996 ◽  
Vol 22 ◽  
pp. 75-84 ◽  
Author(s):  
G. S. Boulton
Keyword(s):  
North American ◽  
Large Scale ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Glacial Cycle ◽  
Erosion And Deposition ◽  
The North ◽  
Sediment Deformation ◽  
Source Materials ◽  
The Last Glacial

A theory of erosion and deposition as a consequence of subglacial sediment deformation over beds of unlithified sediment is reviewed and applied to large-scale till sequences formed on the southern flanks of the North American and British and European ice sheets during the last glacial cycle. The distribution of till thickness, till lithology in relation to source materials and intra-till erosion surfaces along a flowline in the Michigan lobe of the North American ice sheet are shown to be compatible with the deformational theory but not with other modes of till genesis. It is then demonstrated, in the case of the British ice sheet, how the assumption of a deformational origin for tills can be used to infer time-dependent patterns of ice-sheet dynamic behaviour. By reference to an example from the Netherlands, it is argued that many till sequences interpreted as melt-out tills are more likely to have formed by subglacial sediment deformation.

The Dynamic Nature of Holocene Vegetation A Problem in Paleoclimatology, Biogeography, and Stratigraphic Nomenclature

1976 ◽  
Vol 6 (4) ◽  
pp. 581-596 ◽  
Author(s):  
H.E. Wright
Keyword(s):  
Climatic Change ◽  
General Circulation ◽  
Late Holocene ◽  
Western Europe ◽  
Vegetation History ◽  
Hardwood Forests ◽  
Early Holocene ◽  
Forest Composition ◽  
The Holocene ◽  
The North

For more than a century it has been postulated that the Holocene vegetation of western Europe has changed in significant ways. A half-century ago a lively debate revolved on whether there were one or two dry intervals causing bogs to dry out and become forested, or whether instead the climate warmed to a maximum and then cooled. Today none of these climatic schemes is accepted without reservation, because two nonclimatic factors are recognized as significant: the differential immigration rates of dominant tree types (e.g., spruce in the north and beech in the south) brought unexpected changes in forest composition, and Neolithic man cleared the forest for agriculture and thereby disrupted the natural plant associations.In North America some of the same problems exist. In the hardwood forests of the Northeast, which are richer than but otherwise not unlike those of western Europe, the successive spread of white pine, hemlock, beech, hickory, and chestnut into oakdominated forests provides a pollen sequence that may yield no climatic message. On the other hand, on the ecotone between these hardwood forests and the conifer forests of the Great Lakes-St. Lawrence area, the southward expansion of spruce, fir, and tamarack in the late Holocene implies a climatic cooling of regional importance, although the progressive conversion of lakes to wetlands favored the expansion of wetland forms of these genera.In the southeastern states the late-Holocene expansion of southern pines has uncertain climatic significance. About all that can be said about the distribution and ecology of the 10 or so species is that some of them favor sandy soils and are adapted to frequent fires. In coastal areas the expansion of pines was accompanied by development of great swamps like Okefenokee and the Everglades—perhaps related to the stabilization of the water table after the early Holocene rise of sea level. The vegetation replaced by the pines in Florida consisted of oak scrub with prairie-like openings, indicating dry early Holocene conditions, which in fact had also prevailed during the time of Wisconsin glaciation.In the Midwest the vegetation history provides a clearer record of Holocene climatic change, at least along the prairie border in Minnesota. With the withdrawal of the boreal spruce forest soon after ice retreat, pine forest and hardwood forest succeeded rapidly, as in the eastern states. But prairie was not far behind. By 7000 years ago the prairie had advanced into east-central Minnesota, 75 miles east of its present limit. It then withdrew to the west, as hardwoods expanded again, followed by conifers from the north. The sequence easily fits the paleoclimatic concept of gradual warming and drying to a maximum, followed by cooling to the present day. It is supported by independent fossil evidence from lake sediments, showing that lakes were shallow or even intermittently dry during mid-Holocene time.Here we have a paleoclimatic pattern that is consistent with the record from glaciers in the western mountains—a record that involves a late-Holocene Neoglaciation after a mid-Holocene interval of distant glacial recession. Just as the Neoglaciation is time-transgressive, according to the review of its evidence by Porter and Denton, so also is the mid-Holocene episode of maximum warmth, and they are thus both geologicclimate units. The warm episode is commonly termed the Hypsithermal, which, however, was defined by Deevey and Flint as a time-stratigraphic unit that is supposed to have time-parallel rather than time-transgressive boundaries. It was defined on the basis of pollen-zone boundaries in western Europe and the northeastern United States that have a sound biogeographic but questionable paleoclimatic basis. Perhaps it should be redefined as Porter and Denton suggest, as a geologic-climate unit with recognizable time-transgressive boundaries that match the gradual geographic shifts in the general circulation of the atmosphere and the resulting location of storm tracks and weather patterns. Holocene glacial and vegetational progressions provide a good record of climatic change, if one can work out the lag effects related to the glacial economy and the geographic factors controlling tree migration. The terminology for the Holocene, where so much time control is available, should indicate the dynamic character not only of the climate but also of the geologic and biogeographic processes controlled by climate.

