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Author Topic: Surge of WAIS Ice Mass Loss  (Read 82338 times)

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #100 on: June 10, 2013, 05:08:31 AM »
NASA has recently posted some of the data from their Antarctic 2012 IceBridge survey at the following two websites:

ftp://n4ftl01u.ecs.nasa.gov/SAN2/ICEBRIDGE_FTP/IRMCR1B_MCORDSxyEcho_v01/2012_AN_NASA/pdf/

ftp://n4ftl01u.ecs.nasa.gov/SAN2/ICEBRIDGE/ILATM2.001/

The first attached image shows the location of the geometry at the Thwaites Glacier gateway, which can be used to locate the next two echo images from ice tongue portion of this area.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #101 on: June 10, 2013, 05:13:52 AM »
The attached four images are related the Oct 12th 2012 IceBridge radar echo images in the range of the Thwaites Glacier trough (see the first image in the previous post) between 107degrees west and 108 degrees west..
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Laurent

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Re: Surge of WAIS Ice Mass Loss
« Reply #102 on: June 10, 2013, 02:19:39 PM »
Hello AbruptSLR,

Can you explaine what do we see ?
The radar show different density or something else ?
The "1" is some snow above the ice ?
The "2" a layer of dust ?
The "3" the bedrock ?

Thanks !

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #103 on: June 10, 2013, 03:30:27 PM »
Laurent,

I honestly do not know.  However, I assume that the red dashed line (your layer 3) is the top of the bedrock (see the attached bedrock image in this area); and I assume that the zones above layer 3  are ice with different radar propagation properties.  I take this data to imply that most of the Thwaites Trough is filled with solid ice after the September 2012 surge event that displaced the old Thwaites ice tongue.  Note that the profile in my first post on this topic shows a section through the new Thwaites Ice Tongue.
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Bruce Steele

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Re: Surge of WAIS Ice Mass Loss
« Reply #104 on: June 10, 2013, 05:51:56 PM »
In the first frame labeled Tinto et al 2011 the x/y axis are labeled lat /long. If you draw a line on 75.4 South and go from 106.6 W to 108 W ( transecting the D rectangle on the 75.4 line) you get a good picture of where the second radar image ( 03-014) is located. It spans the trough which at it's deepest is ~ 1300 meters. The line #2 that Laurent pointed to looks like water may have been liquid below      ~ 800 meters and then refrozen?   

SteveMDFP

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Re: Surge of WAIS Ice Mass Loss
« Reply #105 on: June 10, 2013, 06:15:02 PM »
In the first frame labeled Tinto et al 2011 the x/y axis are labeled lat /long. If you draw a line on 75.4 South and go from 106.6 W to 108 W ( transecting the D rectangle on the 75.4 line) you get a good picture of where the second radar image ( 03-014) is located. It spans the trough which at it's deepest is ~ 1300 meters. The line #2 that Laurent pointed to looks like water may have been liquid below      ~ 800 meters and then refrozen?
Pure speculation here.  It occurs to me that interpreting this kind of radar imagery is somewhat similar to principles of interpreting sonograms, and I have a bit of experience there.  I'd interpret Laurent's #2 line as a discontinuity between similar media, in this case, ice.  I'd guess that the ice below this line is "fast" against the irregular bedrock below, the ice above this line is glacier in motion.  So we might have glacier ice moving over a bed of "fast" ice.

The arctic is a funny place.  Fast ice doesn't move.  Fresh sea ice is old.

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #106 on: June 11, 2013, 02:25:35 AM »
All,

If you click on the NASA ftp site link that I provided with the Tinto et al image post then you can see all of the NASA data (I provided very little of it); also, if you look at the information in the Glaciology Basics thread then you will see that it is unlikely that the bottom of the Thwaites Glacier is "fast" to the bottom.  If I were to guess, I would say that the material above the "1" line may be ice has is not yet fully consolidated from when it fell as snow, and that the "2" line may be either volcanic ash, or an paleo icemelt refreezing layer.  But as I am not a glaciologist, I am just guessing.

ASLR
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #107 on: June 11, 2013, 05:13:55 PM »
To be a little bit clearer still:  At the opening of this thread I speculated that following the September 2012 Thwaites Ice Tongue "Surge" that the subglacial cavity in the gateway of the Thwaites trough might still be intact; however, (to me) this radar echo information from Oct 12, 2012 indicates that any subglacial cavity that might have been present (due to advective processes) in the Thwaites trough before Sept 2012, has clearly been infilled with glacial ice when the ice stream surged forward; which if true would delay the possible impact of advective action on the grounding line retreat in the trough; but on the other hand the future repetition of this type of "surge" action should eventually thin the ice stream in the trough sufficiently for the ice stream to float in the trough area, which would also result in a grounding line retreat; potential like what occurred at the Jakobshavn Glacier in Greenland.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #108 on: June 26, 2013, 12:11:38 AM »
Per the attached image from NOAA for June 2013, it appears that the current La Nina condition is currently contributing to a brief downturn in the rate of eustatic SLR:
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #109 on: July 03, 2013, 04:45:52 PM »
The attached Aviso SLR trend graph with data through the end of March 2013 concurs with the previously posted NOAA SLR trend graph that the current La Nina event is causing a small decline in eustatic sea level (see data below):

2012.422862 6.078059e-02
2012.450010 6.156758e-02
2012.477157 6.287806e-02
2012.504305 6.423590e-02
2012.531452 6.485447e-02
2012.558600 6.433446e-02
2012.585747 6.309864e-02
2012.612895 6.212927e-02
2012.640042 6.220034e-02
2012.667190 6.326858e-02
2012.694338 6.454812e-02
2012.721485 6.518403e-02
2012.748633 6.491579e-02
2012.775780 6.416396e-02
2012.802928 6.355374e-02
2012.830075 6.338392e-02
2012.857223 6.352537e-02
2012.884370 6.374200e-02
2012.911518 6.400549e-02
2012.938665 6.445165e-02
2012.965813 6.507447e-02
2012.992961 6.556311e-02
2013.020108 6.552975e-02
2013.047256 6.497331e-02
2013.074403 6.441465e-02
2013.101551 6.442661e-02
2013.128698 6.510936e-02
2013.155846 6.591828e-02
2013.182993 6.608698e-02
2013.210141 6.545900e-02
2013.233918 6.448728e-02
2013.268842 6.365161e-02
2013.291584 6.304750e-02

That said, I would like to note that the current rate of eustatic sea level decline is significantly slower than that for most prior La Nina events; raising to possibility that ice mass lose from ice sheets is making a more significant contribution to SLR that in past several decades.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #110 on: July 13, 2013, 11:27:52 PM »
Both earlier in this thread and in the "Tectonic" thread I have noted that prior GRACE estimates of SLR contribution from Antarctica appear to be too low due to the prior use of incorrect GIA factors; which means that the rate of acceleration of ice mass loss from Antarctica (as determined by GRACE) were previously also too low.  Nevertheless, the trend line for SLR appears to be linear; which periodic flucuations (such as from ENSO) aside, means that there appears to be a negative SLR feedback suppressing the positive non-linear influence of the acceleration of AIS ice mass loss that the experts have not accounted for yet.

Here, I examine the evidence that the recent accumulation of water vapor in the atmosphere maybe be making a significant contribution to such a negative SLR feedback.

The first attached figure from NOAA 2013 shows the atmospheric specific humidity from 1948 to 2013 at 600 and 1000 mb (where most of the water vapor is located).  Also, the second image also from NOAA shows the change in atmospheric specific humidity from 1971 to 2011.  Both of this images indicate that since the beginning of the satellite era (circa 1993) the atmospheric specific humidity has increased about 2%.

