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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

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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.
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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 »
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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.
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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 »
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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.
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vox_mundi

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Re: Antarctic Ice Sheet
« Reply #6 on: November 04, 2019, 04:26:16 PM »
Revealing Interior Temperature of Antarctic Ice Sheet
https://phys.org/news/2019-11-revealing-interior-temperature-antarctic-ice.html

ESA’s SMOS mission has been used to show how the temperature of the Antarctic ice sheet changes with depth. The image shows how the ice is colder (blue) at the surface but warmer (red) at the base. Temperature is one of the things that determines how ice flows and slides over the bedrock beneath. In turn, this flow affects the temperature profile through strain heating – so it’s a complicated process. Temperature information is also fundamental for understanding the presence of aquifers inside or at the bottom part of ice sheets. This can be relevant for indicating the presence of sub-glacial lakes, for example, which in turn influence ice-sheet dynamics.

... "We combined SMOS' L-band passive microwave observations over Antarctica with glaciological and emission models to infer information on glaciological properties of the ice sheet at various depths, including temperature"



Giovanni Macelloni et al. On the retrieval of internal temperature of Antarctica Ice Sheet by using SMOS observations, Remote Sensing of Environment (2019)
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gerontocrat

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Re: Antarctic Ice Sheet
« Reply #7 on: November 13, 2019, 08:08:39 PM »
Updated GRACE-FO ice mass @ http://gravis.gfz-potsdam.de/antarctica - courtesy of Germany.

Last measurement date mid-September 2019. It is winter so a slight uptick, i.e. mass gain.
Annual change looks like about 50gt, well under 2002-17 average of about 170 GT.

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gerontocrat

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Re: Antarctic Ice Sheet
« Reply #8 on: November 13, 2019, 09:00:11 PM »
And here is a graph showing how just 3 Antarctic Drainage Basins are losing a helluva lot of ice mass.

Refer to map above for locations.
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Re: Antarctic Ice Sheet
« Reply #9 on: November 24, 2019, 01:50:40 PM »

gerontocrat

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Re: Antarctic Ice Sheet
« Reply #10 on: January 18, 2020, 02:26:28 AM »
After over 2 months, new data from GRACE-FO - at last.

Updated GRACE-FO ice mass @ http://gravis.gfz-potsdam.de/antarctica - courtesy of Germany.

Last measurement date mid-November 2019.
12 month ice mass loss 284 GT, i.e. 0.78 mm sea level rise.

However, a record surface melt started in mid November,
see https://forum.arctic-sea-ice.net/index.php/topic,1759.msg244871.html#msg244871)

So it is the next 2 to 3 months that might see an uptick in ice mass loss.
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gerontocrat

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Re: Antarctic Ice Sheet
« Reply #11 on: February 18, 2020, 07:43:15 PM »
After exactly 1 month, new data from GRACE-FO.

Updated GRACE-FO ice mass @ http://gravis.gfz-potsdam.de/antarctica - courtesy of Germany.

Last measurement date mid-December 2019.
12 month ice mass loss a mere 134 GT, i.e. 0.5 mm sea level rise, much lower than for November, despite a record surface melt started in mid November, on the fringe of Antarctica.

see https://forum.arctic-sea-ice.net/index.php/topic,1759.msg244871.html#msg244871)

It must have snowed in the interior?
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Sciguy

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Re: Antarctic Ice Sheet
« Reply #12 on: February 18, 2020, 09:31:52 PM »
After over 2 months, new data from GRACE-FO - at last.

Updated GRACE-FO ice mass @ http://gravis.gfz-potsdam.de/antarctica - courtesy of Germany.

Last measurement date mid-November 2019.
12 month ice mass loss 284 GT, i.e. 0.78 mm sea level rise.

After exactly 1 month, new data from GRACE-FO.

Updated GRACE-FO ice mass @ http://gravis.gfz-potsdam.de/antarctica - courtesy of Germany.

Last measurement date mid-December 2019.
12 month ice mass loss a mere 134 GT, i.e. 0.5 mm sea level rise, much lower than for November, despite a record surface melt started in mid November, on the fringe of Antarctica.

see https://forum.arctic-sea-ice.net/index.php/topic,1759.msg244871.html#msg244871)

It must have snowed in the interior?

Something seems wrong.  Was November 2018 responsible for 150 (284 - 134) GT mass loss?  Seems like a measurement or reporting error is more likely.

gerontocrat

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Re: Antarctic Ice Sheet
« Reply #13 on: February 18, 2020, 10:01:44 PM »
Checked the data before posting - could well be measurement errorsin the first month or 2 of GRACE-FO results.

