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gerontocrat

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Antarctic Ice Sheet
« on: September 07, 2019, 11:48:01 PM »
Why a new thread?

because stuff is coming out about the Antarctic Ice Sheet in general.
There is a major paper that I am still staggering through, and
it looks like GRACE-FO is becoming something like fully operational.

They are restarting placing files publicly available. More details tomorrow, but here is a taster. I did not realise until I processed the data the scale of the difference between East & West Antarctica

"Para a Causa do Povo a Luta Continua!"
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gerontocrat

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Re: Antarctic Ice Sheet
« Reply #1 on: September 09, 2019, 08:11:17 PM »
I am still studyng the following paper,of which I also post the abstract.

It is an open access paper, with links to the graphs and tables, and a downloadable spreadsheet (see below). There is also an appendix well worth reading.

The paper is :-

https://www.pnas.org/content/116/4/1095
Four decades of Antarctic Ice Sheet mass balance from 1979–2017
Eric Rignot, Jérémie Mouginot, Bernd Scheuchl, Michiel van den Broeke, Melchior J. van Wessem, and Mathieu Morlighem, first published Jan 2019
Quote
Significance Statement
We evaluate the state of the mass balance of the Antarctic Ice Sheet over the last four decades using a comprehensive, precise satellite record and output products from a regional atmospheric climate model to document its impact on sea-level rise. The mass loss is dominated by enhanced glacier flow in areas closest to warm, salty, subsurface circumpolar deep water, including East Antarctica, which has been a major contributor over the entire period. The same sectors are likely to dominate sea-level rise from Antarctica in decades to come as enhanced polar westerlies push more circumpolar deep water toward the glaciers.

Abstract
We use updated drainage inventory, ice thickness, and ice velocity data to calculate the grounding line ice discharge of 176 basins draining the Antarctic Ice Sheet from 1979 to 2017. We compare the results with a surface mass balance model to deduce the ice sheet mass balance. The total mass loss increased from 40 ± 9 Gt/y in 1979–1990 to 50 ± 14 Gt/y in 1989–2000, 166 ± 18 Gt/y in 1999–2009, and 252 ± 26 Gt/y in 2009–2017. In 2009–2017, the mass loss was dominated by the Amundsen/Bellingshausen Sea sectors, in West Antarctica (159 ± 8 Gt/y), Wilkes Land, in East Antarctica (51 ± 13 Gt/y), and West and Northeast Peninsula (42 ± 5 Gt/y). The contribution to sea-level rise from Antarctica averaged 3.6 ± 0.5 mm per decade with a cumulative 14.0 ± 2.0 mm since 1979, including 6.9 ± 0.6 mm from West Antarctica, 4.4 ± 0.9 mm from East Antarctica, and 2.5 ± 0.4 mm from the Peninsula (i.e., East Antarctica is a major participant in the mass loss).

During the entire period, the mass loss concentrated in areas closest to warm, salty, subsurface, circumpolar deep water (CDW), that is, consistent with enhanced polar westerlies pushing CDW toward Antarctica to melt its floating ice shelves, destabilize the glaciers, and raise sea level.

So far, I've only looked at discharge, i.e. not including the annual SMB increase of about 2,100 billion tons from snowfall. Their methodology to produce Net Mass Loss is much more difficult to follow and put int a simple spreadsheet.

So here are some graphs on discharge only. Two reference basin codes - which are on the map also attached. As a result these two images are much bigger than the 700 pixel limit.
I do recommend that you click on the images, as it makes relating the graph to the regions of the Antarctic so much easier.

First graph almost boring, but then. Hint : Thwaites  & Pine Island are in basin G-H.
"Para a Causa do Povo a Luta Continua!"
"And that's all I'm going to say about that". Forrest Gump
"Damn, I wanted to see what happened next" (Epitaph)

KiwiGriff

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Re: Antarctic Ice Sheet
« Reply #2 on: September 11, 2019, 06:59:09 AM »
Others may find this helps to put the information in your last comment in context.
 
 Melting 365 gigatons of ice would add 1 millimeter to global sea level;

https://sealevel.nasa.gov/understanding-sea-level/global-sea-level/ice-melt

edit.
Before I get yelled at... the ice loss above does not include SMB so the rate of sea level rise is not directly deducible.
It is never the less interesting to see the increase in context of future possible sea level rise if trends continue.
« Last Edit: September 11, 2019, 08:34:17 AM by KiwiGriff »

gerontocrat

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Re: Antarctic Ice Sheet
« Reply #3 on: September 13, 2019, 12:43:25 PM »
Others may find this helps to put the information in your last comment in context.
 