This observation is confirmed by  Durack et al in:  “Ocean Salinities Reveal Strong Global Water Cycle Intensification during 1950-2000” By Paul J. Durack, Susan E. Wijffels and Richard J. Matear – published in Science Magazine 27th April 2012 (DOI: 10.1126/science.1212222); which is available at:

http://www.sciencemag.org/content/336/6080/455

Which states:

"The water cycle has become 4 percent stronger from 1950-2000"; and "With a projected temperature rise of 3 degrees Celsius by the end of the century, the researchers estimate a 24 percent acceleration of the water cycle is possible."

Now, according to Gleick (Gleick, P. H., 1996: Water resources. In Encyclopedia of Climate and Weather, ed. by S. H. Schneider, Oxford University Press, New York, vol. 2, pp.817-823) the volume of water in the atmosphere prior to the 1993 was about:

12,900 cubic kilometers (km3) = 12.9 x 1.0E12 m³

Noting that 1 kilogram is equal to 1.0E-12 gigatonne (Gt), and that the weight of one cubic meter of water is 1,000 kg = one tonne of water; thus the weight of water in the atmosphere before the recent warming was about:

12,900 Gt

Noting that 100 Gt of ice mass loss ~ 0.28mm of Eustatic SLR, this pre-1993 atmospheric water content is equal to about:

129 times 0,28mm = 36 mm of equivalent sea level rise

Thus a 2% increase in this amount from 1993 to 2013 is equal to about a - 0.04mm/yr; which could be masking some of the recent acceleration in SLR contribution from the AIS (primarily from the WAIS).

However, as Durack et al 2012 note the atmospheric specific humidity could increase by 24% when the global mean temperature increases by 3 degrees C; which according to the third attached image could happen by about 2050 if we stay on the RCP 8.5 95% trend that we are currently following.  If so this could mask 36mm times 0.24  = 8.7 mm or 8.7/37 = 0.24 mm/yr of SLR contribution from ice sheet melting from now to 2050.  Such masking will likely delay the recognition of the risks of ASLR that will come after 2050.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #111 on: July 14, 2013, 05:26:09 PM »
The following referenced paper (see abstract and selected attached figures).  These researchers acknowledge that their modeling is in the nascent stages; but their efforts are serious and they reflect the seriousness of relative (regional) sea level rise, RSLR, even for cases such as RCP 4.5 50%CL.  Note that the researchers use a semi-empirical model to estimate SLR (which does not consider the risk of the collapse of the WAIS), and they do not consider RCP 8.5 95% CL (which is close to the path that we are currently following:

A scaling approach to project regional sea level rise and its uncertainties
by: M. Perrette, F. Landerer, R. Riva, K. Frieler, and M. Meinshausen; Earth Syst. Dynam., 4, 11–29, 2013; www.earth-syst-dynam.net/4/11/2013/; doi:10.5194/esd-4-11-2013

"Abstract. Climate change causes global mean sea level to rise due to thermal expansion of seawater and loss of land ice from mountain glaciers, ice caps and ice sheets. Locally, sea level can strongly deviate from the global mean rise due to changes in wind and ocean currents. In addition, gravitational adjustments redistribute seawater away from shrinking ice masses. However, the land ice contribution to sea level rise (SLR) remains very challenging to model, and comprehensive regional sea level projections, which include appropriate gravitational adjustments, are still a nascent field (Katsman et al., 2011; Slangen et al., 2011). Here, we present an alternative approach to derive regional sea level changes for a range of emission and land ice melt scenarios, combining probabilistic forecasts of a simple climate model (MAGICC6) with the new CMIP5 general circulation models.  The contribution from ice sheets varies considerably depending on the assumptions for the ice sheet projections, and thus represents sizeable uncertainties for future sea level rise.
However, several consistent and robust patterns emerge from our analysis: at low latitudes, especially in the Indian Ocean and Western Pacific, sea level will likely rise more than the global mean (mostly by 10–20 %). Around the northeastern Atlantic and the northeastern Pacific coasts, sea level will rise less than the global average or, in some rare cases, even fall. In the northwestern Atlantic, along the American coast, a strong dynamic sea level rise is counteracted by gravitational depression due to Greenland ice melt; whether sea level will be above- or below-average will depend on the relative contribution of these two factors. Our regional sea level projections and the diagnosed uncertainties provide an improved basis for coastal impact analysis and infrastructure planning for adaptation to climate change."

The caption for the first attached image is (note that I have deleted results for RCP 3PD from the figure because I believe they will not happen):

"Projected median regional sea level change for all RCP scenarios (from RCP 3PD to RCP 8.5) in the semi-empirical ice sheet case. Contour lines are every 10 cm. Grey shading indicates areas of sea level drop."

The second attached image shows an estimated RSLR for New York, the Dutch Coast, Tokyo and the Bay of Bengal assume a semi-empirical estimate of SLR for RCP 4.5 50% CL
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #112 on: July 14, 2013, 07:46:46 PM »
The supplement to the paper cited in the immediately preceding post can be found at:

http://www.earth-syst-dynam.net/4/11/2013/esd-4-11-2013-supplement.pdf

This supplementary material provides additional information about both the author's methodology and also about their uncertainties, which are summarized by the authors in the first attached image.

The caption for the first attached image is:

"Fig. 12. (a)–(c) Uncertainty in regional sea level change, indicated as “likely” range (roughly 16th to 84th percentiles). Uncertainty in sea level change (a) and its steric component (b), for the RCP 4.5 scenario in the semi-empirical case. The uncertainty resulting from GIS/AIS partition in the semi-empirical approach is illustrated in panel (c), for a total ice sheet contribution equal to the ensemble median. Contours lines indicate 5 cm intervals. Black dots indicate individual locations highlighted in Fig. 9."

The caption for the second attached image is:

"Figure S5: Sea-level rise along the world's coastlines for the four RCP scenarios and the two ice-sheet cases (left: IPCCAR4+, right: Semi-empirical), between 1980-1999 and 2090-2099. The various coastlines are represented in separate panels. Red filled areas represent the upper bound of the uncertainty range in the RCP8.5 scenario (50th to 68th percentiles), and blue filled areas the lower bound in the RCP3PD scenario (16th to 50th percentiles). Global mean sea level rise for each RCP scenario is indicated in the left part of each panel, continued with dotted lines over the rest of the panel. See Figure 9 of the main document to visualize the coastlines on a world map."

The caption for the third attached image is:

"Figure S6: Glacial isostatic adjustment expressed as sea-level change along the world's coastlines, between 1980-1999 and 2090-2099. The data is averaged over a 300 km wide band of coastal waters. Based on ICE-5G (VM2) Peltier (2004)."

The caption for the fourth attached image is:

"Figure S7: Comparison of the IPCCAR+ ice-sheet case (with the RCP 6.0 emission scenario) (_lled) with regional SLR projections from Slangen et al. (2011) (with the SRES A1B emission scenario) (hatched). (a) Total SLR with 16th-84th (this study) and 1-sigma uncertainties (Slangen) (both uncertainty measures are equivalent for a Gaussian distribution). (b) Individual contributions to SLR. GIA is included in this Figure, to ease comparison (in both cases based on the ICE-5G (VM2) model, but with slightly di_erent implementations). The dashed vertical line in (a) indicated the global mean SLR. The RCP 6.0 emission scenario is comparable to SRES A1B, and the IPCCAR4+ ice sheet case is similar to Slangen et al's treatment of the ice sheets (except that they do consider negative AIS SMB and add a dynamic ice-sheet contribution based on the IPCCAR4 on top of GIS and AIS contribution, which leads to slightly higher ice-sheet contributions than our approach of setting Antarctica contribution to zero and ignoring any dynamic contribution from the ice sheets to SLR). These differences in treatment of the ice sheets, as well as slightly higher MGIC contributions in Slangen et al. (2011) than in our approach, explain the overall higher land-ice contribution in Slangen et al. (2011). Location coordinates may differ between both studies, which is an additional source of discrepancy in regions with small-scale SLR features. We choose this combination of emission scenario and ice-sheet case from our results to help focusing on the regional distribution of SLR. Figures 9 and S5 show a more comprehensive comparison between ice-sheet cases and emission scenarios."