scholarly journals The role of North Atlantic–European weather regimes in the surface impact of sudden stratospheric warming events

2020 ◽  
Vol 1 (2) ◽  
pp. 373-388 ◽  
Author(s):  
Daniela I. V. Domeisen ◽  
Christian M. Grams ◽  
Lukas Papritz
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Western Europe ◽  
Storm Track ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Weather Regimes ◽  
The North ◽  
Flow Evolution ◽  
The North Atlantic

Abstract. Sudden stratospheric warming (SSW) events can significantly impact tropospheric weather for a period of several weeks, in particular in the North Atlantic–European (NAE) region. While the stratospheric forcing often projects onto the North Atlantic Oscillation (NAO), the tropospheric response to SSW events, if any, is highly variable, and what determines the existence, location, timing, and strength of the downward impact remains an open question. We here explore how the variable tropospheric response to SSW events in the NAE region can be characterized in terms of a refined set of seven weather regimes and if the tropospheric flow in the North Atlantic region around the onset of SSW events is an indicator of the subsequent downward impact. The weather regime analysis reveals the Greenland blocking (GL) and Atlantic trough (AT) regimes as the most frequent large-scale patterns in the weeks following an SSW. While the GL regime is dominated by high pressure over Greenland, AT is dominated by a southeastward-shifted storm track in the North Atlantic. The flow evolution associated with GL and the associated cold conditions over Europe in the weeks following an SSW occur most frequently if a blocking situation over western Europe and the North Sea (European blocking) prevailed around the SSW onset. In contrast, an AT regime associated with mild conditions over Europe is more likely following the SSW event if GL occurs already around SSW onset. For the remaining tropospheric flow regimes during SSW onset we cannot identify a dominant flow evolution. Although it remains unclear what causes these relationships, the results suggest that specific tropospheric states in the days around the onset of the SSW are an indicator of the subsequent tropospheric flow evolution in the aftermath of an SSW, which could provide crucial guidance for subseasonal prediction.

scholarly journals The role of North Atlantic-European weather regimes in the surface impact of sudden stratospheric warming events

2020 ◽  
Author(s):  
Daniela I. V. Domeisen ◽  
Christian M. Grams ◽  
Lukas Papritz
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Western Europe ◽  
Storm Track ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Weather Regimes ◽  
The North ◽  
The North Atlantic

Abstract. Sudden stratospheric warming (SSW) events can significantly impact tropospheric weather for a period of several weeks, in particular over the North Atlantic and Europe. However, not all SSW events exhibit the same tropospheric response, if any, and it remains an open question what determines the existence, location, timing, and strength of the downward impact. We here explore the role of the state of the tropospheric flow in the North Atlantic region at the onset of SSW events for determining the subsequent surface impact. A refined definition of seven North Atlantic tropospheric weather regimes indicates the Greenland blocking (GL) and Atlantic Trough (AT) regimes as the most frequent large-scale patterns following the weeks after an SSW. While GL is dominated by high pressure over Greenland, AT is dominated by a southeastward shifted storm track in the North Atlantic. We find that a blocking situation over western Europe and the North Sea (European Blocking) at the time of the SSW onset favours the GL response and the associated cold conditions over Europe. In contrast, an AT response and mild conditions are more likely if GL occurs already at SSW onset. For the remaining tropospheric flow regimes during SSW onset, we find no clear response. The results indicate that the tropospheric impact of SSW events critically depends on the tropospheric state during the onset of the SSW, which could provide crucial guidance for subseasonal prediction.

