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Author Topic: Pine Island Glacier (PIG) Calving and Discussion  (Read 489521 times)

baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2700 on: February 27, 2021, 03:03:22 AM »
This video of the Amundsen Sea Embayment shows that it was frozen throughout 2018.  Also, there doesn't seem to be a strong seasonal component, with half of the winters never freezing over.  Since 2015, it froze solid in the winter of 2017 through the winter of 2018 and again in 2020.

All I can say for sure is that once it freezes, it stays frozen for a while and once it breaks up it takes a while to refreeze.  I don't know that it is a cycle as much as a hysteresis effect.


interstitial

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2701 on: February 27, 2021, 06:27:56 AM »
Thanks baking more to think about.

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2702 on: February 27, 2021, 04:01:49 PM »
I think that we have to differentiate between the two problems: the presence of the polynias opposite the PIG and the clearing of the sea ice of the Admunsen Bay opposite the PIG.
Indeed, if the second phenomenon clearly and mainly depends on the outgoing currents (ex CDW), the first is influenced by these currents, but it depends above all on many other factors: weather conditions and currents in the Admunsen Bay.
I had already presented statistics from 2001 to 2019 based on the Modis archives, but to make them more readable I present them graphically: for each month, if there is at least one readable image, I display the status of the image with the most ice free, the status being :
> Not polynyas
> Presence of one to three polynyas
> Presence of a unique and widespread polynya from NSM to SSM
> Admunsen ice-free bay in front of the PIG
I also give examples for these statutes

In a future post I will present the analysis of this year's polynyas.


Click to enlarge 


EDIT: As I mentioned in the previous post, the first decade is the one in which the CDW and the retreat of the grounding line is strongest.

EDIT2 the white boxes correspond to the months for which I don't have any pictures.
« Last Edit: February 27, 2021, 04:08:44 PM by paolo »

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2703 on: March 01, 2021, 10:59:21 PM »
I have already presented summary statistics on the complete clearing of sea ice in front of the PIG front or, alternatively, on the presence of polynyas.
We have seen that the presence of sea ice all year round in front of the PIG is not exceptional, far from it. This presence depends on meteorological factors related to Amundsen Bay: atmospheric conditions, sea surface conditions: sea currents, temperature, salinity, etc., factors which largely escape us: no information on the current situation, not to mention their history ...

But the presence of sea ice has the advantage for us to highlight the polynias which inform us about the outgoing currents: the warm waters of the CDW which, after melting the ice platform in the grounding line zone, rise to the surface by licking the bottom of the ice shelf and continuing in their melting action (clearly their temperature decreases during the return trip, their thermal energy being spent in the melting of the ice shelf.
Clearly in the analysis of the images it is also necessary to take into account elements that can hinder the formation of polynyas:
> presence of thick sea ice, or even worse, presence of a dense mélange of ice and icebergs (no melting possible, nor displacement)
> calvings refilling existing polynyas with an ice mélange (the creation of polynyas always has to be started again)
These two elements are particularly present this year:
> NSM: high frequency of calving (Note: the ice mélange is then moved by surface currents towards the centre where it will contrast the formation of polynyas also in this sector)
> SSM: large calvings that have saturated the sea in front of a thick mélange of ice and icebergs

Using the Sentinel1 images I made statistics on the presence of polynyas from 04/07/20 to 23/02/21 (see first image).

NSM side (see second image) : Following the retreat of the front we currently have two distinct areas of polynya formation :
> NIS: the formation zone is located west of the Ice Rise Evan's knoll: the zone is invaded from time to time in the west by sea ice pushed by the currents and in the east by frequent calving on the MNS side, but the polynyas are very present in time.
> NSM: the action of the outgoing current is indeed there, but it is thwarted by calving and by the presence of a thick mixture of ice and icebergs, but polynyas manage to form and even merge with the polynya on the NIS side, in some cases forming a single large polynya.

Central side (see third image): even if the formation of polynyas is hindered by the presence of an ice mélange of NSM origin (carried by the surface current), their presence remains well identified.  One may also wonder whether the longitudinal rifts which are being revealed in the satellite images in the "future iceberg" are not due to the action of outgoing currents channelled by pre-existing longitudinal crevasses in the bottom of the ice shelf.

SSM side (see fourth image): Following the retreat of the front, there are currently two distinct areas of polynya formation:
> SWT: the zone of formation is located east of the SM (shear margin) between the SWT and the SIS: the zone is invaded from time to time by calving on the SSM side, but the polynyas, even if not very extensive, are present over time.
> SSM: the action of the outgoing current seems to be there, but it is very upset by the calvings and especially by the presence of a very thick mixture of ice and icebergs.

Click to enlarge


EDIT: I have corrected the statistics (first image) by differentiating between the two cases: no polynyas and polynyas of weather origin (winds). In the latter case there may have been a contribution from outgoing currents, but this contribution is drowned in the weather action.
« Last Edit: March 01, 2021, 11:48:35 PM by paolo »