Silicate weathering in antarctic ice-rich permafrost: Insights using magnesium isotopes
Silicate weathering in antarctic ice-rich permafrost: Insights using magnesium isotopes
复制标题
DOI：
10.1016/j.gca.2019.07.031
复制
发表时间：
2020-06-01
影响因子：
5
通讯作者：
Hagedorn, Birgit
中科院分区：
文献类型：
--
作者：
Cuozzo, Nicolas;Sletten, Ronald S.;Hagedorn, Birgit
这项研究报告说，在南极洲麦克默多干燥山谷富含冰盐的永久冻土中，在零下的温度下会发生大量的化学风化。通过测量从融化的富冰沉积物中提取的水的离子组成、pH和镁同位素，在灯塔山谷收集的30.0米岩心中记录了化学风化作用。镁同位素组成和pH值的一致增加揭示了岩石风化的证据。控制风化的主要因素是导致未冻结卤水的盐分含量；这在上面7.0米处最为明显，那里的盐分含量很高，温度超过零下21摄氏度，模拟的未冻水达到冰量的4.0%。在7.0m以上，融化的多年冻土冰中高达60%的可溶镁来自铁质榴辉岩(增量mg-26=-0.22+/-0.07%)风化，导致增量mg-26值在-0.82+/-0.05‰到-0.64+/-0.05‰之间变化。在7.0米以下，温度保持在-21摄氏度以下，未冻水不到冰量的2.0%，平均5%的可溶性镁来自榴辉岩的风化，增量镁-26值在-1.05+/-0.05‰到-0.76+/-0.05‰之间。被模拟为没有未冻水的核心区域很少或根本没有化学风化的证据，相对恒定的增量mg-26值接近泰勒冰川和灯塔谷降雪值(-0.93+/-0.06‰)。这项研究表明，在形成液态卤水的永久冻土中，在零度以下的温度下会发生显著的化学风化。(C)2019爱思唯尔有限公司。保留所有权利。
This study reports that substantial chemical weathering occurs at subzero temperatures in ice-and-salt-rich permafrost in the McMurdo Dry Valleys, Antarctica. Chemical weathering is documented in a 30.0-m core collected in Beacon Valley by measuring the ionic composition, pH, and Mg isotopes of water extracted from thawed ice-rich sediment. Evidence of rock weathering is revealed by coinciding increases in the Mg isotopic composition and pH values. The primary factor that controls weathering is the salt content that leads to unfrozen brine; this is most apparent in the upper 7.0 m where salt content is high, temperatures rise above -21 degrees C and modeled unfrozen water reaches up to 4.0% of ice-content. In the upper 7.0 m, up to 60% of soluble Mg in the thawed permafrost ice is sourced from Ferrar Dolerite (delta Mg-26 = -0.22 +/- 0.07%) weathering, resulting in delta Mg-26 values ranging from of -0.82 +/- 0.05 parts per thousand to -0.64 +/- 0.05 parts per thousand. Below 7.0 m, temperatures remain below -21 degrees C, unfrozen water is less than 2.0% of ice-content, and on average, 5% of soluble Mg is sourced from dolerite weathering with delta Mg-26 values ranging from -1.05 +/- 0.05 parts per thousand to -0.76 +/- 0.05 parts per thousand. Regions of the core that are modeled to have no unfrozen water show little or no evidence of chemical weathering and relatively constant delta Mg-26 values close to Taylor Glacier and Beacon Valley snowfall values (-0.93 +/- 0.06 parts per thousand). This study demonstrates that significant chemical weathering occurs at subzero temperatures in permafrost where liquid brines form. (C) 2019 Elsevier Ltd. All rights reserved.