TerryM Posted June 16, 2012 Share Posted June 16, 2012 'Blue' ice - although on my monitor it appears more as turquoise, seems to be coming more prevalent each year in the Arctic. The most popular interpretation seems to be that it's melt ponds reflecting back into our eyes in the sky, but I have difficulty with this on a couple of grounds. Blue ice areas seem to revert to white ice over time even though temperatures remain well above freezing. Some areas never form blue ice, even though temperatures are high enough to form melt ponds Blue ice remains even as pieces break away from fast ice formations and drift with the current. I think the coloration has something to do with algae, or some other form of beasty growing on the bottom side of otherwise clear ice. Clear ice without snow covering is necessary to see it, and the ice must be quite thin or it would not be visible. I've noticed regions where blue ice has white blotches that conform with MYI chunks that were frozen in place last August - mainly in the fiords in Northern Greenland - as this was an area I was watching intently at the end of last years melt. I don't know whether the lack of coloration is because of a deeper keel on these chunks, or because they may stand above the surface of the surrounding blue ice. I don't think it's impossible that methane seeps have some contribution to blue ice. The thought process is that methane is gobbled by methanophiles, which are subsequently eaten by some form of phytoplankton (with a nice blue/green coloration). The oxygen produced by the phytoplankton is deadly to the methanophlies, which eventually leads to the demise of the phytoplankton unless other nutrients are available. At any rate I think it could make for an interesting topic. The suppositions above are my present interpretation of what I'm seeing, and I'm certainly open to divergent views. Terry Link to comment Share on other sites More sharing options...
Vergent Posted June 16, 2012 Share Posted June 16, 2012 The pixel size on satellite images is in the 1-4 km range. So melt ponds will definitely tint the pixel blue. But the ice itself can appear blue because water has more absorption in the red and yellow than in the blue. This ratio is temperature dependent. Light must have a rather long path length through the ice for the color to be strong. The ice must be free of compacted snow and of bubbles. Ice can also appear blue due to lighting conditions. If snow covered ice is in the shadow of a cloud, but otherwise exposed to the blue sky, just like the snow in shadow on a clear day, it will appear blue because it is reflecting the sky. Link to comment Share on other sites More sharing options...
TerryM Posted June 17, 2012 Author Share Posted June 17, 2012 Verg I'm sure that melt ponds are part of the mix, but I'd ask you to check the area near Chaunskaka Gulf using Arctic.io at a medium zoom. Chaunskaka Gulf is found at the east end of the ESAS. Set the date to the 15th, then flash back a week to the 8th. Can you think of a scenario where all the melt ponds would simultaneously drain while the ice sheet itself remains in tact? Similar areas exist all the way to the delta of the Lena, and MODIS shows the same effect even when zoomed in tight using either sat. Terry Link to comment Share on other sites More sharing options...
dabize Posted June 18, 2012 Share Posted June 18, 2012 Slightly off topic, but triggered by the discussion of melt ponding and the apparent discrepancy induced in SIA measurements, which are thought to mistake melt ponds for open water (connection - both have relatively low albedo and may look blue). Couldn't one use SST as a clue as to whether a site is a melt pond or open sea? Melt ponds would have to be within 1 degree C or so of freezing, whereas seawater could be significantly warmer - and apparently is, according to the SST anomaly maps.. I suppose the hitch here is that the satellites that take light based images are not necessarily the same ones that record SST...... Even so, it might be useful as a post hoc correction for the SIA datasets....... Link to comment Share on other sites More sharing options...
TerryM Posted June 18, 2012 Author Share Posted June 18, 2012 Dabize Not off topic at all - While I may be looking for alternative explanations for the coloration, anything concerning blue ice is definitely on topic. How warm can melt ponds get, remembering that they're open water in an ice lined bowl. My assumption is that most are relatively shallow, fresher than the ice around them due to snow melt and precipitation, and subject to continuous solar radiation at this time of year. Any wind present would disturb thermal stratification and add evaporative cooling. Rather than attaining high temperatures, I would assume that the melt pond would increase both it's surface area and depth, in fact the only paper I found addressing melt pond temperatures emphasized that differences were so small that thermistors accurate to .01C were needed to detect them. https://docs.google.com/viewer?a=v&q=cache:4-7FK1sG4g8J:journal.polar.gov.cn/CN/article/downloadArticleFile.do%3FattachType%3DPDF%26id%3D10122+&hl=en&gl=ca&pid=bl&srcid=ADGEEShXuwYuFZK-gSTuTRIHn_Wzhj2kh_LqjTeJ0L87vFWEqMO_S-FejSWPhGYC8qHNZ7rYnN39kHgVQJiV9Cn0CZpugHjSEDtmnzc5C6cKoiVPNx2aCQPkr9xqXKFYzx8uwYYay3qk&sig=AHIEtbQIxPKAh4nEwn57vYSbHakJmCHtJA NOAA seems to be indicating melt pond temperatures of 0C to +2C south of Victoria Island and open water temperatures of less than -1.5C in James Bay. Environment Canada's Visual & Topographic feed shows James Bay as basically ice free. DMI seems unable to distinguish any temperature difference between open sea water (NEW polynya) and melt ponds (Independence Fjord). Not sure that SST's, at least with the measurements we're getting now would be much of an improvement for determining sea ice cover. Terry Link to comment Share on other sites More sharing options...
dabize Posted June 18, 2012 Share Posted June 18, 2012 Not sure that SST's, at least with the measurements we're getting now would be much of an improvement for determining sea ice cover. Terry The reason I asked is that the anomaly maps at the Sea Ice blog link http://ocean.dmi.dk/arctic/satellite/index.uk.php seem to be able to distinguish an anomaly that appears at a point close to the ice edge from ice itself, which appears dead white on the linked graphic. This does look as if SST can be used to distinguish ice from non-ice, even if the difference is relatively small. Maybe this is a matter of scale, and the "melt pond artifact" kicks in only at a finer level of resolution than can be distinguished by SST. Link to comment Share on other sites More sharing options...