Note that the reference for Slangen et al (2011) is:

Slangen, A. B. A., Katsman, C. A., Wal, R. S. W., Vermeersen, L. L. A., and Riva, R. E. M.: Towards regional projections of twenty-first century sea-level change based on IPCC SRES scenarios, Clim. Dynam., 38, 1191–1209, doi:10.1007/s00382-011-1057-6, 2011.

While the authors admit that their analysis is in the nascent stages, I particularly appreciate their sincere effort to indicate their uncertainties illustrated by the first attached image; which emphasizes the high uncertainties in their studies associated with ice mass loss from ice sheets (sources for such uncertainties probably include: (a) all of the potential collapse mechanisms for the WAIS that I discuss in this Antarctic folder); (b) snow scoured by wind in East Antarctica; (c) Affects of Specific Humidity Changes on SLR; (d) dynamic ice surface melting in Greenland; (e) the steric influences of AABW changes on SLR; (f) etc.  Clearly, this document was generated in time to be referenced as part of the AR5 WGI results to be issued between September 23 and 26th, 2013; and all of the assumptions are compatible with the draft release of the AR5 document (including the normal [non-collapse] Thwaites Ice Tongue surging cited in this thread).

I only hope someday that other researchers will present their uncertainties in this manner; and I also hope that someday researchers will formally include inputs such as RCP 8.5 95% CLR, and possible collapse mechanisms for the WAIS (see the "RCM" thread).
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #113 on: July 17, 2013, 02:08:29 AM »
The information in the following reference (and abstract) implies that the development of basal crevasses may lead to the acceleration collapse of the Thwaites Ice Tongue (which would then lead to an acceleration of the previously buttresses section of Thwaites Glacier).

A novel method for predicting fracture in floating ice
by: Liz LOGAN, Ginny CATANIA, Luc LAVIER, Eunseo CHOI; Journal of Glaciology, Vol. 59, No. 216, 2013 doi:10.3189/2013JoG12J210

"ABSTRACT. Basal crevasses may play an important precursory role in determining both the location and propagation of rifts and iceberg dimensions. For example, icebergs calved recently from Thwaites Glacier, Antarctica, have the same width as surface undulations, strengthening the connection between basal crevasses, rifting and calving. We explore a novel method for estimating the heights of basal crevasses formed at the grounding lines of ice shelves and ice streams. We employ a thin-elastic beam (TEB) formulation and tensional yielding criterion to capture the physics of flexed ice at grounding lines. Observations of basal crevasse heights compare well with model predictions in the Siple Coast region of the Ross Ice Shelf. We find that the TEB method is most accurate in areas of low strain rate. We also test the method in other areas of Antarctica to produce order-of-magnitude maps of grounding-line basal crevasses and find general agreement with reported observations assuming basal crevasses develop in spatio-temporal sequence and are advected downstream. This method is computationally cheap and could be relatively easy to implement into damage-oriented large-scale ice models which aim at physically simulating calving and fracture processes."

The following passage (and the attached image) from the article describes the mechanisms for active calving from the Thwaites Glacier in January 2013:

"A Landsat-7 image from January 2013 (Fig. 6) shows undulated topography which we believe may indicate the onset of basal crevasses. Measurements of the surface depression spacing (yellow bars) were compared to measurements of the freshly calved icebergs (red bars). The average spacing of the surface depressions is 1034 m, and the average width of the freshly calved icebergs is 1035m (standard deviations 217 and 224 m, respectively). This suggests that, at least in areas where basal crevasses persist long enough to reach the calving front, iceberg geometry can be controlled to a first order by the spacing of basal crevasses."
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sidd

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Re: Surge of WAIS Ice Mass Loss
« Reply #114 on: July 17, 2013, 05:05:56 AM »
The Logan(2013) paper is fascinating, especially in the context of refluxing ice. The (two-phase) hydrodynamics is ...complex... and the heat flow more so. O that I had the time.   

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #115 on: July 17, 2013, 05:06:50 PM »
Sidd,

I have to agree that there is a lot of very fascinating work going on now days on many fronts of this complex topic (here focused on the behavior of floating ice shelves and ice tongues).  It would seem that with the high degree of complexity, performing more field work such as that cited below will be critical to developing a more complete understanding:

First and except from the intenet about a new ROV (see attached image) that can travel under floating ice shelves/tongues (first RIS and then hopefully others like FRIS, PIIS and the Thwaites Ice Tongue):

"Northern Illinois University’s 28-foot-long, 2,200-pound robotic submarine, built for exploration beneath the ice shelf in the Antarctic, is getting its maiden voyage this week in one of the nation’s deepest and most celebrated bodies of water—Lake Tahoe.
The unmanned yellow submarine—also known as a remotely operated vehicle (ROV) or sub-ice rover (SIR)—is equipped with a high definition camera and a suite of scientific instrumentation. It will be assessed by a team of scientists and engineers from NIU’s Department of Geology and Environmental Geosciences and DOER Marine, a robotics engineering firm located in the San Francisco Bay area.
DOER built the ROV for NIU, which intends to use the vehicle to study melting beneath the Ross Ice Shelf in Antarctica."

Next two links to NSF field projects that are making progress, but that are still in-progress (including PIG, WISSARD, and WAIS projects):

http://www.nsf.gov/news/news_summ.jsp?cntn_id=126388

http://news.psu.edu/story/264578/2013/02/18/research/research-ice-mapping-water-beneath-antarctic-ice-shelf

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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #116 on: July 18, 2013, 06:20:25 PM »
The attached images come from:

www.climate4you.com/SeaTemperatures.htm#PDO - Pacific Decadal Oscillation

The first attached image emphasizes the point that I made earlier in this thread that the SLR observations show a temporary "surge" that peaked around March 13; while the second attached image shows the Oceanic Nino Index, ONI, that indicates that at the beginning of 2013 there was a weak La Nina period (which tends to temporarily reduces sea level), and that now the world is headed towards a ENSO neutral period through the Fall of 2013.  I point this out again to note that the current La Nina (or ENSO neutral) could be masking some acceleration of ice mass loss from the WAIS.

Furthermore, the last (third) attached image shows the Pacific Decadal Oscillation, PDO, together with the following description of the PDO indicating that the current phase of the PDO is temporarily suppressing SLR (and may continue to do so for several more years); but that eventually this trend will reverse and SLR will accelerate.

The following description of the PDO comes from:

http://jisao.washington.edu/pdo/

"The "Pacific Decadal Oscillation" (PDO) is a long-lived El Niño-like pattern of Pacific climate variability. While the two climate oscillations have similar spatial climate fingerprints, they have very different behavior in time. Fisheries scientist Steven Hare coined the term "Pacific Decadal Oscillation" (PDO) in 1996 while researching connections between Alaska salmon production cycles and Pacific climate (his dissertation topic with advisor Robert Francis). Two main characteristics distinguish PDO from El Niño/Southern Oscillation (ENSO): first, 20th century PDO "events" persisted for 20-to-30 years, while typical ENSO events persisted for 6 to 18 months; second, the climatic fingerprints of the PDO are most visible in the North Pacific/North American sector, while secondary signatures exist in the tropics - the opposite is true for ENSO. Several independent studies find evidence for just two full PDO cycles in the past century: "cool" PDO regimes prevailed from 1890-1924 and again from 1947-1976, while "warm" PDO regimes dominated from 1925-1946 and from 1977 through (at least) the mid-1990's. Shoshiro Minobe  has shown that 20th century PDO fluctuations were most energetic in two general periodicities, one from 15-to-25 years, and the other from 50-to-70 years
Causes for the PDO are not currently known. Likewise, the potential predictability for this climate oscillation are not known. Some climate simulation models produce PDO-like oscillations, although often for different reasons. The mechanisms giving rise to PDO will determine whether skillful decades-long PDO climate predictions are possible. For example, if PDO arises from air-sea interactions that require 10 year ocean adjustment times, then aspects of the phenomenon will (in theory) be predictable at lead times of up to 10 years. Even in the absence of a theoretical understanding, PDO climate information improves season-to-season and year-to-year climate forecasts for North America because of its strong tendency for multi-season and multi-year persistence. From a societal impacts perspective, recognition of PDO is important because it shows that "normal" climate conditions can vary over time periods comparable to the length of a human's lifetime."
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #117 on: July 18, 2013, 11:46:02 PM »
Needless to say, when I see findings such as those cited below by Wouters et al 2013; I wonder what type of an ice mass loss signal that would calculate if: (a) the used GIA corrections such as those published by Ligtenberg et al 2013 (see the "Glaciology" thread); and (b) had access to GRACE data from a positive PDO index (see the preceeding post):

