Note to the Grauniad: “The East Antarctica glacial stronghold” is NOT melting!

Guest rebuttal by David Middleton

East Antarctica glacial stronghold melting as seas warm

Nasa detects ice retreat probably linked to ocean changes in region once thought stable

Damian Carrington Environment editor

Tue 11 Dec 2018

The Totten glacier, East Antarctica. Photograph: Esmee van Wijk/Australian Antarctic Division

A group of glaciers spanning an eighth of the East Antarctica coastline are being melted by the warming seas, scientists have discovered.

This Antarctic region stores a vast amount of ice, which, if lost, would in the long-term raise global sea level by tens of metres and drown coastal settlements around the world.

Freezing temperatures meant the East Antarctica region was until recently considered largely stable but the research indicates that the area is being affected by climate change.

The vast Totten glacier was known to be retreating but the new analysis shows that nearby glaciers in the East Antarctica area are also losing ice.

To the east of Totten, in Vincennes Bay, the height of the glaciers has fallen by about three metres in total since 2008, before which no loss had been recorded.

To the west of Totten, in Wilkes Land, the rate of height loss has doubled since 2009, with glaciers losing height by about two and a half metres to date.

The data comes from detailed maps of ice movement speed and height created by Nasa from satellite information.

[…]

The Grauniad

The vast Totten glacier was known to be retreating but the new analysis shows that nearby glaciers in the East Antarctica area are also losing ice.

Click on the Totten glacier link and you get…

Ocean heat drives rapid basal melt of the Totten Ice Shelf

Stephen Rich Rintoul1,2,*Alessandro Silvano2,3Beatriz Pena-Molino1Esmee van Wijk2Mark Rosenberg1Jamin Stevens Greenbaum4 and Donald D. Blankenship4

  1. Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, Tasmania, Australia.
  2. Commonwealth Scientific and Industrial Research Organization Oceans and Atmosphere, Hobart, Tasmania, Australia.
  3. Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia.
  4. Institute for Geophysics, University of Texas at Austin, Austin, TX 78758, USA.

Science Advances  16 Dec 2016:
Vol. 2, no. 12, e1601610
DOI: 10.1126/sciadv.1601610

Abstract

Mass loss from the West Antarctic ice shelves and glaciers has been linked to basal melt by ocean heat flux. The Totten Ice Shelf in East Antarctica, which buttresses a marine-based ice sheet with a volume equivalent to at least 3.5 m of global sea-level rise, also experiences rapid basal melt, but the role of ocean forcing was not known because of a lack of observations near the ice shelf. Observations from the Totten calving front confirm that (0.22 ± 0.07) × 106m3 s−1 of warm water enters the cavity through a newly discovered deep channel. The ocean heat transport into the cavity is sufficient to support the large basal melt rates inferred from glaciological observations. Change in ocean heat flux is a plausible physical mechanism to explain past and projected changes in this sector of the East Antarctic Ice Sheet and its contribution to sea level.

INTRODUCTION

Ice shelves form where the Antarctic Ice Sheet reaches the ocean and begins to float. Back stress produced by the interaction of the floating ice shelf with side walls and topographic rises buttresses the grounded ice sheet and inhibits the flow of ice into the ocean (1). The thinning or weakening of ice shelves reduces the back stress, increasing the discharge of grounded ice into the ocean and raising sea levels. The thinning of Antarctic ice shelves has been attributed to basal melt by ocean heat flux (23), with the most rapid thinning, grounding line retreat, and acceleration of glacial flow observed in the Bellingshausen Sea and the Amundsen Sea (34). Much of the ice sheet in that sector of Antarctica rests on bedrock below sea level that deepens upstream, a potentially unstable configuration that may result in rapid glacial retreat and mass loss to the ocean (56). Models and observations suggest that increased ocean heat flux may have already initiated the unstable retreat of some West Antarctic glaciers (478). Therefore, the future evolution of the Antarctic Ice Sheet is tightly linked to change in the surrounding ocean.

[…]

Science Advances

What was observed:

Observations from the Totten calving front confirm that (0.22 ± 0.07) × 106m3 s−1 of warm water enters the cavity through a newly discovered deep channel.

What was inferred:

The ocean heat transport into the cavity is sufficient to support the large basal melt rates inferred from glaciological observations.

What was presumed to be plausible:

Change in ocean heat flux is a plausible physical mechanism to explain past and projected changes in this sector of the East Antarctic Ice Sheet and its contribution to sea level.

What was not in the paper:

The vast Totten glacier was known to be retreating but the new analysis shows that nearby glaciers in the East Antarctica area are also losing ice.

