22,000 - 15,000 WÜRM GLACIAL STAGE
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Central and N. Europe were covered with polar desert:
arid tundra with a few plants and animals seasonally.
Farther south steppe tundra: mixture of grassland and tundra plants, with
grazing animals. (biom in Siberia today [Kamarov in: Love, 1988]
DRYAS FLORA: characteristic of the late-Weichsel stadials, its species are
found today in arctic and alpine habitats - they are INDICATORS
of alpine vegetation. The dryas flora is usually preserved in inorganic
sediment at base of bog cores.
Typical Members of Dryas Flora:
Dryas Fauna: Dordogne (Fr) Cave Paintings: reindeer,
bison, horse, mammoth
In addition to the alpine plants, there were grassland plants.
The Dryas flora was a "disharmonious assemblage" ("disharmonious association"):
an example of NO ANALOG environmental conditions.
- Climatic reasons: cold but dry climate = steppe plants now found further south
Artemisia
(sagebrush or
wormwood),
Ephedra (joint-fir)
- Soil reasons: glacial and periglacial activity produce raw, nitrogen-poor soil = nitrogen
fixing plants (Astragalus) (Hippophae)
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| 14,000 - 13,000 yr B.P. (14C) WINDERMERE INTERSTADIAL |
(G.R. Coope, 1977) beetles say warm as today, but flora still treeless,
only change is an increase in Artemisia pollen
(beetles and plants are a Disharmonious Association)
cf. Stage 1A of deglaciation (14,800 ± 770 - 13,600 ± 670 14C) of Mix (1987)
≠ (later than) Heinrich 1 (16.5 Ka cal.)
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n
o
w
"
B
-
A
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| 12,500 - 12,000 BOLLING INTERSTADIAL |
Arrival of the first trees, may be plant migration instead of climate
Betula pubescens (tree birch) arrives in central western Europe.
Pine arrives in Poland.
Corresponds to Stage 1B (12,880±700 - <11,680±540, Mix, 1987)
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| 12,000 - 11,700 OLDER DRYAS STADIAL (300 Yr!) |
Tree birch and pine retreat southward, Dryas Flora common.
Re-advance of Scandinavian and mountain glaciers.
Fauna: Wolf, Reindeer, Bison, Horse, and Reindeer Hunters.
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| 11,700 - 11,000 ALLEROD INTERSTADIAL |
clayworks at Allerod, Denmark (Hartz and Milthers, 1901)
| Clay | Dryas Flora |
| Gyttja | Tree Birch, Aspen |
| Clay | Dryas Flora |
Fauna: Steppe animals + Irish Elk, Beaver, Brown Bear
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11,000 - 10,000 YOUNGER DRYAS STADIAL |
Dryas Flora with steppe elements, steppe fauna. Extensive moraines in Scandinavia
and Scotland. 4-5oC cooling, 400-500 mm dryer (Pons et al. 1987)
Dating (14C)
| Ballybetaugh, Ireland |
10,600 ± 60 - 10,040 ± 60 |
| Grand Pile, France |
10,150 ± 50 - 9750 ± 40 |
| Nova Scotia, CAN |
10,480 ± 80 - 10,090 ± 90 |
| Pyle Site, Ohio |
10,760 ± 179 - 10,170 ± 170 |
Causes of Younger Dryas Oscillation (cold and dry)
(Broecker et al., 1989; Harvey, 1989; Rooth, 1982)
- meltwater lens in N. Atlantic (-2.5oC winter, +1.5oC summer)
- flood of iceburgs North Atlantic (-8oC winter, -4oC summer)
- no North Atlantic Deep Water (-5oC winter, -1oC summer)
Thermohaline Circulation
Thermohaline +
(Bryan, 1986)
- reduced atm CO2 from 300 to 250 ppmv (-1oC winter, -1oC summer)
- effect on atm. 14C (Goslar et al. 1995)
- Y.D. E.T. impact
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Series of Ice-sheet floods
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WAS THERE A MIS 6/5e "YOUNGER DRYAS-LIKE" EVENT?
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| 10,000 - 8000 BOREAL: First stage of the postglacial |
Expansion of Birch (Betula) in "preBoreal," followed (9000) by Hazel (Corylus)
the first warmth-requiring tree. It migrated northward from Mediterranean area via
Yugoslavia and Poland
Aridity of the Boreal in part due to greater continentality. Before the isostatic rebound was
complete, The English Channel was above water.
Evidence for warmth
- Ivy and Mistletoe, which are very sensitive to freezing
temperatures, were common in Denmark where today they are rare.
