Arctic sea ice melt in summer 2007: Sunlight, water, and ice NSIDC Sept 2007

A long list of suspects Examine the mass balance of the ice Warmer air temperature Longer melt season Winds Export of perennial ice Advection of ocean heat Clouds Enhanced solar heating Ice albedo feedback

Sea ice mass balance Simple, but powerful observation Simple concept ice growth surface melt bottom melt Equipment ablation stakes and thickness gauges autonomous buoys Powerful tool – attributes change Above Below

Monitoring the mass balance Observations in Beaufort and North Pole

Summer ice melt Interannual variability, latitude influence on surface melt

Summer ice melt 2007 at North Pole – typical melt

Summer ice melt 2007 Beaufort – typical surface melt

Summer ice melt 2007 Beaufort – huge increase in bottom melt

Beaufort Sea buoy End of August – peak bottom melt km August 27

Beaufort Sea buoy End of August – peak bottom melt km August 27 Warmer air temperature Longer melt season Winds Export of perennial ice Advection of ocean heat Clouds Enhanced solar heating Ice albedo feedback

Estimate of solar heating Incident solar, ice concentration, and albedo -> heat input F ocn = F r (1 –  ) (1 – C) Input: 25 x 25 km equal area grid Incident (F r ) from ERA-40, ECMWF Ice concentration (C) - SSMI Water albedo (  ) = 0.07 Output: Solar input to the ocean (F ocn ) Neglect ice for now

Mean annual input: 1979 – 2005 Ice edge evident, concentric rings from solar input MJ m -2 3 MJ m -2 = 1 cm m -2 of ice melt

Percent anomaly in 2007 Heat input near buoy 400 to 500 % greater through 22 Sept Percent

2007 vs “climatology” Similar incident shortwave, but much less ice

Solar heat input Total heat needed for bottom melting

Solar heat input Twice as much solar heat even without ice transmitted

Conclusions Was there a trigger? North Pole business as usual Beaufort Sea typical surface melt huge bottom melt Solar incident comparable Ice concentration much less Solar input twice melt Ice albedo feedback

…

Solar heat input Peak ocean heat flux with ice convergence/divergence

Total solar heat input to ocean Heat input near buoy from 600 to 800 MJ m -2 through 22 Sept 2007 Units = MJ m -2 3 MJ m -2 ~ 1 cm thinning

Percent anomaly in 2007 General increase

Incident shortwave anomaly Not much of a difference Incident shortwave from reanalysis Pan – Arctic Ocean 25 x 25 km equal area grid Average 1979 – 2005 (2007 – average) % anomaly %

27 year trend of annual ocean solar heat input Units are percent per year Increasing solar heat input in 89% of area