Storm-induced sea ice breakup and the implications for ice extent

Alison Kohout, Mike Williams, Sam Dean (NIWA) Mike Meylan, University of Newcastle, Australia

Motivation

• Assumed the amplitude of all waves decay exponentially in sea ice– Based on single site observations of small waves in

the Arctic in the late 1970’s and early 1980’s– Didn’t fit opportunistic observations

• Desire to understand sea ice changes in both polar regions

• Increased desire to forecast sea ice

The Experiment• Deploy wave buoys at multiple sites• Measure vertical acceleration integrate to get wave

height• Return FFT of 34 min of measurements every 3 hours• Buoys last up to 6 weeks• Analysis focuses on significant wave height (HS)

energywavetotalHs

Photo: Rob Johnson

Photo: Graham Oakley

The deployment

• All ice was first year ice (mean thickness: 0.75 m)

• All deployed on similar sized ice floes

• Floe size in the Marginal Ice Zone increased with distance from the ice edge

Variance

Solid line Dashed line

Types of decay

Calm Period Large wave event

Box Plot

Large wave events Calm periods

• Indications of non-linear wave-wave interactions• Possible explanation why linear theory fails

Ice breaking by waves

Storm waves have the capability to maintain floe

breaking potential hundreds of kilometres

from the ice edge

Relevance

Looked for a relationship in the Arctic, but had insufficient data to test

Note: axis is reversed

Future wave climate

• Climate Models predict that wave heights should increase everywhere at the sea ice edge

• This will be a negative feedback on extent

Historical period (1989-99) 2090-2100 RCP 8.5 2090-2100 RCP 4.5

Increases are over 1850 to 1870

Summary• New waves-in-ice data capturing both calm and storm events• Storm waves decay differently to small waves, can no longer

assume all waves decay exponentially• Predicts energy from waves propagates further

• Storm generated waves play a larger role in the breakup of sea ice than previously thought

• Significant wave height increases predicted in both Antarctic and Arctic, this may enhance sea ice retreat

Thanks to: • Captain and crew of the Aurora Australis• INPROD: Bill Penrose & Scott Penrose• Takenobu Toyota, Martin Doble, Vernon Squire• ACECRC• Australian Antarctic Division• Marsden Fund• Foundation for Research, Science and Technology (FRST)

Future work: • Minimize averaging and study each variable in deeper detail • Planning for another voyage in 2016• Deploying next generation of buoys with the plan to allow routine

deployment• Explore potential of extra sensors for both sea ice and other applications • Implementation of wave processes in sea ice models

Sea ice concentration