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

了解上新世中期温暖时期（约3 Ma前）发生的最大海平面上升对于了解格陵兰和南极冰盖对适度全球变暖的反应至关重要。实现这一目标将需要在模拟冰盖动力学、地幔过程以及气候系统的固体地球、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一个关于全球分布的上新世海岸线高程和日期的综合数据库，该数据库能够提供测试和指导开发冰盖和地壳变形模型所需的数据限制，这些模型将用于预测在更温暖的世界中海平面上升的幅度和分布。 模拟上新世中期使用国家的最先进的气候-冰模型与400 ppm大气压的二氧化碳，代理数据所建议的，未能产生能够导致显着的表面融化在南极洲东部的空气温度。这些结果与通常引用的上新世中期海平面上升+25米（例如，PRISM）并暗示：a）上新世CO2水平可能被低估; B）气候模型对CO2的敏感性可能太低; c）当前一代冰盖模型不能充分代表重要的冰盖物理学; d）这一时期的大多数海平面估计值过高; e）对气候的其他主要影响尚未确定;或f）上述因素的某种组合。在这里，我们建议协同和系统地工作，以减少这些不确定性。 我们认为，我们在四个不同学科的专门知识，侧重于下述三个目标，最终将导致对一个长期存在的问题，即在一个稍微温暖的世界中南极冰盖稳定性问题，找到一个内部一致的解决办法。我们提出的五年计划将提供：1）一个显着改善的数据库上新世海岸线海拔从世界各地。 2)一系列的实验（和映射结果），预测全球均衡响应和上新世海岸线的预期现代海拔在不同的冰盖，地幔和动态地形的情况下。 3)一个耦合的高分辨率大气-海洋-冰盖/冰架-地球模型，这是同类中的第一个。 M.拥有地质年代学和古气候学专业知识的海洋地质学家Raymo和近岸环境野外地质学专家P. Hearty将领导数据收集工作。米特罗维察是一位专门研究冰川等厚线的地幔-地壳动力学专家，他将领导地幔-地壳建模工作。R. DeConto是一位气候学家和地球系统建模师，他将与D。Pollard是一位领先的冰盖数值建模专家，他介绍了气候-冰模型构建工作，包括首次与考虑地幔和重力过程的动态地球模型耦合（与米特罗维察合作）。智力优势：气候系统持续变暖的证据是明确的[IPCC 2007]，由于冰川融化导致的海平面上升正在加速[Rignot等人，2011年]。保守的估计表明，即使温室气体排放量大幅减少，全球气温仍将进一步上升1-2摄氏度。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，可以帮助建模人员评估他们的冰盖/气候模拟在不同的强迫情景下的保真度，是本提案的主要智力目标。提高预测模型的能力是面对持续变暖的基本需求，没有比海平面上升更大的不确定性（或潜在的灾难）。更广泛的影响：对上新世海平面估计的全球阵列的需要有助于广泛的，多研究者的方法，我们致力于让尽可能多的科学家参与这一奋进。这将通过外联和协作以及一个维基网站来实现，该网站将作为与进行实地研究有关的信息库，包括可定制的全球海平面、动态地形和均衡效应预测模型结果的访问。一个由NSF资助的配套项目“海洋变化”已经在为普通观众制作外展材料，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进行。除了两名早期职业科学家作为项目合作者（O ′ Leary和Inglis）之外，作为该项目的一部分，这些PI将培训和指导博士后、研究生和本科生研究人员，他们共同拥有良好的教学和指导记录。一个PI（心）将监督和指导学生在一个机构为学生在地球科学代表不足。

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.