1. Edge of the Arctic multiyear ice @ 83.2N, 62.0E on August 14, 2007 Some thoughts on sea ice retreat in 2007 Takashi Kikuchi (& Jun Inoue) Institute of Observational Research for Global Change Japan Agency for Marine Earth Science and Technology IABP 18 annual meeting At CLS on June 16-18 2008

2. Photo during the USCGC Healy Trans-Arctic cruise between Aug.5 and Sept. 30, 2005 Sea Ice drift speed and Ocean-to-ice heat flux Takashi Kikuchi Institute of Observational Research for Global Change/ Japan Agency for Marine-earth Science and Technology (IORGC/JAMSTEC)

3. Photo during the USCGC Healy Trans-Arctic cruise between Aug.5 and Sept. 30, 2005 Ocean-to-Ice Heat Flux estimation (Kikuchi et al., in preparation) Ocean-to-Ice Heat Flux estimated by using ice-drifting buoy data (e.g., McPhee et al., 2003) ρ: water density, C p : specific heat of seawater, C H : bulk heat transfer coefficient, u *0 : internal friction velocity, δT: temperature above the freezing point κ: von Karman's constant (0.4), V: ice velocity relative to the surface geostrophic flow f: Coriolis parameter, z 0 : hydrographic roughness of the ice undersurface, A & B; constants for neutral static stability (with values 2.12 and 1.91, respectively). Polar Ocean Profiling System (POPS) J-CAD 6/2003 JAMSTEC Compact Arctic Drifter (J-CAD) POPS / 2006

4. Photo during the USCGC Healy Trans-Arctic cruise between Aug.5 and Sept. 30, 2005 Drifting tracks of JAMSTEC buoys deployed near the North Pole since 2000 NB NGR AB LR MB 7 days moving-averaged Ocean-to-Ice Heat Flux detected by J-CAD & POPS data Apr. May Jun. July Aug. Sept. Oct. Nov. Dec. Ocean-to-Ice Heat Flux estimation (Kikuchi et al., in preparation)

5. Ocean-to-Ice Heat Flux estimation Interannual variability in ocean- to-ice heat flux prior to NPEO period using 1979-2005 IABP sea ice motion data (upper panel). Lower panel: Interannual variability in ocean-to-ice heat flux in the Transpolar Drift region estimated by Krishfield and Perovich [2005] Sea ice drift speed in JJ is the most important indicators in determining the annual average ocean-to-ice heat flux. Increasing trend Decreasing trend

6. Courtesy of E. Hudson and C. Haas Trend of Ocean-to-Ice Heat Flux Perovich et al., 2008GRL. Fig.1 (Lower)

7. Conclusion Edge of the Arctic multiyear ice @ 83.2N, 62.0E on August 14, 2007 Apr. May Jun. July Aug. Sept. Oct. Nov. Dec. 1.42 W m -2 15cm 1.39 W m -2 15cm 1.52 W m -2 16cm 1.92 W m -2 21cm 2.89 W m -2 31cm 3.10 W m -2 35cm 1) Using ice-drifting buoy data, we examined ocean-to-ice heat flux ( H f ) in the Transpolar Drift since 2000. The yearly averaged H f was greater in 2000 and 2002 than in 2004-2006. 2) Sea ice drift speed in June and July is the most important factor in determining total heat input from the atmosphere to beneath sea ice during melting season. 3) We suggest that H f displayed an increasing trend before the early 1990s, but weakly decreasing trend after the mid 1990s until at least the mid-2000s.

8. However, ……….

9. Ice concentration of the Arctic Ocean on September 16, 2007. Note that the extent of Arctic summer sea ice in 2007 reached a record minimum. Picture was downloaded from NASA Earth Observatory web site http://earthobservatory.nasa.gov/ As everyone (might) knows, extent of Arctic summer sea ice in 2007 reached a record minimum. Minimum ice extent in September 1979~2000: 7.0 x 10 6 km 2 2005: 5.3 x 10 6 km 2 2007: 4.1 x 10 6 km 2 September sea ice extent [Updated Inoue and Kikuchi (2007,JMSJ)]

10. Minimum ice extent in September 1979~2000: 7.0 x 10 6 km 2 2005: 5.3 x 10 6 km 2 2007: 4.1 x 10 6 km 2 September sea ice extent [Updated Inoue and Kikuchi (2007,JMSJ)] Cf. Japan Is. : 0.38 x 10 6 km 2 * Note that ice reduction in 2007 from 2005 ice extent was about 2.8 times as large as the area of Japan Islands. What is the reason of sea ice reduction in 2007?

