THE HOLOCENE "current interglacial"

Holocene Chronology
"The Blytt-Sernander Sequence"

The first well-developed, widely-used subdivision of the Holocene and Late-Glacial
The Sequence grew out of studies of peat bogs in Northern Europe.
  • Peat is an important fuel in area and many, many exposures.
  • Dau (1829) observed layers of pine stumps buried in bogs, dark, oxidized peat
  • The Danish academy offered an award for an explanation of the layers
  • Axel Blytt 1876 (Norway) sequence
    • assumed that the oxidized layers were produced by drying of the bogs
    • he produced chronology of alternating wet/dry periods
      • drier (continental = Boreal)
      • wetter (oceanic = Atlantic)
  • Rutger Sernander 1908 (Sweden) better known scientist added late-glacial chronology and included temperature.
  • Gerard DeGeer Sweedish Varve Chronology
  • Lenart Von Post (Palynologist) (1930) and Jessen & Iversen (1941) added temperature to produce current the form of the sequence
  ENVIRONMENTAL
PERIOD
AGE (14C)   CLIMATE
SUBATLANTIC 0-2500 (wet) (Cool)
POST- SUBBOREAL 2500-5000 (dry) (Warm)
GLACIAL ATLANTIC 5000-8000 (wet) (Warmest)
BOREAL 8000-10,000 (dry) (Warm)
---------
YOUNGER DRYAS 10,000-11,000 (Cold)
LATE- ALLEROD 11,000-11,700 (Cool)
GLACIAL OLDER DRYAS 11,700-12,000 (Cold)
 



Interglacial Sequence (the Holocene)



22,000 - 15,000 WÜRM GLACIAL STAGE
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)

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.)

n
o
w

"
B
-
A
"
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)

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.


11,700 - 11,000 ALLEROD INTERSTADIAL
clayworks at Allerod, Denmark (Hartz and Milthers, 1901)
ClayDryas Flora
GyttjaTree Birch, Aspen
ClayDryas Flora
Fauna: Steppe animals + Irish Elk, Beaver, Brown Bear


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)
  1. meltwater lens in N. Atlantic (-2.5oC winter, +1.5oC summer)
  2. flood of iceburgs North Atlantic (-8oC winter, -4oC summer)
  3. no North Atlantic Deep Water (-5oC winter, -1oC summer)
    Thermohaline Circulation
    Thermohaline + (Bryan, 1986)
  4. reduced atm CO2 from 300 to 250 ppmv (-1oC winter, -1oC summer)
    • effect on atm. 14C (Goslar et al. 1995)
  5. Y.D. E.T. impact

Series of Ice-sheet floods


WAS THERE A MIS 6/5e "YOUNGER DRYAS-LIKE" EVENT?


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)


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)


5000 - 2500 SUB BOREAL: Elm and Lime decline, Hazel increase
Dry and warm (but cooler than Atlantic): Ivy and Mistletoe decline
Other Environmental Factors:
  1. 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
  2. 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.

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.


SUBDIVISIONS OF THE LATE GLACIAL
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)

SUBDIVISIONS OF THE HOLOCENE
    Middle Holocene warmer ca. 1 - 2 ºC
    Terms:
    • "postglacial warm period" Kerner (1870-1)
    • Atlantic wet 8000-5000 yr. (Blytt-Sernander 1876)
    • Xerothermic dry (Subboreal) 5000-2500 yr. (Sears, 1942)
    • Altithermal dry 7000-4500 yr. (Antevs, 1948)
        wet 7000-4500 yr. (Martin, 1963)
    • Hypsithermal dry-wet-dry 9000-2500 yr. (Deevey & Flint, 1957; Flint, 1971: 524)
    • Prairie Period dry 8500-4000 yr. (McAndrews, 1967)

    Early Holocene Regional Moisture Contrast ca. 11 - 6,000 14C yr B.P.
    • "Early Holocene Xerothermic" for Pacific Northwest (Hebda and Mathewes, 1984)
    • "Early Holocene Pluvial" for the Southwest. (Davis and Sellers, 1994)
      2-5 X wetter

    8200 yr event 2 - 4 ºC (5ºC) cooler 8200 ka (~7350 14C yr)
      Decay of the Laurentide ice sheet
        -- flooding of North Atlantic with fresh water
        -- interrupted thermohaline circulation
      "mini Younger Dryas"

    Bond Cycles (marine [N. Atlantic] cold events)
    • Solar Forcing or NADW "900 or 1500 - year" cycle
    • Cycle number
        0. 600, 400 & 200 yr (LIA)
        1. 1400 & 1100 yr
        2. 3200 & 2700 yr
        3. 4400 & 4100 yr
        4. 5000 yr
        5. 8200 & 7100 yr
        6. 9500 yr
        7. 10,300 yr
        8. 11,100 yr

    Extended list of Holocene Climate Events

SUBDIVISIONS OF THE LATE HOLOCENE

THE HOLOCENE CLIMATIC SEQUENCE OF ERNST VALDEMAR ANTEVS
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)

READINGS

HOMEWORK

LINKS:
NGDC Holocene Climate Records
peat bogs and palaeoclimate records (has Blytt-Sernander table)
The Uses of Pollen Analysis (has Blytt-Sernander table)