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Subatlantic

From Wikipedia, the free encyclopedia
Last climatic phase of the Holocene
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The examples and perspective in this articledeal primarily with Europe and do not represent aworldwide view of the subject. You mayimprove this article, discuss the issue on thetalk page, orcreate a new article, as appropriate.(August 2014) (Learn how and when to remove this message)
Preceded by thePleistocene
Holocene
Epoch

ICSstages/ages (official)


Greenlandian (11.7*8.236*ka)
Northgrippian (8.236–4.2† ka)
Meghalayan (4.2 ka–present)

Blytt–Sernander stages/ages


Preboreal (10.3†–9† ka)
Boreal (9–7.5† ka)
Atlantic (7.55† ka)
Subboreal (52.5† ka)
Subatlantic (2.5 ka–present)

*Relative to year 2000 (b2k).

†Relative to year 1950 (BP/Before "Present").

TheSubatlantic is the currentclimatic age of theHoloceneepoch. It started about 2,500 yearsBP and is still ongoing. Its average temperatures are slightly lower than during the precedingSubboreal andAtlantic. During its course, thetemperature underwent several oscillations, which had a strong influence on fauna and flora and thus indirectly on the evolution of human civilizations. With intensifyingindustrialisation, human society started to stress the natural climatic cycles with increasedgreenhouse gas emissions.[1][2][3]

History and stratigraphy

[edit]

The termsubatlantic was first introduced in 1889 byRutger Sernander[4] to differentiate it fromAxel Blytt'satlantic.[5] It follows upon the previoussubboreal. According toFranz Firbas (1949) and Littet al. (2001) the subatlantic consists of the pollen zones IX and X.[6][7] This corresponds in the scheme ofFritz Theodor Overbeck to the pollen zones XI and XII.[8]

In climate stratigraphy, the subatlantic is usually subdivided into anolder subatlantic and ayounger subatlantic. The older subatlantic corresponds to pollen zone IX (or XI in an alternate nomenclature made of more zones) characterized in central and northern Europe bybeech oroak-beech forests, the younger subatlantic to pollen zone X (or XII in the alternate nomenclature made of more zones).

In easternGermany, Dietrich Franke subdivides the subatlantic into four stages (from young to old):[9]

Ages

[edit]

The beginning of the subatlantic is usually defined as 2,400 calendar yearsBP or 450BC, but this lower limit is not rigid. Some authors[which?] prefer to define the start of the subatlantic as 2,500radiocarbon years, which represents roughly 625 BC.[10] Occasionally, the onset of the subatlantic has been pushed back to 1200 BC.

According to Franz Firbas, the changeover from the subboreal (pollen zone VIII) to the older subatlantic (pollen zone IX) is characterized by the recession ofhazel andlime and the simultaneous spreading ofhornbeam due to anthropogenic influences. This recession was not synchronous. It occurred in the western reaches of the LowerOder valley between 930 and 830 BC,[11] whereas in southwesternPoland this event had taken place already between 1170 and 1160 BC.[12]

The beginning of the younger subatlantic at 1250 AD coincides with the medieval population increase and distinguishes itself by an increase inpine and in indicator plants for human settlements. InSilesia this event can be dated between 1050 and 1270 AD.[12] If one equates the onset of the younger subatlantic with the first maximum of beech occurrence it shifts back toCarolingian times around 700 AD.

Climatic evolution

[edit]
Reconstructed temperatures of the earth during the last 2,000 years.
Rising world average temperatures since 1880.

The summer temperatures of the subatlantic are generally somewhat cooler (by up to 1.0 °C) than during the preceding subboreal, the yearly average temperatures reduced by 0.7 °C. At the same time the winterprecipitations augmented by up to 50%. Overall the climate during the subatlantic therefore tends to cooler and wetter conditions. The lower limit of theglaciers inScandinavia descended during the subatlantic by 100 to 200 meters.[13]

The beginning of the subatlantic opened at the middle of the first millennium BC with the so-calledRoman Warm Period which lasted to the beginning of the 4th century. This corresponds broadly toclassical antiquity. The optimum is marked by a temperature spike centered around 2,500 BP.[14] As a consequence in Europe the winter temperatures were raised by 0.6 °C during this period,[15] yet on average were still by 0.3 °C lower than during the subboreal.Ice cores fromGreenland also demonstrate a distinct temperature rise after the younger subboreal. The cooling that followed coincides with theMigration Period. It was not very pronounced and of short duration – an average temperature drop of 0.2 °C and a winter temperature drop of 0.4 °C center around 350 AD (or 1,600 years BP). This climatic deterioration with the establishment of drier and cooler conditions might have forced theHuns to move west thus in turn triggering the migrations of theGermanic tribes. At about the same time theByzantine Empire reached its first acme andChristianity established itself in Europe as the leadingmonotheistic religion.

