Major glacials and interglacials in Europe
Northern Europe Alps North America
| Glacial | Interglacial | Glacial | Interglacial | Glacial | Interglacial |
| Weichel |
| Wurm |
| Wisconsin |
|
|
| Eem |
| Riss/Wurm |
| Sangamon |
| Saale |
| Riss |
| Illinoian |
|
|
| Holstein |
| Mindel/Riss |
| Yarmouth |
| Elster |
| Mindel |
| Kansan |
|
|
| Cromer |
| Gunz/Mindel |
| Aftonian |
| Menap |
| Mindel |
| Nebraskan |
|
The quaternary is conventionally subdivided into glacials and interglacials with further subdivisions into stadials (shorter cold periods with interstadial or interglacial stages) and interstadials (shorter mild episodes within a glacial phase).
Late Cenzoic Glacier and Climatic variation
Northern Europe
At its maximum Eurasian ice sheet extended eastwards to the Ural mountains, Southeast beyond Kiev, southwards into central Germany and westwards into the British isles. The subdivision into several ice ages is based on morphostatigraphic evidence, with progressively younger terminal moraine systems northwards. The different stages were named (from the oldest) Elster Saale and Weichsel. The Saale glaciations was later subdivided into the Drenth and Wathe Moraine stages. All stages were considered to have been deposited during the last 900,000 years. Deposits from the elster stage represent the earliest definitive evidence of major glaciation in north-western Germany and Europe. These deposits occur in connection with a series of deep, buried channels formed by subglacial meltwater. In contrast with the low or no relief deposits from te Elster Glaciation deposits from the Saalian and especially from the Weichselian glaciation exhibit distinct morphological features. The interglacial stages are represented by deposits of marine transgressions in the lower areas and by terrestrial peat with pollen reflecting the vegetation during different interglacials.
The glacial stages in Britain equivalent to those on mainland Europe are considered to be anglian, wolstonian and devensian. In the British Isles several glaciation centres existed during the Quarternary and combined with frequent phases of coalescing with the Fennoscandian ice sheet, the moraine sequence is less evident there than in mainland Europe
In Northern Europe, The record of glacier variations during the late Cenzoic has been reconstructed from terrestrial data and offshore ice-rafted debris (IRD) from dated ice cores from the Norwegian sea.. The input of IRD is used as proxy for ice-sheet advances reaching the shelf. The first glaciation to each the coast of Nordic Seass occurred at about 11 million yr BP (Late Miocene). Oxygen Isotope records, IRD curves and palynological evidence from the Netherlands indicate that the major glaciations in Scandanavia and Svalbard started around 2.8 million years BP. During the last 2.6 million years, warm interglacials like the Holocene did not last for more than 6-8 per cent of the time, whereas glacial maxima like the 20,000-18,000 yr BP Late weichselian maxima occupied less than 5 percent of the time. The large amplitude climate and ice-sheet fluctuations have occurred mainly during the last 900,000 years.
During the saalian glaciation, western margin of the scandanavian ice sheet advanced on to the shelf, probably reaching the edge of the continental shelf. At the saalian/Eemian transition, the ice sheet retreated rapidly and decayed perhaps within 2000 years or less. The eemian, as initially defined in the Netherlands and correlated with Oxygen isotope stage 5e. During the Early Weichselian, two glacier advance occurred. The first did not reach the coast where as the second advanced to the coastline and released icebergs in some areas. During the early Weichselian , two interstadials occurred in Northern Europe, The brorup/ t.Germain I and Odderade/ St. Germain II. Which has been correlated with oxygen isotope stages 5c and %a respectively. In general, Oxygen isotope stage 5 in Western Scandinavia was Characteriszed by low IRD deposition and short Glacaial phases. In the middle Weichselian, glaciers may have begun to advance during the early part of oxygen isotope stage 4. According to IRD Signal, however ice sheet did not reach its maximum position before ca 63000 yr BP. This glaciation phase was terminated by a deglaciation phase at approximately 54000 yr BP. A glaciation dated to 47000 – 43000 yr BP on the terrestrial record is also found in IRD record. A significant deglacification phase recoreded both in the marine and terrestrial record between 38500 and 32500 yr BP. During the late Weichselian, several ice sheet oscillations occurred, the highest mountains in Scandanavia most probably strode above the ice sheet in nunataks.
The early Late-glacial warming in Europe occurred around 15000 yr BP. In some area there is evidence of warming from around 13500 yr BP. However the most significant warming is record in pollen and coleopteran assemblages from about 1300 yr BP.. The thermal maximum occurred at 1300-12500 yr BP in Britain, Netherlands, Southwest Europe and Switzerland, between 12500 and 12000 yr BP in Southern Sandanavia nd Germany and between 115000 and 11000 yr BP in SW and northern Norway. Marked climatic gradients during this period most probably reflect the cooling effects of the retreating scandanavian ice sheet and changing thermohaline circulation in the North Atlantic.
