Waves in sea ice for monitoring and modelling – WaveSIMM

A network of seismic sensors (measuring horizontal and vertical velocities), of tiltmeters (measuring tilt fluctuations in the ice sheet), and internal stress sensors will be deployed on the Arctic sea ice in autumn 2013 from an icebreaker. The average thickness of the ice will be estimated (i) at large scale from the measurement of the average speed of propagation of the waves, which depends on the thickness, and (ii) within the network (1 - 100 km) from an analysis of the dispersion of flexural waves associated with the swell (always present even in the middle of the pack). A study of quakes induced by sea ice fracturing , in conjunction with an analysis of the deformation within the network (from measured displacements of the stations) and in-situ ice stress measurements, will allow to better understand the process of fracture / fragmentation of sea ice. In the marginal zone (transition to the ice-free ocean ), an analysis of the role played by the swell on the dismantling of local ice will be conducted.

The measurement field campaign is being prepared

Once developed and validated by the project, the proposed methods of thickness measurement will be available for a multi-year monitoring.

yet none for the moment

We propose a highly-integrated and multidisciplinary study of waves in sea ice. The proposed work builds on a successful bid to the European Science Foundation (ESF) by the one partner (LOV), based on the development of satellite-linked buoys for studying the changing Arctic (SATICE). Both projects share common goals to develop and prove novel observation techniques for modelling key ice and ocean parameters, in this time of rapid change. The work builds upon co-operation initiated under the EU DAMOCLES project and takes advantage of logistic opportunities provided to our project at no cost by the US/Canadian Beaufort Gyre study, aboard the icebreaker Louis St Laurent.

The over-arching objective of this project is to increase our knowledge and understanding of the Arctic sea ice cover. The ability of the project to significantly impact these fields of understanding comes from three main directions: (1) Novel cross-disciplinary application of analysis techniques, bringing solid-Earth methods to cryospheric studies; (2) Insight from the proposers’ long experience of field measurement; (3) Technological advances, allowing us to build and deploy low-cost autonomous measurement platforms to actually make the required measurements for the first time. WaveSIMM will conduct ground-breaking investigations at the scales required by the generating processes. Specifically we will:
1. Demonstrate a validated monitoring system for local/regional-scale ice thickness, using noise cross-correlation techniques
2. Demonstrate a validated monitoring system for basin-scale ice thickness, using the thickness-dependent modification of travel time as waves cross the ice cover
3. Measure wave spectra in the summer Arctic Ocean and determine the importance of wave-induced mechanical forces on the breakup and retreat of Arctic sea ice
4. Explore the link between sea ice fracturing and regional deformation, hence develop modelling techniques to replace phenomenological parameters with realistic physics

Waves in sea ice have been measured for a long time (since at least the 1950s), but have, until recently, found little practical application. Technological advances - primarily the Iridium satellite data transmission system - prompted the proposers to initiate a new programme. This bore fruit as part of the DAMOCLES project, showing that long-period swell waves, generated by distant storms in the world oceans, could be used to diagnose ice thickness, by examining the perturbation in travel time of those waves caused by the ice. As a complement to the this method - which requires ‘clean’ wave arrivals from the deep ocean and applies over large scales – the solid-Earth seismic community has developed a technique which relies on the measured wavefield being random, and applies on an essentially local scale. This noise cross-correlation method has the potential to measure ice thickness within a relatively closely spaced array (scale from 1-100 km). The complementary methods thus promise to measure ice thickness at low cost at all scales of interest. The proposed work gives the exciting possibility to ground-truth results and verify the methods, allowing them to take their place as part of a long-term ice thickness monitoring system.

The same GPS/wave measuring instruments will also be used to examine fracture of the ice cover. This discrete deformation, though actually how sea ice deforms, has previously been treated as a continuum process in models, which ascribe phenomenological viscous-plastic properties to the ice in order to make it computationally tractable. The limitations of this approach have been demonstrated, especially as the resolution of models is improving. Clearly, it would be preferable to model the real behaviour of the ice cover, especially since sea ice mechanics and its associated kinematics largely controls the sea ice thickness distribution, and fracturing has a major impact on sea-air exchanges through lead opening.