Limits in detecting acceleration of ice sheet mass loss due to climate variability
by: B. Wouters, J. L. Bamber, M. R. van den Broeke, J. T. M. Lenaerts & I. Sasgen; Nature Geoscience; (2013); doi:10.1038/ngeo1874; Published online14 July 2013

"Abstract
The Greenland and Antarctic ice sheets have been reported to be losing mass at accelerating rates. If sustained, this accelerating mass loss will result in a global mean sea-level rise by the year 2100 that is approximately 43 cm greater than if a linear trend is assumed2. However, at present there is no scientific consensus on whether these reported accelerations result from variability inherent to the ice-sheet–climate system, or reflect long-term changes and thus permit extrapolation to the future3. Here we compare mass loss trends and accelerations in satellite data collected between January 2003 and September 2012 from the Gravity Recovery and Climate Experiment to long-term mass balance time series from a regional surface mass balance model forced by re-analysis data. We find that the record length of spaceborne gravity observations is too short at present to meaningfully separate long-term accelerations from short-term ice sheet variability. We also find that the detection threshold of mass loss acceleration depends on record length: to detect an acceleration at an accuracy within ±10 Gt yr−2, a period of 10 years or more of observations is required for Antarctica and about 20 years for Greenland. Therefore, climate variability adds uncertainty to extrapolations of future mass loss and sea-level rise, underscoring the need for continuous long-term satellite monitoring."
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Lennart van der Linde

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Re: Surge of WAIS Ice Mass Loss
« Reply #118 on: July 19, 2013, 09:04:20 AM »
ASLR,
Maybe you've also seen the new paper in PNAS by Levermann et al on millennial-scale sea level commitment:
http://www.pnas.org/content/early/2013/07/10/1219414110.full.pdf+html

They estimate about 2,3 meters of SLR per degree of warming, so about 9 m of SLR after 2000 years with 4 degrees of warming.

This seems all way too conservative to me in light of the risks of faster and larger SLR that Hansen, Rohling and others have been pointing at over the past years.

What do you make of this paper?

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #119 on: July 19, 2013, 04:33:02 PM »
Lennart,
I think that such papers have their merits in that the vast majority of people are not psychologically prepared to think about the risks of abrupt SLR; and at least this paper makes it clear that we are now absolutely committing our great grandchildren to high sea levels (a message which I believe that most people are now willing to at least hear).  That said, this paper never says that abrupt SLR cannot occur, and they leave that matter for others to evaluate.  For example, the first attached image is Fig. 1-C, D & E [see caption for this figure below] from Levermann et al (2013) [note I have omitted the thermal and mountain glacier and ice cap portion of this image (ie panels A & B) as this data seem reasonable to me], and I note that:

(a) this figure does not talk about time but wrt Panel C, but it is commonly accepted that in the Eemian that the WAIS degraded much faster than the GIS; and

(b) wrt Panel D: (i) this panel uses data from Pollard et al 2009, which is not as sensitive to change as more modern models, so you would not expect to find time sensitive output; and (ii) more importantly, note that many of the small black dots [that represent 1,000-yr averages] in Panel D occur with almost no temperature increase above pre-industrial temperatures; which at least raises the possibility of abrupt SLR.

Caption for the attached image:
"Fig. 1. Sea-level commitment per degree of warming as obtained from physical model simulations of (A) ocean warming, (B) mountain glaciers and ice caps, and (C) the Greenland and (D) the Antarctic Ice Sheets. (E) The corresponding total sea-level commitment, which is consistent with paleoestimates from past warm periods (PI, preindustrial, Plio, mid-Pliocene; see text for discussion). Temperatures are relative to preindustrial. Dashed lines and large dots provide linear approximations: (A) sea-level rise for a spatially homogeneous increase in ocean temperature; (A, D, E) constant slopes of 0.42, 1.2, and 1.8 and 2.3 m/°C. Shading as well as boxes represent the uncertainty range as discussed in the text. (A–C) Thin lines provide the individual simulation results from different models (A and B) or different parameter combinations (C). The small black dots in D represent 1,000-y averages of the 5-million-year simulation of Antarctica following ref. 36."

Therefore, it goes without saying that nothing in this paper disproves Hansen's abrupt SLR projections; and I believe that most of my posts in this Antarctic folder provide support for Hansen's abrupt SLR projections.

Best,
ASLR
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #120 on: July 19, 2013, 05:16:46 PM »
Comparison of the two attached images from the supplemental material for Gunter et al 2013 (see the "Glaciology" thread for the complete reference), makes it clear how sensitivity the thin crust in the Byrd Subglacial Basin, BSB, is to post-glacial rebound (GIA) associated with modern ice mass loss. 

The first image (Fig S2-g, h, I & j) shown the best current understanding of the relatively high GIA uplift rate corrections that need to be made to the GRACE data for Antarctica; which supports the position that prior GRACE estimates of SLR contributions from WAIS need to be increased by about 40%.   It is my opinion that such a large difference between old and new ice mass loss estimates from the WAIS would have been noted earlier in satellite altimetry data, unless a significant portion of this ice mass loss from the ASE glaciers was being contributed by the leakage of basal ice melt (driven by the very high geothermal heat input in the BSB) over a fairly wide area (see the "Subglacial Lake and Hydrology" thread).

For comparison the second attached image (the caption for which is: Fig. S3. Original GIA uplift rates for a) ICE-5G, b) IJ05, and c) W12a, d) Riva09) shows the old/original GIA uplift rates focused too much on assumed paleo-ice-mass-loss from the Weddell and Ross Sea Embayment areas; and not enough on modern ice mass loss and on the unique properties of the West Antarctic lithosphere.
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Lennart van der Linde

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Re: Surge of WAIS Ice Mass Loss
« Reply #121 on: July 19, 2013, 06:11:06 PM »
ASLR,
I share your analysis that Levermann et al does not exclude the risk of abrupt sea level rise. I'm just concerned that by not stressing it explicitly they make it easier for people to deny or ignore this risk.

Also I'm concerned that they seem to exclude the risk of more than 12 meters of SLR by the year 4000, with four degrees of warming, while Hansen, Rohling, Meehl and others point out we should take this risk much more seriously in our policy discussions and decision making today. Goelzer et al 2013 seem to point to a worst-case scenario of about 25 meters of SLR by the year 3000, in their figure 7:
http://iopscience.iop.org/1748-9326/7/4/045401/pdf/1748-9326_7_4_045401.pdf

I think both aspects are, or should be, morally and politically important in deciding about mitigation and adaptation: the rate of SLR and the risk of abrupt acceleration in the coming centuries, and the magnitude of the committed SLR on even longer time scales.