In the Late-Glacial sequence in northern Europe, a series of distinct climatic oscillations occurred mainly recorded in pollen sequences. Bolling was a mild interstadial 13000-12000 yr BP, followed by the cool and short Older Dryas stadial 12000-11800 yr BP. Allerod was a mild interstadial between 11800 and 11000 yr BP followed by the significant Younger Dryas cooling and glacier expansion between about 11000 and 10000 yr BP. This cooling caused readvances of the Scandinavian ice sheet and expansion/reformation of cirque glaciers beyond continental ice sheet, especially along the western margin. In Scotland, a 2000 km2 ice field developed whereas minor valley and cirque glaciers formed in the upland areas in Scotland, England, Wales and Ireland.
Biostatigraphical sequences from fennoscandian sections were correlated by forsstrom and Punkari with reference sequences from Estonia and sections located near or beyond the margins of the last glaciation. Organic sediments previously attributed to early and Middle Weichselian interstadial periods in Finland were argued by them to be redeposited and mixed older material from the last interglacial. They suggested that the Eemian climatic optimum was followed by a continuously cooling clmate and a marine refression. Their reinterpretation suggests that the ice sheet grew over Finland during the first early Weichselian stadial. The preservation of the interglacial beds and the lack of younger non-glacal sediments, they argued, support the interpretation that the area remained covered until the final deglaciation.
During the last glacial-interglacial transition, the movements of the North Atlantic Polar Front have been described as hingling around locations in the western North Atlantic. Iceland, situate in the middle North Atlantic Ocean, has glaciers sensitive to changes in the oceanic and atmospheric front systems. The Late glacial records from Iceland indicate that relatively warm Atlantic water reached Iceland during the Bolling-Allerod interstadial complex with a short colling period corresponding to the older Dryas. The Marine Polar front was located close to Iceland during Bolling-Allerod and Sarnthein concluded that sea-surface circulation was mainly in a Holocene interglacial mode after 12800 yr BP. Like elsewhere in NW Europe an abrupt colling marks the beginning of the younger Dryas. Terrestrial data from Iceland demonstrate a transition from mild climatic conditions by the end of the Allerod to polar conditions and significant glacier expansion. Pollen Influx dropped significantly and the content of organic carbon in lake sediments from northern Iceland demonstrates rapid climatic Change. The sequence of deglacification and terrestrial biostratigraphical records indicating climate and by ca. 8000 yr BP glaciers were similar size as at present.
Ash zone I in Iceland consists of at least five different tephra populations deposited over a period of ca 1500 radiocardon years as in lake sediments from Skagi, northern Iceland of which the Vedde and saksunarvatn ash layers are the most widely recognized.
The Alps
At their maximum, Alpine glaciers covered about 150,000 km2. The alpine glaciers flowed as a network among mountain peaks and ice divides, with coalescing valley and piedmont glaciers. Based on work in the northward-draining valleys of German Alpine foreland, south of Munich, Penck and Bruckner presented a scheme of glacials and interglacials. Subsequently the four part sequence was extended by the discovery of two older glaciations, the Donau and Biber. The four main glacial stages are represented by a series of terraced glaciofluvial outwash plains; each younger and in general lower plain was related to terminal moraine further up valley. During the interglacials, these are eroded to form terraces. Problems with this classic Alpine sequence have been outlined. The sequence of terraces is complicated than originally proposed and contains both interglacial and postglacial material. In addition the erosion is rather glacial than interglacial and the deposits may represent only a few millennia of glaciation. The classical nomenclature therefore only has morphostratigraphic significance in the study area and must be abandoned for external correlations.
The glacial history of the Eastern Europaean Alps during the LGM has been reconstructed by mapping, palynology and radiocarbon dating. During the Glacier build-up toward the LGM, topographical constraints in the form of deep valleys led to glaciers occuping tributary valleys and troughs until about 24000 yr BP. Subsequently rapid glacier expansion in the main valleys led to ice streams and piedment glaciers in the Alpine foreland. Radiocarbon dates are obtained from organic material in the outwash show that the build up ended about 21000 yr BP. According to the outwash deposits, the LGM lasted for about 3000-4000 years. The deglaciation from the LGM was apparently very rapid. The glacier retreat was interrupted minor oscillations at around 16000 yr BP (oldest Dryas), 14000 yr BP (Gschnitz Phase), during the older Dryas at ca 12000 yr BP (Daun Phase) and finally during the younger Dryas between 11000 and 10,000 yr BP (Egesen Phase).
Glacial Evidence in the Gran Sasso Massif of the central Apennines in Italy has led to the reconstruction and dating of the last glacial maximum advance and subsequent readvance phases. During the Campo Imperatore Stade (22600 yr BP0 glaciers reached their maximum extent. During this phase, mean annual temperatures were of the order of 7-8 C lower than at present and the amount of snowfall was similar to present. The glaciers started to retreat approximately 21000 yr BP forming three recessional moraines between 21000 and 16000 yr BP. Glacier retreat subsequent to 15000 yr BP left behind 4 moraines.