Maybe they have gone back & recalibrated - will have a look tomorrow.
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Stephan

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Re: Antarctic Ice Sheet
« Reply #14 on: February 18, 2020, 10:06:45 PM »
Maybe a further smoothing of the data or introducing trailing months averages etc. might be necessary to avoid too big 'jumps' from month to month?
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Re: Antarctic Ice Sheet
« Reply #15 on: February 18, 2020, 11:01:34 PM »
In addition to processing error, correct interpretation of GRACE, & GRACE-FO, data must also consider issue such as atmospheric river events, local ice discharge events (such as from the Thwaites Ice Tongue), and isostatic round (see the linked references):


Whitehouse, P.L., Gomez, N., King, M.A. et al. Solid Earth change and the evolution of the Antarctic Ice Sheet. Nat Commun 10, 503 (2019). https://doi.org/10.1038/s41467-018-08068-y

https://www.nature.com/articles/s41467-018-08068-y

Abstract: "Recent studies suggest that Antarctica has the potential to contribute up to ~15 m of sea-level rise over the next few centuries. The evolution of the Antarctic Ice Sheet is driven by a combination of climate forcing and non-climatic feedbacks. In this review we focus on feedbacks between the Antarctic Ice Sheet and the solid Earth, and the role of these feedbacks in shaping the response of the ice sheet to past and future climate changes. The growth and decay of the Antarctic Ice Sheet reshapes the solid Earth via isostasy and erosion. In turn, the shape of the bed exerts a fundamental control on ice dynamics as well as the position of the grounding line—the location where ice starts to float. A complicating issue is the fact that Antarctica is situated on a region of the Earth that displays large spatial variations in rheological properties. These properties affect the timescale and strength of feedbacks between ice-sheet change and solid Earth deformation, and hence must be accounted for when considering the future evolution of the ice sheet."

&

Eric Rignot, et al. (January 22, 2019), "Four decades of Antarctic Ice Sheet mass balance from 1979–2017", PNAS, 116 (4) 1095-1103; https://doi.org/10.1073/pnas.1812883116

https://www.pnas.org/content/116/4/1095

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.

PS: Isostatic rebound introduces bed mass beneath glaciers that are losing ice mass; thus the GRACE, or GRACE-FO, data must be corrected to subtract the new bed to get the total ice mass lost; however, projecting the new bed mass can be difficult.
« Last Edit: February 18, 2020, 11:53:15 PM by AbruptSLR »
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gerontocrat

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Re: Antarctic Ice Sheet
« Reply #16 on: February 19, 2020, 03:33:57 PM »
In addition to processing error, correct interpretation of GRACE, & GRACE-FO, data must also consider issue such as atmospheric river events, local ice discharge events (such as from the Thwaites Ice Tongue), and isostatic round (see the linked references):
I have checked to see if the GRACE-FO data has been recalibrated - the answer is no.

The GRACE-FO raw data is processed as follows.......

http://gravis.gfz-potsdam.de/corrections
Quote
Corrections and Auxiliary Products
A number of corrections and reductions are applied to the Level-2 spherical harmonics to generate Level-3 products that represent variations of the Earth's surface masses as accurately as possible. These post-processed Level-2 coefficients, denoted as Level-2B products, are provided as an additional data set for users who wish to undertake surface mass inversion starting from spherical harmonic coefficients by themselves.

The Level-2B products as well as individual data sets and models used during the post-processing steps mentioned below are available here.

Mean Field
GRACE/GRACE-FO Level-3 products represent mass anomalies, i.e., positive or negative variations about a long-term mean gravity field of the Earth. Essentially, the choice of this mean field is arbitrary, since using a different mean field only introduces a constant bias to the time series of mass anomalies. However, when comparing these Level-3 products to other data or models, all time series should refer to the same reference epoch.

All Level-2B/Level-3 products currently available at GravIS refer to a long-term mean field calculated as unweighted average of the 156 available GFZ RL06 GSM products in the period from 2002/04 up to and including 2016/08.

Anisotropic Filtering
In order to optimally separate signal and noise in the GRACE/GRACE-FO Level-2 data, filtering is necessary. Due to the observation geometry with its pure along-track ranging on polar orbits GRACE and GRACE-FO gravity fields reveal highly anisotropic error characteristics. An adequate filter technique to account for this is the decorrelation method by Kusche et al. (2009), named DDK, which is deduced from a regularization approach using signal and error information in terms of variance and covariance matrices. The filtering is applied in the spectral domain by multiplying the filter matrix to the unfiltered spherical harmonic (SH) coefficients (residual with respect to a mean field). This method has been adapted by Horvath et al. (2018) taking into account the temporal variations of the error variances and covariances, namely VDK filtering.