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #122 on: July 19, 2013, 07:27:46 PM »
Lennart,

I agree with all of you points, but it seems to me that decision makers want much stronger "proof" (at least 50% CL) before they are willing to take any action; and due complexities of the issues this is difficult to provide.  For example, I think that the greatest risk for ASLR is the potential collapse of the WAIS.  However, until a few months ago researchers thought that the WAIS only contributed 10% to current SLR; which means that decision makers would need to accept strong non-linearity on SLR contribution from the WAIS for this to become significant in the future.  I am working toward highlighting reasons to expect more SLR contributions from the WAIS, such as that the GIA correction implies that the WAIS actually contributes about 14% of current SLR rather than 10%; however, other factors are less certain such as: (a) El Nino events and positve PDO cycles; (b) the ozone hole and possible methane effects; (c) rate of ocean and atmospheric warming in Antarctica; (d) changes in ocean currents; etc.  Therefore, it will take time to reach the burden of proof demanded by decision makers.

Best,
ASLR
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #123 on: July 19, 2013, 09:53:25 PM »
Lennart,

While the information in the following two links are probably more relevant to the "Policey and Solution" folder than this "Antarctica" folder; nevertheless, the information indicates just how far some decision markers will go to avoid reducing antropogenic GHG emissions:

http://www.nextgov.com/emerging-tech/2013/07/turns-out-cia-really-trying-control-weather/67016/

http://www.bloomberg.com/news/2013-07-18/insurance-industry-republicans-split-on-climate-change.html
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #124 on: July 19, 2013, 10:16:57 PM »
Getting back to more technical matters:  Several researchers have claimed that with a 10% SLR contribution from the WAIS that the Sea Level Budget is closed; however, if the SLR contribution from the WAIS is actually 14%, then does the extra 4% need to be covered by uncertainty; or could there be systemic factors that the Sea Level Budget researchers have ignored that account for this 4% difference?  The following systemic reasons may be masking this 4% from sea level measurements: (a) In reply 110, I note that the increase in atmospheric humidity could be decreasing SLR by upto 0.24 mm/yr; while (b) I have cited research that wind scour of EAIS snow may be delivering upto 0.1mm/yr of increased SLR; which gives a 0.14/3.2 x 100% = 4.375% masking of SLR; however, if (c) the increase in coastal groundwater elevation, and flooding of coastal area with rising SLR, were to account for a reduction in SLR of about 0.375% then these three masking factors would exactly mask the higher SLR contribution recently recognized to be coming from the WAIS; ie: 4.375 - 0.375 = 4%.
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Lennart van der Linde

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Re: Surge of WAIS Ice Mass Loss
« Reply #125 on: July 20, 2013, 12:16:32 AM »
ASLR,
Indeed, it’s hard to estimate the risks of catastrophic effects of global warming, including those of abrupt, fast and large SLR. However, policy/decision makers are used to making decisions under uncertainty. And they can be very creative in their risk assessments, as Dick Cheney showed with his One Percent Doctrine in the context of justifying the war against Iraq:
http://uchicagolaw.typepad.com/faculty/2006/06/the_one_percent.html

This doctrine could easily be applied to the risks of global warming, and much more justly so. The application of precaution doesn’t only or mainly depend on (more or less certain) facts or morality, but mostly on perceived interests and political power. So unless morality based on (still uncertain) facts can be organized to become a political power, it seems there’s a good chance that the interests of disempowered people and future generations will be sacrificed to the perceived interests of the powers that be.

I hope all your great work here on the forum will contribute to empowering people all over the world and to mobilizing them into organizing the moral force that’s necessary to still avoid as much as possible the unmanageable and manage as best we can the unavoidable.

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #126 on: July 20, 2013, 01:04:42 AM »
Lennart,

I concur with your points, and thanks for your kind thoughts.

In the way of keeping this issue infront of people, I note that as compared to the data in my reply #109 the following aviso data (see weblink below) show that sea level is slightly up, even though the attached figure from the University of Colorado (see weblink below) indicates that ENSO is trending towards La Nina conditions that normally would be contributing to reduced sea levels (raising the possibility that ice melting is becoming more of a factor in controlling SLR).

http://www.aviso.oceanobs.com/en/news/ocean-indicators/mean-sea-level/

2013.020108 6.691530e-02
2013.047256 6.682843e-02
2013.074403 6.616987e-02
2013.101551 6.547511e-02
2013.128698 6.533345e-02
2013.155846 6.586145e-02
2013.182993 6.652893e-02
2013.210141 6.658044e-02
2013.233918 6.584815e-02
2013.268842 6.486478e-02
2013.291584 6.396900e-02
2013.318731 6.336606e-02



http://sealevel.colorado.edu/
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #127 on: July 30, 2013, 12:43:17 AM »
As you can see from the following Aviso data, SLR is currently trending upwards again (compare to the data in the immediately preceeding post):

http://www.aviso.oceanobs.com/en/news/ocean-indicators/mean-sea-level/

2012.992961 6.642956e-02
2013.020108 6.692315e-02
2013.047256 6.684694e-02
2013.074403 6.620067e-02
2013.101551 6.549651e-02
2013.128698 6.533977e-02
2013.155846 6.583791e-02
2013.182993 6.648508e-02
2013.210141 6.656271e-02
2013.233918 6.584965e-02
2013.268842 6.496983e-02
2013.291584 6.442575e-02
2013.318731 6.440923e-02
2013.345879 6.483498e-02
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #128 on: July 30, 2013, 01:06:21 AM »
While the changes in sea level expressed in terms of centimeters (cm) of equivalent water height as measured by GRACE fluctuate substantially with seasonal atmospheric conditions; it is my opinion (as supported by the two attached images for February and April of 2013) that there is a general trend indicating that ice mass loss from both the GIS and the WAIS is contributing to reduced pressure on the seafloor in these two areas [note that the altimeter measurements of sea level offshore of the WAIS has not been changing significantly (either up or down) recently, possibly due to steric changes and local upwelling]:

ftp://podaac-ftp.jpl.nasa.gov/allData/tellus/L3/ocean_mass/RL05/browse/jpl/
« Last Edit: July 30, 2013, 01:46:36 AM by AbruptSLR »
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Re: Surge of WAIS Ice Mass Loss
« Reply #129 on: August 09, 2013, 02:10:41 AM »
The following reference (see link) provides a good overview of the state of the climate in 2012; indicating that virtually all global warming indicators are trending up from prior years.  In particular this report highlights that the trend for SLR is disturbingly high:

http://www.ncdc.noaa.gov/news/2012-state-climate-report-released

NOAA; State of the Climate in 2012; Bulletin of the American Meteorological Society, Vol. 94 No. 8 August 2013.

The first attached image from this report shows how extremely high the lower stratospheric temperatures were over Antarctica in 2012; which the second attached image shows that sea level at the end of 2012 was the highest in recorded history (up to that date).
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #130 on: August 10, 2013, 02:18:15 AM »
The following linked (with a free pdf available) reference presents a new methodology for determining ice mass loss based on GRACE land-ice measurements:

http://www.igsoc.org/journal/59/216/t12J147.html

Antarctica, Greenland and Gulf of Alaska land-ice evolution from an iterated GRACE global mascon solution
by: Scott B. LUTHCKE, T.J. SABAKA, B.D. LOOMIS, A.A. ARENDT, J.J. McCARTHY,
J. CAMP; Journal of Glaciology, Vol. 59, No. 216, 2013 doi:10.3189/2013JoG12J147


