Clumped isotope constraints on equilibrium carbonate formation and kinetic isotope effects in freezing soils
Clumped isotope constraints on equilibrium carbonate formation and kinetic isotope effects in freezing soils
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结块同位素对冻结土壤中平衡碳酸盐形成的限制和动力学同位素效应
DOI：
10.1016/j.gca.2018.06.006
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发表时间：
2018
影响因子：
5
通讯作者：
B. Hallet
中科院分区：
文献类型：
--
作者：
L. Burgener;K. Huntington;R. Sletten;J. Watkins;J. Quade;B. Hallet
来自寒冷干旱环境的成土碳酸盐的稳定同位素（Δ47、δ 18 O和δ 13 C）组成可能是高纬度或高海拔气候变化敏感地区的有价值的古气候档案。然而，以前的工作表明，寒冷气候土壤碳酸盐的同位素组成是容易受到动力学同位素效应（KIE）。为了评估KIE在寒冷气候土壤碳酸盐中发生的条件，我们研究了南极洲（干谷，77°S），高北极（斯瓦尔巴特群岛79°N），智利和阿根廷的安第斯山脉，西藏高原（3800-4800米）土壤碳酸盐垂悬物的Δ47，δ 18 O和δ 13 C组成，并将结果与当地气候和水δ 18 O记录进行比较。在每个站点，我们计算预期的平衡土壤碳酸盐Δ 47和δ 18 O值，并估计碳酸盐Δ 47和δ 18 O异常（观测的Δ 47或δ 18 O减去预期的平衡Δ 47或δ 18 O）。此外，我们将测量的碳酸盐δ 13 C与平衡土壤碳酸盐δ 13 C值的预期范围进行了比较。为了提供解释Δ 47和δ 18 O异常的背景，将土壤碳酸盐结果与两个不同地点的冰下碳酸盐结果进行了比较，这两个地点显示出较大的Δ 47异常（高达-0.29 ‰）。南极和4700 masl智利安第斯山脉样品的Δ 47负异常和δ 18 O正异常与KIE一致，这是由于在低温碳酸盐形成过程中碳酸氢盐快速脱水所致。相比之下，低海拔智利安第斯山脉、阿根廷安第斯山脉、青藏高原和高北极地区的结果与平衡、夏季碳酸盐形成一致。我们将Δ 47和δ 18 O异常的差异归因于卵石间基质粒度的变化及其对有效土壤孔隙空间、渗透率（导水率）、水分和碳酸氢盐脱水速率的影响。南极和4700 masl智利安第斯土壤具有粗粒基质，有利于快速碳酸氢盐脱水。相比之下，海拔较低的智利安第斯山脉，阿根廷安第斯山脉，高北极和青藏高原的土壤具有细粒基质，减少土壤孔隙空间，土壤渗透性和CO2气体通量，促进平衡碳酸盐形成。冰下碳酸盐样品产生高度可变的Δ 47和δ 18 O异常，我们提出两个冰川站点之间的差异可能是由于当地冰下排水条件，pCO 2和pH值的变化。我们的研究结果表明，粗粒基质土壤中的碳酸盐可能在寒冷的气候中表现出KIE，使它们成为不良的古气候指标。具有细粒基质的土壤更有可能产生适合于古气候重建的平衡碳酸盐，而与气候无关。因此，在古气候研究中，在评价碳酸盐稳定同位素和团聚同位素值时应考虑古土壤基质粒度。
The clumped and stable isotope (Δ47, δ18O, and δ13C) composition of pedogenic (soil) carbonates from cold, arid environments may be a valuable paleoclimate archive for climate change-sensitive areas at high latitudes or elevations. However, previous work suggests that the isotopic composition of cold-climate soil carbonates is susceptible to kinetic isotope effects (KIE). To evaluate the conditions under which KIE occur in cold-climate soil carbonates, we examine the Δ47, δ18O, and δ13C composition of soil carbonate pendants from Antarctica (Dry Valleys, 77°S), the High Arctic (Svalbard 79°N), the Chilean and Argentinian Andes, and the Tibetan plateau (3800–4800 m), and compare the results to local climate and water δ18O records. At each site we calculate the expected equilibrium soil carbonate Δ47and δ18O values and estimate carbonate Δ47and δ18O anomalies (observed Δ47or δ18O minus the expected equilibrium Δ47or δ18O). Additionally, we compare the measured carbonate δ13C to the expected range of equilibrium soil carbonate δ13C values. To provide context for interpreting the Δ47and δ18O anomalies, the soil carbonate results are compared to results for sub-glacial carbonates from two different sites, which exhibit large Δ47anomalies (up to −0.29‰). The Antarctic and 4700 masl Chilean Andes samples have negative Δ47anomalies and positive δ18O anomalies consistent with KIE due to rapid bicarbonate dehydration during cryogenic carbonate formation. In contrast, the lower elevation Chilean Andes, Argentinian Andes, Tibetan Plateau and High Arctic results are consistent with equilibrium, summer carbonate formation. We attribute the differences in Δ47and δ18O anomalies to variations in inter-cobble matrix grain size and its effects on the effective soil pore space, permeability (hydraulic conductivity), moisture, and bicarbonate dehydration rate. The Antarctic and 4700 masl Chilean Andean soils have coarse-grained matrices that facilitate rapid bicarbonate dehydration. In contrast, the lower elevation Chilean Andes, Argentinian Andes, High Arctic and Tibetan Plateau soils have finer-grained matrices that decrease the soil pore space, soil permeability and CO2gas flux, promoting equilibrium carbonate formation. The sub-glacial carbonate samples yield highly variable Δ47and δ18O anomalies, and we propose that the differences between the two glacier sites may be due to variations in local sub-glacial drainage conditions, pCO2, and pH. Our findings suggest that carbonates from soils with coarse-grained matrices may exhibit KIE in cold climates, making them poor paleoclimate proxies. Soils with fine-grained matrices are more likely to yield equilibrium carbonates suitable for paleoclimate reconstructions regardless of climate. Paleosol matrix grain size should therefore be taken into account in the evaluation of carbonate stable and clumped isotope values in paleoclimate studies.
影响因子：
2.3
作者：
Huntington, K. W.;Eiler, J. M.;Came, R.
通讯作者：
Came, R.
DOI：
10.1002/rcm.6609
发表时间：
2013-07
期刊：
Rapid communications in mass spectrometry : RCM
影响因子：
--
作者：
U. Wacker;J. Fiebig;B. Schoene
通讯作者：
U. Wacker;J. Fiebig;B. Schoene