Författare Ämne: Snigelskal avslöjar istidens kronologi  (läst 6955 gånger)

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Snigelskal avslöjar istidens kronologi
« skrivet: augusti 12, 2011, 16:56 »
Aminosyrer från snigelskal och snäckor ger nya rön om istidens variationer i NV Europa:


A chronological framework for the British Quaternary based on Bithynia opercula

Marine and ice-core records show that the Earth has experienced a succession of glacials and interglacials during the Quaternary (last ~2.6 million years), although it is often difficult to correlate fragmentary terrestrial records with specific cycles. Aminostratigraphy is a method potentially able to link terrestrial sequences to the marine isotope stages (MIS) of the deep-sea record1, 2. We have used new methods of extraction and analysis of amino acids, preserved within the calcitic opercula of the freshwater gastropod Bithynia, to provide the most comprehensive data set for the British Pleistocene based on a single dating technique.

This new aminostratigraphy is consistent with the stratigraphical relationships of stratotypes, sites with independent geochronology, biostratigraphy and terrace stratigraphy. The method corroborates the existence of four interglacial stages between the Anglian (MIS 12) and the Holocene in the terrestrial succession. It establishes human occupation of Britain in most interglacial stages after MIS 15, but supports the notion of human absence during the Last Interglacial (MIS 5e). Suspicions that the treeless ‘optimum of the Upton Warren interstadial’ at Isleworth pre-dates MIS 3 are confirmed. This new aminostratigraphy provides a robust framework against which climatic, biostratigraphical and archaeological models can be tested.

“It's easier to fool people than to convince them that they have been fooled.”

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Istidens kronologi
« Svar #1 skrivet: mars 27, 2012, 21:29 »
Oxygen-isotoper som indikator på istidens kronologi:


Marine Isotope Stages (abbreviated MIS), sometimes referred to as Oxygen Isotope Stages (OIS), are the discovered pieces of a chronological listing of alternating cold and warm periods on our planet, going back to at least 2.6 million years. [...]

The problem is, however, that although scientists have been able to identify an extensive record of global ice volume changes through time, the exact amount of sea level rise, or temperature decline, or even ice volume, is not generally available through measurements of isotope balance, because these different factors are interrelated. However, sea level changes can be sometimes be identified directly in the geological record: for example datable cave encrustations which develop at sea levels (see Dorale and colleagues). This type of additional evidence ultimately helps sorts out the competing factors in establishing a more rigorous estimation of past temperature, sea level, or the amount of ice on the planet.

The following table lists a paleochronology of life on earth, including how the major cultural steps fit in, for the past 1 million years. (Scholars have taken the MIS/OIS listing well beyond that.)

MIS Stage Start Date      Cultural Events

MIS 1     11,600   warmer   Holocene
MIS 2     24,000   cooler   Last glacial maximum, Americas populated
MIS 3     60,000   warmer   Upper Paleolithic; Australia populated, cave walls painted, Neanderthals disappear
MIS 4     71,000   cooler      
MIS 5a    85,000   warmer   Howieson's Poort/Still Bay complexes in southern Africa
MIS 5b    93,000   cooler   
MIS 5c   106,000   warmer   "EMH at Skuhl and Qazfeh in Israel"
MIS 5d   115,000   cooler   
MIS 5e   130,000   warmer   "Early modern humans (EMH) leave Africa"
MIS 6     190,000   cooler   Middle Paleolithic begins, EMH evolves, at Bouri and Omo Kibish in Ethiopia
MIS 7     244,000   warmer   
MIS 8     301,000   cooler   
MIS 9     334,000   warmer   
MIS 10    364,000   cooler   Homo erectus at Diring Yuriahk in Siberia
MIS 11    427,000   warmer   Neanderthals evolve in Europe. This stage is thought to be the most similar to MIS 1
MIS 12    474,000   cooler   
MIS 13    528,000   warmer   
MIS 14    568,000   cooler   
MIS 15    621,000   cooler   
MIS 16    659,000   cooler   
MIS 17    712,000   warmer   H. erectus at Zhoukoudian in China
MIS 18    760,000   cooler   
MIS 19    787,000   warmer   
MIS 20    810,000   cooler   H. erectus at Gesher Benot Ya'aqov in Israel
MIS 21    865,000   warmer   
MIS 22    1,030,000    cooler   

“It's easier to fool people than to convince them that they have been fooled.”

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SV: Snigelskal avslöjar istidens kronologi
« Svar #2 skrivet: oktober 25, 2014, 13:10 »
Golfströmmens inverkning på klimatet gjorde Skandinaviens kustlandskap isfria - även under istidens senare och kallaste perioder: 


Golfstrømmen stoppet ikke under siste istid

– Det er en gjengs oppfatning at det varme atlanterhavsvannet sluttet å strømme inn i de nordiske hav under siste istid. Våre resultater tyder på det motsatte, forteller Mohamed Ezat. Han er doktorgradsstipendiat ved Senter for arktisk gasshydrat, miljø og klima (CAGE), UiT, Norges arktiske universitet.

Ikke bare fortsatte Golfstrømmen sin flyt inn i kalde nordiske hav. Den gikk også dypere og varmet opp bunnvannet. Ezat og hans kolleger ved CAGE har dokumentert at bunnvannet utenfor Færøyene faktisk ble varmet opp - opp mot 5 grader på 1200 meters dyp - under istidens kaldeste perioder.

Bunnvannstemperaturen i de varme istidsperiodene var til gjengjeld 0,5 grader, som er ganske likt det vi har i dag.

Hvordan var dette mulig?

“It's easier to fool people than to convince them that they have been fooled.”