9/19 - Arctic Ice Still Has Not Hit Minimum - "Unusual Polynya" Discussion

[hatrack]

Overview of current sea ice conditions
Current sea ice conditions have been fluctuating downward since our last update; as of yesterday afternoon, we have not yet reached the sea ice minimum. If sea ice were to stop melting now, 2006 would hold fourth place for the September minimum. For more details, see below. Sea ice data are obtained from satellites; see Frequently Asked Questions for more about data sources.

Figure 1: Sea ice extent for September 18, 2006



Current sea ice conditions: September 18, 2006

As compared to the last report, the polynya in the Beaufort Sea has opened (Figure 1). For more details, see Figure 3, below.

Some areas of the ocean show evidence of new ice formation as autumn cooling begins to take hold. However, at the same time, some areas south of the polynya that were formerly ice covered have continued to melt out. Total Arctic sea ice extent has declined slightly as compared to the last report, but we are probably close to the turning point in the season.

White indicates areas where sea ice is present. Areas in blue are open ocean, while gray indicates land masses. The pink line shows the average ice extent for September, the end of the summer melt season. The September average is calculated from 1979 through 2000.

Current sea ice conditions in context

Figure 2: Summer melt season Arctic sea ice extent



Figure 2 shows an updated time series. If current conditions represent the end of the melt season, then the September 2006 sea ice minimum would now be the fourth lowest on record (5.758 million square kilometers, or 2.22 million square miles), barely beating 2004 (5.812 million square kilometers, or 2.24 million square miles). What happens in the next week will represent a race between new ice formation in some areas and continued melt in others.

Interestingly, while the chances seem low that September 2006 will set a new record for ice extent, it is close to upsetting 2002 as the record low in terms of ice area. Ice extent is based on summing all regions with at least 15% ice concentration (15% ice and 85% open water). Ice area is the total area of ice once open water areas are removed from the calculation. In other words, ice area can be thought of as the total area of ice if it were squished together so there were no gaps.

A new record low for sea ice area would indicate that the ice pack as a whole is spread out. Much of this diffuse, low-concentration ice is in the vicinity of the polynya. See Figure 3, below, for more details on the polynya.

More on the Unusual Polynya

Figure 3: Polynya on September 11, 2006



The polynya mentioned in our previous reports, is extremely unusual. The only time we've seen a similar polynya was in 2000. However, the 2000 formation was much smaller and closer to the ice edge, barely enclosed with ice.

To get a better idea of what the ice near the Beaufort Sea polynya looks like, we used an image from a satellite sensor that is different than the one used to generate Figure 1. The sensor, called the Moderate Resolution Imaging Spectroradiometer (MODIS), flies on the NASA Terra and Aqua satellites.

Figure 3 is a MODIS image from September 11, 2006, at 11:00 pm Greenwich Meridian Time, chosen because of nearly cloud-free conditions. Green outlines show the north coast of Alaska, ruddy with autumn color. The red box encloses the ice just south of the polynya; the polynya itself is the dark shape in the ice just to the north (right) of the red box.

The bluish tint of the ice near the polynya indicates that the ice is wet from surface melting. Cooler weather in the next several days may slow or stop the melting.

For images of the polynya from yet another NASA sensor, visit the Daily Updated AMSR-E Sea Ice Maps Web site.

EDIT/END

http://nsidc.org/news/press/2006_seaiceminimum/20060816_arcticseaicenews.html

NOTE: Check the same page for the high-resolution image of the polynya - I'd include it here, but it's awfully big.

[phantom power]

1. Is anybody looking for some kind of warm-water upwelling?

[hatrack]

2. There's been an anomaly near Svalbard for about 5 years now

It's grown in intensity, esp. in 2005 - but whether an upwelling issue, I can't remember. It's in AGU - I'll have to look up just what they think the mechanism.