"ABSTRACT. We have determined the ice mass evolution of the Antarctic and Greenland ice sheets (AIS and GIS) and Gulf of Alaska (GOA) glaciers from a new GRACE global solution of equal-area surface mass concentration parcels (mascons) in equivalent height of water. The mascons were estimated directly from the reduction of the inter-satellite K-band range-rate (KBRR) observations, taking into account the full noise covariance, and formally iterating the solution. The new solution increases signal recovery while reducing the GRACE KBRR observation residuals. The mascons were estimated with 10 day and 1 arcdeg equal-area sampling, applying anisotropic constraints. An ensemble empirical mode decomposition adaptive filter was applied to the mascon time series to compute annual mass balances.  The details and causes of the spatial and temporal variability of the land-ice regions studied are discussed. The estimated mass trend over the total GIS, AIS and GOA glaciers for the time period 1 December 2003 to 1 December 2010 is –380+/-31 Gt a–1, equivalent to –1.05+/-0.09mma–1 sea-level rise. Over the same time period we estimate the mass acceleration to be –41+/-27 Gt a–2, equivalent to a –0.11+/-0.08mma–2 sea-level acceleration. The trends and accelerations are dependent on significant seasonal and annual balance anomalies."
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Darrencwood

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Re: Surge of WAIS Ice Mass Loss
« Reply #131 on: August 12, 2013, 04:45:19 AM »
Hi, First time posting and trying to follow but struggling TBH , thought this might be of interest, I know it's not the WAIS   

http://www.nature.com/news/chain-reaction-shattered-huge-antarctica-ice-shelf-1.13540

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #132 on: August 12, 2013, 04:46:25 PM »
Darrencwood,

Thanks for the input on the Larsen B ice shelf collapse, and congratulations on your first post.  I am sorry that this topic is so complicated that I think that it may require that events actually unfold before eveyone will agree on the potential contribution of the AIS to SLR; but it is valuable to discuss it anyway.  I will be traveling for the next few days so, by post rate will slow down significantly.

Best,
ASLR
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #133 on: August 15, 2013, 05:40:35 PM »
Darrencwood,

Obviously, the Larsen B chain reaction mechanism findings that you linked to must be viewed in context for the other related Antarctic Peninsula ice shelves; and the information at the following link (you need to click on the "View More" buttons at the website); presents this context including extensive discussion about the role of sub-ice shelf crevasses that not only weaken the shelves, but also contribute to the formation of surface depressions that can accumulate future surface meltwater on the shelves into ponds that might then be subject to the chain reaction meltpond mechanism that you referenced.  Particularly, the Larsen C ice shelf is a concern in this regards:

http://gcmd.nasa.gov/KeywordSearch/Metadata.do?Portal=amd&KeywordPath=%5BSource_Name%3A+Short_Name%3D'FIELD+SURVEYS'%5D&EntryId=steffen_0732946&MetadataView=Full&MetadataType=0&lbnode=mdlb5
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #134 on: August 21, 2013, 12:21:13 AM »
According to the Mid-August IRI/CPC Plume-Based Forecast (see the attached image and/or the following weblinks) posted on August 15, 2013, there is an increasing chance of an El Nino event occurring by late Spring to Summer of 2014; which, if this were to occur, could markedly accelerate ice mass loss from the WAIS (as discussed in many posts in this thread).

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.html

http://iri.columbia.edu/climate/ENSO/currentinfo/QuickLook.html
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #135 on: August 23, 2013, 07:41:33 PM »
The following linked (see also links in reply #128 of this thread) reference provides a summary of the recent re-processing of GRACE Release -05 data focused on interannual ocean bottom pressure and its relation to sea level:

http://onlinelibrary.wiley.com/doi/10.1002/grl.50549/abstract


Piecuch, C. G., K. J. Quinn, and R. M. Ponte (2013), Satellite-derived interannual ocean bottom pressure variability and its relation to sea level, Geophys. Res. Lett., 40, 3106–3110, doi:10.1002/grl.50549.


Abstract:

"Knowledge of the relationship between bottom pressure pb and sea level ζ is important for understanding ocean circulation and climate. We use recent Gravity Recovery and Climate Experiment (GRACE) Release-05 data along with altimetry to investigate the relationship between ζ and pb over long periods (>1 year) and large scales (>750 km). Elevated pb signals are observed over deep extratropical regions (e.g., Southern Ocean basins) and shallow or semi-enclosed areas (e.g., Indonesian and Nordic seas). In these places, considerable ζ variance is explained by pb variance. Correlation between ζ and pb is significant in many regions, including instances of significant negative correlation suggestive of active baroclinic processes. Results exemplify the good quality of GRACE Release-05 data and demonstrate that contemporary regional ζ variability cannot always be interpreted in terms of steric changes alone."
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #136 on: August 26, 2013, 10:55:07 AM »
Recent trends indicate that ice mass loss from the ASE comes primarily from three ice streams: Thwaites, Pine Island and Smith Glaciers; however these three ice streams have different characteristics.  In particular, the cause of the interior thinning associated with Thwaites Glacier, TG, is less obvious (I wonder whether basal ice melting is contributing to mass loss in the interior) and satellite observations indicate that the TG ice stream has widened, while experiencing only a moderate acceleration of velocity between 1992 and 2004.  Thus the link between ice shelf change and ice mass loss may well be different for TG in comparison to PIG. For instance, the complete loss of the TG ice tongue appears to be associated with only a moderate change in velocity of the ice stream; while the weakening and un-grounding of portions of the Thwaites eastern ice shelf could have triggered the observed widening. In addition, Smith Glacier has accelerated while the flow of its immediate neighbors Pope and Kohler Glaciers has remained approximately constant. These recent trends indicate that individual ice streams may respond differently to current and future oceanographic forcing.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #137 on: August 27, 2013, 01:29:46 AM »
The following linked references (with free access pdf's of the paper and supplement material); uses iron input into the Southern Ocean from Antarctic Ice Sheets as a means of tracking the source of the ice mass loss (see also attached images).  The extract from the supplementary material indicates that the current ice mass loss from subglacial meltwater export to the Southern Ocean is very large:

http://www.biogeosciences-discuss.net/10/12551/2013/bgd-10-12551-2013.pdf

http://www.biogeosciences-discuss.net/10/12551/2013/bgd-10-12551-2013-supplement.pdf



Citation: Death, R., Wadham, J. L., Monteiro, F., Le Brocq, A. M., Tranter, M., Ridgwell, A., Dutkiewicz, S., and Raiswell, R.: Antarctic Ice Sheet fertilises the Southern Ocean, Biogeosciences Discuss., 10, 12551-12570, doi:10.5194/bgd-10-12551-2013, 2013.

"Abstract. Southern Ocean (SO) marine primary productivity (PP) is strongly influenced by the availability of iron in surface waters, which is thought to exert a significant control upon atmospheric CO2 concentrations on glacial/interglacial timescales. The zone bordering the Antarctic Ice Sheet exhibits high PP and seasonal plankton blooms in response to light and variations in iron availability. The sources of iron stimulating elevated SO PP are in debate. Established contributors include dust, coastal sediments/upwelling, icebergs and sea ice. Subglacial meltwater exported at the ice margin is a more recent suggestion, arising from intense iron cycling beneath the ice sheet. Icebergs and subglacial meltwater may supply a large amount of bioavailable iron to the SO, estimated in this study at 0.07–1.0 Tg yr−1. Here we apply the MIT global ocean model (Follows et al., 2007) to determine the potential impact of this level of iron export from the ice sheet upon SO PP. The export of iron from the ice sheet raises modelled SO PP by up to 40%, and provides one plausible explanation for very high seasonally observed PP in the near-coastal zone. The impact on SO PP is greatest in coastal regions, which are also areas of high observed marine PP. These results suggest that the export of Antarctic runoff and icebergs may have an important impact on SO PP and should be included in future biogeochemical modelling."



