CZ-tope at Susquehanna Shale Hills CZO: Synthesizing multiple isotope proxies to elucidate Critical Zone processes across timescales in a temperate forested landscape
CZ-tope at Susquehanna Shale Hills CZO: Synthesizing multiple isotope proxies to elucidate Critical Zone processes across timescales in a temperate forested landscape
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DOI：
10.1016/j.chemgeo.2016.05.012
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发表时间：
2016-12
期刊：
影响因子：
3.9
通讯作者：
P. Sullivan;Lin Ma;N. West;Lixin Jin;D. Karwan;J. Noireaux;Grit Steinhoefel;K. Gaines;D. Eissenstat;J. Gaillardet;L. Derry;K. Meek;S. Hynek;S. Brantley
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文献类型：
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作者：
P. Sullivan;Lin Ma;N. West;Lixin Jin;D. Karwan;J. Noireaux;Grit Steinhoefel;K. Gaines;D. Eissenstat;J. Gaillardet;L. Derry;K. Meek;S. Hynek;S. Brantley
多个同位素替代物在关键区（CZ）内的同一位置上的应用，我们称之为“CZ-tope”，阐明了地球化学，地貌，水文和生物过程的相互作用，以及在CZ的人为影响，跨越广泛不同的时间尺度。通过总结美国宾夕法尼亚州萨斯奎汉纳页岩山CZ天文台（SHCZO）同位素测量的新假设，我们对CZ-tope方法进行了验证。在SHCZO，对风化层中U系列同位素和大气10 Be的测量提供了证据，表明流域在山脊处接近稳定状态，在那里风化层的产生与侵蚀损失相平衡。风化层、基岩和水中的δ 13 C、87 Sr/86 Sr和δ 34 S的同位素测量，以及各种水库（降水、土壤水、河水和地下水）中的3 H、δ 2 H和δ 18 O的同位素测量，支持了嵌套反应锋在数千年的时间尺度上在地下发展的假设。结合基岩和风化层中的U-系列和大气10 Be以及土壤水δ 18 O的测量结果，提出了冻融是控制风化层通量和山坡的主要土壤蠕变机制的假设。利用CZ-tope方法测量相同样品的δ 26 Mg、δ 56 Fe和δ 11 B同位素，我们还提出了一个工作假设，即地下颗粒迁移代表了集水区的显著风化损失。同样地，利用木质部来源沃茨（降水、土壤、溪流和地面）中的δ 18 O、Ge/Si和87 Sr/86 Sr比值，沿着来自土壤的87 Sr/86 Sr比值，导致O同位素分馏发生在粘土表面附近的假设。最后，对坡地土壤中206 Pb/204 Pb、207 Pb/204 Pb、208 Pb/204 Pb和137 Cs的分析也揭示了人类活动的痕迹。CZ-tope -对同一景观中相同样品的多种元素同位素比率进行定量解释-因此描绘了SSHCZO作为相对快速侵蚀但缓慢风化景观的新画面，其中：i）养分通过植被紧密循环，ii）土壤主要通过冻融向下坡移动，iii）地下颗粒迁移是质量损失的重要通量，iv）移动的和非移动的水库将水和阳离子压裂成树木和溪流，以及v）人类的印记表现在表层土壤的金属含量中。
The application of multiple isotope proxies on the same location within a Critical Zone (CZ), which we term “CZ-tope”, elucidates the interactions of geochemical, geomorphological, hydrological and biological processes together with anthropogenic influences in the CZ across widely disparate timescales. We exemplify the CZ-tope approach by summarizing the emerging hypotheses developed from isotopic measurements at the Susquehanna Shale Hills CZ Observatory (SSHCZO), Pennsylvania (U.S.A).At SSHCZO, measurements of U-series isotopes and meteoric10Be in regolith provide evidence that the catchment is approaching a steady state at the ridgetops where regolith production is balanced by erosive loss. Isotopic measurements of δ13C,87Sr/86Sr, and δ34S in the regolith, bedrock and water, together with3H, δ2H and δ18O in various water reservoirs (precipitation, soil water, stream water and groundwater) support the hypothesis that nested reaction fronts have developed in the subsurface over timescales of millennia. Combinations of U-series and meteoric10Be in bedrock and regolith and measurements of soil water δ18O led to the hypothesis that freeze-thaw is the dominant soil creep mechanism controlling regolith fluxes and hillslopes. Utilizing the CZ-tope approach of measuring δ26Mg, δ56Fe and δ11B isotopes on identical samples, we also developed a working hypothesis that particle transport in the subsurface represents a significant weathering loss from the catchment. Likewise, the use of δ18O, Ge/Si and87Sr/86Sr ratios in xylem source waters (precipitation, soil, stream- and ground-), along with87Sr/86Sr ratios from soils, led to the hypothesis that O isotope fractionation occurs near clay surfaces. Finally, analyses of206Pb/204Pb,207Pb/204Pb,208Pb/204Pb and137Cs in soil from hillslope profiles have also revealed the imprint of widespread human activity. CZ-tope — the interpretation of multiple elements' isotopic ratios quantified for identical samples in one landscape — thus paints an emerging picture of SSHCZO as a relatively fast-eroding but slow-weathering landscape in which: i) nutrients are tightly cycled by vegetation, ii) soils move downslope largely by freeze-thaw, iii) subsurface particle transport is an important flux for mass loss, iv) mobile and immobile reservoirs act to fractionate water and cations into trees and stream water, and v) the imprint of humans is manifested in the metal contents of the topsoil.