Fragmentation and melting of the seasonal sea ice cover
Lead Research Organisation:
University of Reading
Department Name: Meteorology
Abstract
Recent years have seen a rapid reduction in the summer extent of Arctic sea ice, renewing interest in the physical processes responsible for summer sea ice retreat. Sea ice components of atmosphere-ocean coupled Global Climate Models contain a simplified representation of physical processes at the edge of the sea ice cover. In particular sea ice climate models treat the floe size as a constant whereas observations show there to be a distribution of floe sizes, with significant spatial and temporal variability, especially in the seasonal and marginal ice zones. Smaller floes have an enhanced lateral melt, so providing a feedback when ocean the ocean is warm, potentially accelerating summer sea ice retreat. This PhD project will examine the impact of the observed heterogeneity in floe size on the summer melt and retreat of sea ice.
The seasonal reduction of the sea ice cover is driven by a combination of mechanical floe break up, and melting at the floe edges and upper and lower surfaces. Mechanical floe breakup occurs due to brittle failure in response to heterogeneity in imposed wind stresses, confining stresses, and, especially near the ice edge, by failure in flexure in response to incoming ocean waves and tidal motions, e.g. Squire[2007]. As floes break up, the total perimeter, or edge length, of a given area of sea ice increases. The reduction in floe size affects the response of the ice cover to the incoming wave field and promotes lateral melting. The process of floe breakup is currently absent from climate models: new, physics-based model development will allow its contribution to ice-climate feedbacks, relative to surface melt, to be evaluated for the first time. This PhD project will:
(1)Examine factors controlling the floe size distribution in the seasonal and marginal ice zone.
Observations show that the floe size distribution(FSD)in the marginal ice zone follows a power law distribution [Toyota et al, 2011]. New evidence from ICESAT and forthcoming Marginal Ice Zone campaigns (Office of Naval Research funded Arctic campaign, 2014) will be examined. A model of FSD evolution will be developed including fragmentation and flocculation (freezing together of floes[extending Dumont et al, 2011]. At the sea ice edge in summer, the lack of floe refreezing, and rapid response to storm-driven incoming ocean waves,will allow us to diagnose the FSD from the gross variables included in existing climate models. This FSD model will be ported to the sea ice model CICE.
(2)Examine lateral melt in CICE model.
The CICE model will be used to examine the impact of FSD on lateral melt at floe perimeters. The model will be driven with summer melt season atmospheric forcing and used to examine solar heat distribution into surface melt of the ice (and snow),warming of the mixed layer, and lateral melt. As solar heat is absorbed in the mixed layer and as ice melt occurs, the mixed layer is expected to shallow enabling concentration of heat in the mixed layer. The sensitivity of ice mass balance (concentration and thickness) to the FSD,formulation of lateral melt, and forcing conditions will be explored.
(3)Examine the impact of lateral melting in a coupled climate model
The HadGEM3 climate model will be modified to include the new version of CICE, containing the FSD model, and used to examine Arctic sea ice retreat in the seasonal and marginal ice zones (e.g. Barent's Sea, Fram Strait etc) in historical simulations to identify any enhanced sea ice - climate feedback.
References
Dumont D,A Kohout, and L Bertino (2011), A wave-based model for the marginal ice zone including a floe breaking parameterization, J.Geophys.Res.,116, doi:10.1029/2010JC006682.
Squire, VA, Of ocean waves and sea-ice revisited,Cold Reg.Sci.&Tech.,49,110-133, 2007.
Toyota T,C Haas, and T Tamura (2011),Size distribution and shape properties of relatively small sea-ice floes in the Antarctic marginal ice zone in later winter,Deep Sea Res. II, 58, 1182-1193.
The seasonal reduction of the sea ice cover is driven by a combination of mechanical floe break up, and melting at the floe edges and upper and lower surfaces. Mechanical floe breakup occurs due to brittle failure in response to heterogeneity in imposed wind stresses, confining stresses, and, especially near the ice edge, by failure in flexure in response to incoming ocean waves and tidal motions, e.g. Squire[2007]. As floes break up, the total perimeter, or edge length, of a given area of sea ice increases. The reduction in floe size affects the response of the ice cover to the incoming wave field and promotes lateral melting. The process of floe breakup is currently absent from climate models: new, physics-based model development will allow its contribution to ice-climate feedbacks, relative to surface melt, to be evaluated for the first time. This PhD project will:
(1)Examine factors controlling the floe size distribution in the seasonal and marginal ice zone.
