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

该项目将研究在上新世晚期和更新世早期气候记录中41000年(41kA)周期的物理机制。此前，研究人员表明，观测到的41kA冰量循环是由太阳辐射中的赤道极梯度强迫的，这控制了经向大气热量和水汽通量，最终影响了冰盖的生长和衰退。然而，当他们使用一个简单的气候-冰耦合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41kA振荡，并且显示出比底栖有孔虫氧同位素信号或冰排碎片(IRD)记录更大的进动功率(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结合在一起时，这项分析促使研究人员考虑了以下科学问题。*为什么模拟的北半球冰量如此之小，而冰川提晶石沉积物显示冰最南达北纬35度？我们对模型或数据的解释有问题吗？*如果北美有一个大的(空中扩张的)低海拔冰盖，冰盖气候模型表明它会有一个大的消融区。那么，为什么我们没有像冰盖模型所建议的那样，在海底有孔虫的氧同位素记录中看到更强的进动信号？*可能是41kA的振荡是由于气候系统内部的机制，而不是仅仅由于米兰科维奇的强迫而存在的？为了确定北美冰盖变化是否有岁差成分，研究人员将在625号站点(墨西哥湾)生成海底同位素地层学，在浮游有孔虫氧同位素记录中记录融水脉冲，以限制北美冰川在上新世晚期和更新世早期的频率历史，进而限制冰盖建模。研究人员的目标是开发一个新的气候-冰盖耦合模式，并用它来研究41kA振荡的不同情景，并利用模型结果重新分析替代记录，目的是确定41kA振荡是否存在于米兰科维奇强迫，或者是只受米兰科维奇强迫影响(锁相)的内部(自维持)振荡。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，并结合古气候、大气动力学、物理海洋学和气候模拟领域，寻求自然气候变异性的基本研究路线。该项目将支持研究生和博士后学者跨越学科界限并与挪威同事合作，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.