FESD Type I: PLIOcene MAXimum sea level (PLIOMAX): Dynamic ice sheet-Earth response in a warmer world

了解上新世中期暖期（~3 Ma前）发生的最大海平面上升对理解格陵兰岛和南极冰盖对温和全球变暖的响应至关重要。要实现这一目标，需要在模拟冰盖动力学、地幔过程以及气候系统中固体地球、海洋、大气和冰冻圈组成部分的相互作用耦合方面取得进展。一个重要的缺失因素是全球分布和上新世海岸线海拔的综合数据库，能够提供测试和指导冰盖和地壳变形模型发展所需的数据约束，这些模型将用于预测变暖世界海平面上升的幅度和分布。根据代理数据，利用最先进的气候-冰模式，在二氧化碳浓度为400ppm的情况下对上新世中期进行模拟，无法产生能够导致东南极洲显著地表融化的空气温度。这些结果与通常引用的上新世中期海平面上升+25米的说法不一致（例如PRISM），并暗示：a)上新世CO2水平可能被低估；b)气候模式对二氧化碳的敏感性可能太低；C)当前一代的冰盖模式不能充分代表重要的冰盖物理特性；D)大多数对这一时期海平面的估计都太高了；E)尚未确定的对气候的其他主要影响；或者f)以上几点的组合。在此，我们建议通过协作和系统的工作来减少这些不确定性。我们认为，我们在四个不同学科的专门知识，集中于下面所述的三个目标，将最终为一个长期存在的问题，即在稍微变暖的世界中南极冰盖的稳定性问题，提供一个内部一致的解决办法。我们提出的五年计划将提供：1)一个显著改进的世界各地上新世海岸线海拔数据库。2)在不同冰盖、地幔和动态地形情景下，预测全球均衡响应和上新世海岸线现代预期高程的一系列实验（和制图结果）。3)首次建立高分辨率大气-海洋-冰盖/陆架耦合模型。具有地质年代学和古气候学专长的海洋地质学家雷莫（M. Raymo）和近岸环境野外地质学专家哈迪（P. Hearty）将领导数据收集工作。J. Mitrovica是一位专注于冰川均衡的地幔-地壳动力学专家，他将领导地幔-地壳建模工作。气候学家和地球系统建模师R. DeConto将与领先的数值冰盖建模师D. Pollard合作，进行气候-冰模型的构建工作，包括首次与考虑地幔和引力过程的动态地球模型耦合（与Mitrovica合作）。知识价值：气候系统持续变暖的证据是明确的[IPCC 2007]，冰川融化导致的海平面上升正在加速[Rignot et al., 2011]。保守估计表明，即使大量减少温室气体排放，全球气温也将进一步上升1-2°C。建立一个完全耦合的冰-海洋-大气-地幔-地壳模型，能够预测地球系统未来的气候和海平面响应，并提供数据，帮助建模者评估不同强迫情景下冰盖/气候模拟的保真度，这是本提案的主要智力目标。面对持续的变暖，提高预测模式的能力是一项基本需要，没有比海平面上升更大的不确定性（或潜在的灾难）了。更广泛的影响：对全球上新世海平面估计的需求使其成为一个广泛的，多研究者的方法，我们致力于让尽可能多的科学家参与这项努力。这将通过外联和合作以及一个wiki站点来完成，该站点将作为与开展实地研究相关的信息存储库，包括可定制访问预测的全球波动、动态地形和均衡效应的建模结果。美国国家科学基金会资助的一个伙伴项目“海洋变化”已经在为普通观众制作外联材料，这些努力，包括我们的“神奇星球”项目，也将在这个项目中继续下去。除了两位早期职业科学家（O’Leary和Inglis）作为项目合作者外，这些在教学和指导方面有着丰富经验的pi将作为项目的一部分，培训和指导博士后、研究生和本科生研究人员。一名PI （Hearty）将在一个为地球科学领域代表性不足的学生服务的机构中监督和指导学生。

Knowing the maximum eustatic sea level rise that occurred during the mid-Pliocene warm period (~3 Ma ago) is critical to understanding the response of Greenland and Antarctic ice sheets to a modest global warming. Achieving this objective will require advances in modeling ice sheet dynamics, mantle processes, and the interactive coupling of solid Earth, ocean, atmosphere, and cryosphere components of the climate system. An essential missing element is a comprehensive database of globally distributed and dated Pliocene shoreline elevations, capable of providing the data constraints needed to test and guide the development of ice sheet and crustal deformation models that will be used to predict the magnitude and distribution of sea-level rise in a warmer world. Simulations of the mid Pliocene using state-of-the-art climate-ice models with 400 ppm atm CO2, as suggested by proxy data, fail to produce air temperatures capable of causing significant surface melt in East Antarctica. These results are at odds with the +25 m sea level rise typically cited for the mid-Pliocene (e.g., PRISM) and imply: a) Pliocene CO2 levels may be underestimated; b) climate model sensitivity to CO2 may be far too low; c) the current generation of ice sheet models do not adequately represent important ice sheet physics; d) most sea level estimates for this time period are too high; e) some alternative major influence on climate that has yet to be identified; or f) some combination of the above. Here we propose to collaboratively and systematically work to reduce these uncertainties. We submit that our expertise in four distinct disciplines, focused on the three objectives described below, will ultimately result in one internally consistent solution to a long-standing question, namely that of Antarctic ice sheet stability in a slightly warmer world. Our proposed five-year plan will deliver: 1) A dramatically improved database of Pliocene shoreline elevations from around the world. 