Impacts of Cenozoic global cooling, surface uplift, and an inland seaway on South American paleoclimate and precipitation δ18O
Impacts of Cenozoic global cooling, surface uplift, and an inland seaway on South American paleoclimate and precipitation δ18O
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DOI：
10.1130/b30480.1
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发表时间：
2012-03
影响因子：
4.9
通讯作者：
M. Jeffery;C. Poulsen;T. Ehlers
中科院分区：
文献类型：
--
作者：
M. Jeffery;C. Poulsen;T. Ehlers
降水δ 18 O (δ 18 O prec ) 的稳定同位素记录已被用作造山带的古气候和古海拔档案。然而，对这些记录的解释受到关于 δ 18 O prec 如何响应造山事件期间全球和区域气候变化的了解的限制。在这项研究中，使用具有同位素跟踪功能的 GENESIS v3 大气环流模型量化了大气 CO 2 水平、南极冰盖范围、安第斯表面海拔变化以及南美内陆海道的存在对南美洲气候和 δ 18 O prec 的影响。结果是在新生代南美气候和 δ 18 O prec 变化的背景下提出的。更具体地说，我们发现： (1) 安第斯山脉的降水率对安第斯山脉表面海拔、航道以及较小程度上的 CO 2 水平敏感。安第斯山脉海拔的升高和航道的存在都会导致降水量大幅增加，但在安第斯山脉的不同地区。研究发现，南极冰盖的增长对南美降水的影响很小。 (2) 降水的稳定同位素组成对所有研究的参数都很敏感。在大气 CO 2 较高的模拟中发现 δ 18 O prec 增加了高达 8‰。与之前的研究一致，δ 18 O prec 随着安第斯山脉海拔的增加而减少，其减少量大于现代绝热递减率所预测的减少量。此外，内陆航道的存在导致安第斯山脉北部和中部的 δ 18 O prec 减少 1-8‰。消耗量取决于航道的同位素组成。在没有南极冰盖的情况下进行的模拟得出的 δ 18 O prec 比现代值低 0–3‰。最后，中新世和始新世的特定时间模拟表明，δ 18 O prec 在新生代期间有所下降，而 δ 18 O prec 的局部地理梯度有所增加，特别是在现代高海拔地区。我们证明，除了安第斯山脉隆起和相关的气候变化之外，CO 2 水平和内陆航道也可能影响了南美洲的 δ 18 O 碳水化合物记录。在根据 δ 18 O prec 稳定同位素记录解释古气候或古海拔时，必须考虑这些全球和古地理变化。
Stable isotope records of precipitation δ 18 O (δ 18 O prec ) have been used as paleoclimate and paleoelevation archives of orogens. However, interpretation of these records is limited by knowledge of how δ 18 O prec responds to changes in global and regional climate during mountain-building events. In this study the influence of atmospheric CO 2 levels, the extent of the Antarctic ice sheet, changes in Andean surface elevation, and the presence of the South American inland seaway on climate and δ 18 O prec in South America are quantified using the GENESIS v3 atmospheric general circulation model with isotope-tracking capabilities. Results are presented in the context of Cenozoic South American climate and δ 18 O prec changes. More specifically, we find: (1) Precipitation rates in the Andes are sensitive to Andean surface elevation, the seaway and, to a lesser extent, CO 2 levels. Increasing Andean elevations and the presence of a seaway both cause large increases in precipitation, but in different parts of the Andes. The growth of the Antarctic ice sheet is found to have a small influence on South American precipitation. (2) The stable isotopic composition of precipitation is sensitive to all of the parameters investigated. An increase in δ 18 O prec of up to 8‰ is found in simulations with higher atmospheric CO 2 . In agreement with previous studies, δ 18 O prec decreases with increasing Andean elevation by an amount greater than that predicted by the modern adiabatic lapse rate. Furthermore, the presence of an inland seaway causes a decrease in δ 18 O prec of 1–8‰ in the northern and central Andes. The amount of depletion is dependent on the isotopic composition of the seaway. Simulations without the Antarctic ice sheet result in δ 18 O prec that is 0–3‰ lower than the modern. Finally, time-specific simulations for the Miocene and Eocene show that δ 18 O prec has decreased during the Cenozoic and that local geographical gradients of δ 18 O prec have increased, particularly in regions of high modern elevation. We demonstrate that in addition to Andean uplift and associated climate change, CO 2 levels and an inland seaway are likely to have influenced δ 18 O carb records from South America. Consideration of these global and paleogeographic changes is necessary when interpreting paleoclimate or paleoelevation from stable isotope records of δ 18 O prec .