Hence, our Level-2B products are optionally decorrelated and smoothed with an adaptive filter that explicitly takes into account the error covariance information of the corresponding Level-2 product. We provide the following variants of Level-2B products: filtered with VDK2, VDK3, and VDK5 as well as unfiltered (NFIL) solutions. These variants are distinguishable by respective strings in the product file names.
C20 Time Series
The spherical harmonic coefficient of degree 2 and order 0 (C20) is related to the flattening of the Earth. Since it is known that monthly GRACE estimates of C20 are affected by spurious systematic effects (e.g. Cheng & Ries, 2017), the C20 coefficients and their formal errors are replaced by estimates derived from satellite laser ranging (SLR) observations that are regarded to be more reliable.

Here, we use a C20 time series processed at GFZ (König et al., 2019) that is based on the six geodetic satellites LAGEOS-1 and -2, AJISAI, Stella, Starlette, and LARES (starting from March 2012) and uses the same background models and standards as applied during GFZ GRACE/GRACE-FO processing, including the Atmosphere and Ocean De-aliasing model AOD1B.

GIA Correction
Glacial Isostatic Adjustment (GIA) denotes the surface deformation of the solid Earth (lithosphere and mantle) caused by ice-mass redistribution over the last 100,000 years, dominated by the termination of the last glacial cycle. Due to the Earth's viscoelastic response to mass redistribution between the ice sheets and the ocean, the Earth's gravity field is affected by long term secular trends mainly in previously glaciated regions such as North America, Fennoscandia and Antarctica. Moreover, also coefficients of low degrees and orders are affected.

The Level-2B/Level-3 products provided here are corrected using a GIA model based on ICE-5G ice load history (Peltier, 2004) as applied to the 3D-Viscoelastic Lithosphere and Mantle Model VILMA (Martinec, 2000; Klemann et al., 2008).

I downloaded the PNAS AIS & GIS papers from Rignot et al, together with the spreadsheets included, last year. Fascinating stuff. What I found fascinating was that the Net Antarctic Mass Loss is the relatively small difference between SMB addition (snowfall) and ice mass loss.
(see graph attached).

The spreadsheet also showed that annual SMB addition averaged circa 2,100 GT per annum over the 39 years analysed, but during that time increased by at least 200 GT per annum.

The SMB simulated by MARv3.10  looks like annual SMB increase is now circa 2,500 GT per annum. (see 2nd graph attached)

This means that for the NET MASS BALANCE of the AIS to reduce at an accelerated rate (as it has), Ice Mass Loss has had to increase at an even greater rate.

I was hoping to compare basin data from GRACE-FO with PNAS basin data (which has area in KM")- BUT
- GRACE-FO uses 25 basins,
-PNAS uses 27 basins.
The match is close but not exact (sea map attached) 

ps: The same problem applies to the GIS


So all I can do is use what I've got - i.e. GRACE-FO monthly data and SMB graphs from http://climato.be/cms/index.php?climato=the-2020-melt-season-over-antarctica-as-simulated-by-marv3-10
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AbruptSLR

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Re: Antarctic Ice Sheet
« Reply #17 on: February 19, 2020, 04:25:51 PM »
...
GIA Correction
Glacial Isostatic Adjustment (GIA) denotes the surface deformation of the solid Earth (lithosphere and mantle) caused by ice-mass redistribution over the last 100,000 years, dominated by the termination of the last glacial cycle. Due to the Earth's viscoelastic response to mass redistribution between the ice sheets and the ocean, the Earth's gravity field is affected by long term secular trends mainly in previously glaciated regions such as North America, Fennoscandia and Antarctica. Moreover, also coefficients of low degrees and orders are affected.

The Level-2B/Level-3 products provided here are corrected using a GIA model based on ICE-5G ice load history (Peltier, 2004) as applied to the 3D-Viscoelastic Lithosphere and Mantle Model VILMA (Martinec, 2000; Klemann et al., 2008).[/size]


[/quote]

I believe that the GIA correction for GRACE-FO uses the same isostatic model used by GRACE not because it is an accurate model but rather because of a shortage of field data (see the first linked reference); however, the second linked reference indicates that corrections from this model is likely 40% too low for the ASE area:

Li, F., Ma, C., Zhang, S. et al. Evaluation of the glacial isostatic adjustment (GIA) models for Antarctica based on GPS vertical velocities. Sci. China Earth Sci. (2020). https://doi.org/10.1007/s11430-018-9532-5

