Stable carbon isotope ratios of intact GDGTs indicate heterogeneous sources to marine sediments
Stable carbon isotope ratios of intact GDGTs indicate heterogeneous sources to marine sediments
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DOI：
10.1016/j.gca.2016.02.034
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发表时间：
2016-05
影响因子：
5
通讯作者：
A. Pearson;Sarah J. Hurley;S. R. S. Walter-S.-R.-S.-Walter-39267913;S. Kusch;S. Lichtin;Yi Ge Zhang
中科院分区：
文献类型：
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作者：
A. Pearson;Sarah J. Hurley;S. R. S. Walter-S.-R.-S.-Walter-39267913;S. Kusch;S. Lichtin;Yi Ge Zhang
Thaumarchaeota是海洋甘油二联植烷基甘油四醚脂（GDGT）的主要来源，据信其大部分碳直接从溶解无机碳（DIC）固定。GDGT的δ 13 C值（δ 13 CGDGT）如果能与δ 13 CDIC值相关联，则可能成为重建海洋碳循环变化（包括古生产力和水团环流）的有力工具。迄今为止，同位素测量主要是在GDGT的C40联植烷骨架上进行的，而不是在完整的四醚结构上。这种方法擦除的GDGT在样品中的同位素异质性所揭示的信息，并可能赋予与醚裂解相关的同位素分馏。为了解决这些问题，我们提出了12个代表10个大陆边缘位置的最近沉积物GDGT的δ 13 C值。样品经高效液相色谱（HPLC）正交试验净化后，用绕丝微燃烧（SWiM）-同位素比值质谱（IRMS）测定δ 13 C值，精密度为1σ，准确度为±0.25‰。使用这种方法，我们确认GDGT，通常约为-19 ‰，与其他海洋脂质相比，同位素“重”。然而，测量的δ 13 CGDGT值与基于上覆水柱中DIC的13 C含量和先前发表的纯培养的自养海洋thaumarchaeon的生物合成同位素分馏的预测值不一致。在某些沉积物中，个别GDGT的同位素组成不同，表明多源输入。这些数据似乎证实了crenarchaeol主要是Thaumarchaeota的生物标志物，但其δ 13 C值仍然不能仅用自养碳固定来解释。总的来说，结果的复杂性表明，有机碳同化（约占总碳的25%）和外源GDGT的多个来源（通常贡献<30%的沉积物输入）是解释观测到的δ 13 CGGT值所必需的。结果表明，谨慎解释GDGT的沉积记录的总输入时。生物或开放的斜坡沉积物，而不是碎屑盆地或浅陆架沉积物，是产生最小偏差GDGT代理记录的首选位置。
Thaumarchaeota, the major sources of marine glycerol dibiphytanyl glycerol tetraether lipids (GDGTs), are believed to fix the majority of their carbon directly from dissolved inorganic carbon (DIC). Theδ13C values of GDGTs (δ13CGDGT) may be powerful tools for reconstructing variations in the ocean carbon cycle, including paleoproductivity and water mass circulation, if they can be related to values ofδ13CDIC. To date, isotope measurements primarily are made on the C40biphytane skeletons of GDGTs, rather than on complete tetraether structures. This approach erases information revealed by the isotopic heterogeneity of GDGTs within a sample and may impart an isotopic fractionation associated with the ether cleavage. To circumvent these issues, we presentδ13C values for GDGTs from twelve recent sediments representing ten continental margin locations. Samples are purified by orthogonal dimensions of HPLC, followed by measurement ofδ13C values by Spooling Wire Microcombustion (SWiM)-isotope ratio mass spectrometry (IRMS) with 1σprecision and accuracy of ±0.25‰. Using this approach, we confirm that GDGTs, generally around −19‰, are isotopically “heavy” compared to other marine lipids. However, measuredδ13CGDGTvalues are inconsistent with predicted values based on the13C content of DIC in the overlying water column and the previously-published biosynthetic isotope fractionation for a pure culture of an autotrophic marine thaumarchaeon. In some sediments, the isotopic composition of individual GDGTs differs, indicating multiple source inputs. The data appear to confirm that crenarchaeol primarily is a biomarker for Thaumarchaeota, but itsδ13C values still cannot be explained solely by autotrophic carbon fixation. Overall the complexity of the results suggests that both organic carbon assimilation (ca.25% of total carbon) and multiple source(s) of exogenous GDGTs (contributing generally <30% of input to sediments) are necessary to explain the observedδ13CGDGTvalues. The results suggest caution when interpreting the total inputs of GDGTs to sedimentary records. Biogenic or open-slope sediments, rather than clastic basinal or shallow shelf sediments, are preferred locations for generating minimally-biased GDGT proxy records.