TEX86

**TEX<sub>86</sub>** ne na kwayoyin halitta paleothermometer wanda ya dogara da membrane lipids na mesophilic marine Nitrososphaerota (tsohon "Thaumarchaeota", "Marine Group 1 Crenarchaeota").

## Abubuwan da suka fi dacewa
Membra*n* lipids *n* Nitrososphaerota sun hada da glycerol dialkyl glycerol tetraethers (GDGTs) wanda ke dauke da kashi 0-3 Cyclopentane (wanda aka fi sani da GDGT-n inda n = lambobin cyclopentine). Nitrososphaerota kuma ya hada crenarchaeol (cren) wanda ya ƙunshi kashi huɗu na cyclopentane da kashi ɗaya na cyclohexane da kuma regio-isomer (cren'). Zobba na cyclohexane da cyclopentane, waɗanda aka kafa ta hanyar cyclisation na ciki na ɗaya daga cikin sarƙoƙi na biphytane,  suna da tasiri sosai a kan wuraren canjin zafi na membrane na Nitrososphaerota. Nazarin Mesocosm ya nuna cewa matakin cyclisation gabaɗaya ana sarrafa shi ta hanyar zafin jiki.

## Kwatanta
Dangane da rarraba dangi na isoprenoidal GDGTs, ScH et al. (2002)  sun ba da shawarar ƙididdigar tetraether na ƙwayoyin carbon 86 (TEX86) a matsayin wakili don zafin jiki na teku (SST). GDGT-0 an cire shi daga daidaitawa saboda yana iya samun tushe da yawa  yayin da aka cire cren saboda ba ya nuna alaƙa da SST kuma sau da yawa tsari ne na girman da ya fi yawa fiye da isomer da sauran GDGTs. Kwanan nan na TEX86 daidaitawa yana kiran alamomi biyu daban-daban da daidaitawa:  TEX86H yana amfani da haɗin GDGTs kamar yadda yake a cikin asalin TEX86 dangantaka:

## Caveats
Akwai gargadi da yawa ga wannan wakili kuma wannan jerin ba cikakke ba ne. Don ƙarin bayani, duba Schouten et al. 2013.

### Bayani na duniya
Za a iya amfani da ma'aunin ma'auni vs isoprenoidal tetratether (BIT) don auna ma'aunin shigar da kwayoyin halitta na duniya (TOM) zuwa cikin duniyar ruwa.  Ƙididdigar BIT ta dogara ne akan yanayin cewa crenarchaeol ya samo asali ne daga Nitrososphaerota na ruwa da kuma GDGTs masu rassa suna samuwa daga kwayoyin ƙasa na ƙasa. Lokacin da ƙimar BIT ta wuce 0.4, karkatacciyar> 2&nbsp;An haɗa °C cikin ƙididdiga na tushen TEX 86 na SST. Koyaya, ana iya haɗa GDGTs isoprenoidal akan ƙasa (ta hanyar terrestrial archaea) kuma yana iya sa ƙimar BIT ba ta dogara ba; isoGDGT ya zama mafi girma tare da mafi girman ƙasa pH.  : §7.1.2 Ƙaƙƙarfan bambance-bambance tsakanin GDGT-4 da GDGTs masu rarrafe a cikin ruwa na zamani da mahalli na ruwa kuma yana nuna tushen gama gari ko gauraye don isoprenoidal da GDGTs (Fietz et al., 2012).

### Anaerobic oxidation na methane (AOM)
An gabatar da Methane Index (MI) don taimakawa wajen rarrabe shigarwar dangi na methanotrophic Euryarchaeota a cikin saitunan da ke nunawa ta hanyar yaduwar methane da anaerobic oxidation na methane (AOM).  Wadannan shafuka suna da bambancin rarraba GDGT, wato rinjaye na GDGT-1. -2 da -3. Babban darajar MI (>0.5) yana nuna babban ƙimar gas-hydrate-related AOM.

### Ragewa
Ana tunanin tsufa na zafi kawai ya shafi GDGTs lokacin da zafin jiki ya wuce 240 ° C. Ana iya gwada wannan ta amfani da rabo na takamaiman isomers na hopane. Rashin lalacewar Oxic, wanda shine tsari na zaɓaɓɓu kuma yana lalata mahadi a ƙididdiga daban-daban, an nuna cewa yana shafar dabi'un TEX86 kuma yana iya nuna bambancin dabi'un SST har zuwa 6 ° C.&nbsp;&nbsp;

## Aikace-aikacen
Tsohon rikodin TEX86 ya fito ne daga tsakiyar Jurassic (~160Ma) kuma yana nuna yanayin zafi na teku. An yi amfani da TEX86 don sake gina zafin jiki a duk zamanin Cenozoic (65-0 Ma)   kuma yana da amfani lokacin da wasu wakilai na SST suka canza (misali planktonic foraminifera ) ko babu (misali alkenones ).

### Eocene
An yi amfani da TEX86 sosai don sake gina Eocene (55-34Ma) SST. A lokacin farkon Eocene, dabi'un TEX86 suna nuna zafi mai zurfi na kudancin SSTs (20-25 ° C) bisa ga yarjejeniya da wasu, masu zaman kansu (misali alkenones, CLAMP, Mg / Ca). A lokacin tsakiyar da marigayi Eocene, wuraren latitude na kudanci sun yi sanyi yayin da wurare masu zafi suka kasance masu ɗorewa da dumi. Dalilan da za su iya haifar da wannan sanyaya sun haɗa da canje-canje na dogon lokaci a cikin carbon dioxide da / ko canje-canje a cikin sake tsara ƙofar (misali Tasman Gateway, Drake Passage).

## Manazarta