Observations show that the floe size distribution(FSD)in the marginal ice zone follows a power law distribution [Toyota et al, 2011]. New evidence from ICESAT and forthcoming Marginal Ice Zone campaigns (Office of Naval Research funded Arctic campaign, 2014) will be examined. A model of FSD evolution will be developed including fragmentation and flocculation (freezing together of floes[extending Dumont et al, 2011]. At the sea ice edge in summer, the lack of floe refreezing, and rapid response to storm-driven incoming ocean waves,will allow us to diagnose the FSD from the gross variables included in existing climate models. This FSD model will be ported to the sea ice model CICE.
(2)Examine lateral melt in CICE model.
The CICE model will be used to examine the impact of FSD on lateral melt at floe perimeters. The model will be driven with summer melt season atmospheric forcing and used to examine solar heat distribution into surface melt of the ice (and snow),warming of the mixed layer, and lateral melt. As solar heat is absorbed in the mixed layer and as ice melt occurs, the mixed layer is expected to shallow enabling concentration of heat in the mixed layer. The sensitivity of ice mass balance (concentration and thickness) to the FSD,formulation of lateral melt, and forcing conditions will be explored.
(3)Examine the impact of lateral melting in a coupled climate model
The HadGEM3 climate model will be modified to include the new version of CICE, containing the FSD model, and used to examine Arctic sea ice retreat in the seasonal and marginal ice zones (e.g. Barent's Sea, Fram Strait etc) in historical simulations to identify any enhanced sea ice - climate feedback.
References
Dumont D,A Kohout, and L Bertino (2011), A wave-based model for the marginal ice zone including a floe breaking parameterization, J.Geophys.Res.,116, doi:10.1029/2010JC006682.
Squire, VA, Of ocean waves and sea-ice revisited,Cold Reg.Sci.&Tech.,49,110-133, 2007.
Toyota T,C Haas, and T Tamura (2011),Size distribution and shape properties of relatively small sea-ice floes in the Antarctic marginal ice zone in later winter,Deep Sea Res. II, 58, 1182-1193.
Publications
Bateson A
(2022)
Sea ice floe size: its impact on pan-Arctic and local ice mass and required model complexity
in The Cryosphere
Bateson A
(2020)
Impact of sea ice floe size distribution on seasonal fragmentation and melt of Arctic sea ice
in The Cryosphere
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| NE/M009637/1 | 11/01/2016 | 31/07/2021 | |||
| 1813889 | Studentship | NE/M009637/1 | 01/10/2016 | 30/11/2020 | Adam Bateson |
| Description | The summer extent of Arctic sea ice has shown a rapidly decreasing trend in recent years, highlighting the need to better understand the mechanisms that drive seasonal retreat of Arctic sea ice. One area of interest is the size of floes (discrete areas of sea ice that make up the overall cover). Climate models assume these adopt a constant size, but observations show that they adopt a wide range of sizes. These observations show that a truncated power law generally produces a good fit to the floe size distribution (FSD). In the course of this research, we have considered two alternative models to represent the FSD within the Los Alamos sea ice model (CICE). The first assumes that the FSD follows a truncated power law (called the WIPoFSD model), whereas the second is a prognostic model where the shape of the FSD is emergent from individual parameterisations rather than imposed. Simulations with both the prognostic model and the WIPoFSD model where the model setup was optimised to produce the best fit to observations only resulted in small impacts on pan-Arctic metrics such as the sea ice extent and volume, however impacts were larger on more localised scales. In addition, the inclusion of FSD processes preferentially reduced sea ice concentration in sea ice locations closer to the open ocean, partially correcting known model biases. Both FSD models demonstrated high sensitivity to parameters within observational constraints. This highlights the need for further observations of both the FSD and related processes to improve parameterisations, constrain model parameters, and validate FSD model output. A new metric, the effective floe size, was demonstrated to be a useful tool to characterise FSD evolution and variability. Brittle fracture processes have also been explored as potentially important for the emergence and evolution of the FSD. These processes include brittle fracture events in winter, and the melting and breakup of floes along existing cracks and linear features within the sea ice cover in summer. It has been shown that the inclusion of a simple representation of brittle fracture processes in the prognostic FSD model significantly improves model performance against observations of the FSD. Overall, we have found that the WIPoFSD model is a flexible tool for assessing the importance of a floe size distribution in the evolution of Arctic sea ice. Whilst parallel efforts to develop FSD models without the assumption of a power law such as the prognostic model do exist, these require the introduction of further parameters to constrain and are more computationally expensive. The power law FSD model hence remains suitable for applications where a simple but realistic floe size distribution model is required. In comparison, the prognostic FSD model has been found to be useful for providing physical insights into observations of FSD evolution over time and for being able to better constrain WIPoFSD model parameters. In addition, it will be useful for applications where detailed knowledge of the sea ice state over localised or regional scales is required. |