- Pond tortoise also present. ± 2 oC higher than today
Fauna: Elk, Aurochs, Deer, Boar, humans (stone ax, dog)
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| 8000 - 5000 ATLANTIC: shade-tolerant forest species |
Elm, Oak, Lime (=Basswood) and Alder: Quercicetum mixitum become dominant
Hazel and other pioneer trees are shaded out
Very Warm and Moist: Ivy and Mistletoe most abundant, Trapa natans
(Water Chestnut) is present in Denmark.
Fauna: Boar, Deer (sparse)
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| 5000 - 2500 SUB BOREAL: Elm and Lime decline, Hazel increase |
Dry and warm (but cooler than Atlantic): Ivy and Mistletoe decline
Other Environmental Factors:
- Human impact responsible elm decline and other changes (Iversen, 1956)
Clearing of Forest - Crops and Domesticated Animals
- flint axes and fire, forest soil diagrams
- girdling and coppicing
- first cereals, weeds: Plantain, Dock
- Tree pathogen may also have been important
- Modern examples: Dutch Elm Disease, Chestnut Blight
- Prehistoric example:
Hemlock Decline
4700 B.P. in the eastern U.S.
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| 2500 - 0 SUB ATLANTIC: immigration of Beech & Hornbeam |
Cold and Moist: Ivy & Mistletoe gone. Beginning of very rapid growth of blanket bogs
Human Impact: Extensive Clearing of Forest
- decline of forest trees
- increased abundance of herbs, particularly weeds
Paludification - leaching and acidification of soils permits growth of
blanket bogs. In nutrient-poor conditions, Sphagnum (peat moss)
grows above water table, the dead stems conducting water from below.
Spreads across landscape.
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SUBDIVISIONS OF THE LATE GLACIAL
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Is the Younger Dryas a Global climatic event? Computer models
(Rind et al., 1986) indicate intense cooling in N. Atlantic & W. Europe,
but warming or no change in some regions of the globe (e.g., N. Alaska)
- Eastern North America correlations with Allerod / Younger Dryas
- Interstadials:
Two Creeks Interstade - Lake Michigan, 11,750 - 12,050 14C yr B.P.
Before the Allerod (Kaiser, 1994) -
- Stadials:
- New York: "Younger Dryas" 11-10,000 14C yr B.P. AMS dates of macrofossils
(Rind, Peteet, 1986)
- Ohio: "Younger Dryas" 10,760 ± 179 - 10,170 ± 170
- Canadian subdivision
Killarny Oscillation 11,290 - 10,960 14C yr B.P.; Younger Dryas
Oscillation 10,820 - 9,500 14C yr B.P. (Levesque et al., 1994)
- Western North America correlations with Allerod / Younger Dryas
- Pluvials:
- Increased lake levels in Southwest 12,000 - 10,000 ya
- Greater abundance of moisture-indicating plants 12 - 10,000 ya
(Spaulding & Graumlich 1984)
- Clovis-Age drought 10,900 ± 50 14C yr Haynes (1991)
(cf. 10,960 - 10,820 for Killarny-Younger Dryas interstadial)
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THE HOLOCENE CLIMATIC SEQUENCE OF
ERNST VALDEMAR ANTEVS
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applied concept of Globalclimate Change in establishing
the Holocene climatic chronology for western North America
- 1888 Born Vartofta, Sweden,
- 1917 Ph.D. University of Stockholm: Studied with Gerard De Geer - Swedish Varve Chronology
- 1920's Geological Survey of Canada
- 1922 Funded by Carnegie Institution to correlate Bonneville, Lahontan, and Mono Lake Pluvial chronologies - use European climate, chronology
- 1931 Subdivided Holocene into Early, Middle (hottest), and Late postglacial
- 1938 Albert and Summer Lakes, OR; Owens Lake, CA, dry before 4000 yr, based on rate of salt accumulation and modern salinity, Warm-Dry 5,500-2,000 B.C.
- 1948 Published 3-part Neothermal Climatic Sequence based on Great Basin arroyo geomorphology and lake chronologies. Preceded Libby's discovery of radiocarbon dating. Time scale based on Swedish Varve Chronology and the European climatic sequence
| Neothermal |
14C YEARS |
CALENDAR |
| Medithermal |
0 - 4500 |
0 - 4000 |
| Altithermal (hot-dry) |
4500 - 7000 |
4000 - 6100 |
| Anathermal |
7000 - 10,150 |
6100 - 9150 |
- 1959 E.V. Anteves described dark layer (unit 'k') associated with extinct megafauna at Lehner Ranch, Arizona
- 1968 Haynes described similar stratigraphy at Murray Springs, near Lehner Ranch. Named it the Black Mat
- 1990 Keigwin & Jones date 1‰ 18O oscillation in Gulf of Calif. 10,800 ± 90 14C yr B.P.
- 1991 Haynes proposes Clovis-Age drought 10,900 ± 50: cf. 10,960 - 10,82014C yr for Killarny-Younger Dryas (Levesque et al., 1994)
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