Constraining Arctic wave-ice interactions and the sea ice floe-size distribution

University Of Washington, Seattle WA

Investigators

Abstract

1. Arctic sea ice has declined in area over recent decades. Ocean surface waves are becoming more common in the Arctic as sea ice loss exposes the ocean surface directly to wind producing waves. Sea ice floats on the ocean in pieces called floes that flex and fracture under the influence of waves. Although waves traveling into the sea ice lose amplitude, waves propagate deeper into sea ice as floes are fractured into smaller pieces and are more widely spaced. Sea ice that is highly fractured is more prone to side melt, therefore further enabling wave production and propagation, floe fracture, and sea ice retreat. The intellectual merit of this award is the furthering of wave-ice interaction theory and developments to an Earth system model that simulates sea ice floes, ocean surface waves and their interactions. Observations will inform the model developments. Climate simulations with these model advances will be the first ever to treat sea ice and wave interactions. Previous climate simulations have generally simulated too little Arctic sea ice decline compared to measurements over the last 45 years. Including wave-ice interactions in the model is expected to improve the simulation of the past, produce a better estimate of expected sea ice and climate change over the next century, and yield better forecasts of the sea ice response to storms. This work has broader impacts due to the importance of understanding past and future climate change. Future projections of Arctic sea ice cover, warming, snowfall, and sea level rise are necessary to inform policy decisions. Simulating Arctic waves in sea ice is also important for warning communities about coastal erosion and hazardous coastal conditions. The project results will be disseminated by publishing in standard scientific journals. The project findings will contribute to the content of courses the science team teaches on global warming, climate and climate change, ice and climate interactions, and climate modeling. The project team will give lectures on research findings to the public, to high-school students, and broadly to other scientists. 2. The decline of Arctic sea ice exposes larger open water areas in the Arctic Basin and subpolar seas, enabling greater production of local wind driven ocean surface waves in the Arctic. In addition, thinner, less concentrated, and more fractured sea ice floes permit waves to propagate deeper into the sea ice pack. Sea ice floe are heavily fractured near the sea ice edge due to wave-induced flexural motion. Floes are also fractured in the interior of the sea ice pack from sea ice deformation driven by wind and current stresses. Heavily fractured sea ice can enhance lateral melt, which further accelerates the rate of sea ice decline. Observations have shown that the width of the wave-induced fracture zone varies by region and seasonal and extends up to a few hundred kilometers into the sea ice. The evolution of the sea ice cover and the near surface heat exchange of atmosphere and ocean depend on the geometric distribution of floes and the open water surrounding them. The distribution of floes has the greatest impact on the sea ice state near the edge, where ocean heat content tends to be greatest. Observations suggest that a single large storm can cause severe floe fracture and mix ocean heat upward into leads, subsequently accelerating the loss of sea ice area. The intellectual merit of this award is the furthering of wave-ice interaction theory and developments to a prognostic floe-size distribution of sea ice in a widely-used sea ice model. Improvements to wave attenuation in sea ice will also be made to a wave model. Objective methods to estimate parameters dynamically while combining models and observations with data assimilation will be employed. Code improvements to the floe-size distribution in sea ice and wave components will be incorporated into the Community Earth System Model, in fully-coupled mode. Simulations with these model advances will be the first ever to quantify the role of dynamical sea ice fracture in the coupled climate system. The new dynamics are expected to increase Arctic climate feedbacks and improve the predictive capability of the model. Increased sea ice feedbacks are expected to strengthen sea ice loss during Arctic storms, where winds are southerly on the eastern flank of storms. The model will permit new fundamental research about how sea ice floes evolve in the climate system. This work has broader impacts due to the importance of understanding past and future climate change from rising greenhouse gas concentrations and other climate forcings. Future projections of Arctic temperature, precipitation, ice mass balance and sea level rise are necessary to inform policy decisions. Simulating Arctic waves in sea ice is also important for predicting coastal erosion and hazardous coastal conditions. The project results will be disseminated by publishing in standard scientific journals. The project findings will contribute to the content of courses that the science team teaches on global warming, climate and climate change, ice and climate interactions, and climate modeling. The project team will give lectures on research findings to the public, to high-school students, and broadly to other scientists. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.