"Antarctic meltwater export
2.1. Evidence for meltwater export


There is mounting evidence that meltwater generated at the bed of the Antarctic Ice Sheet is exported to the Southern Ocean (SO) from the ice sheet margin. Land-based and sub-marine geomorphological data display paleo-channels and other hydrological features indicative of the occurrence of outburst floods (Sugden et al., 2006; Lowe and Anderson, 2003) , which is also supported by direct observations of such flood events from the ice margin (Goodwin, 1988). Traces of channels incised into the base of a large number of ice shelves around the continent have also been recently observed in satellite images of the ice shelf surface and suggests extensive meltwater export at the ice sheet margins by large subglacial channels (Le Brocq et al., submitted). Continuous discharge of water from the ice sheet is also supported by sand and/clay deposits in ice-marginal core records which indicate that sediment-laden meltwater plumes originate beneath the ice sheet (Lowe and Anderson, 2002). Sub-marine groundwater discharge has also recently been measured from the East Antarctic coast, at rates that were two orders of magnitude higher than rates reported for mid latitude sites (Uemura et al., 2011). Hence, the notion that meltwater generated at the bed of the ice sheet is ultimately exported is now becoming well established."
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #138 on: August 30, 2013, 06:14:28 PM »
According to the following website, a leaked portion of the AR5 contains the following information:

http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/08/20/leaked-climate-report-ten-nuggets-worth-noting/

"The Antarctic Ice Sheet lost mass nearly 5 times faster between 2002-2011 compared to the period from 1992-2001."
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Re: Surge of WAIS Ice Mass Loss
« Reply #139 on: September 24, 2013, 01:27:14 AM »
The following linked reference (with a free pdf) provides improved analysis of the GRACE satellite data indicating more ice mass loss from the WAIS than estimated by many previous analyses; however, this paper still cannot fully correct for GIA, which will require some more years of field data collection:

http://www.the-cryosphere.net/7/1411/2013/tc-7-1411-2013.html

Barletta, V. R., Sørensen, L. S., and Forsberg, R.: Scatter of mass changes estimates at basin scale for Greenland and Antarctica, The Cryosphere, 7, 1411-1432, doi:10.5194/tc-7-1411-2013, 2013

Abstract. During the last decade, the GRACE mission has provided valuable data for determining the mass changes of the Greenland and Antarctic ice sheets. Yet, discrepancies still exist in the published mass balance results, and comprehensive analyses on the sources of errors and discrepancies are lacking. Here, we present monthly mass changes together with trends derived from GRACE data at basin scale for both the Greenland and Antarctic ice sheets, and we assess the variability and errors for each of the possible sources of discrepancies, and we do this in an unprecedented systematic way, taking into account mass inference methods, data sets and background models. We find a very good agreement between the monthly mass change results derived from two independent methods, which represents a cross validation. For the monthly solutions, we find that most of the scatter is caused by the use of the two different data sets rather than the two different methods applied. Besides the well-known GIA trend uncertainty, we find that the geocenter motion and the recent de-aliasing corrections significantly impact the trends, with contributions of +13.2 Gt yr−1 and −20 Gt yr−1, respectively, for Antarctica, which is more affected by these than Greenland. We show differences between the use of release RL04 and the new RL05 and confirm a lower noise content in the new release. The overall scatter of the solutions well exceeds the uncertainties propagated from the data errors and the leakage (as done in the past); hence we calculate new sound total errors for the monthly solutions and the trends. We find that the scatter in the monthly solutions caused by applying different estimates of geocenter motion time series (degree-1 corrections) is significant – contributing with up to 40% of the total error. For the whole GRACE period (2003–2011) our trend estimate for Greenland is −234 ± 20 Gt yr−1 and −83 ± 36 Gt yr−1 for Antarctica (−111 ± 15 Gt yr−1 in the western part). We also find a clear (with respect to our errors) increase of mass loss in the last four years.
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #140 on: October 29, 2013, 10:30:11 PM »
The following link leads to an article about research that indicates that ice mass loss from PIG is accelerating:

http://www.uafsunstar.com/archives/25842
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Re: Surge of WAIS Ice Mass Loss
« Reply #141 on: November 22, 2013, 01:52:11 AM »
The following link (with a free pdf)/citation/abstract indicate that the Jakobshavn Glacier could contribute more to SLR by the end of the century than has been previously estimated; which in-turn could help to reduce the stability of Antarctic marine glaciers and ice sheet, by increasing the local sea level around Anatarctica:

http://www.the-cryosphere-discuss.net/7/5461/2013/tcd-7-5461-2013.pdf

The Cryosphere Discuss., 7, 5461–5473, 2013
www.the-cryosphere-discuss.net/7/5461/2013/
doi:10.5194/tcd-7-5461-2013

Abstract:

"We have extended the record of flow speed on Jakobshavn Isbræ through the summer of 2013. These new data reveal large seasonal speedups, 30 to 50% larger than previous summers. At a point a few kilometres inland from the terminus, the mean annual speed for 2012 is nearly three times as large as that in the mid 1990s, while the peak summer speeds are more than a factor of 4 greater. These speeds were achieved as the glacier terminus retreated to the bottom of an overdeepened basin with a depth of  ∼ 1300m below sea level. While retreat may slow slightly as the terminus retreats farther – to a moderate rise in the bed – it is likely to reach the deepest section of the trough within a few decades, at which point it should rapidly retreat to the shallower regions  ∼ 50 km farther upstream, potentially by the end of this century."
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Lennart van der Linde

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Re: Surge of WAIS Ice Mass Loss
« Reply #142 on: November 22, 2013, 03:56:48 PM »
ASLR,
Thanks for the reference here as well - in addition to sidd's reference at the Greenland/Jakobshavn hread - to the (draft?) discussion paper by Joughin & Smith. As posted there (and at RealClimate) I'm trying to understand how exactly this compares to Pfeffer et al 2008:
http://www3.geosc.psu.edu/~jfk4/Geosci_500/Discussion%20papers/Last%20week%202/Science%202008%20Pfeffer.pdf

Pfeffer et al say:
"Average (present day to 2100) outlet glacier speeds required to meet 2- and 5-m SLR targets range from 26.8 km/year to 125 km/year, depending on the scenario considered [table 2 and supporting online material (SOM)]. These velocities must be achieved immediately on all [33?] outlets considered and held at that level until 2100."

So about an average speed of 27 km/yr is needed from now until 2100 for all (33 considered?) GIS outlet glaciers, in combination with a 10x higher surface melt rate, to get a GIS-contribution to global SLR of 2 meters this century.

It seems Joughin & Smith argue in their last sentence this seems unlikely to be possible. However, Pfeffer et al also show a scenario of 2 meter total SLR by 2100 in which GIS contributes about 54 cm. In this scenario:
"Greenland SMB was accelerated at present-day rates of change, but dynamic discharge was calculated by accelerating outlet glacier velocities by an order of magnitude in the first decade."

This implies that over 2020-2100 all (33 considered?) GIS outlet glaciers should reach an average speed of about 12 km/yr in this scenario, if I understand correctly. Marine outlet glaciers could then reach a higher average speed and land outlet glaciers a lower average, but it's not obvious from Joughin & Smith that such average speeds could be sustained for eight decades, I think.

Jim Hansen for one seems to think Pfeffer et al may under-estimate in particular the potential AIS contribution, so all this is not to say that 2 meter of total SLR by 2100 would be impossible. And how about the GIS outlet glaciers that were apparently not considered by Pfeffer et al? How substantial could their contribution be?

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #143 on: November 22, 2013, 05:15:19 PM »
Lennart,

Unfortunately my time constaints limits my ability to address the GIS situation with any reasonable degree of confidence, and my main purposes of citing the Joughin & Smith (2013) papers are: (a) I believe that several WAIS ice stream and marine glaciers are considerably less stable than the Jakobshavn Glacier (once their groundling lines have retreated past the lip of their respective subglacial basins) an in particular, the Thwaites Glacier retreat is likely to accelerate well beyond anything currently recorded for Jakobshaven sometime between 2025 and 2100; and (b) SLR contribution from the GIS reduces the stability of the WAIS.