After this relatively short cool interlude the climate ameliorated again and reached between 800 and 1200 almost the values of the Roman Warm Period (used temperature proxies are sediments in the North Atlantic).[16] This warming happened during theHigh Middle Ages wherefore this event is known asMedieval Global Warming or theMedieval Warm Period. This warmer climate peaked around 850 AD and 1050 AD, and raised thetree line inScandinavia and inRussia by 100 to 140 meters;[17] it enabled theVikings to settle inIceland andGreenland. During this period theCrusades took place and the Byzantine Empire was eventually pushed back by the rise of theOttoman Empire.

The end of the Medieval Warm Period coincides with the early 14th century reaching a temperature minimum around 1350, and by theCrisis of the Late Middle Ages. Many settlements wereabandoned and leftdeserted. As a consequence, the population inCentral Europe drastically receded by as much as 50 percent.[citation needed]

After a short warming pulse around 1500, theLittle Ice Age followed, lasting from c. 1550 until 1860. TheNorthern Hemispheresnow line descended by 100 to 200 meters.[18] Human history during this time includesthe Renaissance and theAge of Enlightenment, and also major rebellious events like theThirty Years War and theFrench Revolution. The beginning of theIndustrial Revolution also dates back to this period, whileSoutheast Asia experienced thePost-Angkor Period.

From 1860 onwards, the temperatures started to rise again and initiated the modern climatic optimum. This warming was severely amplified by anthropogenic influences (i.e. increasing industrialisation,greenhouse gas emissions andglobal warming). The modern warming shows a distinct temperature rise from the 1970s onwards. According to NASA, this is not expected to change within the 21st century.[19]

Atmosphere

[edit]
Evolutionary trends of greenhouse gases and CFCs

Ice core analyses fromGreenland andAntarctica show a very similar evolution ingreenhouse gases. After a temporary minimum during the preceding subboreal and atlantic the concentrations ofcarbon monoxide,nitrous oxide andmethane slowly started to rise during the Subatlantic. Since 1800 onwards this rise has dramatically accelerated paralleling roughly the concomitant temperature rise. For example, the CO2-concentration increased from 280 ppm to a recent value of nearly 400ppm, methane from 700 to 1800ppb and N2O from 265 to 320 ppb.[20] A comparable rise had already taken place at the changeover to the Holocene, but this process then took nearly 5,000 years. This sudden release of greenhouse gases into the atmosphere by human society represents an unprecedented experiment with unpredictable consequences for Earth's climate.[21][22][23] Within the same context the release of juvenilewater tied up in fossil fuels likecoal,lignite,gas andpetrol is generally overlooked.

Sea level

[edit]
Post-glacialsea level rise.

During the 2,500 year duration of the subatlantic globalsea level kept on rising by about 1 meter. This corresponds to a rather low rate of 0.4 millimeters per year. Yet at the end of the 19th century a drastic change can be witnessed with a rate increase to 1.8 mm per year in the period 1880 to 2000. In the last twenty years alonesatellite measurements document a rise of 50 millimeters which corresponds to a sixfold increase on the pre-industrial rate and a new rise of 2.5 millimeters per year.

