TEX 86

from Wikipedia, the free encyclopedia

TEX 86 (also tetraether index of 86 carbon atoms ) is a biochemical method for determining the sea surface temperature of earlier climates ( palaeothermometer ).

Basics

Molecular structure and HPLC detection of GDGTs

TEX 86 is based on the analysis of membrane lipids of mesophilic marine thaumarchaeota (formerly marine group I Crenarchaeota ). The membrane lipids of Thaumarchaeota consist of glycerol-dialkyl-glycerol-tetraethers (GDGTs), which between zero and three cyclopentyl - substituents wear, the characteristic GDGT whereas Crenarchaeol four cyclopentane group and a cyclohexane containing group. Thaumarchaeota also synthesize a regio- isomer of Crenarchaeol.

The cyclohexane and cyclopentane rings, which were formed by an internal cyclic connection of one of the biphytane chains, have an influence on the thermal transition points of the cell membrane of Thaumarchaeota. Mesocosmic studies show that the degree of cyclization is generally determined by your growth temperature.

calibration

Based on the relative distribution of isoprenoid GDGTs, Schouten and others suggested the tetraether index of 86 carbon atoms (TEX 86 ) as a proxy for the sea ​​surface temperature SST ( sea ​​surface temperature ) in 2002 . GDGT-0 is excluded from calibration because it is influenced by many factors. GDGT-4 is omitted as it does not show any correlation with the SST. It is often an order of magnitude stronger than its isomer and the other GDGTs. The latest TEX 86 calibration is based on two separate indices and calibrations. The TEX 86 H uses the same combination of GDGTs as the original TEX 86 relationship:

The GDGT ratio-2 is correlated with the SST using the calibration equation : TEX 86 H = 68.4 · log (GDGT ratio − 2) + 38.6). TEX 86 H has a calibration error of ± 2.5 ° C and is based on the 255 upper core segments.

The TEX 86 L uses a combination of GDGTs that differs from the TEX 86 H , with GDGT-3 being removed from the meter and GDGT-4 'being completely omitted:

GDGT Ratio-1 is correlated to the SST using this calibration equation: (TEX 86 L = 67.5 x log (GDGT Ratio-1) + 46.9). TEX 86 L has a calibration error of ± 4 ° C and is based on 396 upper core segments.

There are also other calibrations (including 1 / TEX 86 , TEX 86 'and pTEX 86 ) that should be considered during temperature reconstruction .

restrictions

There are several limitations on this indicator value and the list below is not exhaustive. Schouten et al.

Terrestrial contributions

The index of branched vs. Isoprenoid tetraether ( English branched vs. isoprenoidal tetraether , BIT) can be used to determine the relative input of terrestrial organic matter (TOM) from rivers into the marine kingdom. The BIT index is based on the assumption that GDGT-4 (also known as Crenarchaeol) comes from the marine life Thaumarchaeota and the branched GDGT from mainland soil bacteria. For BIT values ​​higher than 0.4, an uncertainty greater than 2 ° C is included in the TEX 86 -based estimate of the SST. Nonetheless, isoprenoid GDGTs can be synthesized in a mainland environment and the BIT values ​​can no longer be relied on. A pronounced covariation between GDGT-4 and branched GDGTs in modern marine and freshwater environments suggests a common or mixed source of isoprenoid and branched GDGTs.

Anaerobic methane oxidation (AOM)

The methane index (MI) was proposed to diffuse between the relative influence of methanotrophic euryarchaeota and the ammonia-oxidizing Thaumarchaeota in an environment of methane flow and anaerobic methane oxidation ( anaerobic oxidation of methane to be able to AOM) differ. These places are characterized by a pronounced GDGT distribution; specifically, it is a preponderance of GDGT-1, -2 and -3. High MI values ​​(greater than 0.5) reflect high rates of gas hydrate- related AOM and low values ​​(less than 0.3) reflect normal sedimentation conditions, i.e. H. no significant AOM entry.

Decay

It is assumed that GDGTs are only affected by thermal decay at temperatures above 240 ° C. This can be tested by evaluating the ratio of specific hopane isomers. It has been shown that aerobic degeneration affects TEX 86 and shifts the SST values ​​by up to 6 ° C. This is a selective process that causes the preparation to degenerate at different rates.

application

The oldest TEX 86 documents come from the Jura and indicate relatively warm SSTs. TEX 86 was used to reconstruct the temperature of the entire Cenozoic Era (65-0 mya ) and has proven useful when other SST proxies are altered by diagenesis (e.g. foraminifera of plankton ) or missing (e.g. alkenones ).

Eocene

TEX 86 has been extensively tested to reconstruct the Eocene (55–34 mya) SSTs . TEX 86 values ​​indicate high SST values ​​(20-25 ° C) in the high latitudes of the southern hemisphere, which is consistent with other, independently derived proxies (Alkenone, CLAMP , Mg / Ca). Areas of high, southern latitude cooled in the mid and late Eocene, while the tropics remained stable and warm. The reasons for this cooling include long-term changes in carbon dioxide concentration and / or changes in ocean currents (Tasmanian Gate, Drake Passage ).

