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blumenkraft

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Re: Antarctic Icebergs
« Reply #200 on: February 21, 2020, 10:02:58 AM »
Looks like A68A bumped into something.

In today's SAR picture, you can see new small icebergs.

The GIF is showing yesterday's position with bathymetry.
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Tor Bejnar

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Re: Antarctic Icebergs
« Reply #201 on: February 21, 2020, 04:01:46 PM »
Polar View image from February 20 - two views (11% and 100% enlargement ["en-small-ment"].  11% view includes Elephant Island (etc.).  100% view is 'close up' of the 'calving'.  I agree it probably hit something.  GIF's bathymetry map from Researchgate.
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baking

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Re: Antarctic Icebergs
« Reply #202 on: February 21, 2020, 04:12:25 PM »
Looks like A68A bumped into something.
A two and a half year old iceberg can break apart without bumping into anything.  Bathymetry without depth measurements isn't really bathymetry.  I doubt there is anything at that location shallow enough to cause a grounding.

blumenkraft

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Re: Antarctic Icebergs
« Reply #203 on: February 21, 2020, 05:20:27 PM »
Baking, your opinion, your knowledge is very valuable to me.

But here i'm pretty sure you are wrong. It's snaking along this underwater mountain for weeks and months now. It's amazingly obvious to me that it had a big say in the route the iceburg was taking.

Of course, you are right the iceberg can lose parts at any time, but look at this debris. It's not just one part breaking up randomly. It's multiple parts as if it hit something.

Quote
Bathymetry without depth measurements isn't really bathymetry

Could you elaborate on that one, please? Not sure i understand. Is the NASA bathymetry map wrong?
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baking

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Re: Antarctic Icebergs
« Reply #204 on: February 21, 2020, 11:55:15 PM »
Could you elaborate on that one, please? Not sure i understand. Is the NASA bathymetry map wrong?
It's not wrong, it's just not labeled with any depth measurements.  The area where the break-off occurred was in water more than 800 meters deep.  There is no way that any part of the iceberg is much deeper than 300 meters, or it never would have left the shelf.

blumenkraft

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Re: Antarctic Icebergs
« Reply #205 on: February 22, 2020, 08:05:48 AM »
Yes, A68A is thinner than 300m. According to turned over icebergs it lost it's rather 200-250 meters thick. (https://forum.arctic-sea-ice.net/index.php/topic,2245.msg241647.html#msg241647)

And you are also right, the waters there are deeper in the east. But on it's western side, where the breakoff occurred there is an underwater mountain in the map.

How do you rule out that it can have peaks that are, say 200m below the surface?

Sorry, Baking, i honestly don't understand where you are coming from. I clearly see an underwater mountain in the bathymetry map and really don't understand your opposition.

Given the track the iceberg took, the alignment if the bathymetry map must be wrong, but only by a smidgeon. If you move the bathymetry map only a little to the right, all the movement of A68A makes total sense.

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baking

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Re: Antarctic Icebergs
« Reply #206 on: February 22, 2020, 03:49:45 PM »
How do you rule out that it can have peaks that are, say 200m below the surface?
Unless I completely misunderstand how bathymetry charts work, when it says 800 meters or more deep, that is what I assume.  If there is a peak, it is still 800 meters or more deep, not 200.  Yes if you move the map a little it will be shallower, but that isn't where the iceberg is.  Find a single chart with depth measurements that supports your conclusion.  I cannot.

Bathymetry maps are designed for sailors who might want to stay away from shallow water or for fishing boats who don't want to lose their nets on underwater formations.  Or maybe even submarines.  If a chart says 800 meters or deep there isn't an asterisk that says "on average" or some such nonsense.  The users of those charts want to know the minimum depth in the area.  That is their primary purpose.

blumenkraft

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Re: Antarctic Icebergs
« Reply #207 on: February 22, 2020, 04:03:58 PM »
Baking, thanks for your answer.

Here is a bathymetry map with a deepness scale (we don't have that with the NASA Blue Marple layer on EO-Browser). The track of the iceburg was following that red dotted line (ocean current) quite accurately. And this map claims 0-250m water depth for the western side of A68A. This fits my theory quite well IMHO.