https://link.springer.com/article/10.1007/s11430-018-9532-5

Abstract: "Due to the scarcity of data, modeling the glacial isostatic adjustment (GIA) for Antarctica is more difficult than it is for the ancient ice sheet area in North America and Northern Europe. Large uncertainties are observed in existing GIA models for Antarctica. Modern space-based geodetic measurements provide checks and constraints for GIA models. The present-day uplift velocities of global positioning system (GPS) stations at 73 stations in Antarctica and adjacent regions from 1996 to 2014 have been estimated using GAMIT/GLOBK version 10.5 with a colored noise model. To easily analyze the effect of difference sources on the vertical velocities, and for easy comparison with both GIA model predictions and GPS results from Argus et al. (2014) and Thomas et al. (2011), seven sub-regions are divided. They are the northern Antarctic Peninsula, the Filchner-Ronne Ice Shelf, the Amundsen Sea coast, the Ross Ice Shelf, Mount Erebus, inland Southwest Antarctica and the East Antarctic coast, respectively. The results show that the fast uplift in the north Antarctic Peninsula and Pine Island Bay regions may be caused by the elastic response to snow and ice mass loss. The fast subsidence near Mount Erebus may be related to the activity of a magma body. The uplift or subsidence near the East Antarctic coast is very slow while the uplift for the rest regions is mainly caused by GIA. By analyzing the correlation and the associated weighted root mean square (WRMS) between the GIA predictions and the GPS velocities, we found that the ICE-6G_C (VM5a) model and the Geruo13 model show the most consistency with our GPS results, while the W12a and IJ05_R2 series models show poor consistency with our GPS results. Although improved greatly in recent years, the GIA modeling in Antarctica still lags behind the modeling of the North American. Some GPS stations, for example the Bennett Nunatak station (BENN), have observed large discrepancies between GIA predictions and GPS velocities. Because of the large uncertainties in calculating elastic responses due to the significant variations of ice and snow loads, the GPS velocities still cannot be used as a precise constraint on GIA models."

Therefore, I am re-posting the following from Reply #71 of the "Surge" thread, reminding all that the GRACE satellite SLR contributions previously reported by NASA are probably 40% too low for at least the ASE area and probably for all of the WAIS due to treating the GIA correction for the WAIS like any other part of the earth when, as I have indicated in my prior posts in this thread, West Antarctica has a relatively unique tectonic history and current condition:

A. Groh; H. Ewert, M. Scheinert, M. Fritsche, A. Rülke, A. Richter, R. Rosenau, R. Dietrich (2012), "An investigation of Glacial Isostatic Adjustment over the Amundsen Sea sector, West Antarctica", Global and Planetary Change, Vol 98-99, pp 45-53, http://dx.doi.org/10.1016/j.gloplacha.2012.08.001

https://www.sciencedirect.com/science/article/pii/S0921818112001567?via%3Dihub

"Abstract
The present study focuses on the Amundsen Sea sector which is the most dynamical region of the Antarctic Ice Sheet (AIS). Based on basin estimates of mass changes observed by the Gravity Recovery and Climate Experiment (GRACE) and volume changes observed by the Ice, Cloud and Land Elevation Satellite (ICESat), the mean mass change induced by Glacial Isostatic Adjustment (GIA) is derived. This mean GIA-induced mass change is found to be 34.1 ± 11.9 Gt/yr, which is significantly larger than the predictions of current GIA models. We show that the corresponding mean elevation change of 23.3 ± 7.7 mm/yr in the Amundsen Sea sector is in good agreement with the uplift rates obtained from observations at three GPS sites. Utilising ICESat observations, the observed uplift rates were corrected for elastic deformations due to present-day ice-mass changes. Based on the GRACE-derived mass change estimate and the inferred GIA correction, we inferred a present-day ice-mass loss of − 98.9 ± 13.7 Gt/yr for the Amundsen Sea sector. This is equivalent to a global eustatic sea-level rise of 0.27 ± 0.04 mm/yr. Compared to the results relying on GIA model predictions, this corresponds to an increase of the ice-mass loss or sea-level rise, respectively, of about 40%."

The first accompanying figure shows an overview of the Amundsen Sea sector, West Antarctica. The red line defines the generalized drainage basins of Pine Island Glacier, Thwaites Glacier and Smith Glacier (PITS). Locations of three GPS campaign sites are marked by red triangles.

The second figures shows the GRACE data from 2003 to 2009 which the papers says needs to be corrected to indicate about 40% more ice mass loss than previously reported
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wdmn

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Re: Antarctic Ice Sheet
« Reply #18 on: February 22, 2020, 06:58:40 AM »

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Re: Antarctic Ice Sheet
« Reply #19 on: April 09, 2020, 10:17:17 AM »
Tracking Southern Hemisphere black carbon to Antarctic snow


https://phys.org/news/2020-04-tracking-southern-hemisphere-black-carbon.html
  by Chinese Academy of Sciences




"Black carbon, or BC, commonly known as soot, is a particle originated from the incomplete combustion of fossil fuels and biomass burning that warms the atmosphere. When deposited in snow and ice, BC increases surface radiation absorption and can cause melt," explains Mr. Marquetto. "Some scientists say that BC is second only to CO2 in its warming effects on the climate, and studies have shown that BC concentrations have risen since the industrial revolution in several places in the world, including Greenland, the Himalayas, the Alps and even Antarctica."

