Palaeogeographic controls on climate and proxy interpretation
Palaeogeographic controls on climate and proxy interpretation
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DOI：
10.5194/cp-12-1181-2016
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发表时间：
2016-01-01
影响因子：
4.3
通讯作者：
Wrobel, Neil
中科院分区：
文献类型：
--
作者：
Lunt, Daniel J.;Farnsworth, Alex;Wrobel, Neil
在大约1.5亿年前到3500万年前的冰-古新世-始新世（CPE）期间，地球处于“温室”状态，两极几乎没有冰。这也是一个相当大的全球变化的时期，从白垩纪中期最温暖的时期，到始新世末的冰室条件的门槛。然而，古地理变化，太阳变化和碳循环变化对这些气候变化的相对贡献是未知的。在这里，利用计算能力的最新进展，和一套独特的古地理地图，我们进行了19个全球环流模型模拟涵盖这一时期，每个地层阶段一个模拟的合奏。通过保持大气CO2浓度恒定的模拟，我们能够确定的贡献，从古地理和太阳强迫全球变化的CPE，并探讨其内在机制。我们发现，全球平均表面温度是非常恒定的模拟，从太阳和古地理变化的相反趋势的取消。然而，在区域范围内存在重大的模拟差异。表现出最大气候变化的地层阶段阶段的过渡与海洋环流模式的过渡有关，它们本身往往与海洋门户的变化有关，并通过与发射率和行星自转相关的反馈放大。我们还发现了大陆面积和全球平均地形对全球平均温度的控制作用。我们的研究结果具有重要意义的单点古代理记录的解释。特别是，我们的研究结果允许非CO2（即古地理和太阳常数）组件的代理记录被删除，留下一个更全球性的组成部分与碳循环变化。这个“调整系数”用于调整海面温度，因为深海在模型中没有完全平衡。在CPE的七个关键站点的调整系数说明，并适用于从福克兰高原的代理数据，我们提供的数据，以便类似的调整可以在CPE内的任何网站和任何时间段。最终，这将使分离的CO2强迫气候信号从多个代理记录从地球仪周围提取，允许区域信号和极地放大的程度，以响应在CPE期间的CO2变化的评价。最后，在整个CPE中调整因子恒定的区域可以指示未来代理可以作为目标的地方，以便重建最纯粹的二氧化碳诱导的温度变化，其中其他过程的复杂贡献被最小化。因此，结合其他考虑因素，这项工作可以为钻探地点和露头研究提供有用的信息。
During the period from approximately 150 to 35 million years ago, the Cretaceous-Paleocene-Eocene (CPE), the Earth was in a "greenhouse" state with little or no ice at either pole. It was also a period of considerable global change, from the warmest periods of the mid-Cretaceous, to the threshold of icehouse conditions at the end of the Eocene. However, the relative contribution of palaeogeographic change, solar change, and carbon cycle change to these climatic variations is unknown. Here, making use of recent advances in computing power, and a set of unique palaeogeographic maps, we carry out an ensemble of 19 General Circulation Model simulations covering this period, one simulation per stratigraphic stage. By maintaining atmospheric CO2 concentration constant across the simulations, we are able to identify the contribution from palaeogeographic and solar forcing to global change across the CPE, and explore the underlying mechanisms. We find that global mean surface temperature is remarkably constant across the simulations, resulting from a cancellation of opposing trends from solar and palaeogeographic change. However, there are significant modelled variations on a regional scale. The stratigraphic stage-stage transitions which exhibit greatest climatic change are associated with transitions in the mode of ocean circulation, themselves often associated with changes in ocean gateways, and amplified by feedbacks related to emissivity and planetary albedo. We also find some control on global mean temperature from continental area and global mean orography. Our results have important implications for the interpretation of single-site palaeo proxy records. In particular, our results allow the non-CO2 (i.e. palaeogeographic and solar constant) components of proxy records to be removed, leaving a more global component associated with carbon cycle change. This "adjustment factor" is used to adjust sea surface temperatures, as the deep ocean is not fully equilibrated in the model. The adjustment factor is illustrated for seven key sites in the CPE, and applied to proxy data from Falkland Plateau, and we provide data so that similar adjustments can be made to any site and for any time period within the CPE. Ultimately, this will enable isolation of the CO2-forced climate signal to be extracted from multiple proxy records from around the globe, allowing an evaluation of the regional signals and extent of polar amplification in response to CO2 changes during the CPE. Finally, regions where the adjustment factor is constant throughout the CPE could indicate places where future proxies could be targeted in order to reconstruct the purest CO2-induced temperature change, where the complicating contributions of other processes are minimised. Therefore, combined with other considerations, this work could provide useful information for supporting targets for drilling localities and outcrop studies.