scholarly journals Palaeogeographic and palaeoenvironmental characteristics of major marine incursions in northwestern Europe during the Westphalian C (Bolsovian)

2001 ◽  
Vol 3 (3-4) ◽  
pp. 331-347 ◽  
Author(s):  
Michiel DUSAR ◽  
Eva PAPROTH ◽  
Maurice STREEL ◽  
Martin J.M. BLESS
Keyword(s):  
Environmental Conditions ◽  
Large Scale ◽  
Western Europe ◽  
Sedimentary Facies ◽  
Close Correlation ◽  
Climatic Changes ◽  
Delta Plain ◽  
Tree Ferns ◽  
The Relationship ◽  
Stratigraphic Interval

The Westphalian C was a time of marked tectonic and climatic changes within the Variscan Foreland, but our understanding of these changes is hampered by a poor appreciation of large-scale palaeogeography and palaeogeographic evolution within this key stratigraphic interval. The distribution of tonsteins, marine bands and faunal occurrences related to marine incursions or the proximity of marine conditions in Britain and on the European mainland during the Westphalian C (Bolsovian) is briefly summarised. The favoured environmental conditions of some selected fossil taxa (Lingula, arenaceous foraminifers, Geisina, conchostracan faunas and Torispora producing tree ferns) are highlighted. A palaeogeographic model shows the relationship between major sedimentary facies belts in the Westphalian C of western Europe and the influence of major marine incursions on the distribution pattern of incursion-related faunas. The frequent succession of transgressive-regressive faunal phases in beds with marine faunas and the close correlation between the distribution of these beds and the distribution of upper delta plain environments in the Westphalian C of northwestern Europe suggest that marine incursions were long-lived, related to glacio-eustatic events, and cannot be regarded as catastrophic « flash floods ».

scholarly journals Linking Large-scale Circulation Descriptors to Precipitation Variability in the Northern French Alps

2021 ◽  
Author(s):  
Antoine Blanc ◽  
Juliette Blanchet ◽  
Jean-Dominique Creutin
Keyword(s):  
Pressure Difference ◽  
Large Scale ◽  
Western Europe ◽  
Precipitation Variability ◽  
Medium Size ◽  
Maximum Pressure ◽  
Large Scale Circulation ◽  
French Alps ◽  
Mountainous Catchment ◽  
The North

<p>This work analyses the link between Western Europe large-scale circulation and precipitation variability in the Northern French Alps from 1950 to 2017. We consider simple descriptors characterizing the daily 500hPa geopotential height fields. They are the Maximum Pressure Difference - representing the range of geopotential heights over Western Europe -, and the singularity - representing the mean distance between a geopotential shape and its closest analogs, i.e. the way this geopotential shape is reproduced in the climatology. These descriptors are compared to the occurrence of different atmospheric influences - Atlantic, Mediterranean, Northeast, Anticyclonic - and to the leading mode of large-scale circulation variability over Europe - the North Atlantic Oscillation (NAO) - for explaining precipitation variability in the Isère River catchment from one day to 10 years. We show that the Maximum Pressure Difference and the singularity of geopotential shapes explain a significant part of precipitation variability in the Northern French Alps from 10 days to 10 years, especially in winter (correlation values of 0.7). These descriptors provide much better performance than NAO and the same performance as the occurrence of the Atlantic influence, which is the best performing atmospheric influence. This means that simple characteristics of large-scale circulation - that are easy to implement - provide as much information as weather pattern classification to explain precipitation variability over a medium size mountainous catchment. Furthermore, we show that NAO does not drive the pressure gradient in a domain spreading from the Iberic Peninsula to Southern Great Britain and weakly explains precipitation variability in the Northern French Alps.</p>

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