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Wednesday, December 3, 2014

Shifting into high gear: Amundsen Sea Embayment melt - Antarctica

Sou | 1:47 PM Go to the first of 28 comments. Add a comment

While WUWT has slowed to a crawl the science hasn't. So today I'll just write about a new paper in Geophysical Research Letters (GRL).

A large team led by Tyler C. Sutterley has found that in fast-melting regions of Antarctica, the rate of melt has tripled during the last decade. The team includes scientists from the USA, France, the Netherlands and the UK and includes some whose names you'll probably recognise, such as Eric Rignot and Isabella Velicogna. They did a comprehensive analysis of measurements of glaciers in the Amundsen Sea Embayment over last 21 years, evaluating and reconciling observations from four different measurement techniques. The loss has been accelerating, a lot.

UCI and NASA glaciologists, including Isabella Velicogna and Tyler Sutterley, have discovered that the melt rate of glaciers in West Antarctica has tripled, with the loss of a Mt. Everest's worth of water weight every two years.
Credit: Michael Studinger / NASA  Source: UC Irvine



From the ScienceDaily.com press release:
"The mass loss of these glaciers is increasing at an amazing rate," said scientist Isabella Velicogna, jointly of the UC Irvine and NASA's Jet Propulsion Laboratory. Velicogna is a coauthor of a paper on the results, which has been accepted for Dec. 5 publication in the journal Geophysical Research Letters.
Lead author Tyler Sutterley, a UCI doctoral candidate, and his team did the analysis to verify that the melting in this part of Antarctica is shifting into high gear. "Previous studies had suggested that this region is starting to change very dramatically since the 1990s, and we wanted to see how all the different techniques compared," Sutterley said. "The remarkable agreement among the techniques gave us confidence that we are getting this right."
The researchers reconciled measurements of the mass balance of glaciers flowing into the Amundsen Sea Embayment. Mass balance is a measure of how much ice the glaciers gain and lose over time from accumulating or melting snow, discharges of ice as icebergs, and other causes. Measurements from all four techniques were available from 2003 to 2009. Combined, the four data sets span the years 1992 to 2013.
The glaciers in the embayment lost mass throughout the entire period. The researchers calculated two separate quantities: the total amount of loss, and the changes in the rate of loss.
The total amount of loss averaged 83 gigatons per year (91.5 billion U.S. tons). By comparison, Mt. Everest weighs about 161 gigatons, meaning the Antarctic glaciers lost a Mt.-Everest's-worth amount of water weight every two years over the last 21 years.
The rate of loss accelerated an average of 6.1 gigatons (6.7 billion U.S. tons) per year since 1992.
From 2003 to 2009, when all four observational techniques overlapped, the melt rate increased an average of 16.3 gigatons per year -- almost three times the rate of increase for the full 21-year period. The total amount of loss was close to the average at 84 gigatons.
The four sets of observations include NASA's Gravity Recovery and Climate Experiment (GRACE) satellites, laser altimetry from NASA's Operation IceBridge airborne campaign and earlier ICESat satellite, radar altimetry from the European Space Agency's Envisat satellite, and mass budget analyses using radars and the University of Utrecht's Regional Atmospheric Climate Model.
The scientists noted that glacier and ice sheet behavior worldwide is by far the greatest uncertainty in predicting future sea level. "We have an excellent observing network now. It's critical that we maintain this network to continue monitoring the changes," Velicogna said, "because the changes are proceeding very fast."
You can read the full press release at ScienceDaily.com.


Related articles


This research complements other studies I've written about before, for example:


There are more - you can use the search bar up top for other articles on Antarctica.


Tyler C. Sutterley, Isabella Velicogna, Eric Rignot, Jeremie Mouginot, Thomas Flament, Michiel R. van den Broeke, Jan M. van Wessem, Carleen H. Reijmer. "Mass loss of the Amundsen Sea Embayment of West Antarctica from four independent techniques". Geophysical Research Letters, 2014; DOI: 10.1002/2014GL061940

28 comments:

  1. While you're on the subject of ice loss, I saw this visual of the ice volume "death spiral" in the Arctic to be quite illuminating (and disturbing):

    https://www.youtube.com/watch?v=qUO23Y179pU

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  2. Yet more evidence that the 'alarmist' IPCC is in fact conservative to its roots.

    No matter how you survey or what instrument is used, the results are consilient. Cryosat-2 data are just becoming available for analysis, and guess what:

    We use 3 years of Cryosat-2 radar altimeter data to develop the first comprehensive assessment of Antarctic ice sheet elevation change. This new data set provides near-continuous (96%) coverage of the entire continent, extending to within 215 km of the South Pole and leading to a fivefold increase in the sampling of coastal regions where the vast majority of all ice losses occur. Between 2010 and 2013, West Antarctica, East Antarctica, and the Antarctic Peninsula changed in mass by −134 ± 27, −3 ± 36, and −23 ± 18 Gt yr−1, respectively. In West Antarctica, signals of imbalance are present in areas that were poorly surveyed by past missions, contributing additional losses that bring altimeter observations closer to estimates based on other geodetic techniques. However, the average rate of ice thinning in West Antarctica has also continued to rise, and mass losses from this sector are now 31% greater than over the period 2005–2010.

