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首页> 外文学位 >Oxygen isotopes in diatom silica: A new understanding of silica-water oxygen isotope fractionation in diatom frustules and an application of diatom delta-oxygen-18 values as a record of paleohydrologic variability in a middle-pleistocene lacustrine core from the Valles Caldera, New Mexico.
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Oxygen isotopes in diatom silica: A new understanding of silica-water oxygen isotope fractionation in diatom frustules and an application of diatom delta-oxygen-18 values as a record of paleohydrologic variability in a middle-pleistocene lacustrine core from the Valles Caldera, New Mexico.

机译：硅藻硅中的氧同位素：对硅藻壳中硅水氧同位素分馏的新认识，以及硅藻δ-氧18值的应用，作为新墨西哥州Valles Caldera中更新世湖相岩心中古水文变异性的记录。

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摘要

I present oxygen isotope data from modern diatom frustules that were collected from freshwater systems in the Jemez Mountains of northern New Mexico. The frustules display a constant silica-water fractionation over the measured temperature range (5.1 to 37.8°C) regardless of species. This relationship is in close agreement with other published silica-water fractionation factors for laboratory cultured diatom samples; vii however, it is as much as 8‰ lower than equilibrium quartz-water fractionations and 3--4‰ lower than observed silica-water fractionations in diatomaceous silica collected from sediment traps and sediment cores.;Post mortem loss of organic material results in an alteration or 'maturation' of diatom silica in which silica reequilibrates with a silica-water fractionation closer to the equilibrium quartz-water fractionation. Post-mortem alteration of silica delta18O values occurs within 0.5 years in diatom frustules from a lacustrine setting in the Valles Caldera, New Mexico resulting in an increase of ∼7.4‰ in the delta18O values. The rapid post-mortem alteration of diatom delta18O values explains much of the disparate data regarding silicawater fractionation for diatom silica and has profound implications for the use of diatom silica delta 18O values as a paleoclimate proxy. In the setting of open basin lacustrine environments where bottom temperatures are nearly constant at 4ºC, the maturation effect may facilitate reconstruction of variations in paleowater delta 18O values without the conflating influence of fluctuating water temperature and variable delta18O water values that occur at the surface.;Lastly, I present delta18O values of diatom silica from a middle-Pleistocene lacustrine core (VC-3) from the Valles Caldera, northern New Mexico, which record considerable (>25‰) variability in lake water delta 18O values during interglacial Marine Isotope Stage 11 (MIS 11) and glacial MIS 12. There is a strong correspondence between the delta 18O values of diatoms throughout the VC-3 core and mean annual temperatures recorded by MBT/CBT indices in the core. Average delta18O values of diatom silica for MIS 11 and MIS 12 are 26.5‰ (+/- 5.3; n=62) and 18.5‰ (+/- 6.3; n= 27), respectively. At the MIS 12 termination at ∼430 kya, there is abrupt (2 ka) increase in the delta 18O values of the diatom silica from ∼11 to ∼34 ‰. Throughout the core the delta18O values of the diatom silica are strongly correlated with mean annual temperature (MAT) reconstructed from MBT/CBT indices in the VC-3 core on orbital (precessional) and millennial time scales. Rapid changes in the delta18O values during both MIS 11 and the millennial scale variations in MIS 12 termination indicate the extreme hydroclimatological sensitivity of this region, and present a strong argument linking long term aridity in the southwestern United States to decreases in summer precipitation.
机译：我展示了来自现代硅藻壳的氧同位素数据，这些硅藻是从新墨西哥州北部杰米兹山的淡水系统收集的。壳壳在所测量的温度范围（5.1至37.8°C）中显示出恒定的硅水分离度，而与物种无关。这种关系与实验室培养的硅藻样品的其他公开的二氧化硅-水分离因子非常吻合。 vii但是，它比从沉积物捕集器和沉积物核心收集的硅藻硅石中的石英-水分馏量低8‰，比观察到的硅水分馏量低3--4‰。硅藻硅的一种改变或“成熟”，其中二氧化硅通过接近于平衡石英水分馏的二氧化硅水分馏而重新平衡。在新墨西哥州的Valles Caldera的湖相环境中，硅藻壳中硅δ的验尸变化发生在0.5年内，导致δ18O值增加了约7.4‰。硅藻δ18O值的事后快速变化解释了许多有关硅藻硅土的硅水分馏的不同数据，并且对于将硅藻硅δ18O值用作古气候代用品具有深远的意义。在底部温度几乎恒定在4ºC的开放流域湖相环境中，成熟效应可能有助于重建古水三角洲18O值的变化，而不会混淆水温波动和表面出现的delta18O水值变化的影响。最后，我介绍了来自新墨西哥州北部Valles Caldera的中更新世湖相岩心（VC-3）的硅藻硅的δ18O值，该值在冰间海洋同位素阶段记录了湖水δ18O值的可观变化（> 25‰）。 11（MIS 11）和冰川MIS12。整个VC-3岩心的硅藻δ18O值与岩心中的MBT / CBT指数记录的年平均温度之间存在很强的对应关系。 MIS 11和MIS 12的硅藻土的平均delta18O值分别为26.5‰（+/- 5.3; n = 62）和18.5‰（+/- 6.3; n = 27）。在MIS 12端接处约430 kya处，硅藻硅的δ18O值突然从（11 ka）增至〜34‰（<2 ka）。在整个岩心中，硅藻硅的delta18O值与从VC-3岩心中的MBT / CBT指数在轨道（进阶）和千年时间尺度上重建的年平均温度（MAT）密切相关。在MIS 11和MIS 12终止的千年尺度变化期间delta18O值的快速变化表明该地区的极端水文气候敏感性，并提出了强有力的论据，将美国西南部的长期干旱与夏季降水的减少联系起来。

著录项

  • 作者

    Dodd, Justin Paul.;

  • 作者单位

    The University of New Mexico.;

  • 授予单位 The University of New Mexico.;
  • 学科 Geology.;Biogeochemistry.;Climate Change.
  • 学位 Ph.D.
  • 年度 2011
  • 页码 118 p.
  • 总页数 118
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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