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Stenålder / SV: Istidens abrupta dynamik
« Senaste inlägg av Boreas skrivet maj 06, 2015, 01:57 »Yngre Dryas var tydligen präglat av såväl tektoniska såväl som glaciala rörelser av massiv karaktär. Tidpunkterna ikring 12,8 och 12,1 lär vara dom allra kallaste man mätt på Grönland, vilket faller samman med två större vulkanutbrott:
The 12.8 14C ka-old volcanic ash in Western Norway
http://www.sciencedirect.com/science/article/pii/S0277379107003575
The 12.1 ka Icelandic Vedde Ash?
http://www.sciencedirect.com/science/article/pii/S0277379111003544
Dating, synthesis, and interpretation of palaeoclimatic records of the Last Glacial cycle and model-data integration: advances by the INTIMATE
http://www.sciencedirect.com/science/article/pii/S0277379114004272
Hur påverkades livet i det yttersta norden av Dryas-perioderna?
Ikring Nordkap lär den allra kallaste delen av Yngre Dryas ligga ikring 12.400 år f.n. Värkningen av den massiva isavsmältningen fick tydligen lite olika effekter på Skandinavien och NV Europa gentemot Grönland.
The 12.8 14C ka-old volcanic ash in Western Norway
http://www.sciencedirect.com/science/article/pii/S0277379107003575
The 12.1 ka Icelandic Vedde Ash?
http://www.sciencedirect.com/science/article/pii/S0277379111003544
Dating, synthesis, and interpretation of palaeoclimatic records of the Last Glacial cycle and model-data integration: advances by the INTIMATE
http://www.sciencedirect.com/science/article/pii/S0277379114004272
Hur påverkades livet i det yttersta norden av Dryas-perioderna?
Ikring Nordkap lär den allra kallaste delen av Yngre Dryas ligga ikring 12.400 år f.n. Värkningen av den massiva isavsmältningen fick tydligen lite olika effekter på Skandinavien och NV Europa gentemot Grönland.
Citera
From cold to cool in northernmost Norway:
Lateglacial and early Holocene multi-proxy environmental and climate reconstructions from Jansvatnet, Hammerfest
A multi-proxy palaeoecological study of the lateglacial and early Holocene sediments of Jansvatnet, Hammerfest, northernmost Norway (70°39′ N) showed that cold and arid conditions prevailed in both the lateglacial interstadial and the Younger Dryas.
Terrestrial proxies are macrofossils and pollen. Aquatic proxies are plant and invertebrate macrofossils, pollen, diatoms, and chironomids. Mean July temperatures were reconstructed using pollen and chironomid calibration functions and ecological knowledge of the fossil flora and fauna. Lake-water pH was reconstructed using a diatom pH-calibration function.
Above sterile basal deglacial silts, biotic activity was detected around 14.600 years ago in the interstadial (chronologically equivalent to the Bølling-Allerød in the Greenland Ice-Core Chronology). Catchment vegetation resembled polar desert and ultra-cold stenothermic chironomids lived in the lake. However, diatom assemblages were diverse and dynamic.
In the Younger Dryas stadial, conditions deteriorated. In the early Younger Dryas chironomid-inferred air temperatures (CI-Tjul) fell about 1 °C. Pollen-inferred temperatures (PI-Tjul) did not fall and the terrestrial vegetation hardly changed because of the extreme aridity. The lake water was turbid from suspended clay which diminished aquatic life.
Later in the Younger Dryas (ca 12.400 cal yr BP) reconstructed mean July temperatures fell by a further 3 °C and were close to the minimum to support life, at around 3–4 °C. However, decreased turbidity allowed moss growth on the lake bottom that provided habitats for invertebrates and diatoms.
In the last 200 years of the Younger Dryas temperatures increased by 2–3 °C and terrestrial and aquatic organisms responded quickly. At the start of the Holocene a rapid increase of more than 3 °C in PI-Tjul to 9.5 °C initiated the replacement of sparse arctic tundra by low-arctic dwarf-shrub heath.
Simultaneously, a further 2 °C increase in CI-Tjul to 10–11 °C reflected a regime shift in the lake. Aquatic macrophytes rapidly replaced the moss carpet, diatom assemblages stabilised, diatom plankton developed and cold stenotherm chironomids were replaced by cool-temperate taxa. Productivity increased as CI-Tjul reached a steady maximum of around 12 °C and PI-Tjul reached 10.5 °C at about 10.000 cal yr BP.
http://www.sciencedirect.com/science/article/pii/S0277379111003568