Ice shelves are not glaciers. The “vast Totten glacier” has not been known to be retreating.  One small portion of the “vast Totten glacier” has been retreating.

Totten Glacier

Abstract

Totten Glacier has the largest ice discharge in East Antarctica and a basin grounded mostly below  sea level. Satellite altimetry data have revealed ice thinning in areas of fast flow. Here we  present a time series of ice velocity measurements spanning from 1989 to 2015 using Landsat and  interferometric synthetic-aperture radar data, combined with ice thickness from Operation  IceBridge, and surface mass balance from Regional Atmospheric Climate Model. We find that the  glacier speed exceeded its balance speed in 1989 – 1996, slowed down by 11 ± 12% in 2000 to bring  its ice flux in balance with accumulation (65 ± 4 Gt/yr), then accelerated by 18 ± 3% until 2007, and remained constant thereafter. The average ice mass loss (7 ± 2 Gt/yr) is dominated by ice  dynamics (73%). Its acceleration (0.6 ± 0.3 Gt/yr2) is dominated by surface mass balance (80%). Ice  velocity apparently increased when ocean temperature was warmer, which suggests a linkage between  ice dynamics and ocean temperature.

1. Introduction

Totten Glacier has the largest ice discharge in East Antarctica. Its ice flux into the southern  ocean was about 71 ± 3 Gt/yr in 2003 – 2008 [Rignot et al., 2013]. Most of its drainage basin is  grounded well below sea level [Young et al., 2011]. If all ice contained in its basin were to melt  into the ocean, the glacier would raise global sea level by 3.9 m [Li et al., 2015]. Oceanographic  data are few in this part of Antarctica, but existing data indicate the presence of warm modified  Circumpolar Deep Water (mCDW) at about 0°C below 500 m depth on the continental shelf [Bindoff et  al., 2000; Williams et al., 2011]. The bathymetry beneath and in front of its 130 km long ice shelf  holds potential pathways for intrusion of this mCDW into the ice shelf cavity [Greenbaum et al.,  2015]. This would explain the high area-average ice shelf melt rate recorded on Totten Ice Shelf  (10.5 ± 0.7 m/yr) compared to other ice shelves in East Antarctica [Rignot et al., 2013].

Examination of changes in ice surface elevation over time indicates ice shelf thinning in 2003 –  2008 but no significant long-term trend for the time period 1994 – 2012 [Paolo et al., 2015]. In  contrast, the satellite radar altimetry record on land indicates that ice thinning took place in  areas of fast flow, with little to no thinning in the surrounding, slower-moving areas [Zwally et  al., 2005; Davis et al., 2005; Shepherd and Wingham, 2007; Flament and Rémy, 2012; Horwath et al.,  2012; McMillan et al., 2014]. Ice thinning at the grounding line of the fastest portion of Totten  Glacier averaged 1.7 ± 0.2 m/yr for the period 2003 – 2008 with ICESat [Pritchard et al., 2009,  2012] and 0.5 ± 0.01 m/yr with Cryosat-2 for 2010 – 2013 [McMillan et al., 2014]. Time-variable  gravvity data from the Gravity Recovery and Climate Experiment (GRACE) for the time period 2003 – 2013 suggest an accelerating mass loss for Totten, Moscow University, and Frost combined [Velicogna et al., 2014; Williams et al., 2014]. Comparison of the mass loss derived from GRACE with time series of surface mass balance (SMB) anomalies from the Regional Atmospheric Climate Model (RACMO2)  [Lenaerts et al., 2012] over the same time period suggests that only 40% of the signal is explained by SMB [Velicogna et al., 2014].

A recent analysis showed that the glacier grounding line retreated by 1 to 3 km between 1996 and  2013, corresponding to an average ice thinning rate of 0.7 ± 0.1 m/yr [Li et al., 2015]. This magnitude thinning is consistent with the altimetry record and suggests that ice has been flowing faster than the speed required to maintain a state of mass balance with snowfall in the interior region.

[…]

5. Conclusions

We assembled a 26 year long time series of ice velocity measurements on Totten Glacier to conclude that the glacier speed has fluctuated up to 18% during the time period, with low values around 2000, high values prior to 1996 and after 2002. In the last 10 years, the glacier has maintained a relatively steady speed but has been flowing above equilibrium conditions. The glacier has been losing mass at a rate of 6.8 ± 2.4 Gt/yr or 10% of the total flux on average for the past 26 years. The main loss is caused by the speedup of the glacier along its main flow. Our results also suggest that the glacier may be strongly sensitive to ocean temperature. More detailed studies are needed to quantify the impact of ocean temperature on ice dynamics in this important sector of East Antarctica.