 Melting 365 gigatons of ice would add 1 millimeter to global sea level;

https://sealevel.nasa.gov/understanding-sea-level/global-sea-level/ice-melt

edit.
Before I get yelled at... the ice loss above does not include SMB so the rate of sea level rise is not directly deducible.
It is never the less interesting to see the increase in context of future possible sea level rise if trends continue.
I have been hurting my brain looking at the PNAS paper and the spreadsheet, and now various pennies have dropped.

The data for SMB (i.e. snowfall) for individual basins, let alone individual glaciers and sub-basins is extremely sparse. So they have not analysed SMB additions by each year but estimated totals for 1979-2017.

So I cannot produce Net Mass Loss/Gain (i.e. SMB minus Discharge) by individual years.

BUT - We have GRACE-FO data from 2002 to May 2019 (and soon every month). That gives us Net Mass Gain / Loss by 25 basins - BUT in some cases the basin boundaries are the same as in the PNAS paper, in some cases not.

So for 2002 to 2017 I should be able to match the the 2 sets of data for at least some basins and in total to give a year by year analysis of Net Mass Balance changes, and an estimate of SMB gain by year.

This will take some time.I am doing the easy option first - Greenland, only 7 basins.

I attach the basin maps for PNAS and GRACE-FO data.
____________________________________________________
ps: Ignore the Graph above for tons per sq km discharge .  It is wrong - very wrong.  But various idiots on the Forum Suggestions thread persuaded Neven to limit the time to amend postings.

I spotted it too late to change it. So my very bad data will be there forever.
"Para a Causa do Povo a Luta Continua!"
"And that's all I'm going to say about that". Forrest Gump
"Damn, I wanted to see what happened next" (Epitaph)

gerontocrat

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Re: Antarctic Ice Sheet
« Reply #4 on: September 13, 2019, 03:34:41 PM »
Corrected PNAS Graphs

Annual Discharge is greatest in the West, in the basin that includes the PIG and Thwaites, and shows the greatest increase in discharge. A large basin in the East is second, but discharge is stable over the years.

Annual Discharge by area is greatest on the pensinsula, and also shows the greatest rate of change.
_____________________________________________________________
NEW GRAPHS

Net Mass Balance


This graph shows that the Total Net Mass Loss 1979-2017 is a small fraction of the SMB gain and Discharge Loss.

The total of SMB gain is about   82,000 GT,
The total of Discharge  is about 87,000 GT,

Giving a total Net Mass Ice Sheet Loss of just under 5,000 GT, i.e. SMB gain is only 5.5% out of balance with Discharge.

This is a Sea Level Rise of 1.3 cms.

But discharge in the late 2010's is about 200 GT per annum greater than that in the early 1980's. This out of balance figure is likely to have changed from less than 2% to a current value of circa 10%.

i.e. The Antarctic was nearly in balance up to the early 1980's. Now it is definitely not.

The last graph assumes SMB gain was constant from 1972 to 2017. It suggests a steady increase in annual net mass loss, that even on an X2 polynomial trend, only gradually accelerates in the future.

BUT one day the Antarctic's defences against AGW will break down?


« Last Edit: September 13, 2019, 05:20:05 PM by gerontocrat »
"Para a Causa do Povo a Luta Continua!"
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"Damn, I wanted to see what happened next" (Epitaph)

gerontocrat

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Re: Antarctic Ice Sheet
« Reply #5 on: October 08, 2019, 06:38:42 PM »
GRACE-FO Data to July 2019 ... http://gravis.gfz-potsdam.de/antarctica

It looks like GRACE-FO data on ice sheets mass changes will now come out at around the 6th of the month, with data 3 months in arrears courtesy of Germany.

So here are some graphs & a map of the 25 drainage basins- also look at the map on the link.

Ice mass loss is mostly all about one relatively small patch on the west coast - i.e. the WAIS, but part of the EAIS is waking up.
_________________________________________
Noe: Ignore the up & down blip in late 2016 early 2017- I think that is when the 1st GRACE satellite started to go wobbly being ages past its design life.
"Para a Causa do Povo a Luta Continua!"
"And that's all I'm going to say about that". Forrest Gump
"Damn, I wanted to see what happened next" (Epitaph)