Evolution in the Baltic

[edit]

Today's sea level was already reached during the oldest subatlantic by thethird Litorina transgression. The sea level rise had amounted to 1 meter, since then it oscillated around the zero mark. The transgression established during thepostlitorine phase theLimnea Sea,[24] which is characterized by lowersalinity compared with the precedingLittorina Sea due to anisostatic shallowing of theDanish sea straits (Great Belt,Little Belt andÖresund). As a consequence thesea snailLittorina littorea was gradually replaced by the freshwater snailLimnaea ovata.[25]

During the middle subatlantic about 1,300 years ago another rather weak sea level rise took place. Yet the salinity kept falling and therefore new freshwater species were able to immigrate. During the younger and youngest subatlantic about 400 years ago the Limnea Sea was replaced by theMya Sea as distinguished by the immigration of theclamMya arenaria which eventually gave way to the recentBaltic Sea.[26]

Evolution of the North Sea area

[edit]

In theNorth Sea area, which had experienced a slight sea level fall and sea level stagnation during the subboreal, the renewed transgressive pulses of theDunkerque transgression during the older subatlantic achieved the recent level.

Vegetation history

[edit]

The wet and cool older subatlantic (pollen zone IX a) is characterized in central Europe by anoak forest intruded more and more bybeech (mixed oak forests withlime andelm or mixed oak forests withash and beech). Humid terrains were generally occupied byalder and ash. The mixed oak forests lasted until the middle subatlantic (pollen zone IX b), which also had a wet but somewhat milder climate. Interspersed within the middle subatlantic are peaks in the occurrence ofEuropean beech andEuropean hornbeam (mixed oak forests with beech or mixed oak forests with elm, hornbeam and beech).

During the younger subatlantic (pollen zone X a), whose wet and temperate climate resembled already today's conditions, a mixed or an almost pure beech forest established itself. Anthropogenic influences (i. e. agricultural land uses, grazing and forestry) that date back to theBronze Age started to become dominant. The actual youngest subatlantic (pollen zone X b) with its wet and temperate climate shows a distinctprecipitation gradient with decreasing rainfall from west to east. Natural and indigenous forest communities were severely diminished and more and more replaced by artificially managed forest communities.

In northwesternGermany mixed oak forests take up 40% amongst the total tree pollen during the older subatlantic and are therefore dominant. Afterwards their count starts fluctuating and they are definitely receding during the younger subatlantic. The percentage of elms and limes as members of the mixed oak forests yet stayed constant. Alders receded from 30 to 10%.Pine trees were also receding but peaked during the youngest subatlantic due to forestry.Hazel (15%),birch (5%) andwillow (<1%) roughly kept their numbers. Significant was the spreading of beech (from 5 to 45%) and hornbeam (from 1 to 15%).[27] According to H. M. Müller the spreading of beech was caused by an increase in humidity since 550 BC and later favoured by a decrease in human settlements during the migrations.[28]

Herbs likecornflower,atriplex,sorrel andplantago also show a pronounced rise from 15 to 65% amongst the total pollen.Cereals were also on the increase – they augmented from 5 to 30% and clearly document an expanding agriculture during the younger subatlantic.

In northern Germany (Ostholstein) the vegetational evolution was very similar.[29] Remarkable here is the rapid rise of non-tree pollen from 30 to more than 80% (including an increase in cereals from 2 to over 20%) during the younger subatlantic. Amongst the tree pollen the mixed oak forest was able to keep its share of 30%. Alders were also retreating from 40 to 25%. Let alone small fluctuations birch, beech and hornbeam overall conserved their share (hornbeam showed a distinct peak at the beginning younger subatlantic). Pine trees were also augmenting during the youngest subatlantic.

Several distinct events could be recognized (from young to old):

  • spreading of pine trees (K) – at about 1800 – due to forestry
  • second beech peak (F 2)
  • first beech peak (F 1) – at about 1300 AD,[30] inLower Saxony already at about 800 AD.
  • fifth hazel peak (C 5) – at about 200 to 400 AD[31] – due to climatic reasons

Fauna and flora

[edit]

Faunal diversity has severely suffered since the middle of the 19th century by forcedindustrialisation and the concomitantpollution of the environment. This trend has reached alarming proportions since 1975. According to theLiving Planet Indexvertebrates have so far suffered a loss of 40% of their species.Freshwater taxa have even been more severely affected – they have lost up to 50%, mainly due to biotope loss and water pollution. According to NASA, agriculture, fisheries and ecosystems will be increasingly compromised in the Northeastern United States. In the Southeastern United States, increasing wildfires, insect outbreaks and tree diseases are causing widespread tree die-off.[32]

See also

[edit]