There has been a growing recognition that the Egesen Moraines in the Alps were deposited during the younger Dryas. Surface exposure dates of Egesen moraines in Julier Pass, Switzerland, showed that the moraines were deposited during the early part of the younger Dryas chromozone. In some valleys, numerous Egesen moraines are present, indicating complex glaciers. The moraine complex has been divided into three or in places our distinct groups. Snowlines, tree lines and rock glaciers have been used to calculate temperature depressions and precipitation changes of the younger dryas using glacial-meterological and statistical models. From these Calculations, summer tempeatures may have been about 3C lower than at present while annual temperatures were atleast 4-6C lower in the Central Alps. Precipitation during the Younger Dryas was probably about the same as at present in the northern and western parts of the Alps and decrased significantly towards the interior and the south. At the end of the younger Dryas, precipitation decreased and in the Central Alps of Austra and eastern Switzerland the climate was almost semi-arid.
North America
The Laurentide ice sheet extended from the Arctic Ocean in the Canadian Arctic archipelago to the mid western states in the south and from the Canadian Rocky mountains in the west. The most extensive record of fluctuation along its southern margin comes from the north central United States. Named after the states where they are best characterized, the Nebraskan, Kansan, Illinoian and Wisconsin Glaciations represent the glacial sequence, the Kansan considered to be the most extensive glaciation. The earliest three glaciations are based on till sheets, while the Wisconsin was based on terminal moraines. The interglacials were based on palaeosols develop on tills. Based on new evidence provided means of new methods and extensive fieldwork, the original strtigraphic nomenclatura has been challenged.
During periods of maximum Quaternary glaciation, including the Wisconsin glaciation, the continental ice sheet was more or less continuous over North American continent. The ice sheet consisted of two main parts: the Cordillera ice sheet, centered in the coastal range and Rocky Mountains in the west and the laurentide ice sheet in the east. The former was most extensive in the British Colombian Mountains. The southern limit for the continuous ice was at the Colombia River south of the Canada/USA border. The Laurentide ice sheet was, together with the Eurasian ice sheet, responsible for most of the glacio-eustatic lowering of sea level of ca. 120 m during the LGM. Inferred from the pattern of postglacial uplift, the ice was thickest over Hudson Bay. The different parts of the Laurentide ice sheet reached their maximum extent between 22000 and 17000 yr BP. The Cordillera ice sheet, however reached its maximum extent approximately 15000-14000 yr BP. During its maximum extent., the laurentide ice sheet was more than twice as big as the north European Ice Sheet. To the north, the ice sheet may have coalesced with ice over the Queen Elizabeth Islands. Morphological evidence suggests that the Laurentide ice Sheet had two ice centres, one over Labrador and one over Keewatin.
In the Canadian and north American Rockies, glacier fluctuations have been reconstructed using statigraphy of glacial deposits, geomorphology, and lake and peat deposits. The history of glacier recession of the Lake Wisconsin Valley glaciers in the Canadian and northen Amercan rockies is not well documented. Evidence presented so far suggests that glaciers retreated to within tens of kilometres of the present ice margins before ca. 12000 yr BP. Moraines, a few kilometres beyond little ice age moraines indicate one or several readvances or stillstands. The piper Lake moraine suggests readvance before 11200 yr BP from sediments above the Late Wisconsin till at Crowfoot advance, most glaciers in the rockies retreated as demonstrated by wood radiocarbon-dated at 8200 yr BP washed out from the base of the Athabasca Glacier. Osborn compared modern and Crowfoot ELA using the median altitude approach. ELA depression during the Crowfoot advance ranged from about 5 m for small basin-filled glaciers to 195m for the large and steep Jackson Glacier with a mean of 40m ELA difference.
Based on organic content and magnetic susceptibility of continuous lake sediment records of glaciations in Sierra Nevada, California, at least 20 stadial-interstadial oscillations between 52600 and 14000 yr BP are indicated. The recod shows that a glaciation started at approximately 24500 yr Bp and terminated at around 13600 yr BP. Alpine Glacier oscillations in Sierra Nevada have occurred at a frequency of approximately every 1900 years during the most of the last 50000 years. The late glacial Recess Peak advance after retreat from the local Lat Wisconsin (Tioga advance) glaciers. Dated lake cores suggest that the Sierra Nevada show that the last significant pre-Little ice age advances (the Recess peak of Late Pleistocene Age) resulted from ELA lowering of about twice that of the Little Ice Age (Matthes Advance). Tephrochronology and radiocarbon dats from lacustrine sedimets provide time constraints on the two advances. The absence of a young Tephra on Matthes moraines in the central Sierra shows that they formed subsequent to 700 yr BP (ca 650 cal Years). The termination of the recess peak advaces was established at 11200 yr BP by extensive AMS radiocarbon dating on gyttja peat and macrofosils from cores. The evidence presented suggested that if there was an advance related to younger Dryas cooling, it was less extensive than the Matthes advance. In addition the Matthes advance wa the most extensive and most probably the only Neoglacial advance in the Sierra Nevada.
