Correlations between microbial tetraether lipids and environmental variables in Chinese soils: Optimizing the paleo-reconstructions in semi-arid and arid regions
Correlations between microbial tetraether lipids and environmental variables in Chinese soils: Optimizing the paleo-reconstructions in semi-arid and arid regions
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DOI：
10.1016/j.gca.2013.10.041
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发表时间：
2014-02
影响因子：
5
通讯作者：
Huan Yang;R. Pancost;X. Dang;Xinying Zhou;R. Evershed;G. Xiao;Chang Tang;Li Gao;Zhengtang Guo;S. Xie
中科院分区：
文献类型：
--
作者：
Huan Yang;R. Pancost;X. Dang;Xinying Zhou;R. Evershed;G. Xiao;Chang Tang;Li Gao;Zhengtang Guo;S. Xie
基于细菌膜脂质的大陆古温度计，MBT/CBT或MBT′-CBT替代（支链四醚的甲基化指数/支链四醚的环化），在半干旱和干旱地区应用时会导致较大的温度偏差。在这里，我们提出了新的校准模型的基础上，调查了超过100个表层土壤在一个大的气候梯度，特别是在中国的半干旱和干旱地区，并将其应用到黄土-古土壤序列。如其他地方所报道的，MBT值与MAAT的相关性比与夏季温度的相关性高得多，表明季节性偏差最小;然而，MBT对温度<5 °C或>20 °C显然不敏感。在碱性和干旱土壤中，额外的复杂性是显而易见的，其特征在于与完整的中国（或全球）数据集相比，与气候参数的关系不同。例如，MBT和CBT指数在碱性和干旱土壤中表现出负相关，而在酸性土壤中则呈正相关。此外，环化率bGDGT（CBT），以前定义为土壤pH值的代理，显然是主要由MAAT在这些碱性土壤中控制。因此，我们建议（1）MBT-CBT代理的中国当地校准和（2）用于半干旱和干旱地区的bGDGT的分数丰度的基础上的替代温度代理;后者有一个显着更高的决定因素和更低的均方根误差在碱性土壤比中国当地的校准，并建议在中国黄土/古土壤序列的古温度重建的首选。这些新的bGDGT指标已被应用于中国黄土高原（CLP）渭南全新世古土壤剖面。在渭南全新世古土壤中应用分数丰度校正，得到的全新世总温度变化为5.2 °C，最上层样品的温度与现代温度一致。在此之前，我们发现在MAP < 600 mm时，古生类异戊二烯GDGT与bGDGT的比值（Ri/B）增加，CLP中升高的Ri/b值（>0.5）表明华北全新世晚期存在增强的干旱。高Ri/bratios（>0.5）和低MBT值（<0.4）的组合揭示了干旱和寒冷事件的共同发生，特别是在全新世晚期，在CLP的黄土-古土壤序列中，也可能在CLP以外的寒冷和干旱地区。
The bacterial membrane lipid-based continental paleothermometer, the MBT/CBT or MBT′–CBT proxy (methylation index of branched tetraethers/cyclization of branched tetraethers), results in a large temperature deviation when applied in semiarid and arid regions. Here we propose new calibration models based on the investigation of >100 surface soils across a large climatic gradient, with a particular focus on semiarid and arid regions of China, and apply them to a loess–paleosol sequence. As reported elsewhere, MBT values exhibit a much higher correlation with MAAT than with summer temperature, suggesting a minimal seasonality bias; however, MBT is apparently insensitive to temperature <5 °C or >20 °C. Additional complexities are apparent in alkaline and arid soils, which are characterized by different relationships to climatic parameters than those in the complete Chinese (or global) dataset. For example, MBT and CBT indices exhibit a negative correlation in alkaline and arid soils, in contrast to their positive correlation in acid soils. Moreover, the cyclization ratio of bGDGTs (CBT), previously defined as a proxy for soil pH, is apparently primarily controlled by MAAT in these alkaline soils. Thus, we propose (1) a local Chinese calibration of the MBT–CBT proxy and (2) an alternative temperature proxy for use in semiarid and arid regions based on the fractional abundances of bGDGTs; the latter has a markedly higher determination factor and lower root mean square error in alkaline soils than the Chinese local calibration and is suggested to be preferred for paleotemperature reconstruction in Chinese loess/paleosol sequences. These new bGDGT proxies have been applied to the Weinan Holocene paleosol section of the Chinese Loess Plateau (CLP). The fractional abundance calibration, when applied in the Weinan Holocene paleosol, produces a total Holocene temperature variation of 5.2 °C and a temperature for the topmost sample that is consistent with the modern temperature. Previously, we showed that the ratio of archaeal isoprenoid GDGTs to bGDGTs (Ri/b) increases at MAP < 600 mm, and elevatedRi/bvalues (>0.5) in the CLP suggest the presence of enhanced aridity in the late Holocene in North China. In combination, the highRi/bratios (>0.5) and the associated low MBT values (<0.4) reveal the co-occurrence of dry and cold events, especially in the latest Holocene, in the loess–paleosol sequences in CLP, and probably also in cold and arid regions outside of CLP.