References

[edit]
  1. ^"Changes since the Industrial Revolution". Archived fromthe original on 12 January 2014. Retrieved12 January 2014.
  2. ^"Help finding information | US EPA". 12 August 2013.
  3. ^"The Greenhouse Effect".
  4. ^Sernander, R. (1889). Om växtlämningar i Skandinaviens marina bildningar. Bot. Not. 1889, p. 190-199, Lund.
  5. ^Blytt, A. (1876a). Immigration of the Norvegian Flora. Alb. Cammermeyer, Christiania (Oslo), p. 89.
  6. ^Firbas, F. (1949). Spät- und nacheiszeitliche Klimageschichte Mittel-Europas nördlich der Alpen. I. Allgemeine Waldgeschichte, p. 480, Jena.
  7. ^Litt, T.; et al. (2001). "Correlation and synchronisation of Lateglacial continental sequences in northern central Europe based on annually laminated lacustrine sediments".Quaternary Science Reviews.20 (11):1233–1249.Bibcode:2001QSRv...20.1233L.doi:10.1016/S0277-3791(00)00149-9.
  8. ^Overbeck, F. (1950a). Die Moore Niedersachsens. 2. Aufl. Veröff. d. niedersächs. Amtes f. Landesplanung u. Statistik, Reihe A I, Abt. Bremen-Horn, vol. 3, 4.
  9. ^Franke, D. (2010). Regionale Geologie von Ostdeutschland – Ein Wörterbuch.
  10. ^Mangerud, J.; et al. (1974). "Quaternary stratigraphy of Norden, a proposal for terminology and classification".Boreas.3 (3):109–128.Bibcode:1974Borea...3..109M.doi:10.1111/j.1502-3885.1974.tb00669.x.
  11. ^Jahns, S. (2000). "Late-glacial and Holocene woodland dynamics and land-use history of the Lower Oder valley, north-eastern Germany, based on two, AMS14C-dated, pollen profiles".Vegetation History and Archaeobotany.9 (2):111–123.Bibcode:2000VegHA...9..111J.doi:10.1007/BF01300061.S2CID 128772330.
  12. ^abHerking, C. M. (2004).Pollenanalytische Untersuchungen zur holozänen Vegetationsgeschichte entlang des östlichen unteren Odertals und südlichen unteren Wartatals in Nordwestpolen (Ph.D.). Göttingen: Georg-August-Universität.hdl:11858/00-1735-0000-0006-B6D8-E.
  13. ^Dahl, S. O.; Nesje, A. (1996). "A new approach to calculating Holocene winter precipitation by combining glacier equilibrium-line altitudes and pine-tree limits: a case study from Hardangerjøkulen, central southern Norway".The Holocene.6 (4):381–398.Bibcode:1996Holoc...6..381D.doi:10.1177/095968369600600401.S2CID 129377143.
  14. ^Broecker, W. S. (2001)."Was the Medieval Warm Period global?".Science.291 (5508):1497–1499.doi:10.1126/science.291.5508.1497.PMID 11234078.S2CID 17674208.
  15. ^Bond, G.; et al. (2001)."Persistent Solar Influence on North Atlantic Climate During the Holocene".Science.294 (5594):2130–2136.Bibcode:2001Sci...294.2130B.doi:10.1126/science.1065680.PMID 11739949.S2CID 38179371.
  16. ^Keigwin, L. D. (1996). "The Little Ice Age and Medieval Warm Period in the Sargasso Sea".Science.274 (5292):1504–1508.Bibcode:1996Sci...274.1504K.doi:10.1126/science.274.5292.1504.PMID 8929406.S2CID 27928974.
  17. ^Hiller, A.; Boettger, T.; Kremenetski, C. (2001). "Medieval climatic warming recorded by radiocarbon dated alpine tree-line shift on the Kola Peninsula, Russia".The Holocene.11 (4):491–497.Bibcode:2001Holoc..11..491H.doi:10.1191/095968301678302931.S2CID 129178062.
  18. ^Porter, S. C. (1986). "Pattern and Forcing of Northern Hemisphere Glacier Variations during the Last Millennium".Quaternary Research.26 (1):27–48.Bibcode:1986QuRes..26...27P.doi:10.1016/0033-5894(86)90082-7.S2CID 129080980..