Individual evidence

  1. ↑ Stefan Schouten, Ellen C. Hopmans, Enno Schefuß, Jaap S. Sinninghe Damsté: Distributional variations in marine crenarchaeotal membrane lipids: a new tool for reconstructing ancient sea water temperatures? In: Earth and Planetary Science Letters . tape 204 , no. 1–2 , November 30, 2002, pp. 265-274 , doi : 10.1016 / S0012-821X (02) 00979-2 .
  2. ↑ Jung-Hyun Kim, Stefan Schouten, Ellen C. Hopmans, Barbara Donner, Jaap S. Sinninghe Damsté: Global sediment core-top calibration of the TEX 86 paleothermometer in the ocean . In: Geochimica et Cosmochimica Acta . tape 72 , no. 4 , February 15, 2008, p. 1154–1173 , doi : 10.1016 / j.gca.2007.12.010 .
  3. ^ A b Stefan Schouten, Ellen C. Hopmans, Jaap S. Sinninghe Damsté: The organic geochemistry of glycerol dialkyl glycerol tetraether lipids: A review . In: Organic Geochemistry . tape 54 , January 2013, p. 19-61 , doi : 10.1016 / j.orggeochem.2012.09.006 .
  4. ↑ Cornelia Wuchter, Stefan Schouten, Marco JL Coolen, Jaap S. Sinninghe Damsté: Temperature-dependent variation in the distribution of tetraether membrane lipids of marine Crenarchaeota: Implications for TEX86 paleothermometry . In: Paleoceanography . tape 19 , no. 4 , December 1, 2004, p. PA4028 , doi : 10.1029 / 2004PA001041 .
  5. ↑ Y. Koga, M. Nishihara, H. Morii, M. Akagawa-Matsushita: Ether polar lipids of methanogenic bacteria: structures, comparative aspects, and biosyntheses. In: Microbiological Reviews . tape 57 , no. 1 , January 3, 1993, p. 164-182 , PMID 8464404 .
  6. ↑ Jung-Hyun Kim et al. a .: New indices and calibrations derived from the distribution of crenarchaeal isoprenoid tetraether lipids: Implications for past sea surface temperature reconstructions . In: Geochimica et Cosmochimica Acta . tape 74 , no. 16 , August 15, 2010, p. 4639-4654 , doi : 10.1016 / j.gca.2010.05.027 .
  7. ↑ Zhonghui Liu et al. a .: Global Cooling During the Eocene-Oligocene Climate Transition . In: Science . tape 323 , no. 5918 , February 27, 2009, p. 1187–1190 , doi : 10.1126 / science.1166368 , PMID 19251622 .
  8. ↑ Appy Sluijs u. a .: Subtropical Arctic Ocean temperatures during the Palaeocene / Eocene thermal maximum . In: Nature . tape 441 , no. 7093 , June 1, 2006, p. 610–613 , doi : 10.1038 / nature04668 .
  9. ↑ Christopher J. Hollis et al. a .: Early Paleogene temperature history of the Southwest Pacific Ocean: Reconciling proxies and models . In: Earth and Planetary Science Letters . tape 349-350 , October 1, 2012, pp. 53-66 , doi : 10.1016 / j.epsl.2012.06.024 .
  10. ↑ HC Jenkyns, L. Schouten-Huibers, S. Schouten, JS Sinninghe Damsté: Warm Middle Jurassic – Early Cretaceous high-latitude sea-surface temperatures from the Southern Ocean . In: Clim. Past . tape 8 , no. 1 , February 2, 2012, p. 215-226 , doi : 10.5194 / cp-8-215-2012 .
  11. ↑ Appy Sluijs et al .: Warm and wet conditions in the Arctic region during Eocene Thermal Maximum 2 . In: Nature Geoscience . tape 2 , no. November 11 , 2009, p. 777-780 , doi : 10.1038 / ngeo668 .
  12. ^ JC Zachos et al .: Extreme warming of mid-latitude coastal ocean during the Paleocene-Eocene Thermal Maximum: Inferences from TEX86 and isotope data . In: Geology . tape 34 , no. 9 , January 9, 2006, p. 737-740 , doi : 10.1130 / G22522.1 .
  13. ^ Paul N. Pearson et al.: Stable warm tropical climate through the Eocene Epoch . In: Geology . tape 35 , no. 3 , January 3, 2007, p. 211-214 , doi : 10.1130 / G23175A.1 .
  14. ^ Peter K. Bijl, Stefan Schouten, Appy Sluijs, Gert-Jan Reichart, James C. Zachos, Henk Brinkhuis: Early Palaeogene temperature evolution of the southwest Pacific Ocean . In: Nature . tape 461 , no. 7265 , October 8, 2009, p. 776-779 , doi : 10.1038 / nature08399 .