But studying BC in Antarctica is logistically challenging, and only in the last decade the topic has gained more attention. "Antarctica is a vast continent, and there are regions with no BC data yet. As climatic and atmospheric models rely on field data, studying BC concentrations in Antarctic snow is essential to improve these models," adds Mr. Marquetto.

Mr. Marquetto was part of a team of Brazilian researchers led by Dr. Jefferson Cardia Simões (Polar and Climatic Center) who carried out a traverse in West Antarctica in the 2014/2015 austral summer. They travelled more than 1400 km, collecting several shallow snow cores and samples along the way to investigate the snow chemistry (and consequently the atmospheric chemistry) in the last 50 years or so. One of these shallow cores was analyzed for BC in cooperation with Dr. Susan Kaspari (Central Washington University, U.S.).


"As for sectorial sources, we know biomass burning represents around 80% of all BC emitted to the atmosphere in the Southern Hemisphere, which means that the fires happening in Australia, New Zealand and South America ultimately leave a mark in Antarctic snow."

See also:
https://phys.org/news/2013-08-arctic-sensitive-black-carbon-emissions.html
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gerontocrat

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Re: Antarctic Ice Sheet
« Reply #20 on: April 15, 2020, 02:39:21 PM »
Attached are AIS Mass Loss Graphs to mid-Feb 2020 as calculated by GRACE-FO.

Total mass loss 521 GT, of which half was in the western sector ( basins 19-25 ), see map attached. That equates to a 1.44 mm sea level rise (9.5 mm since 2002)

You may remember that surface melt was at a record high from mid-November 2019 to February 2020. Over 370 GT of that annual mass loss happened in the one month December to January.

Winter has arrived in the Antarctic, only question now is of mass gain this year c.f. the average?

data source :- ftp://isdcftp.gfz-potsdam.de/grace-fo/GravIS/GFZ/Level-3/ICE/AIS/
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gerontocrat

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Re: Antarctic Ice Sheet
« Reply #21 on: June 10, 2020, 05:32:27 PM »
Attached are AIS Mass Loss Graphs to mid-Feb 2020 as calculated by GRACE-FO.


It looks like the scientists have recalibrated the data going right back to 2002 - hence a long delay. Perhaps now monthly updates will resume a bit earlier.

Some may remember posts about unprecedented surface melting + run-off during the last Antipodean summer. The result is clear - surface and ocean melting meant that from mid-November to mid-February the Antarctic Ice Sheet lost nearly 800 GT of ice - i.e. equal to more than 2 mms of sea-level. That mass loss was pretty much everywhere.
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Re: Antarctic Ice Sheet
« Reply #22 on: June 10, 2020, 05:37:19 PM »
Gerontocrat,
I admire all the work you're doing on all fronts... ;)

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Re: Antarctic Ice Sheet
« Reply #23 on: June 10, 2020, 06:15:11 PM »
That is a massive recalibration, 750 GT~ less ice melted than they originally said. What does that mean for sea level rise...Will that have to be recalibrated as well?

gerontocrat

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Re: Antarctic Ice Sheet
« Reply #24 on: July 14, 2020, 03:17:46 PM »
Attached are AIS Mass Loss Graphs to mid-May 2020 as calculated from GRACE-FO data.


IPerhaps now monthly updates will be monthly. At least the JPL data and the data from the German end match pretty well - unlike for the Greenland Ice Sheet.
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FishOutofWater

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Re: Antarctic Ice Sheet
« Reply #25 on: July 14, 2020, 03:41:56 PM »
GC - you should have special permission to be able to modify all of your posts because you are so meticulous with your data sets and so generous with your time. Unfortunately, a few bad actors motivated some folks to seek a change in the modification rules.

An increase in the flow of warm water along the western side of the Antarctic Penn. has had catastrophic effects on the glaciers there. East Antarctic glaciers are pretty stable now, but there will come a point when they destabilize if global warming continues unabated. These results are reassuring that we have not yet reached that point.

gerontocrat

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Re: Antarctic Ice Sheet
« Reply #26 on: December 07, 2020, 06:50:45 PM »
GRACE-FO data became very erratic in timing and in the variation between the JPL/PO-DACCV data and the data by basin from Germany.

Things seem to have become more settled on both fronts so here is the latest from Germany  @ ftp://isdcftp.gfz-potsdam.de/grace-fo/GravIS/GFZ/Level-3/ICE/

It's always a bit later (to mid Sept 20) than the text files from JPL/PO-DACC, but it's down to basin level.

Note the massive ice mass gain of over 1,000 GT (yes, one thousand) from Feb 20 to August 20.
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gerontocrat

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Re: Antarctic Ice Sheet
« Reply #27 on: February 15, 2021, 11:51:40 PM »
ftp://isdcftp.gfz-potsdam.de/grace-fo/GravIS/GFZ/Level-3/ICE/

After 2  months another GRACE-FO update from Germany.