    From McMillan et al. (2014). Observant readers will notice that the popular denialist talking point about EAIS ice mass gain has now passed its sell-by date.

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  3. This comment has been removed by a blog administrator.

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    1. @RR: You have not read the literature on wind-driven changes in Amundsen Sea circulation of warm subsurface offshore waters onto the continental shelf and under the ice shelves. Please do so, then come back with questions.

      Some names to look for in the literature: S. Jacobs, A. Jenkins, P. Dutrieux, R. Bindschadler, M. Thoma, M. Schodlok, E. Steig, Q. Ding, D. Walker.

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    2. Antarctica as a whole is losing land ice mass and at an accelerating rate. and RSS doesn't measure surface temps. and where does that southern ocean data come from?

      cabc

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    3. and geothermal activity wouldn't explain a long-term trend in ice loss unless geothermal activity was increasing, and by an amount necessary to cause said ice losses. are you suggesting that it is?

      cabc

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    4. http://berkeleyearth.lbl.gov/regions/antarctica

      Looks like an increasing temperature to me. And actually 2m air temperature.

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    5. Victor, do you know of any plots or data of temp anomalies for the southern ocean such as rum runner has provided by tisdale? it seems suspect, though it certainly may very well be correct. but knowing tisdale's history, I'm suspicious that he's presented something else and is calling it southern ocean anomalies. of course I could be wrong.

      cabc

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    6. No, sorry. Sea surface temp goes outside of my expertise. But it is likely not very reliable. It is estimated using ship observations and they are very sparse in that region and always tricky near to the coast (bigger modern ships stay away from the coast more, which can produce a bias).

      (Also the above BEST plot is likely not optimal. There are only little stations in Antarctica and you need neighbouring stations to see non-climatic changes that can create trend errors.)

      What the ice is doing is may well be the most reliable indicator of what is happening there. That averages over long periods and responds to the actual temperatures.

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    7. Southern Ocean SST records are limited by low ship activity, and Argo floats being limited to sea-ice-free regions. Instrumented seals are starting to offset this limit, but the record is short and the instruments are generally not recalibrated (they are lost the next time the seal moults).

      SST in the seasonal ice range (between the summer min and the winter max) will also be determined to a large extent by mixing processes acting on the fresh water left behind as the sea ice melts. So, it depends on generation of sea ice inshore that flows north, and so SST is not directly coupled to local Southern Ocean processes.

      However, the important issue for ice shelves is *SUB*surface ocean temperature and changes in circulation of warm subsurface water onto the continental shelves caused by shifting wind patterns; I'd call that "climate change" rather than AGW, although at least part of it goes back to AGW especially as it looks like the Amundsen Sea is strongly teleconnected to the tropical Pacific.

      Finally (for RR), the calculation to do is "If area-averaged geothermal changed by, say, 5 mW/m^2 (a massive number, given that there is *no* evidence of *any* increase in this region), what is the increased rate of ice melt, and how does that compare to mass loss measured by gravity and altimetry satellites?" I suggest to Sou that she require an answer from RR to this as an act of good faith by RR on this post.

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    8. UAH is quite specific about Antarctic Tempeatures for 2013.

      Quote : 2013 was the fourth warmest year in the satellite era,
      trailing only 1998, 2010 and 2005, according to Dr. John
      Christy, a professor of atmospheric science and director of
      the Earth System Science Center at the University of
      Alabama in Huntsville. The warmest areas during the year
      were over the North Pacific and the Antarctic, where
      temperatures for the year averaged more than 1.4 C (more
      than 2.5 degrees Fahenheit) warmer than normal

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    9. RR: As I said, read some papers, *then* come back with questions. Do Google Scholar searches for the author's name plus "Amundsen Sea" or "Pine Island".

      You're also out of sync with knowledge of ice mass balance. East Antarctic Ice Sheet is not presently growing, another case where the IPCC projection ("Ice growth in EAIS will offset loss from WAIS") turned out to be conservative.

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    10. That UAH paper on geothermal flux under the ice sheet has been absurdly misinterpreted ever since it came out. (The lead author even says so: https://news.vice.com/article/no-volcanoes-are-not-the-primary-cause-for-the-melting-ice-caps)

      The point of the study was to develop better models for the variable slipperiness of the bedrock under the ice, which is helpful in accurately modeling the movement of the ice sheet. Where the surface is marginally warmer, there's more meltwater, and the sheet is more mobile.

      If you think a paper that explicitly attributes glacier melting to warmer seawater is instead attributing that melting to geothermal activity, ask yourself this: What percentage of glacier melting does it attribute to geothermal? 100% 50% 10% 1% <1%

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    11. RR, just to follow up: If subsurface ocean T near the ice shelves is what you're interested in, then Jacobs et al. 2013 and Dutrieux et al. 2014 are the best places to start.

      http://www.ccpo.odu.edu/~klinck/Reprints/PDF/jacobsJGR13.pdf

      http://www.ccpo.odu.edu/~klinck/Reprints/PDF/dutrieuxScience14.pdf

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    12. Why is this dishonest clown still commenting on this blog?