Li et al., 2016

Figure 1 from Li et al., 2016.  “(a) Ice velocity magnitude and (b) direction of Totten Glacier, East Antarctica, color coded on a  logarithmic scale and overlaid on MODIS Mosaic of Antarctica image [Scambos et al., 2007] using ALOS PALSAR  data from 2006 to 2010 and 2011 TDX/TSX, 2013 TDX/TSX, CSK, and Landsat-8 data. The grounding line
(GL) from 2013 is solid white. Flux gates are solid yellow (GL) and orange (along Operation  IceBridge (OIB) ground tracks). Green boxes A and B delineate the area used to generate the  velocity time series (Figure 2a). Brown box is the map outline of Figures 1b and 3. BEDMAP2 surface elevation [Fretwell et al., 2013] contours are plotted at 300 m intervals.

Figure 2 from Li et al., 2016. “Time series of (a) ice velocity, (b) ice discharge (D) and surface mass balance (SMB), (c) subsurface ocean potential temperature (450–600 m depth), and (d) cumulative mass anomalies on Totten Glacier, East Antarctica. Figure 2a shows velocity change at the grounding line (box A in Figure 1) and at the east tributary (box B). Error bars for the bottom time series are the same as the top one. Red dots in Figure 2b show average potential temperature for each velocity data epoch in Figure 2a. Grey dashed lines are fitted using a piecewise linear regression. SMB values in Figure 2c are smoothed with a 12 month running filter. The total mass anomalies (black) in Figure 2d are partitioned between the anomalies in SMB (red) and in ice discharge (D, in blue).”

Figure 3 from Li et al., 2016. “Change in flow speed from year (a) 2000 to 2007, (b) 2007 to 2013, and (c) 2009 to 2010 on Totten Glacier, East Antarctica, overlaid on a MODIS Mosaic of Antarctica [Scambos et al., 2007]. Grounding line from Li et al. [2015] is in black.”

Key points about Totten Glacier:

It has the largest discharge of any Antarctic outlet glacier.  It already had this when they started measuring glaciers in Antarctica.

  • Surface mass balance exhibits very little in the way of a coherent trend,
  • Thinning exhibits “no significant long-term trend for the time period 1994 – 2012.”
  • “Ice thinning took place in  areas of fast flow, with little to no thinning in the surrounding, slower-moving areas.”
  • Ice velocity in the discharge area has widely fluctuated.
  • “The glacier grounding line retreated by 1 to 3 km between 1996 and  2013.”
  • “If all ice contained in its basin were to melt  into the ocean, the glacier would raise global sea level by 3.9 m.”
  • “The glacier has been losing mass at a rate of 6.8 ± 2.4 Gt/yr… on average for the past 26 years.”

Is 6.8 Gt/yr significant?

We can calculate the volume of water required to raise global sea levels by 1 mm:

Volume = area x height

Area = 3.618 x 10km2

Height = 10-6 km (1 mm)

Volume (km3) = (3.618 x 10km) x (10-6 km) = 3.618 x 10km= 361.8 kmwater.

We can convert km3 of water to Gt of water as we did above; 1 kmwater = 1 Gt water.  In the same way, 1 Gt of ice = 1 kmwater. So, 361.8 Gt of ice will raise global sea levels by 1 mm. 361.8 Gt of ice is equivalent to 394.67 km3 ice.

If we took our 458.30 Gt of ice (as calculated above), then we could calculate the global sea level equivalent by:

SLE (mm) = mass of ice (Gt) x (1 / 361.8)

SLE = 458.30 x (1 / 361.8)

SLE = 1.27 mm

However, we should note that some of the world’s glaciers have parts that are below sea level. This ice will not affect sea level if it melted. The volume of glacier ice below the surface of the ocean should therefore be subtracted from the total volume of glaciers and ice caps when calculating sea level equivalents [15].

Antarctic Glaciers

If “most of its drainage basin is  grounded well below sea level,” then “if all ice contained in its basin were to melt  into the ocean, the glacier would raise global sea level by” less than  3.9 m.  But this number enables us to calculate the mass of Totten Glacier.

If 361.8 Gt of ice melt will raise sea level by 1 mm, the ice mass of Totten Glacier is:

  • 368.1 Gt/mm x 3,900 mm = 1,411,020 Gt

The current ice mass is around 1.4 million Gt.

  • 6.8 Gt ÷ 1,411,020 =  0.000005 = 0.0005%

According to Li et al., 2016, Totten Glacier has cumulative mass balance loss of about 180 Gt from 1988-2016.