The data is up to mid-November, but there is still a mass gain.

_____________________________________________________________
Note that FTP protocol is used on this site so google won't access the data. I used Firefox but apparently they will abandon FTP as well this year.

The science community needs to wake up - FTP is used all over the science websites.

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Alphabet Hotel

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Re: Antarctic Ice Sheet
« Reply #28 on: February 16, 2021, 01:56:42 AM »
You can always use a command-line tool like wget to fetch things from FTP sites. It's open source and available for pretty much any platform. For Windows I highly recommend using chocolatey to install it (chocolatey.org). I copy the link from my browser and paste it into the command line.

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Re: Antarctic Ice Sheet
« Reply #29 on: February 21, 2021, 04:23:23 AM »
   wget      I downloaded a couple of gigabytes from Alberta of EIA's in pdf on coal  mines and both types of bitumen extraction via "wget" until Alberta closed it up. That was back in the days of TheOilDrum.   (Note - I did nothing wrong, it was decided to have it be free to download.)   "wget"  really is a gem for getting things from ftp sites.  And actually you can have  chrooted (I believe) Debian (or other linux) on your Windows 10 or Windows 10 pro. It is in the app store.    You do have to do "sudo apt install wget"  to install in the Debian chroot.   I have not tried it out on any ftp sites via Windows, but I possibly could. 



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Re: Antarctic Ice Sheet
« Reply #30 on: February 21, 2021, 07:27:34 AM »
Whats wrong with good old ftp or sftp from the command line ?  I thiink its available for windows, mac and builtin to linuxen

sidd

gerontocrat

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Re: Antarctic Ice Sheet
« Reply #31 on: February 21, 2021, 12:05:55 PM »
Whats wrong with good old ftp or sftp from the command line ?  I thiink its available for windows, mac and builtin to linuxen

sidd
You get a browser and you spend time bookmarking and organising your bookmarks because that makes life simple to access the data you want.

And then the browser tell you to fuck off and to go back nearly 40 years to ms-dos and the C: prompt. Yes, sir, no sir, three bags full sir.

Yes, I can do it the old-fashioned way. Or I can dump google and use a browser that isn't going to dump me.

To quote the song - "I'm going backwards to Xmas, across the Irish Sea".
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Re: Antarctic Ice Sheet
« Reply #32 on: February 22, 2021, 07:49:37 AM »
Re: get a browser

that's a different problem, perhaps not best discussed on this thread. I will just point out that "getting a browser" and "organizing bookmarks" therein locks you into the browser's gestalt and the browser's "upgrades."

But as i said, best discussed elsewhere. The Antarctic Ice Sheet does no much care about our software choices ...

sidd

gerontocrat

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Re: Antarctic Ice Sheet
« Reply #33 on: March 11, 2021, 01:49:09 PM »
ftp://isdcftp.gfz-potsdam.de/grace-fo/GravIS/GFZ/Level-3/ICE/

Another GRACE-FO update from Germany. The data is up to December, and there is a substantial monthly mass loss of 450GT.
_____________________________________________________________
Note how nearly all cumulative mass loss is confiined to 3 very small basins on the coast of the Amundsen sea.

Note also how ice-mass loss is occuring in the East on the coast facing the West Pacific Ocean

(see next post for maps)
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gerontocrat

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Re: Antarctic Ice Sheet
« Reply #34 on: March 11, 2021, 01:53:45 PM »
Maps showing location of concentration of AIS mass loss attached
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Re: Antarctic Ice Sheet
« Reply #35 on: March 12, 2021, 07:32:32 AM »
in the east, I dont like what totten is doing but i am relieved that amery is holding. In the west, pig/thwaites/getz/dotson/cross  is just disastrous, that sector is toast, we are just talking halflife in decades now. We will see that repeated at Totten, mebbe worse there, for right now it looks about 15 yr behind Thwaites. That could change.

sidd

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Re: Antarctic Ice Sheet
« Reply #36 on: March 12, 2021, 07:57:09 PM »
Maps showing location of concentration of AIS mass loss attached
Is the grace map cumulative or 1 month or what?

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Re: Antarctic Ice Sheet
« Reply #37 on: March 12, 2021, 09:46:41 PM »
Maps showing location of concentration of AIS mass loss attached
Is the grace map cumulative or 1 month or what?

The map shows the current mass anomaly compared to the long term mean (2002-2020). Right now the winter of 2010/2011 is near zero. If they increase the timeperiod in the future the zero point will change as well.

For other months check:
http://gravis.gfz-potsdam.de/antarctica

Quote
Mean Field

GRACE/GRACE-FO Level-3 products represent mass anomalies, i.e., positive or negative variations about a long-term mean gravity field of the Earth. Essentially, the choice of this mean field is arbitrary, since using a different mean field only introduces a constant bias to the time series of mass anomalies. However, when comparing these Level-3 products to other data or models, all time series should refer to the same reference epoch.

