کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5161539 | 1502279 | 2015 | 34 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
The 6-methyl branched tetraethers significantly affect the performance of the methylation index (MBTâ²) in soils from an altitudinal transect at Mount Shennongjia
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موضوعات مرتبط
مهندسی و علوم پایه
شیمی
شیمی آلی
پیش نمایش صفحه اول مقاله
چکیده انگلیسی
The methylation index (MBT or MBTâ²) of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in soils along altitudinal transects of some mountains, e.g. Mount (Mt.) Shennongjia and Mt. Gongga, exhibited no correlation with altitude or mean annual air temperature (MAT) alone. However, a significant correlation between MBTâ², cyclization ratio (CBT) of brGDGTs and MAT for each transect could still be found. To investigate the reason, we reanalyzed the brGDGTs in soils from Mt. Shennongjia using an improved liquid chromatography method and examined whether the newly described 6-methyl brGDGTs were the main cause of the large scatter in the correlation between MBTâ² and MAT. In contrast to MBTâ², the MBTâ²5ME, based on 5-methyl brGDGTs alone, correlated significantly with MAT (R2 0.89, p < 0.001) but had no relationship with soil pH. However, MBTâ²6ME, based only on 6-methyl brGDGTs, was strongly dependent on soil pH. This suggests that pH dependent 6-methyl brGDGTs introduce large scatter in the correlation between MBTâ² and MAT, which is likely to mechanistically explain the poor relationship between MBTâ² and MAT, yet good correlation between MBTâ², pH and MAT. A series of indices derived from 6-methyl brGDGTs, including IRIIIaâ² and IRIIaâ² (isomer ratio of structures IIIaâ² and IIaâ², respectively), correlated with soil pH and can be used as new paleo pH indicators to supplement the classic CBT proxy. The tetramethylated brGDGTs with 0-1 cyclopentyl rings (Ia and Ib) were found to comprise unknown isomers, whose abundances also appear to increase with soil pH. A further optimized liquid chromatography method is needed to quantify these new isomers more accurately and to determine the environmental controls on them.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Organic Geochemistry - Volume 82, May 2015, Pages 42-53
Journal: Organic Geochemistry - Volume 82, May 2015, Pages 42-53
نویسندگان
Huan Yang, Xiaoxia Lü, Weihua Ding, Yanyan Lei, Xinyue Dang, Shucheng Xie,