TerryM Posted June 18, 2012 Author Share Posted June 18, 2012 I think the point I was trying to make is that the SST's don't distinguish between melt ponds and open water, although I'm due to have a cataract operation and may not be able to distinguish between similar shadings. Terry Link to comment Share on other sites More sharing options...
Vergent Posted June 18, 2012 Share Posted June 18, 2012 Verg I'm sure that melt ponds are part of the mix, but I'd ask you to check the area near Chaunskaka Gulf using Arctic.io at a medium zoom. Chaunskaka Gulf is found at the east end of the ESAS. Set the date to the 15th, then flash back a week to the 8th. Can you think of a scenario where all the melt ponds would simultaneously drain while the ice sheet itself remains in tact? Similar areas exist all the way to the delta of the Lena, and MODIS shows the same effect even when zoomed in tight using either sat. Terry A couple of things: On the 15th there were high light clouds, quite visable if you look at the other bands. Air quality, aerosols, etc is significantly effects the blue end of the spectrum. Here in L.A. the sky is seldom deep blue. Up at mount Wilson, nearly always deep blue. Remember the atmosphere is an ever changing filter. Remember the light the satellites see goes through the filter twice. Link to comment Share on other sites More sharing options...
TerryM Posted June 18, 2012 Author Share Posted June 18, 2012 A couple of things: On the 15th there were high light clouds, quite visable if you look at the other bands. Air quality, aerosols, etc is significantly effects the blue end of the spectrum. Here in L.A. the sky is seldom deep blue. Up at mount Wilson, nearly always deep blue. Remember the atmosphere is an ever changing filter. Remember the light the satellites see goes through the filter twice. A little OT, but I've still got a home in Riverside, and remember it before the smog started flowing in, and then years later when it cleared up enough to see that their were mountains all around. I'll check some dates around the 15th to see how things look. One of the advantages of this topic is that with MODIS we can look back for years trying to find patterns, and even after freeze-up, when things slow way down, we'll be able to debate the subject. Do you consider the melt ponds to be stable, or deep enough to survive even when quite small chunks of ice have broken free of the pack and are subject to wave action? Terry Link to comment Share on other sites More sharing options...
Vergent Posted June 19, 2012 Share Posted June 19, 2012 A little OT, but I've still got a home in Riverside, and remember it before the smog started flowing in, and then years later when it cleared up enough to see that their were mountains all around. I'll check some dates around the 15th to see how things look. One of the advantages of this topic is that with MODIS we can look back for years trying to find patterns, and even after freeze-up, when things slow way down, we'll be able to debate the subject. Do you consider the melt ponds to be stable, or deep enough to survive even when quite small chunks of ice have broken free of the pack and are subject to wave action? Terry The Healy web cam archive from last year shows that melt-ponds and melt holes were ubiquitous last year. http://icefloe.net/Aloftcon_Photos/index.php?album=2011 Once they are deeper than the draft of the ice sheet they are stable. Wave action only applies to the edge, if there was wave action sufficient to empty them, they would be refilled with salt water over-wash from the waves. I do not recall seeing any high and dry empty melt ponds except at the pole cams, that were placed on a piece of calved ice shelf. It was quite unique. The Healy didn't see any ice that thick. Link to comment Share on other sites More sharing options...
TerryM Posted June 19, 2012 Author Share Posted June 19, 2012 The Healy web cam archive from last year shows that melt-ponds and melt holes were ubiquitous last year. http://icefloe.net/Aloftcon_Photos/index.php?album=2011 Once they are deeper than the draft of the ice sheet they are stable. Wave action only applies to the edge, if there was wave action sufficient to empty them, they would be refilled with salt water over-wash from the waves. I do not recall seeing any high and dry empty melt ponds except at the pole cams, that were placed on a piece of calved ice shelf. It was quite unique. The Healy didn't see any ice that thick. The study I linked to earlier mentioned melt ponds capped with a thin layer of clear ice. This could keep the water in place even if severe wave action was tossing a chunk around. The empty melt pond you recall from last year. Is there a chance that it simply dug itself a hole and drained into the sea? I still haven't spent the time to dig through the MODIS images in the ESS region, but I was wondering if in your reference to atmospheric smog etc. you were expecting the areas to show as darker(bluer) ice or whiter (faded) ice. Either way if the color of the ice is effected, the color of surrounding areas should also be impacted. Terry Link to comment Share on other sites More sharing options...
TerryM Posted June 21, 2012 Author Share Posted June 21, 2012 Over the past couple of days I've been convinced that my theory is completely wrong. No excuses, I just looked at the evidence and drew the wrong conclusion. The correct sequence is freeze-up (white), growing melt ponds (blue) drained melt ponds = rotten ice (grey). Sorry if I lead any on a goose chase. Terry Link to comment Share on other sites More sharing options...
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