GRGC: Examining Isotopic Signals in the Geologic Record Through a General Circulation Model Approach

一个令人印象深刻的氧和氢同位素记录网络，来自冰芯、湖芯、深海芯和树木年轮，现在可以编制各种时期的记录。这些记录可能为过去气候过程的变化提供定量的见解，但如果不了解降水同位素的基本驱动力，就无法充分认识其真正的气候意义。简单的气包模式不能解释控制区域同位素分布的过程范围，因此，同位素示踪剂与环流模式（GCM）的耦合是迈向更完整地理解地质记录中记录的同位素信号的必要的第一步。我们建议利用戈达德空间研究所的大气环流模式（GISS GCM）对这些同位素记录进行研究。我们将探讨的主要问题是，水源特征、气团轨迹和气团混合的变化——所有这些因素都必须随着气候系统的主要组成部分在气候周期中发生变化——如何影响区域同位素分布。在接下来的两年里，我们将进行大量的古气候模拟，以确定模式的水汽源贡献和同位素场对边界条件（冰盖、海冰、海面温度等）具体变化的敏感性。古气候模拟的结果将与观测结果进行比较，我们将整理这些观测结果。这种数据模型比较将有助于确定北半球气候系统中对形成同位素记录最重要的组成部分。这一对比也将为GCM水文循环的可靠性和敏感性提供检验。

9316691 Charles An impressive network of oxygen and hydrogen isotopic records from ice cores, lake cores, deep sea cores and tree rings can now be compiled for a variety of time periods. These records potentially offer quantitative insight to past changes in climate processes, but their true climatic significance cannot be fully realized without knowledge of the fundamental driving forces for isotopes in precipitation. Simple air parcel models cannot account for the range of processes which control regional isotope distributions, and therefore the coupling of isotope tracers to a general circulation model (GCM) represents a necessary first step towards a more complete understanding of the isotope signals recorded in the geologic record. We propose to investigate these isotopic records by means of the Goddard Institute for Space Studies General Circulation Model (GISS GCM). The major issue we will pursue is how the changes in sourcewater characteristics, air mass trajectories, and air mass mixing-- all factors which must have varied over climate cycles with the major components of the climate system--affect regional isotopic distributions. Over the next two years, we will conduct a number of paleoclimatic simulations to determine the sensitivity of the model moisture source contributions and isotope fields to specific changes in boundary conditions (ice sheets, sea ice, sea surface temperature, etc.) Results of the paleoclimatic simulations will be compared to the observations, which we will compile. This data-model comparison will help identify the components of Northern Hemisphere climate system that are most important in shaping the isotope records. The comparison will also provide a test for the reliability and sensitivity of the GCM's hydrological cycle.