  19. ^"Global temperature rise".NASA Climate Change. NASA. Retrieved8 September 2016.
  20. ^Jansen, E.et al. "Palaeoclimate". In:Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor & H.L. Miller (eds). Cambridge University Press. Cambridge and New York.[page needed][ISBN missing]
  21. ^"Greenhouse gas concentrations in atmosphere reach new record – 'Unprecedented in at least the last 800,000 years'". 7 November 2013. Archived fromthe original on 12 January 2014. Retrieved12 January 2014.
  22. ^"Greenhouse gases alone are causing unprecedented Arctic warming". 29 October 2013.
  23. ^"FAQ 7.1 – AR4 WGI Chapter 7: Couplings Between Changes in the Climate System and Biogeochemistry". Archived fromthe original on 2 November 2018. Retrieved12 January 2014.
  24. ^Hupfer, Peter (1981).Die Ostsee – kleines Meer mit großen Problemen (Third ed.). Leipzig: BSB B. G. Teubner Verlagsgesellschaft.OCLC 465125579.[page needed]
  25. ^Hyvärinen, H.et al. (1988). The Litorina Sea and Limnea Sea in the northern and central Baltic. Donner, J. &Raukas, A. (editors): Problems of the Baltic Sea History. Annales Academiae Scientiarum Fennicae, Series A, III. Geologica-Geographica, 148, pp. 25–35.
  26. ^Hessland, I. (1945). "On the Quaternary Mya Period in Europe".Arkiv för Zoologi.37 (8):1–51.ISSN 0004-2110.
  27. ^Schmitz, H. (1956). "Die pollenanalytische Gliederung des Postglazials im nordwestdeutschen Flachland".Eiszeitalter und Gegenwart.6:52–59.
  28. ^Müller, H. M. (1969). "Die spätpleistozäne und holozäne Vegetationsentwicklung im östlichen Tieflandsbereich der DDR zwischen Nördlichem und Südlichem Landrücken".Wissenschaftliche Abhandlungen der Geographischen Gesellschaft der DDR.10:155–165.
  29. ^Schmitz, H. (1953)."Die Waldgeschichte Ostholsteins und der zeitliche Verlauf der postglazialen Transgression an der holsteinischen Ostseeküste".Ber. Dtsch. Bot. Ges.66 (3):151–166.doi:10.1111/j.1438-8677.1953.tb00116.x.S2CID 250467021.
  30. ^Mikkelsen, V. M. (1952). Pollenanalytiske undersogelser ved Bolle, et bidrag til Vegetationshistorien i subatlantisk tid. Nationalmuseets 3. afd. Arkaeologiske Landsbyundersegelser, 1, pp. 109–132, Kopenhagen.
  31. ^Schütrumpf, R. (1951). "Die pollenanalytische Untersuchung eisenzeitlicher Funde aus dem Rüder Moor, Kreis Schleswig".Offa [de].9:53–57.ISSN 0078-3714.
  32. ^"US Regional Effects".NASA Global Climate Change. Retrieved8 September 2016.
ICSstages/ages (official)
Blytt–Sernander stages/ages
*Relative to year 2000 (b2k).
†Relative to year 1950 (BP/Before "Present").
Cenozoic Era
(present–66.0 Ma)
Quaternary(present–2.58 Ma)
Neogene(2.58–23.0 Ma)
Paleogene(23.0–66.0 Ma)
Mesozoic Era
(66.0–252 Ma)
Cretaceous(66.0–145 Ma)
Jurassic(145–201 Ma)
Triassic(201–252 Ma)
Paleozoic Era
(252–539 Ma)
Permian(252–299 Ma)
Carboniferous(299–359 Ma)
Devonian(359–419 Ma)
Silurian(419–444 Ma)
Ordovician(444–485 Ma)
Cambrian(485–539 Ma)
Proterozoic Eon
(539 Ma–2.5 Ga)
Neoproterozoic(539 Ma–1 Ga)
Mesoproterozoic(1–1.6 Ga)
Paleoproterozoic(1.6–2.5 Ga)
Archean Eon(2.5–4 Ga)
Hadean Eon(4–4.6 Ga)
 
ka = kiloannum (thousand years ago);Ma = megaannum (million years ago);Ga = gigaannum (billion years ago).
See also:Geologic time scale  • iconGeology portal  • World portal
Authority control databases: NationalEdit this at Wikidata

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