« Last Edit: February 22, 2020, 08:51:43 PM by blumenkraft »
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baking

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Re: Antarctic Icebergs
« Reply #208 on: February 22, 2020, 04:53:33 PM »
Unfortunately, the iceberg is well off that map so it is useless.  The map I used is below.

EDIT:  Added bonus, the map below uses the same projection as PolarView so you only need to scale the images to overlay them.

blumenkraft

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Re: Antarctic Icebergs
« Reply #209 on: February 22, 2020, 05:06:04 PM »
Baking, i saw this map when i googled bathymetry maps. I dismissed it because the 0-400m scale tells us absolutely nothing since the iceberg wouldn't go that deep, even if we assume maximum thickness.
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oren

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Re: Antarctic Icebergs
« Reply #210 on: February 22, 2020, 05:29:14 PM »
Interesting argument.
Baking and BL, are you able to put the iceberg's contour overlaid on any of these maps? I'm afraid I am clueless as to its current location.

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Re: Antarctic Icebergs
« Reply #211 on: February 22, 2020, 06:21:40 PM »
Interesting argument.
Baking and BL, are you able to put the iceberg's contour overlaid on any of these maps? I'm afraid I am clueless as to its current location.
It is a huge PITA to scale these maps, but here it is on the day of the break-off.  The point in question is the Northwestern corner.

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Re: Antarctic Icebergs
« Reply #212 on: February 22, 2020, 06:30:41 PM »
are you able to put the iceberg's contour overlaid on any of these maps

Hell no!  ;D

Just tried my Gimp luck. It's not my lucky day i guess.

I will try again, but no guarantee.
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Tor Bejnar

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Re: Antarctic Icebergs
« Reply #213 on: February 22, 2020, 06:34:37 PM »
Just curious if I'm on "Ignore", 'cause my GIF in Post 201 (above) attempted to overlay a ice island PolarView image with a 'bathymetry' map (albeit there are better maps to be had - I just didn't find one).
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blumenkraft

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Re: Antarctic Icebergs
« Reply #214 on: February 22, 2020, 06:36:32 PM »
Could you do it with the map i provided above, Tor?
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Tor Bejnar

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Re: Antarctic Icebergs
« Reply #215 on: February 22, 2020, 06:56:51 PM »
I'd do it on Baking's map too, but I don't have the technology at home (same map projection, per Baking). 

I also want to compare ice island shape 'before' and 'after'.  The February 21 PolarView image shows very distinct edges.  Attempting to do this with the Feb. 20 image suggested smaller calvings in other areas than the obvious one (forward left corner), but that image doesn't have such sharp edges delineated.  Also, comparing 3 or 4 PolarView images in a GIF might suggest the ice island's movement was 'adjusted' by [what I'm convinced was] the impact with a seamount (or shoal). 

A 100 m deep (shallow) rock would not affect the navigation of any boat, I would think, so not a big issue for shipping concerns, not that there is any 'shipping' in these waters...
« Last Edit: February 22, 2020, 07:06:23 PM by Tor Bejnar »
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baking

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Re: Antarctic Icebergs
« Reply #216 on: February 22, 2020, 07:07:04 PM »
Just curious if I'm on "Ignore", 'cause my GIF in Post 201 (above) attempted to overlay a ice island PolarView image with a 'bathymetry' map (albeit there are better maps to be had - I just didn't find one).
Different projections, not triangulated, the scale looked off from what I had done on my own, and no depth measurements.  In short, I didn't trust it and it provided no new information.  Sorry.

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Re: Antarctic Icebergs
« Reply #217 on: February 22, 2020, 07:18:04 PM »
Odd we can have such a contentious discussion about something that is just the "tip of an iceberg".  ;)

baking

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Re: Antarctic Icebergs
« Reply #218 on: February 22, 2020, 07:27:38 PM »
Could you do it with the map i provided above, Tor?
If you really must do it with that projection, at least use the map below which extends to the area where the iceberg actually is and has more detailed bathymetry.