| Exploitation Route | My findings highlight key uncertainties within observations, which can help to clarify the important research questions that future data collection expeditions should answer. The output from the model approach developed in Bateson et al. (2020) and Bateson et al. (2022) can in future be compared against the results of newly completed expeditions such as MOSAiC (https://mosaic-expedition.org/) alongside the output of other floe size distribution models. My research into the floe size distribution is relevant to the NERC funded 'Towards a marginal Arctic sea ice cover' project. As I result, I have presented my research findings at meetings for this project and my results have informed some of the model choices made. This work has also helped to motivate a further NERC funded research project, 'Fragmentation and melt of Arctic sea ice'. As the primary investigator on this award is supervised by researchers from three different institutions (UK Met Office, National Oceanography Centre Southampton and the University of Reading), the findings will help develop future research directions at all three institutions. In particular, NERC centres and the UK Met Office are moving towards the use of a new European sea ice model, SI3. The research produced from this award will hence help inform choices regarding the representation of floe size and wave-sea ice interactions within this new model. The SI3 model will have numerous applications including operational forecasting (used by shipping companies traversing the Arctic ocean) and within climate models. |
| Sectors | Aerospace, Defence and Marine,Environment,Transport |
| Title | Simulations of the Arctic sea ice comparing different approaches to modelling the floe size distribution and their respective impacts on the sea ice cover |
| Description | This dataset has been produced by implementing either a power law derived or prognostic sea ice floe size distribution model within the CICE sea ice model. This dataset is used within the thesis 'Fragmentation and melting of the seasonal sea ice cover' (Bateson, 2021) to investigate the impact of the sea ice floe size distribution on the evolution of the Arctic sea ice cover and to compare different approaches to modelling floe size. Results are presented to show how variable floe size changes the seasonal retreat of the Arctic sea ice cover via changes to lateral melt volume and momentum exchange between the sea ice, ocean, and atmosphere. Winter floe formation and growth processes are found to strongly influence FSD impacts on the seasonal retreat of the sea ice, and the need to include brittle fracture processes in floe size distribution models is also demonstrated. A high sensitivity is found to poorly constrained FSD parameters, highlighting the need for further observations of floe size. |
| Type Of Material | Database/Collection of data |
| Year Produced | 2021 |
| Provided To Others? | Yes |
| Impact | This dataset consists of the majority of data used to support the thesis, 'Fragmentation and melting of the seasonal sea ice cover' (DOI: 10.48683/1926.00098821) associated with this award. Some of this dataset has also been used to support the (currently in review) publication Bateson et al. (2021; DOI: 10.5194/tc-2021-217). |
| URL | https://researchdata.reading.ac.uk/id/eprint/300 |
| Title | Simulations with the sea ice model CICE investigating the impact of sea ice floe size distribution on seasonal Arctic sea ice retreat. |
| Description | This dataset has been generated by implementing a power law derived sea ice floe size distribution model within the CICE sea ice model. We use this dataset within the associated paper (Bateson et al., 2019) to investigate the impact of floe size on the seasonal fragmentation and melt of Arctic sea ice. We document several findings including that the floe size distribution model has a spatially and temporally dependent impact on the sea ice cover, in particular enhancing the role of the marginal ice zone in sea ice loss. We also show a strong model sensitivity to floe size distribution parameters within limits constrained by observations. We furthermore find that the impact of waves on floe size and the sea ice cover is strongly moderated by the wave attenuation rate. |
| Type Of Material | Database/Collection of data |
| Year Produced | 2019 |
| Provided To Others? | Yes |
| Impact | This dataset was heavily drawn upon in the published paper Bateson et al. (2020, doi:10.5194/tc-14-403-2020). |
| URL | https://researchdata.reading.ac.uk/id/eprint/223 |