That said, I provide the following quote from Joughlin & Smith (2013):

"If, as the glacier recedes up the trough, it is able to maintain the peak speeds year round, then a sustained speedup by a factor of 4 of 5 is conceivable based on recent behavior, which is about half of the ad hoc tenfold upper limit on speed proposed by Pfeffer et al. (2008). Nevertheless, these speeds would occur in a trough roughly twice as deep as prior to the speedup. Hence, a tenfold increase in ice flux may be possible for Jakobshavn Isbræ if the trough does not narrow substantially with distance upstream. Equivalently, while the increase in terminus speed and the glaciers overall maximum speed may remain under a factor of five, as the terminus retreats farther inland where the speeds now are comparatively slow, the relative speedup is much greater (e.g., if the terminus retreated to M26 with a speed of 16 000 m yr−1, this would represent a twelve-fold speedup). Thinning by hundreds of meters to a terminus near flotation, however, yields something closer to a ten-fold flux increase."

I also note that Pfeffer et al (2008) does not provide any confidence levels for their estimates, nor do they tie their estimates to any emissions pathway or mean global temperature rise projections.  This makes it very difficult to compare apples to apples as one is never quite sure what case Pfeffer et al (2008) is actually evaluating.  Nevertheless, it is my personal expectation that for the 2100 BAU 95% CL case the GIS SLR contribution (from both surface melt and calving) will be less than 0.75m; while I believe that the SLR contribution from the WAIS could be as high as 2 to 3m (at the 95% CL BAU case).  If you want my opinion on lower confidence level BAU cases then review my discussion in the "Philosophical" thread at:

http://forum.arctic-sea-ice.net/index.php/topic,60.0.html 
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #144 on: December 12, 2013, 12:52:57 AM »
The linked article states that CryoSat satellite measures indicates that the current SLR contribution from the WAIS is currently 15% greater (0.32 mm/yr) than the 2005 to 2010 average (0.28 mm/yr):

http://www.universetoday.com/107111/melting-glaciers-may-push-the-west-antarctics-ice-loss-ever-higher/

"The West Antarctic Ice Sheet is losing the equivalent of a Lake Tahoe in ice every single year, according to new measurements from the European Space Agency CryoSat satellite — quite a bit more than what was measured earlier. That’s 36 cubic miles or 150 cubic kilometers every single year.
The measured loss also affects sea levels around the world. Between 2005 and 2010, polar scientists previously calculated, oceans rose about 0.0110 inches (0.28 mm) a year due to West Antarctic melting. The new results suggest that the melting is about 15% higher. That would put the new sea-rise rate at 0.0115 inches (0.32 mm) a year.
“We find that ice thinning continues to be most pronounced along fast-flowing ice streams of this sector and their tributaries, with thinning rates of between 4–8 m [13 to 26 feet] per year near to the grounding lines – where the ice streams lift up off the land and begin to float out over the ocean – of the Pine Island, Thwaites and Smith Glaciers,” stated Malcolm McMillan, a research fellow at the United Kingdom’s University of Leeds.
West Antarctic thinning between 2010 and 2013, as measured by the European Space Agency’s CryoSat satellite. Credit: CPOM/ESA
What scientists don’t know is whether the ice is thinning faster due to melting glaciers or if CryoSat — the European Space Agency satellite that made these measurements by radar following its launch in 2010 — is simply mapping the same rate of loss but in higher resolution as what was seen before."
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Shared Humanity

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Re: Surge of WAIS Ice Mass Loss
« Reply #145 on: December 12, 2013, 06:37:17 PM »
Thank you AbruptSLR. I come and read your posts almost daily and have learned a lot. I have a question. You may have already answered this and I have missed it.

Could the transport of Antarctic ice melt water into the southern ocean actually be a source for the increase in sea ice?  Could this cold, relatively salt free  and less dense water at the surface be more prone to freezing in the Antarctic winter?

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #146 on: December 12, 2013, 07:47:51 PM »
Shared Humanity,

Certainly having more meltwater is one of the secondary factors contributing to the current trend for greater sea ice area in Antarctica; however, I believe that the most important factor is the changes to the wind patterns over the Southern Ocean that both causes rafting of the sheet ice and pushes the sea ice around to make more room in the high ice generating areas to make more ice rapidly.  Other factors include changes in current patterns, also the NASA website has a discussion of other contributing factors.

Here is one link of many to discussions about the causes of the Antarctic sea ice growth related to NASA's findings:

http://phys.org/news/2013-10-antarctic-sea-ice.html
« Last Edit: December 12, 2013, 11:34:54 PM by AbruptSLR »
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Re: Surge of WAIS Ice Mass Loss
« Reply #147 on: December 12, 2013, 10:56:11 PM »
Thanks ASLR.....read linked article.

AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #148 on: December 14, 2013, 04:39:36 PM »
Colorado Bob (at the ASIB) provided the following link as an update to the Chen et al 2013 research that I discussed in posts #97 & #99 of this thread about the shifting of the earth's rotational poles.  The update indicates that particularly when the GRACE satellite's orbit collapses, and until GRACE's replacement is launched, monitoring the shifts in the earth's pole can serve as a means to measure ice mass loss from Antarctica, particularly after the GIA issue is better understood for the WAIS:

http://www.newscientist.com/article/dn24755-earths-poles-are-shifting-because-of-climate-change.html#.Uqxa2STnbIV

Here is a link directly to the Chen et al 2013 preprint pdf:

http://ftp://ftp.csr.utexas.edu/pub/ggfc/papers/2013GL056164_preprint.pdf]ftp://ftp.csr.utexas.edu/pub/ggfc/papers/2013GL056164_preprint.pdf
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AbruptSLR

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Re: Surge of WAIS Ice Mass Loss
« Reply #149 on: December 15, 2013, 03:21:04 AM »
I would like to highlight the following quote from the linked article: "Regional linear trends for 14 ocean basins since 1970 show the fastest sea level rise for the Antarctica (4.1 ± 0.8 mm / yr- 1) and Arctic (3.6 ± 0.3 mm / yr- 1)."  This quote indicates that the Antarctica ice sheets are being destabilized by regional rising sea level faster than any other place on Earth:

http://www.sciencedirect.com/science/article/pii/S0921818113002750

S. Jevrejeva, J.C. Moore, A. Grinsted, A. Matthews, and G. Spada; (2013), "Trends and acceleration in global and regional sea levels since 1807", Global and Planetary Change; Available online 11 December 2013; http://de.doi.org/10.1016/j.gloplacha.2013.12.004


"Abstract
We use 1277 tide gauge records since 1807 to provide an improved global sea level reconstruction and analyse the evolution of sea level trend and acceleration. In particular we use new data from the polar regions and remote islands to improve data coverage and extend the reconstruction to 2009. There is a good agreement between the rate of sea level rise (3.2 ± 0.4 mm / yr- 1) calculated from satellite altimetry and the rate of 3.1 ± 0.6 mm / yr- 1 from tide gauge based reconstruction for the overlapping time period (1993–2009). The new reconstruction suggests a linear trend of 1.9 ± 0.3 mm / yr- 1 during the 20th century, with 1.8 ± 0.5 mm / yr- 1 since 1970. Regional linear trends for 14 ocean basins since 1970 show the fastest sea level rise for the Antarctica (4.1 ± 0.8 mm / yr- 1) and Arctic (3.6 ± 0.3 mm / yr- 1). Choice of GIA correction is critical in the trends for the local and regional sea level, introducing up to 8 mm / yr- 1 uncertainties for individual tide gauge records, up to 2 mm / yr- 1 for regional curves and up to 0.3-0.6 mm / yr- 1 in global sea level reconstruction. We calculate an acceleration of 0.02 ± 0.01 mm / yr- 2 in global sea level (1807–2009). In comparison the steric component of sea level shows and acceleration of 0.006 mm / yr- 2 and mass loss of glaciers accelerates at 0. 003 mm / yr- 2 over 200 year long time series."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson