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(约3 Ma前)的最大海平面上升对于了解格陵兰和南极冰盖对全球温和变暖的响应至关重要。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耦合方面取得进展。缺少的一个基本要素是一个关于全球分布和确定日期的上新世海岸线高度的综合数据库，该数据库能够提供测试和指导开发冰盖和地壳形变模型所需的数据约束，这些模型将用于预测全球变暖时海平面上升的幅度和分布。根据代理数据的建议，使用最先进的气候-冰模型和400ppm的大气二氧化碳模拟上新世中期，无法产生能够导致东南极表面显著融化的气温。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)不一致，并意味着：a)上新世二氧化碳水平可能被低估；b)气候模型对二氧化碳的敏感性可能太低；c)当前一代冰盖模型不能充分代表重要的冰盖物理；d)这一时期的大多数海平面估计值太高；e)尚未确定对气候的某些替代重大影响；或f)以上各项的某种组合。在这里，我们建议合作和系统地工作，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，侧重于下文所述的三个目标，最终将为一个长期存在的问题带来一个内部一致的解决方案，即在略微变暖的世界中南极冰盖的稳定性问题。我们提出的五年计划将提供：1)世界各地上新世海岸线高程数据库的显著改进。2)预测上新世海岸线在不同冰盖、地幔和动态地形情景下的全球均衡响应和预期现代高程的一系列实验(和制图结果)。3)首次建立了高分辨率的大气-海洋-冰盖/陆架-地球耦合模式。在地质年代学和古气候学方面有专长的海洋地质学家M·雷莫和近海环境野外地质专家P·哈蒂将领导数据收集工作。J·米特罗维察是一位专门研究冰川均衡的地幔-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合作建立气候-冰模型，包括首次耦合到考虑地幔和重力过程的动态地球模型(与Mitrovica)。学术价值：气候系统持续变暖的证据是明确的[政府间气候变化专门委员会，2007]，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。建立一个能够预测未来气候和地球系统海平面响应的完全耦合的冰-海-气-地幔-壳模式，并提供能够帮助模型者评估在不同强迫情景下他们的冰盖/气候模拟的逼真度的数据，是这一提议的主要智力目标。面对持续变暖，提高预测模型能力是一项基本需要，没有比海平面上升更大的不确定性(或潜在灾难)了。更广泛的影响：对全球上新世海平面估计数组的需求有助于采取广泛的、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努力。这将通过外联和协作以及一个维基网站实现，维基网站将作为与开展实地研究有关的信息的储存库，包括可定制地获取预测的全球海平面、动态地形和均衡效应的模拟结果。NSF资助的一个配套项目--海洋变化--已经在为普通观众制作外展材料，这些努力，包括我们的魔法星球项目，也将在这个项目中继续下去。除了让两位早期职业科学家(O‘Leary和Inglis)作为项目合作者外，作为该项目的一部分，PI们在教学和指导方面都有很好的记录，他们将培训和指导博士后、研究生和本科生研究人员。一名PI将在一所为地球科学中代表性不足的学生提供服务的机构监督和指导学生。

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.