Twenty-first century ocean forcing of the Greenland ice sheet for modelling of sea level contribution
Twenty-first century ocean forcing of the Greenland ice sheet for modelling of sea level contribution
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DOI：
10.5194/tc-14-985-2020
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发表时间：
2020-03
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影响因子：
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通讯作者：
D. Slater;D. Felikson;F. Straneo;H. Goelzer;Christopher M. Little;M. Morlighem;X. Fettweis;S. Nowicki-S
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作者：
D. Slater;D. Felikson;F. Straneo;H. Goelzer;Christopher M. Little;M. Morlighem;X. Fettweis;S. Nowicki-S
摘要。海洋温度和盐度的变化预计将是格陵兰冰盖对未来海平面上升贡献的一个重要决定因素。然而，由于关键物理过程（如峡湾环流和羽流动力学）的尺度较小，以及对崩解和海底融化等关键过程的了解不足，在大陆尺度的冰盖模型中模拟这些变化的影响仍然具有挑战性。在此，我们介绍了参与CMIP6冰盖模型比较计划（ISMIP6）的格陵兰冰盖模型的海洋强迫策略，这是为政府间气候变化专门委员会第六次评估报告提供21世纪海平面预测的主要社区努力。从全球大气 - 海洋环流模式出发，我们描述了为格陵兰冰盖模型提供海洋边界条件的两种互补方法，称为“后退”和“海底融化”实施方式。“后退”实施方式将冰川后退参数化为预测的冰下排放和海洋热强迫的函数，旨在可被所有冰盖模型采用，在RCP2.6和8.5情景下，到2100年分别导致约1公里和15公里的后退。“海底融化”实施方式仅提供估计的海底融化量，让冰盖模型来解决由此产生的崩解和冰川后退问题，并表明在RCP2.6情景下海底融化速率变化不大，但在RCP8.5情景下到2100年将大约增加两倍。这两种实施方式都必然使用了简化假设和约束性较差的参数化，因此，对海底融化、崩解和峡湾 - 陆架交换的进一步研究仍应是优先事项。尽管如此，所提出的框架将首次使一组格陵兰冰盖模型能够受到海洋的系统且一致的强迫，并应使格陵兰冰盖对未来海平面变化贡献的预测有显著改进。
Abstract. Changes in ocean temperature and salinity are expected to be an important determinant of the Greenland ice sheet's future sea level contribution. Yet, simulating the impact of these changes in continental-scale ice sheet models remains challenging due to the small scale of key physics, such as fjord circulation and plume dynamics, and poor understanding of critical processes, such as calving and submarine melting. Here we present the ocean forcing strategy for Greenland ice sheet models taking part in the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), the primary community effort to provide 21st century sea level projections for the Intergovernmental Panel on Climate Change Sixth Assessment Report. Beginning from global atmosphere–ocean general circulation models, we describe two complementary approaches to provide ocean boundary conditions for Greenland ice sheet models, termed the “retreat” and “submarine melt” implementations. The retreat implementation parameterises glacier retreat as a function of projected subglacial discharge and ocean thermal forcing, is designed to be implementable by all ice sheet models and results in retreat of around 1 and 15 km by 2100 in RCP2.6 and 8.5 scenarios, respectively. The submarine melt implementation provides estimated submarine melting only, leaving the ice sheet model to solve for the resulting calving and glacier retreat and suggests submarine melt rates will change little under RCP2.6 but will approximately triple by 2100 under RCP8.5. Both implementations have necessarily made use of simplifying assumptions and poorly constrained parameterisations and, as such, further research on submarine melting, calving and fjord–shelf exchange should remain a priority. Nevertheless, the presented framework will allow an ensemble of Greenland ice sheet models to be systematically and consistently forced by the ocean for the first time and should result in a significant improvement in projections of the Greenland ice sheet's contribution to future sea level change.