  • 180 Gt ÷ 1,411,020 =  0.0001 = 0.01%

99.99% of Totten glacier did not ablate from 1988-2016.  At 6.8 Gt/yr, it would take 207,503 years for the melting of Totten Glacier to raise sea level by 3.9 m.  So, one has to ask, “Why in the Hell did Li et al., 2016 mention this in their paper?”  Yes, that was a rhetorical question.

Back to The Grauniad:

A group of glaciers spanning an eighth of the East Antarctica coastline are being melted by the warming seas, scientists have discovered.

This Antarctic region stores a vast amount of ice, which, if lost, would in the long-term raise global sea level by tens of metres and drown coastal settlements around the world.

The red areas on the Grauniad map are glacial discharge areas.  These are areas of higher ice velocity.  Although glaciers often move at a glacially slow pace, they are suppose to move.

A glacier is a persistent body of dense ice that is constantly moving under its own weight; it forms where the accumulation of snow exceeds its ablation (melting and sublimation) over many years, often centuries.

–Wikipedia

If all of the glaciers that feed the red areas on the map flowed into the ocean and melted, sea level would rise by 10’s of meters… “If ifs and buts were candy and nuts, we’d all have a Merry Christmas.”  There’s no scenario by which all of this ice could melt and flow into the ocean… So, why even mention it in the article?  Yes… another rhetorical question.

If the ice shelves supposedly buttressing these glaciers melted, sea level would barely notice.

However, the loss of these ice shelves would supposedly cause the glaciers to collapse into the sea.  This is based entirely on models.

Abstract

[1] Reduction or loss of a restraining ice shelf will cause speed‐up of flow from contiguous ice streams, contributing to sea‐level rise, with greater changes from ice streams that are wider, have stickier beds, or have higher driving stress. Loss of buttressing offsetting half of the tendency for ice‐stream/ice‐shelf spreading for an ice stream similar to Pine Island Glacier, West Antarctica is modeled to contribute at least 1 mm of sea‐level rise over a few decades. These results come from a new, simple model that includes relevant stresses in a boundary‐layer formulation, and allows rapid estimation of ice‐shelf impacts for a wide range of configurations.

Dupont & Alley, 2005

Scambos et al., 2004 ostensibly documented “a two‐ to six‐fold increase in centerline speed of four glaciers” after the collapse of the Larsen B ice shelf.  However, this is on the Antarctic Peninsula and unlikely to be analogous the vast East Antarctic Ice Sheet, which has been stable since at least the Pliocene and likely to have been stable since at least the Mid-Miocene.

Conclusion

Antarctic glaciers aren’t doing anything now, that they haven’t been doing for the past 12,000 years.

The history of deglaciation of the West Antarctic Ice Sheet (WAIS) gives clues about its future. Southward grounding-line migration was dated past three locations in the Ross Sea Embayment. Results indicate that most recession occurred during the middle to late Holocene in the absence of substantial sea level or climate forcing. Current grounding-line retreat may reflect ongoing ice recession that has been under way since the early Holocene. If so, the WAIS could continue to retreat even in the absence of further external forcing…

Conway et al, 1999

 

References

Conway, H. et al, 1999. Past and Future Grounding-Line Retreat of the West Antarctic Ice Sheet. Science 8 October 1999: Vol. 286 no. 5438 pp. 280-283

Dupont, T. K., and R. B. Alley (2005), Assessment of the importance of ice‐shelf buttressing to ice‐sheet flowGeophys. Res. Lett.32, L04503, doi:10.1029/2004GL022024.

Li, X., E. Rignot, J. Mouginot, and B. Scheuchl (2016), Ice flow dynamics and mass loss of Totten Glacier, East Antarctica, from  1989 to 2015, Geophys. Res. Lett., 43, 6366 – 6373, doi:10.1002/2016GL069173.

Rintoul, Stephen & Silvano, Alessandro & Pena-Molino, Beatriz & van Wijk, Esmee & Rosenberg, Mark & Greenbaum, Jamin & D. Blankenship, Donald. (2016). Ocean heat drives rapid basal melt of the Totten Ice Shelf. Science Advances. 2. 10.1126/sciadv.1601610.

Scambos, T. A., J. A. Bohlander, C. A. Shuman, and P. Skvarca (2004), Glacier acceleration and thinning after ice shelf collapse in the Larsen B embayment, AntarcticaGeophys. Res. Lett.31, L18402, doi:10.1029/2004GL020670.

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December 13, 2018 at 03:09PM

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