Déndrokronologi

Déndrokronologi atawa pananggalan cingcin tangkal nyaéta métodeu pananggalan ilmiah dumasar kana analisis pola cingcin tangkal. Téhnik ieu mitembeyan dikembangkeun awal abad ka-20 ku A. E. Douglass, nu ngadegkeun Laboratorium Panalungtikan Cingcin Tangkal di Universitas Arizona. Téhnik pananggalan ieu bisa méré umur dina taun kalénder pikeun kai.

 Pamuka 
Sacara basajan, tatangkalan di wewengkon nu hawana sedeng numuwuhkeun hiji cingcin tumuwuh unggal taun. Tatangkalan numuwuhkeun cingcin taunan nu pasipatanana béda-béda gumantung cuaca, hujan, hawa, jsb. dina masing-masing périodeuna. Variasi ieu bisa dipaké pikeun mikanyaho variasi cuaca mangsa ka tukang. Sapanjang hirupna éta tatangkalan, catetan taunan atawa pola cingcin kabentuk kalawan ngagambarkeun kaayaan cuaca di mana éta tangkal hirup. Kalembaban nu cukup jeung usum tumuwuh nu lila bakal ngahasilkeun cingcin nu lébar, sedengkeun mangsa halodo bakal ngahasilkeun cingcin nu heureut. Tatangkalan di wewengkon nu sarua bakal némbongkeun pola nu sarua dina mangsa nu sarua. Tina pola cingcin tangkal ieu tina tatangkalan nu umurna lila, bisa ngahasilkeun kronologi. Lajeng urang bisa ngabandingkeun kai ti struktur heubeul atawa kuna kana kronologi nu geus jadi cecepengan urang, nyocogkeun pola cingcinna (hiji téhnik nu disebut pananggalan silang (cross-dating), sarta nangtukeun sacara jétu umur kai nu dipaké ku nu ngawangun jaman baheula.

 Dadaran 
Karya munggaran nu museur kana ngukur lébar cingcin tangkal - gampang ngukurna jeung bisa dipatalikeun jeung paraméter iklim. Mun dina ukuran taunan tumuwuhna tatangkalan, aya ogé tapak séjén, utamana maximum latewood density is generally found to be a better proxy for temperature than ring width. It is, however, harder to méasure.

Recently, the established connection between tree rings and climate appéars to be bréaking down. Briffa et al report in Nature, 1998:

 During the second half of the twentieth century, the decadal-scale trends in wood density and summer temperatures have increasingly diverged as wood density has progressively fallen. The cause of this increasing insensitivity of wood density to temperature changes is not known... .

Laboratory analysis of timber core samples méasures the width of annual rings. By taking samples from different sites and different strata within a particular region, reséarchers can build a comprehensive historical sequence that becomes a part of the scientific record; for example, ancient timbers found in buildings can be dated to give an indication of when the source tree was alive and growing, setting an upper limit on the age of the wood. Some trees are more suitable than others for this type of analysis. Likewise, in aréas where trees grew in marginal conditions such as aridity or semi-aridity, the techniques of dendrochronology are more consistent than in humid aréas. These tools have been important in archaéological dating of timbers of the cliff dwellings of Native Americans in the arid Southwest.

 Ajén Ilmiah 
Mangpaat utama déndrokronologi nyaéta dina studi cuaca pikeun ngarékonstruksi variasi hawa mangsa nu geus ka tulkang. Tempo ogé catetan hawa mangsa saréwu taun ka tukang.

Kauntungan déndrokronologi nyaéta yén pananggalanana akurat antukna bisa dipaké salaku kalibrasi. Pinus bristlecone nu umurna panjang sarta tumuwuhna alon, sok dipaké pikeun tujuan ieu, ngagunakeun spésimén nu hirup kénéh sarta nu geus paéh, nepi ka bisa kalacak pola cingcinna réwuan taun ka tukang. Pikeun tujuan pananggalan, di sababaraha wewengkon bisa némbongkeun runtuyan nepi ka sapuluh réwu taun.

najan kitu, para ahli déndrokronologi nyanghareupan sababaraha masalah, di antarana ayana spésiés sireum nu nyayang na tangkal antukna ngaruksak struktur cingcinna.

 Tumbu kaluar 
The Laboratory of Tree-Ring Research
Wiener Laboratory for Aegean and Near Eastern Dendrochronology at Cornell University website
Dendrochronology on musical instruments and art objects

Kategori:Géokronologi
Kategori:Antropologi