All Level-2B/Level-3 products currently available at GravIS refer to a long-term mean field calculated as unweighted average of the 183 available GFZ RL06 Level-2 products in the period from 2002/04 through 2020/03.



gerontocrat

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Re: Antarctic Ice Sheet
« Reply #38 on: March 17, 2021, 01:43:57 PM »
JPL has updated their Grace-FO data to Jan 21. It is total AIS mass balance only.

At the moment the long-term trend of mass loss is for acceleration.

In the last 2 months (Dec Jan) mass loss was an extreme 500 GT, which meant a large volume of freshwater was ejected into the Antarctic Ocean where it would tend to form a surface layer of very cold low salinity water. Some papers posit that this is likely to cause a sudden increase in sea ice extent as winter draws in.

In late February 21 a truly massive increase in Antarctic sea ice extent happened.

Coincidence or a cause and effect in action?
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Re: Antarctic Ice Sheet
« Reply #39 on: March 17, 2021, 06:27:53 PM »
I vote for the latter although that does not mean anything.
Thanks for keeping tabs on all these datasets. Slowly studying but it is big and far away and quite different from the other end.  :)
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gerontocrat

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Re: Antarctic Ice Sheet
« Reply #40 on: March 17, 2021, 06:39:04 PM »
I vote for the latter although that does not mean anything.
Thanks for keeping tabs on all these datasets. Slowly studying but it is big and far away and quite different from the other end.  :)
Always nice to know someone is not just looking but alao seeing and perhaps even thinking.

And attached is the sea ice area graph for the Bellinghausen-Amundsen sea which borders the West coast where most AIS mass loss happens. This is where most of the February sea ice extent growth happened (contrasted with the Weddell Sea - to the East round the corner - see map).

Should have a better idea when the GTZ data for AIS mass loss for January arrives (in a month or so).
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Re: Antarctic Ice Sheet
« Reply #41 on: March 18, 2021, 03:15:59 AM »
JPL has updated their Grace-FO data to Jan 21. It is total AIS mass balance only.

At the moment the long-term trend of mass loss is for acceleration.

In the last 2 months (Dec Jan) mass loss was an extreme 500 GT, which meant a large volume of freshwater was ejected into the Antarctic Ocean where it would tend to form a surface layer of very cold low salinity water. Some papers posit that this is likely to cause a sudden increase in sea ice extent as winter draws in.

In late February 21 a truly massive increase in Antarctic sea ice extent happened.

Coincidence or a cause and effect in action?
Could the mass loss be associated with abnormally low snowfall? Do we have figures for the surface mass balance only?

gerontocrat

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Re: Antarctic Ice Sheet
« Reply #42 on: March 18, 2021, 12:28:58 PM »
JPL has updated their Grace-FO data to Jan 21. It is total AIS mass balance only.

At the moment the long-term trend of mass loss is for acceleration.

In the last 2 months (Dec Jan) mass loss was an extreme 500 GT, which meant a large volume of freshwater was ejected into the Antarctic Ocean where it would tend to form a surface layer of very cold low salinity water. Some papers posit that this is likely to cause a sudden increase in sea ice extent as winter draws in.

In late February 21 a truly massive increase in Antarctic sea ice extent happened.

Coincidence or a cause and effect in action?
Could the mass loss be associated with abnormally low snowfall? Do we have figures for the surface mass balance only?
NOPE.
I do have a paper https://cp.copernicus.org/articles/13/1491/2017/cp-13-1491-2017.pdf that tells me average SMB increase (i.e snowfall) has increased from an average of around 2,400 GT per annum in 1900 to well over 2500 GT per annum this century, and that most of this is concentrated in the Antarctic Peninsula. (AGW = warmer wetter weather)****

But this is long-term trends stuff.

However, NSIDC on Greenland Today has added an Antarctica Melting Season section (http://nsidc.org/greenland-today/). It shows that most melt is on the Antarctic Peninsular, and any run-off of meltwater from the area with the highest +ve melt day anomaly would likely end up in the Weddell Sea.

Antarctica - the place where we need to know the most and know the least, and systematised continuous data collection is almost non-existent.