2) A series of experiments (and mapped results) that predict the global isostatic response and expected modern elevations of Pliocene shorelines under different ice sheet, mantle, and dynamic topography scenarios. 3) A coupled high-resolution atmosphere-ocean-ice sheet/shelf-Earth model, the first of its kind. M. Raymo, a marine geologist with expertise in geochronology and paleoclimatology, and P. Hearty, an expert in field geology of near-shore environments, will lead the data collection effort. J. Mitrovica, an expert on mantle-crustal dynamics with a specific focus on glacial isostasy, will lead the mantle-crust modeling effort. R. DeConto, a climatologist and Earth System modeler, will work with D. Pollard, a leading numerical ice sheet modeler, on climate-ice model construction efforts including coupling, for the first time, to a dynamic Earth model accounting for mantle and gravitational processes (with Mitrovica). Intellectual Merit: Evidence for ongoing warming of the climate system is unequivocal [IPCC 2007] and sea level rise due to melting glaciers is accelerating [Rignot et al., 2011]. Conservative estimates suggest a further 1-2 ¢ªC of global temperature rise will occur, even if massive reductions in GHG emissions were made. Building a fully-coupled ice-ocean-atmosphere-mantle-crust model capable of predicting future climate and sea level response of the Earth system and providing the data that can help modelers evaluate the fidelity of their ice sheet/climate simulations under different forcing scenarios, are the primary intellectual goals of this proposal. Improving predictive model capability is an essential need in the face of ongoing warming and no greater uncertainty (or potential catastrophe) exists than that of sea level rise. Broader Impacts: The need for a global array of Pliocene sea level estimates lends itself to a broad, multi-investigator approach and we are committed to engaging as many scientists as possible in this endeavor. This will be accomplished through outreach and collaboration, as well as with a wiki site that will serve as a repository for information relevant to undertaking field studies, including customizable access to modeling results of predicted global eustatic, dynamic topography, and isostatic effects. An NSF-funded companion project, Sea Change, is already creating outreach material for a general audience and these efforts, including our Magic Planet project, will continue in this project as well. In addition to involving two early career scientists as project collaborators (O¡¯Leary and Inglis), the PIs, who collectively have a strong record of teaching and mentoring, will train and mentor post-doctoral, graduate student, and undergraduate researchers as part of this project. One PI (Hearty) will supervise and mentor students at an institution serving students under-represented in the Geosciences.