11. Ice concentration of the Arctic Ocean on September 16, 2007. Note that the extent of Arctic summer sea ice in 2007 reached a record minimum. Picture was downloaded from NASA Earth Observatory web site http://earthobservatory.nasa.gov/ As everyone (might) knows, extent of Arctic summer sea ice in 2007 reached a record minimum. 1. Thermodynamical reason Sea ice formation and melting Radiation, wind, cloud, snow, ice thickness, ocean heat content e.g., Shimada et al., 2006 GRL Catastrophic reduction of Arctic Sea Ice (Warming of the western Arctic Ocean) Perovich et al., 2008 GRL Sunlight, water, and ice: Extreme Arctic Sea ice melt during the summer of 2007 Inoue et al., 2008 JGR Transmittance of SW radiation through sea ice and melt pond 2. Dynamical reason Sea ice motion Wind and/or ocean current e.g., Inoue and Kikuchi, 2007 JMSJ Outflows of summertime Arctic sea ice

12. Transmittance of SW radiation through sea ice and melt pond Inoue, Kikuchi and Perovich [JGR 2008] Using XCTD and sea ice monitoring data during the Healy trans-Arctic cruise in 2005, we examined a relationship between sea ice condition (concentration, pond fraction) and ocean mixed-layer temperature and quantified transmittance of SW radiation through sea ice and melt pond. (Left) Panorama view of sea ice condition on August 14, 2005 at 78.2N, 153.5W. Inoue et al. [2008] Schematic of Inoue et al. [2008] 2007 4.1 million km 2 IPCC model Ice extent In September For reducing uncertainness of the model prediction of the Arctic ice condition…..

13. Edge of the Arctic multiyear ice @ 83.2N, 62.0E on August 14, 2007 Outflow of Summertime Arctic Sea Ice Observed by Ice Drifting Buoys and its Linkage with Ice Reduction and Atmospheric Circulation Patterns Inoue and Kikuchi [2007, JMSJ] J-CAD 6/2003 POPS / 2006 H L Color contours: Drifting trajectories for each year (thick line: June-September) Black contour: mean SLP from June to September 2005 Shading: anomalies of sea-ice in September 2005 relative to previous 5-year average In the summer of 2005, our drifting buoy went out from the Arctic Ocean with the fastest speed in the 2000s Siberian low Beaufort high and Siberian low pressure systems were dominant in 2005 summer. accelerated sea ice drift These systems made strong pressure gradient over the Transpolar Drift region and accelerated sea ice drift toward the Fram Strait.

14. Edge of the Arctic multiyear ice @ 83.2N, 62.0E on August 14, 2007 Summer SLP (JJAS) regressed on sea-ice extent in September Similar pattern emerged in summer 2005 Summer SLP change regressed on raw Arctic sea-ice extent in Sept. Strong SLP gradient between Canadian Basin & Siberia Ice Extent of the Arctic Ocean in September Summer SLP gradient over Transpolar Drift Sea ice decrease in the Arctic Ocean ↓ SLP decreasing trend over the Siberian shelf of the Arctic Ocean ↓ Produce strong pressure gradient over Transpolar Drift ↓ Enhance ice export from the Arctic Ocean 2005: SLP gradient had a maximum record !!

15. How was 2007 ? L L H Ice Extent of the Arctic Ocean in September Summer SLP gradient over Transpolar Drift Maximum SLP gradient AGAIN !! 7 Sea ice decrease in the Arctic Ocean ↓ SLP decreasing trend over the Siberian shelf of the Arctic Ocean ↓ Produce strong pressure gradient over Transpolar Drift ↓ Enhance ice export from the Arctic Ocean

16. L L H Strong SLP gradient accelerated Warm air & water advection !!

17. Ice concentration of the Arctic Ocean on September 16, 2007. Note that the extent of Arctic summer sea ice in 2007 reached a record minimum. Picture was downloaded from NASA Earth Observatory web site http://earthobservatory.nasa.gov/ As everyone (might) knows, extent of Arctic summer sea ice in 2007 reached a record minimum. Warming of the Arctic Ocean Outflow of sea ice