Breaking the Ice

Reporting by Helen Hill for MITgcm

 

Under the constant agitation of waves and wind, sea ice tends to be rather granular in nature, composed of ice floes of different sizes and shapes. In most large-scale models, sea ice is treated as a viscous–plastic continuum, deforming plastically when the internal stress becomes critical in compression, shear, or tension; creeping viscously when the internal stress is relatively small.

While recent high-resolution pan-Arctic simulations have been developed to include sea-ice fracturing, the models produce wider fracture angles than those seen in high-resolution satellite images. Getting sea-ice fracturing wrong in such simulations can lead (no pun intended) to changes in the subsequent dynamics, mass balance, and the heat and matter exchanges between the ocean, ice, and atmosphere.

Motivated by this, Damien Ringeisen, Martin Losch, and Nils Hutter from the Alfred-Wegner Institute of the Helmholtz Zentrum fur Polar und Meeresforschung (AWI) Bremerhaven Germany working with Bruno Tremblay from the Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, Canada, set about exploring what might be causing this discrepancy, work that was recently published in journal The Cryosphere.

To investigate whether sea ice fracture is represented accurately in continuum sea ice models, Ringeisen et al used MITgcm, the sea-ice package of which allows for use of different rheologies – alternative prescriptions for how the sea-ice should respond to an applied force.

The team set up a simple uni-axial loading test, to compare the response of an ideal section of sea-ice 8 km by 25 km to compression using two different mathematical expressions defining the ice’s resistance to the compressive force, one with an elliptical yield curve and a normal flow rule (the most common rheology used to describe sea-ice behavior) and the other with a Coulombic yield curve and a normal flow rule applying only to the elliptical part of the ice cap.

Fracture of an Ice Flow – (Note movie loops through compression cycle four times) A sea ice floe of size 8 per 25 km is forced to deform in compression with an increasing stress on the top boundary. This animation shows the first 10 seconds of integration time. The deformation appears with the shape of an X through the ice floe, showing the creation of 2 new leads. Panels: a) is the shear deformation, b) is the divergence (here positive as the ice opens), c) is the difference to initial thickness (here negative as the ice opens), d) shows the stress states (red) that are confined inside the elliptical yield curve (black). Simulation/ animation credit: D. Ringeisen

The authors report that although at first sight, the large-scale patterns appear realistic when compared to satellite observations, the standard rheology overpredicted fracture angle and showed results that were often in opposition with ice’s granular nature. However, the alternative rheology they tried, although it yielded a fracture angle closer to the observations, introduced unwelcome instabilities.

To find out more about this work contact Damien

This Month’s Featured Publication

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Martin Losch, Dimitris Menemenlis, Jean-Michel Campin, Patick Heimbach, Chris Hill (2010), On the formulation of sea-ice models. Part 1: Effects of different solver implementations and parameterizations, Ocean Modelling, doi: 10.1016/j.ocemod.2009.12.008

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Thaddeus D. Komacek, Adam P. Showman, and Vivien Parmentier (2019), Vertical Tracer Mixing in Hot Jupiter Atmospheres, arXiv:1904.09676 [astro-ph.EP]

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Larry J. Pratt, Gunnar Voet, Astrid Pacini, Shuwen Tan, Matthew H. Alford, Glenn S. Carter, James B. Girton, and Dimitris Menemenlis (2019), Pacific abyssal transport and mixing: through the Samoan Passage vs. around the Manihiki Plateau, Journal of Physical Oceanography, doi: 10.1175/JPO-D-18-0124.1

Yu-Kun Qian, Shiqiu Peng, and Chang-Xia Liang (2019), Reconciling Lagrangian Diffusivity and Effective Diffusivity in Contour-Based Coordinates, Journal of Physical Oceanography, doi: 10.1175/JPO-D-18-0251.1

S. M. Reckinger, et al. (2019), The Effect of Numerical Parameters on Eddies in Oceanic Overflows: A laboratory and numerical study, Int. J. Comp. Meth. and Exp. Meas., Vol. 7, No. 2 (2019) 142–153, https://www.witpress.com/Secure/ejournals/papers/CMEM070205f.pdf

Jianfen Wei, Xiangdong ZhangEmail authorZhaomin Wang (2019), Reexamination of Fram Strait sea ice export and its role in recently accelerated Arctic sea ice retreat, Climate Dynamics, doi: 10.1007/s00382-019-04741-0

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Yanxu Zhang, Hannah Horowitz, Jiancheng Wang, Zhouqing Xie, Joachim Kuss, and Anne L. Soerensen (2019), A Coupled Global Atmosphere-Ocean Model for Air-Sea Exchange of Mercury: Insights into Wet Deposition and Atmospheric Redox Chemistry, Environmental Sciences and Technology, doi: 10.1021/acs.est.8b06205

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Do you have news about research using MITgcm? We are looking for contributions to these pages. If you have an interesting MITgcm project (ocean, atmosphere, sea-ice, physics, biology or otherwise) that you want to tell people about, get in touch. To make a post, contact Helen