But you are going to need to scale it AND rotate it and it will STILL be wrong because of the different projection.  You will however get the same result as I did.

Kavanaugh 2015 "Effect of continental shelf canyons on phytoplankton biomass and community composition along the western Antarctic Peninsula"

blumenkraft

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Re: Antarctic Icebergs
« Reply #219 on: February 22, 2020, 07:50:13 PM »
+1!

This one is better!
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Tor Bejnar

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Re: Antarctic Icebergs
« Reply #220 on: February 22, 2020, 07:54:43 PM »
Thanks for saying , Baking. 

I agree with the 'different projections' issue, however I wonder if scale makes it somewhat less an issue - but better to use the same map projection, for sure. 

As to triangulation, the two islands show on both map and image, and were aligned on a 3x enlargement of the images, albeit the map had very blurry island corners then, and I'll agree the triangulation points (island locations not 'surrounding' the iceberg location) was less then ideal.  I think I should use a screen print of the PolarView map that shows 'all' the image locations to have many more points to overlap a bathymetry map.

Better, the red ice island outline, also placed on the 3x enlargement, was drawn on a full-computer-screen-width ice island image (from a week ago), and at the size reduction in the final, the differences are a pixel here and there.   
« Last Edit: February 22, 2020, 09:24:19 PM by Tor Bejnar »
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Tor Bejnar

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Re: Antarctic Icebergs
« Reply #221 on: February 22, 2020, 09:23:01 PM »
Nautical chart of South Shetland Islands (including Elephant Island)

That "364" spot looks to be about where I place the "point of contact".  What are the units? Feet
« Last Edit: February 22, 2020, 09:33:55 PM by Tor Bejnar »
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blumenkraft

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Re: Antarctic Icebergs
« Reply #222 on: February 22, 2020, 09:29:03 PM »
There you have it, folks. 128 meters is shallow enough for my theory! \o/  8)
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baking

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Re: Antarctic Icebergs
« Reply #223 on: February 22, 2020, 10:34:03 PM »
Or fathoms.

Tor Bejnar

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Re: Antarctic Icebergs
« Reply #224 on: February 22, 2020, 11:38:19 PM »
Baking,
I wondered too, so I searched the website with the nautical map and found (and provided a screen print above) the scale.  Apparently you can purchase the map with the scale in "metres", feet or fathoms.
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Re: Antarctic Icebergs
« Reply #225 on: February 23, 2020, 12:08:40 AM »
Baking,
I wondered too, so I searched the website with the nautical map and found (and provided a screen print above) the scale.  Apparently you can purchase the map with the scale in "metres", feet or fathoms.
No, changing that setting doesn't change the map.

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Re: Antarctic Icebergs
« Reply #226 on: February 23, 2020, 12:17:34 AM »
Just keep scrolling, down and to the left, down and to the left . . .

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Re: Antarctic Icebergs
« Reply #227 on: February 23, 2020, 01:50:35 AM »
Hmmm,
First, when I click on the three-bars button in the upper left corner, it indicates "feet".  That window indicates one can purchase the map in meters, fathoms or feet.  Yes, changing the units drop-down box and clicking "Apply" doesn't change the numbers on the map.

Second, when I scroll the linked map over to New Zealand (or England/France), I note near-shore contours of "98.4" and "164".  These, if in feet, convert to 30 m and 50 m.  But who's to say one part of the world map uses the same scale as another?  (But it is suggestive!)  Some detailed areas of the map show no contours; around Elephant Island there are contours in even thousands, and one at "200".  Around Germany I identified a contour at "65.6" which, if in feet, converts to 20 m.

Scrolling on what gives that paper, Baking?  (Scrolling the map down takes me to mid-Antarctica [and no further], and scrolling left takes me around the world until I'm dizzy.)

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baking

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Re: Antarctic Icebergs
« Reply #228 on: February 23, 2020, 05:58:01 AM »
Scrolling on what gives that paper, Baking?  (Scrolling the map down takes me to mid-Antarctica [and no further], and scrolling left takes me around the world until I'm dizzy.)

