Collaborative Research: Dynamics of the 41-Ka Climate Cycle: Ice Volume and Insolation Forcing

该项目将研究上新世晚期和更新世早期气候记录中41,000年（41-Ka）周期的物理机制。此前，研究人员发现，观测到的41-Ka冰量周期是由太阳日照赤道到极点的梯度所强迫的，太阳日照的赤道到极点的梯度控制了经向大气的热通量和水分通量，最终影响了冰盖的生长和衰减。然而，当使用简单的耦合气候-冰模型进一步研究这一假设时，他们发现该模型仍然无法产生合理的41-Ka振幅振荡，并且表现出比底栖有孔虫氧同位素信号或冰筏碎片（IRD）记录更强的进动能力（可能是由于夏季日照对消融的强烈影响）。当这些数据与来自世界其他地区的其他数据相结合时，分析促使研究人员考虑以下科学问题。*为什么模拟的北半球冰体积如此之小，而冰碛石沉积物显示的冰最远可到达北纬35度？我们对模型或对数据的解释有问题吗？*如果北美有一个大的（空中膨胀的）低海拔冰盖，冰盖气候模型表明它将有一个大的消融带。那么，为什么我们在底栖有孔虫的氧同位素记录中没有像冰盖模型所显示的那样看到更强的岁差信号呢？* 41-Ka振荡是否可能是由于气候系统内部的机制，而不是仅仅由于米兰科维奇强迫而存在？为了确定北美冰盖变化是否存在进动成分，研究人员将在625（墨西哥湾）站点生成底栖生物同位素地层学，该地层学记录了浮游有孔虫氧同位素记录中的融水脉冲，从而为上新世晚期和更新世早期北美冰川的频率历史提供约束，并由此扩展为冰盖建模提供约束。研究人员的目标是建立一个新的耦合气候-冰盖模式，并利用该模式研究41-Ka振荡的不同情景，并利用模式结果重新分析代理记录，以确定41-Ka振荡是由于米兰科维奇强迫而存在，还是内部（自持续）振荡仅受米兰科维奇强迫的影响（锁相）。研究人员还将调查南极冰盖对上新世晚期和更新世早期全球冰量变化的可能贡献。该项目涉及高度跨学科的研究，涉及古气候、大气动力学、物理海洋学和气候建模等领域，以追求自然气候变化的基本研究方向。该项目将支持研究生和博士后学者跨越学科界限与挪威的同事合作，从而促进美国和挪威研究界之间的科学合作。

This project will investigate physical mechanisms responsible for the 41,000-year (41-Ka) cycle in late Pliocene and early Pleistocene climate records. Previously, the researchers showed that the observed 41-Ka cycle in ice volume was forced by the equator to pole gradient in solar insolation, which controlled the meridional atmospheric heat and moisture fluxes which ultimately influenced the growth and decay of ice sheets. However, when investigating this hypothesis further using a simple coupled climate-ice model, they found that the model still fails to produce reasonable amplitude 41-Ka oscillations, and exhibits far more precessional power than do benthic foraminifera oxygen isotope signals or ice rafted debris (IRD) records (presumably due to the strong influence of summer insolation on ablation). When these data were combined with other data from other areas of the world, the analysis prompted the researchers to consider the following science questions. * Why is modeled Northern hemisphere ice volume so small when glacial tillite deposits show ice reaching as far south as 35 degrees North latitude? Do we have problems with the models or with the interpretation of the data? * If there was a large (aerially-expansive), low elevation ice sheet on North America, ice sheet-climate models suggest it would have a large ablation zone. Why then do we not see a stronger precession signal in benthic foraminfera oxygen isotope records as ice sheet models suggest? * Could it be that the 41-Ka oscillations are due to a mechanism internal to the climate system, rather than exist only due to Milankovitch forcing? To determine whether there is a precessional component to ice sheet variation on North America, the researchers will generate a benthic isotope stratigraphy for site 625 (Gulf of Mexico) which records meltwater pulses in planktonic foraminfera oxygen isotope records to provide a constraint on the frequency history of North American glaciation in the late Pliocene and early Pleistocene and, by extension, a constraint for ice sheet modeling. The researchers aim to develop a new coupled climate-ice sheet model and use it to investigate different scenarios for the 41-Ka oscillations, and use the model results to reanalyze the proxy records with the objective to determine if the 41-Ka oscillations exist due to Milankovitch forcing, or are internal (self-sustained) oscillations only influenced (phase locked) by Milankovitch forcing. The researchers also will investigate the possible contribution by the Antarctic ice sheet to changes in global ice volume in the late Pliocene and early Pleistocene.This project involves highly interdisciplinary research and enlists the fields of paleoclimate, atmospheric dynamics, physical oceanography, and climate modeling in pursuing a fundamental line of inquiry in natural climate variability. The project will support a graduate student and post-doctoral scholars working collaboratively across disciplinary boundaries and with colleagues in Norway, thus fostering a scientific collaboration between research communities in the U.S. and Norway.