Lokacin Boreal

A cikin paleoclimatology na Holocene, **Boreal** shine na farko na jerin Blytt-Sernander na matakan yanayi na arewacin Turai waɗanda suka samo asali ne daga nazarin bogs na Danish, mai suna Axel Blytt da Rutger Sernander, waɗanda suka fara kafa jerin. A cikin turɓaya, ana kuma gane Boreal ta hanyar halayensa na pollen. Younger Dryas ne ya riga shi, sanyi na ƙarshe na Pleistocene, sannan Atlantic ya biyo baya, lokacin zafi da zafi fiye da yanayinmu na baya-bayan nan. Boreal, mai sauyawa tsakanin lokutan biyu, ya bambanta sosai, a wasu lokuta yana da yanayin yanayi kamar na yau.

## Rarraba Boreal
Bayan asalin shirin Blytt-Sernander, an raba matakin farko na Boreal a matsayin matakin canji na **Pre-boreal**, sannan Boreal ya biyo baya. Wasu tsare-tsaren yanzu da suka danganci yankunan pollen suma suna rarrabe pre-Boreal (zankin pollen IV), farkon Boreal (Zone pollen V) da marigayi Boreal ("zankin p Pollen VIa, b, da c).

## Yin soyayya

Kwanan wata da aka fi ambata don ƙarshen Ƙananan Dryas da farkon Pre-Boreal shine 11,500 Kafin Present calibrated.  Farkon lokacin yana da ƙayyadaddun ƙayyadaddun ƙayyadaddun ƙayyadaddun haɓakar 7&nbsp;°C a cikin shekaru 50 a Kudancin Greenland.  Kwanan kwanan wata ya dogara ne akan ƙananan kankara na Greenland, wanda ke ba da 11,640 BP don marigayi Younger Dryas da 11,400 BP don farkon Pre-Boreal.

Amma kimantawa na wasu kwanakin ya bambanta har zuwa shekaru 1000, saboda dalilai da yawa. Na farko, "Boreal" na iya gano yanayin yanayi, yankin pollen ko kuma lokacin da aka daidaita na ɗan lokaci, kuma waɗannan tushe uku na ma'anar suna ba da damar kwanakin daban-daban. Na biyu, hanyoyi daban-daban na soyayya suna samun kwanakin daban-daban. Matsalar ita ce yanayin da pollen sun bambanta daga yanki zuwa yanki. Masana kimiyya na kowane yanki suna amfani da hanyoyin da ake samu a yankin su, ko tafkin ya kasance, yadudduka na shekara-shekara na laka daga tsohuwar ko na zamani, ƙwayoyin kankara ko ƙididdigar zoben bishiyoyi (Dendrochronology).

Daidaitawa ya zama abin damuwa ga masana kimiyya a ko'ina. Kwanaki daga hanyoyi da yawa suna ci gaba da ninkawa yayin da masu binciken yanayi ke neman mafi girma. Amma ba a san ko bambancin yanki zai ba da damar daidaitawa mai tsawo ba.

Duk da haka, akwai wasu kwanakin da suka dace na Pre-Boreal da Boreal. Saksunarvatn tephra (wani ash layer na dutsen wuta) an tsara shi a cikin kankara na Greenland zuwa 10,180±60 BP; a cikin ajiyar tafkin a Krakenes a Norway, zuwa shekaru 10,010-9,980 BP daidaita; a cikin tabkuna na arewa maso yammacin Jamus, zuwa 10,090 BP daidaita. Tephra yana faruwa a farkon yanayin Boreal. Don haka, yana da tabbacin cewa farkon Boreal (zankin pollen V) ya haɗa da shekara 10,000 BP. Hakazalika, marigayi Boreal ya haɗa da Kilian / Vasset tephra na Swiss da tabkuna na kudu maso yammacin Jamus a 8200 BP, duk an daidaita su. Amma iyakokin ba su da tabbas.

Nazarin bogs a arewa maso yammacin Rasha shine tushen rarraba PreBoreal (PB) zuwa PB-1, 10,000-9800, da PB-2, 9800-9300 BP incal. Shirin ya ci gaba da raba Boreal (BO) zuwa BO-1, 9300-9000, BO-2, 9000-8500, da BO-3, 8500-8000, incal. CalPal da aka yi amfani da shi a waɗannan kwanakin yana nuna iyakokin 11,500 da 10,500 BP don Pre-Boreal, da kuma ƙarshen Boreal a 8900.

Kwanakin da aka bayar kwanan nan yawanci sun kasance a baya fiye da waɗanda aka bayar fiye da shekaru 10 da suka gabata. Misali, Iverson (1973) da Rud (1979) sun ba da kwanakin 10,000-9000 BP don PreBoreal da 9000-8000 BP don Boreal, waɗanda ba a daidaita kwanakin C-14 ba bisa ga stratigraphy na Scandinavia.

Wataƙila, kwanakin baya-bayan nan sun fi dacewa, yayin da fasaha ke inganta tare da lokaci, sau da yawa da sauri. Duk da haka, yanayin pollen da yanayi har zuwa wani mataki na iya dogara da latitude, don haka babu kwanan wata da za a iya ɗauka kamar yadda ba daidai ba. Masana kimiyya suna neman tsarin kwanakin gaba ɗaya, amma wannan dabarar ba 100% abin dogaro ba ce, ko dai.

## Manazarta