Just follow the East coast of the Antarctic Peninsula.

Tor Bejnar

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Re: Antarctic Icebergs
« Reply #229 on: February 23, 2020, 06:56:09 AM »
Thanks, Baking; found it!  It seems you have to scroll at the 'right' enlargement to see 'the paper'  The two named islands (Brabant and Adelaide) are on the west side of the Antarctic Peninsula, west (and south) of the area we're interested in.  It does make things confusing, given that water depths are clearly in feet elsewhere.  The area covered by that 'paper' is tiny compared to the world which the map covers.
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baking

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Re: Antarctic Icebergs
« Reply #230 on: February 23, 2020, 04:17:05 PM »

baking

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Re: Antarctic Icebergs
« Reply #231 on: February 23, 2020, 04:33:26 PM »
Look at the shallows surrounding Bransfield Island.  Using standard chartmaking practice, depths less than ten fathoms are shown as fathomsfeet.  E.g. 74 is 7 fathoms and 4 feet, 32 is 3 fathoms and 2 feet, and even 02 which is 0 fathoms and 2 feet.  This is the only time feet are used to show depth on this chart.

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Re: Antarctic Icebergs
« Reply #232 on: February 23, 2020, 11:21:12 PM »
Thank you, Baking - excellent evidence of fathoms being used, there (and even just NE of d'Urville I.).  This area that includes fathom depths is in a box with a "(see Note-POSITIONS) 225" associated with it.  The Elephant Island area is not in this box.  Just below the right corner of this box is some information about high tides and low tides, duplicated below. (it includes a "bay" which wouldn't normally have any 'above 0' heights; obviously the islands would, but the chart is about tides.)

Please explain the "98.4", "164" and "65.6" contours referenced in Reply #227!

And why would A68-A have a calving event right above a seamount whose peak was significantly below the bottom of the ice island?
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Tor Bejnar

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Re: Antarctic Icebergs
« Reply #233 on: February 23, 2020, 11:27:12 PM »
Here's another information box, identifying tides in meters, whereas the previous one was in feet.
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Tor Bejnar

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Re: Antarctic Icebergs
« Reply #234 on: February 23, 2020, 11:39:20 PM »
Near the South Orkney Islands is an explanation box that includes "Soundings in fathoms" (etc.) but there is a little area in blue with a "656.2" contour. 656.2 feet just happens to equal 200.01 m.

Does anybody know what that pop-up box in upper left corner means? "DEPARE (656.17 ft - 3280.84 ft) [Depth area]" might be associated with areas in blue.  (656.17 feet is 200.000616 meters.  3280.84 is 1000 meters.)
« Last Edit: February 23, 2020, 11:55:37 PM by Tor Bejnar »
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uniquorn

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Re: Antarctic Icebergs
« Reply #235 on: February 23, 2020, 11:54:24 PM »
https://www.gmrt.org/GMRTMapTool/sp/
may be helpful, zoom in and hover over location, lat/lon/elevation bottom left

baking

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Re: Antarctic Icebergs
« Reply #236 on: Today at 02:53:27 AM »
Please explain the "98.4", "164" and "65.6" contours referenced in Reply #227!

And why would A68-A have a calving event right above a seamount whose peak was significantly below the bottom of the ice island?
I was not the person who found this website.  It is quite bizarre and I can't explain why they do what they do.  I'm only referencing the depth soundings on this particular source map where we have multiple sources for the bathymetry that agree with the units being fathoms.

I agree there is an underwater peak.  I have posted an image of the peak in a more detailed map shown in my GIF, but as I have said repeatedly:

1.  The peak is too deep to have caused a collision with the Iceberg,

AND

2.  The peak is too far South and is NOT at the site of the break-off.

I explained that the iceberg is 2 and a half years old and will certainly continue to have calving events at any time.  I think it is up to you guys to explain why you think that a peak that is clearly too deep and not even at the location of the supposed collision could be the cause.

I know you guys are stubborn, but this is really too much.