Monitoring of Sierra Nevada Caves Reveals the Potential for Stalagmites to Archive Seasonal Variability
Monitoring of Sierra Nevada Caves Reveals the Potential for Stalagmites to Archive Seasonal Variability
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DOI：
10.3389/feart.2021.781526
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发表时间：
2021-12
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通讯作者：
B. Wortham;I. Montañez;Kimberly S. Bowman;Daphne Kuta;Nora Soto Contreras;Eleana Brummage;Allison Pang;J. Tinsley;Greg Roemer-Baer
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作者：
B. Wortham;I. Montañez;Kimberly S. Bowman;Daphne Kuta;Nora Soto Contreras;Eleana Brummage;Allison Pang;J. Tinsley;Greg Roemer-Baer
在美国西南部，加利福尼亚州 (CA) 是气候最敏感的地区之一，因为其季节性降水量较低（≤250 毫米/年），且水文气候固有变化，且受大幅度调制影响。为了重建加利福尼亚州过去的气候变化，洞穴方解石沉积物（石笋）已被用作环境敏感指标的档案，例如稳定同位素组成（δ18O、δ13C）和微量元素浓度（例如，Mg、Ba、Sr）。监测洞穴和相关的地表环境、洞穴滴水的化学演化、滴水中沉淀的方解石以及这些系统对降水和温度季节变化的响应对于解释石笋代理至关重要。在这里，我们展示了在加利福尼亚州红杉国王峡谷国家公园（内华达山脉南部）利尔本洞穴监测的滴水和物理参数，并测量了两年期间（2018 年 11 月至 2021 年 2 月）滴水和玻璃基板上沉淀的方解石 (δ18O) 的微量元素浓度（Mg、Sr、Ba、Cu、Fe、Mn）和稳定同位素组成（δ18O、δ2H），以更好地了解该地点的化学变化如何受到当地和区域降水和温度变化的影响。尽管地表温度、降水量和来源地区（北太平洋与亚热带太平洋）变化很大，但利尔本洞穴全年呈现出恒定的洞穴环境。在洞穴内三个地点中的两个地点，滴水 δ18O 和 δ2H 受到蒸发富集的季节性影响。在洞穴的第三个收集点，滴水 δ18O 仅响应降水 δ18O 变化。 Mg/Ca、Ba/Ca 和 Sr/Ca 比率对所有地点先前的方解石降水都有季节性响应，但对水-岩石相互作用的影响最小。最后，我们研究了痕量金属（例如 Mn2+ 和 Cu2+）作为补给地球化学指标的潜力，发现它们浓度的变化很有可能表明研究区域雨季的开始。方解石中记录了滴水成分，表明来自 Lilburn 洞穴的石笋以及可能更广泛的区域的石笋可以记录天气的季节变化，即使在降雨量大幅减少的时期也是如此。
In the southwestern United States, California (CA) is one of the most climatically sensitive regions given its low (≤250 mm/year) seasonal precipitation and its inherently variable hydroclimate, subject to large magnitude modulation. To reconstruct past climate change in CA, cave calcite deposits (stalagmites) have been utilized as an archive for environmentally sensitive proxies, such as stable isotope compositions (δ18O, δ13C) and trace element concentrations (e.g., Mg, Ba, Sr). Monitoring the cave and associated surface environments, the chemical evolution of cave drip-water, the calcite precipitated from the drip-water, and the response of these systems to seasonal variability in precipitation and temperature is imperative for interpreting stalagmite proxies. Here we present monitored drip-water and physical parameters at Lilburn Cave, Sequoia Kings Canyon National Park (Southern Sierra Nevada), CA, and measured trace element concentrations (Mg, Sr, Ba, Cu, Fe, Mn) and stable isotopic compositions (δ18O, δ2H) of drip-water and for calcite (δ18O) precipitated on glass substrates over a two-year period (November 2018 to February 2021) to better understand how chemical variability at this site is influenced by local and regional precipitation and temperature variability. Despite large variability in surface temperatures and precipitation amount and source region (North Pacific vs. subtropical Pacific), Lilburn Cave exhibits a constant cave environment year-round. At two of the three sites within the cave, drip-water δ18O and δ2H are influenced seasonally by evaporative enrichment. At a third collection site in the cave, the drip-water δ18O responds solely to precipitation δ18O variability. The Mg/Ca, Ba/Ca, and Sr/Ca ratios are seasonally responsive to prior calcite precipitation at all sites but minimally to water-rock interaction. Lastly, we examine the potential of trace metals (e.g., Mn2+ and Cu2+as a geochemical proxy of recharge and find that variability in their concentrations has high potential to denote the onset of the rainy season in the study region. The drip-water composition is recorded in the calcite, demonstrating that stalagmites from Lilburn Cave, and potentially more regionally, could record seasonal variability in weather even during periods of substantially reduced rainfall.