NSIDC June 3rd Update - Arctic Sea Still On Track For Extreme Melt - Includes May Summary

[hatrack]

June 3, 2008

Arctic sea ice still on track for extreme melt

Arctic sea ice extent has declined through the month of May as summer approaches. Daily ice extents in May continued to be below the long-term average and approached the low levels seen at this time last year. As discussed in our last posting, the spring ice cover is thin. One sign of thin and fairly weak ice is the formation of several polynyas in the ice pack.

A note on satellite update and intercalibration

The DMSP F13 satellite that has been central to our Arctic sea ice analysis for the past several years is nearing the end of its mission. As is standard data practice, we have transitioned to a newer sensor, in this case the DMSP F15. The DMSP F15 has the same type of sensor as the DMSP F13.

NSIDC has done preliminary intercalibration to assure consistency with the historical record. Further calibration and processing will be necessary, which may slightly affect final reported ice extent values (on average +/- 30,000 square kilometers or 11,600 square miles per preliminary number reported).

Overview of conditions

Arctic sea ice extent for May stood at 13.18 million square kilometers (5.09 million square miles), which is 0.28 million square kilometers (0.11 million square miles) greater than May 2007, but is still 0.42 million square kilometers (0.16 million square miles) less than the 1979 to 2000 average for the month.



EDIT

Multi-year ice continues to be low

The relative lack of thick, resilient multi-year ice in the Arctic discussed in earlier postings finds further support in the latest analysis from the United States National Ice Center (NIC). NIC uses a variety of satellite imagery, expert analysis, and other information to provide information on the amount and quality of sea ice for ships operating in the Arctic. NIC scientist Todd Arbetter suggests that much of the first-year ice is likely to melt by the end of summer, saying that despite the total ice extent appearing normal, the relative amount of multi-year ice going into this summer is very low when compared to climatological averages. NIC has found that the relative fraction of multi-year ice in the central Arctic has plummeted since the mid-1990s, creating an Arctic prone to increased melt in summer. Arbetter said, “This may be a primary reason for record summertime minimums in recent years.”

However, the unusual location of some of this year's first-year ice may help more of it survive than otherwise might be expected. This year, much of the first-year ice is farther north than normal, and those northern areas receive weaker solar radiation. So, northern first-year ice may be less vulnerable to melt than first-year ice in typical locations.



Thinner ice already showing weakness

As mentioned, the thin ice that covers much of the Arctic Ocean is showing signs of early breakup, with large polynyas off the coast of Alaska, the Canadian Archipelago, and Baffin Bay. Coastal polynyas are not unusual, at this time of year, but the polynyas we are currently seeing appear larger and more numerous than usual. This is partly because of the thinner, weaker ice cover.

Thorsten Markus at the NASA Goddard Space Flight Center has noted the size of the North Water polynya at the northern end of Baffin Bay, which typically forms in May. The polynya is much larger than normal, possibly nearing its largest area on record.

Inuit report that sea ice is starting to break up near Baffin Bay much earlier than normal this year. They have observed wide cracks in the ice already forming, according to NSIDC scientist Shari Gearheard, who lives and works in the Baffin Island hamlet of Clyde River.

Polynyas are a source of heat for the atmosphere in spring; in summer, however, they are large absorbers of solar energy. Resultant warm ocean surface waters then eat away at the ice edge, accelerating melt.



References

Francis, J.A. and E. Hunter. 2006. New insight into the disappearing Arctic sea ice. Eos, Trans. Amer. Geophys. Union 87,509-524.

Francis, J.A. and E. Hunter. 2007. Changes in the fabric of the Arctic’s greenhouse blanket. Environmental Research Letters 2, doi:10.1088/1748-9326/2/4/045011.

Markus, T. , and B.A. Burns. 1995. A method to estimate subpixel-scale coastal polynyas with satellite passive microwave data. J. Geophys. Res.100, 4473-4487.

END

http://nsidc.org/arcticseaicenews/index.html

[phantom power]

1. I'm kind of waiting to see what things look like in July.