_________________________________________________
**** From https://cp.copernicus.org/articles/13/1491/2017/cp-13-1491-2017.pdf
Quote
Our study reveals that SMB for the total AIS has increased at a rate of 7 ± 1.3 Gt decade−1
since 1800 AD, which is equivalent to a net reduction in sea level of 0.02 mm decade−1. The largest contribution is from the AP where the annual average SMB during the most recent
decade (2001–2010) is 123 ± 44 Gt yr−1 higher than the annual average at the start of the 19th century. The AP is the only region where both the most recent 50-year and 100-year trends are outside of the observed range for the past 300 years. This contradicts some previous studies which suggest a negligible change in Antarctic SMB since 1957 (Monwww.clim-past.net/13/1491/2017/ )


click to enlarge images
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gerontocrat

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Re: Antarctic Ice Sheet
« Reply #43 on: June 11, 2021, 04:48:29 PM »
https://podaac-tools.jpl.nasa.gov/drive/files/allData/tellus/L4/ice_mass/RL06/v02/mascon_CRI

PODACC - JPL have updated the Grace AIS mass balance data to mid-April 2021. (Data is always to mid-month)

It's a quiet period, melt season over and freeze not really underway. So Iwas surprised at the strong gains.
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gerontocrat

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Re: Antarctic Ice Sheet
« Reply #44 on: June 27, 2021, 11:06:53 PM »
And GFZ German Research Centre for Geosciences @ http://gravis.gfz-potsdam.de/ have released their 2-monthly update for the AIS and GIS to mid-April '21

The first image is the map of the basins they use (boundaries according to Zwally).

The next are the total cumulative, regional totals and basin total graphs.

Of note is that in the last 2 years summer ice mass loss and winter ice mass gains are far higher than in previous years. Also basin 21, which contains the PIG and Thwaites catchment areas is the only one resisting ice mass gains in these months. Speculation - sub-glacial melt from warmer CDW at depth.

click images to enlarge

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

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Re: Antarctic Ice Sheet
« Reply #45 on: June 29, 2021, 05:09:02 PM »
And GFZ German Research Centre for Geosciences @ http://gravis.gfz-potsdam.de/ have released their 2-monthly update for the AIS and GIS to mid-April '21

The first image is the map of the basins they use (boundaries according to Zwally).

The next are the total cumulative, regional totals and basin total graphs.

Of note is that in the last 2 years summer ice mass loss and winter ice mass gains are far higher than in previous years. Also basin 21, which contains the PIG and Thwaites catchment areas is the only one resisting ice mass gains in these months. Speculation - sub-glacial melt from warmer CDW at depth.

click images to enlarge


Basin 21 includes the Thwaites Glacier but Basin 22 contains the PIG.
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gerontocrat

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Re: Antarctic Ice Sheet
« Reply #46 on: August 28, 2021, 07:52:48 PM »
https://podaac-tools.jpl.nasa.gov/drive/files/allData/tellus/L4/ice_mass/RL06/v02/mascon_CRI

JPL has just produced GRACE+GRACE-FO data for Antarctic Mass Change up to mid-June 2021.

The graph attached shows that mass loss continues to suggest a faster than linear loss of mass (i.e. ice).
"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 #47 on: October 06, 2021, 08:08:27 PM »
A research letter that associates Antarctic sea ice expansion with Antarctic glacial melt.
But can it explain the unprecented rise in sea ice extent in 2014-15 followed by the equally unprecedented fall in 2016-17 plus the 3 week early maximum and steep fall afterwards in August-September 2021?

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2019GL086892
Antarctic Glacial Melt as a Driver of Recent Southern Ocean Climate Trends
Abstract
Quote
Recent trends in Southern Ocean (SO) climate—of surface cooling, freshening, and sea ice expansion—are not captured in historical climate simulations. Here we demonstrate that the addition of a plausible increase in Antarctic meltwater to a coupled climate model can produce a closer match to a wide range of climate trends. We use an ensemble of simulations of the Goddard Institute for Space Studies Earth system model to compute “climate response functions” (CRFs) for the addition of meltwater. These imply a cooling and freshening of the SO, an expansion of sea ice, and an increase in steric height, all consistent with observations since 1992. The CRF framework allows one to compare the efficacy of Antarctic meltwater as a driver of SO climate trends, relative to greenhouse gas and surface wind forcing. The meltwater CRFs presented here strongly suggest that interactive Antarctic ice melt should be included in climate models.

Plain Language Summary
Climate models do not capture recent Southern Ocean (SO) climate trends of surface cooling, freshening, and sea ice expansion. Here we demonstrate that including a realistic increase in Antarctic meltwater can improve a model's representation of SO trends. We use an ensemble of simulations of the Goddard Institute for Space Studies Earth system model. Model results suggest that Antarctic meltwater drives a cooling and freshening of the SO and an expansion of winter sea ice, all consistent with observations. Results suggest that a better representation of Antarctic ice melt should be included in climate models.
"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 #48 on: October 24, 2021, 03:50:30 PM »
https://podaac-tools.jpl.nasa.gov/drive/files/allData/tellus/L4/ice_mass/RL06/v02/mascon_CRI

JPL has produced GRACE+GRACE-FO data for Antarctic Mass Change up to mid-August 2021.

The graph attached shows that the AIS continues to suggest a slightly faster than linear rate of mass loss.
"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)