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    13. As well as RR's long list of previous lies and refusals to admit fatal errors, I'm talking about this:

      Me:

      [quotes from McMillan (2014):]

      "Between 2010 and 2013, West Antarctica, East Antarctica, and the Antarctic Peninsula changed in mass by −134 ± 27, −3 ± 36, and −23 ± 18 Gt yr−1, respectively."]

      [...]

      From McMillan et al. (2014). Observant readers will notice that the popular denialist talking point about EAIS ice mass gain has now passed its sell-by date.


      Followed immediately by RR:

      Note the GAIN of land ice elsewhere in Antarctica where there's no geothermal.


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    14. @BBD: I realize RR has a record. Some days I have a little more time to waste, and the Antarctic ice sheet problem is fascinating, so I don't mind. In all likelihood, Sou will get another HotWhoppery post out of it, and passers-by will get more evidence that some visitors are lazy, ill-informed or dishonest.

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    15. rum runner, the ice cap as a whole is melting, not just the WAIS

      cabc

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    16. RR

      It's not geothermal. See Pritchard et al. (2012)

      This has just been confirmed by field studies using ROVs.

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    17. Rum Runner is like Tony Abbott on a sad little scale. He's his enemies' best friend! Though I agree almost everything he sprays deserves deletion, or to end up in the HotWhoppery, a more pristine example of the bad-faith and bloody-minded refusal to engage with inconvenient facts that characterises denial is hard to imagine.

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    18. @RR: You did *not* read the papers; you don't read Jacobs et al. (2013) and Dutrieux et al. (2014) in an hour or two and understand them. It sounds like what you mean is "I (RR) looked for 'geothermal heat flux' and didn't find it." But I've got my doubts that you even went that far. You also didn't read the original paper on geothermal heat flux, or the press statement that "Anon" pointed you to, otherwise you'd realize that even the high measured geothermal heat fluxes cannot explain the measured ice loss, even if the entire measured rate was a recent step up from a much lower value.

      You'd find the science of how the oceans affect land ice loss to be quite interesting if you were genuinely curious.

      BTW, are you just another Tisdale sock?

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    19. PL

      No idea if RR=BT (in fact I doubt it) but Rum Runner is commenting as "David Blake" at AndThenThere'sPhysics. Same shite, different blog. I was happy to out him.

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  4. Rum Runner will please explain
    "TLT is constructed by calculating a weighted difference between MSU2 (or AMSU 5) measurements from near limb views and measurements from the same channels taken closer to nadir, as can be seen in Figure 1 for the case of MSU. This has the effect of extrapolating the MSU2 (or AMSU5) measurements lower in the troposphere, and removing most of the stratospheric influence. Because of the differences involves measurements made at different locations, and because of the large absolute values of the weights used, additional noise is added by this process, increasing the uncertainty in the final results. For more details see Mears et al., 2009b."
    to me.

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    1. Exactly. I guess Rum Runner has already demonstrated below previous posts that he has no interest in science. For the interested reader, let me cite a comment Carl Mears made on my blog:

      "The south pole is more complicated. We view the TLT product as a atmospheric temperature product. For areas with low surface elevations, this is true, with ~90% of the signal coming from atmospheric emission. For regions with high surface elevations, the portion that comes from the atmosphere is reduced, because the atmosphere is thinner, and thus
      more transparent. Much of the Antarctic continent is above 2000m, so the portion of the signal that comes from the atmosphere is sharply reduced, to as low as 60%. So TLT is no longer an atmospheric product.

      There is a second problem as well. To calculate the TLT product, we use a method developed by the UAH group, where we calculate the weighted difference between satellite measurements at different viewing angles AND at different locations. When some of the views are on the Antarctic continent, and some are in the surrounding ocean, there is a large spatial gradient in the measurements that pollutes the TLT retrieval (which is based on vertical gradients). Away from the poles, this problem averages out when we make monthly mean maps, but doesn't do so near the poles for geometric reasons. You can look in Mears and Wentz, 2009 http://images.remss.com/papers/rsspubs/Mears_JTECH_2009_TLT_construction.pdf
      for more details.

      These problems lead us to not provide TLT data south of 70S."

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  5. I strongly support this new idea of writing about science, with or without the excuse of demolishing anti-science. The anti-science is getting really boring.

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    1. Yes, much more interesting provided moderation is "on".

      Delete
  6. What are the actual melt rates for the 90s, 00s and 10s? Some lazy mental maths suggests the rate must have been 40ish Gt in the 90s and 180-odd now?

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    1. Fig. 2 of the paper gives time series of cumulative mass loss. If you just take blocks of data, you get 40 Gt/yr for 1992-2000, 78 GT/yr for 2000-2010, and about 170 Gt/yr for 2010-2014.

      Delete

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