Global calibration of novel 3-hydroxy fatty acid based temperature and pH proxies
Global calibration of novel 3-hydroxy fatty acid based temperature and pH proxies
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DOI：
10.1016/j.gca.2021.03.010
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发表时间：
2021-03
影响因子：
5
通讯作者：
Canfa Wang;J. Bendle;Huan Yang;Yi Yang;A. Hardman;A. Yamoah;A. Thorpe;I. Mandel;S. Greene-S.-G
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文献类型：
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作者：
Canfa Wang;J. Bendle;Huan Yang;Yi Yang;A. Hardman;A. Yamoah;A. Thorpe;I. Mandel;S. Greene-S.-G
3-羟基脂肪酸（3-OH-FAs），来自革兰氏阴性细菌的外膜，最近受到关注，作为新的陆地pH值和温度的古气候研究代理的潜力。从当代土壤的垂直断面的初步研究-相关的细菌3-OH-FA组合物的空气温度和pH值-已经显示出有希望的结果。但最近校准的地理范围是有限的。在这项研究中，我们分析了全球分布的186个土壤样品中的3-OH-FA脂质分布，以研究控制3-OH-FA异构体相对分布的环境因素。我们的样品组涵盖了广泛的温度范围（−0.4至27 °C）和pH值范围（3.6-9.2）。在全球范围内，我们发现C15或C17同系物（RAN 15或RAN 17）的反同位素正态3-OH-FA比值与年平均气温（MAAT）呈强线性关系（分别为R2= 0.48，p < 0.001和R2= 0.41，p < 0.001）。3-OH-FAs总量与总含量比值（RIAN）的负对数与土壤pH值呈显著负相关（R2= 0.66，p < 0.001）。然而，我们发现，我们的3-OH-FA为基础的代理有显着差异的斜率和截距的线性校正在区域尺度。因此，当地或区域的校准可能是更可取的（在这个阶段的3-羟基-FA代理开发）应用到特定的古气候档案。我们还探讨了3-OH-FA异构体分数丰度与环境参数的关系，使用机器学习工具（高斯过程（GP）仿真器）。这证实了经验方程所强调的环境参数的一阶关系，并且还推导出用于重建MAAT和pH的几种替代GP仿真器模型，与全球范围内的简单线性回归相比，这些模型给出了更高的R2值（MAAT为0.66; pH为0.63）和更低的RSME值（MAAT为3.5 °C; pH为0.76）。我们比较我们的3-OH-FA为基础的指数与细菌支链甘油二烷基甘油四醚（brGDGT）为基础的指数从相同的土壤样品。在全球范围内，RAN 15和RAN 17与MBT′ 5 ME-MAAT（MBT′ 5 ME，5-甲基支链四醚的甲基化指数）呈负相关（分别为r= − 0.59，p < 0.001和r = − 0.42，p < 0.001），而RIAN与支链四醚的环化率（CBT）呈强线性相关（r= 0.77，p < 0.001）。与基于3-OH-FA的温度代理相似，基于GDGT的温度代理MBT′ 5 ME也表现出不同的区域校正。我们的新的基于场的相关性证明了革兰氏阴性细菌细胞膜对全球范围内外部环境变化的广泛生理反应。我们建议，3-OH-FA为基础的代理有广泛的潜力，古环境研究，以估计过去的MAAT和土壤pH值，但区域/当地和具体情况下的校准可能需要应用。
3-Hydroxy fatty acids (3-OH-FAs), derived from Gram-negative bacterial outer membranes, have received recent attention for their potential as new terrestrial pH and temperature proxies for palaeoclimate studies. Initial studies from altitudinal transects of contemporary soils – correlating bacterial 3-OH-FA compositions to air temperature and pH – have shown promising results. But the geographical extent of recent calibrations is limited. In this study, we analyse 3-OH-FA lipid distributions in 186 globally distributed soil samples to study the environmental factors controlling the relative distribution of the 3-OH-FA isomers. Our sample-set covers a wide range of temperatures (−0.4 to 27 °C) and pH (3.6–9.2). For the global compilation we find that the ratio ofanteisotonormal3-OH-FAs of the C15or C17homologues (RAN15or RAN17) shows a strong linear relationship with mean annual air temperature (MAAT) (R2= 0.48,p< 0.001 and R2= 0.41,p< 0.001, respectively). Additionally, the negative logarithm of the ratio of the summedisoandanteisoto the total amount ofnormal3-OH-FAs (RIAN) is also strongly anticorrelated with the soil pH (R2= 0.66,p< 0.001). However, we find that for our 3-OH-FA based proxies there are significant differences in slope and intercept of the linear corrections at regional scales. Thus local or regional calibrations are likely preferable (at this stage of 3-OH-FA proxy development) for application to specific palaeoclimate archives. We also explore the relationship of 3-OH-FA isomer fractional abundances to environmental parameters using machine learning tool (a Gaussian Process (GP) emulator). This confirms the first order relationships to environmental parameters highlighted by the empirical equations and also derives several alternative GP emulator models for reconstructing MAAT and pH which give higher R2values (0.66 for MAAT; 0.63 for pH) and lower RSME values (3.5 °C for MAAT; 0.76 for pH) compared to simple linear regressions at the global scale. We compare our 3-OH-FA based indices with bacterial branched glycerol dialkyl glycerol tetraethers (brGDGTs) based indices from the same soil samples. At a global scale RAN15and RAN17show negative correlations with the MBT′5ME-MAAT (MBT′5ME, methylation index of 5-methyl branched tetraethers) (r= −0.59,p< 0.001 andr= −0.42,p< 0.001, respectively), whilst RIAN shows strong linear correlations with the cyclisation ratio of branched tetraethers (CBT) (r= 0.77,p< 0.001). Similar to 3-OH-FA based temperature proxies, GDGT based temperature proxy MBT′5MEalso showed different regional calibrations. Our new field-based correlations demonstrate the broad physiological response of Gram-negative bacterial cell membranes to external environmental changes on a global scale. We suggest that 3-OH-FA based proxies have widespread potential for palaeoenvironmental studies to estimate past MAAT and soil pH, but that regional/local and context specific calibrations may need to be applied.