Petermann Gletscher / Petermann Fjord / North West Greenland

[Espen]

Petermann Gletscher: Another crack study July 7 and July 16 2022. Almost there? Judge yourself !
But I am convinced it will happen soon!

Please click on image to enlarge and animate!

[sidd]

Agreed, and look at all the water on the thing. Altho there has been water in the past, this looks wetter to me.

sidd

[johnm33]

Seemed to be some movement against the shore[?] so I took a look, same dates first pair top would be just in Espens gif second pair immediately upstream, maybe something of the order of 100m movement but a little more on the left than the right.

[icy voyeur2]

I think I'm seeing an extension of the crack, visible in my imagination on 25.7.2022 bit with less imagination and even longer yesterday 3.8.2022. Is it just me?

[gerontocrat]

A new study on Petermann (open access)
Well above my pay grade

https://tc.copernicus.org/articles/16/3021/2022/
Ongoing grounding line retreat and fracturing initiated at the Petermann Glacier ice shelf, Greenland, after 2016

Abstract
The Petermann ice shelf is one of the largest in Greenland, buttressing 4 % of the total ice sheet discharge, and is considered dynamically stable. In this study, we use differential synthetic aperture radar interferometry to reconstruct the grounding line migration between 1992 and 2021.

Over the last 30 years, we find that the grounding line of Petermann retreated 4 km in the western and eastern sectors and 7 km in the central part. The majority of the retreat in the central sector took place between 2017 and 2021, where the glacier receded more than 5 km along a retrograde bed grounded 500 m below sea level. While the central sector stabilized on a sill, the eastern flank is sitting on top of a down-sloping bed, which might enhance the glacier retreat in the coming years. This grounding line retreat followed a speedup of the glacier by 15 % in the period 2015–2018. Along with the glacier acceleration, two large fractures formed along flow in 2015, splitting the ice shelf in three sections, with a partially decoupled flow regime.

While these series of events followed the warming of the ocean waters by 0.3 ∘C in Nares Strait, the use of a simple grounding line model suggests that enhanced submarine melting may have been responsible for the recent grounding line migration of Petermann Glacier.
_________________________________

Figure 2 Selection of double-difference SAR interferograms of Petermann Glacier, Greenland, collected between 1992 and 2021. Solid light green lines indicate the digitized grounding line positions for a given year. White arrows show the location of across-shelf fractures.
__________________________________
4 Discussion
Our results indicate that the surface velocity has remained relatively constant between 1986 and 2010 (Fig. 4a). The significant glacier speedup observed after summer 2015 coincides with the development of the two along-flow shear fractures within the same time period (Figs. 2e–i and 3a). It is worth noting that the pronounced abrupt transitions in ice flow velocity (Fig. 3c–d) are spatially consistent with the development of these breakup zones along the ice shelf length (Fig. 4), showing a partially decoupled flow regime, meaning that the three different parts of the ice shelf flow at a slightly different pace. The development of these large fractures along the shelf may also be responsible for the difference in flow regime between the floating and the grounded ice, where the abrupt transitions are not present (Fig. 3c and d).

The loss of ice shelf resistance to flow, following the 2012 calving event, may have triggered the later increase in ice flow velocity observed in 2015, causing further ice shelf thinning and consequently a grounding line retreat that happened later on between 2017 and 2018. This result is consistent with the potential reduction in ice shelf buttressing after 2012 as it was calculated by Rückamp et al. (2019). After 2018, the surface velocity of Petermann remained stable, at 1200 m yr−1 (Fig. 3b), while the grounding line continued to retreat rapidly on a retrograde bed slope (Fig. 3a). This is consistent with the hypothesis that changes in ice dynamics may be the cause of the glacier retreat and that the recession of the grounding line did not affect the flow of Petermann Glacier yet.
______________________________________________________
5 Conclusions
In this study, we report on recent developments concerning the stability of Petermann Glacier. In 2015, the glacier surface flow velocity increased markedly for the first time in the last few decades before stabilizing in 2018. Markedly after 2016, large fractures formed and split up the ice shelf in three sections with high strain rates and a partially decoupled flowing regime. Since 2017, the grounding line has begun to retreat rapidly, while it was considered stable in the previous 25 years (Hogg et al., 2016). The central section of the grounding line is now more than 7 km upstream of the 1992 position. This recession initiated after 2017 and is proceeding along topographic depressions of the bedrock. Large sections of the grounding line sitting on down-sloping beds could retreat further in the coming years. We posit that these changes are the consequences of the rapid rise in ocean temperature observed in Nares Strait.

[oren]

Very bad.

[Tealight]

Does anyone know why Sentinel 1 stopped imaging Petermann? ESA stops just south of the glacier.
Thermal imaging from the NASA SUOMI satellite isn't very detailed. It's only good enough to determine it hasn't calved yet.

[grixm]

Does anyone know why Sentinel 1 stopped imaging Petermann? ESA stops just south of the glacier.
Thermal imaging from the NASA SUOMI satellite isn't very detailed. It's only good enough to determine it hasn't calved yet.

Not sure if I'm misunderstanding but polarview.aq still has sentinel 1 radar images. Here's one of the glacier from three days ago: https://www.polarview.aq/images/105_S1jpgfull/S1A_IW_GRDH_1SDH_20221130T113610_F733_N_1.final.jpg

[johnm33]

The alternative answer is night fell.

[Tealight]

Not sure if I'm misunderstanding but polarview.aq still has sentinel 1 radar images. Here's one of the glacier from three days ago: https://www.polarview.aq/images/105_S1jpgfull/S1A_IW_GRDH_1SDH_20221130T113610_F733_N_1.final.jpg

Interesting! I stopped using polarview because they have weird image artifacts which make some regions a complete mess.

[grixm]

Comparison of the crack frontier between september last year, and now, aligned to the crack.

In short, seemingly almost no progress.

[John_the_Younger]

I’m guessing the tributary glacier on the north side is no longer pressing on Petermann, so the almost-formed ice island will remain attached for some time. I wouldn’t be surprised if it doesn’t separate this year. (Don’t call this a prediction as I’m lousy at those.)

[Espen]

Petermann Gletscher:

"A Feast for Deniers" Petermann Gletscher will not retreat if the next calving follows the present crack line, if the glacier calved today it would in theory have retreated +/- 430 meters but that is passed in less than 3 months from April 23 2023, considering Petermann Gletscher is moving at a speed of 1.250 meters per year.

Please click on image to enlarge and animate!

[A-Team]

Whoa ... surely with 1895 members, could we not keep up with major developments and even provide added value given an active, dedicated forum on Petermann Glacier?

Warm tides are eating away at the underside of Petermann's grounding line far worse than previously thought. Petermann itself is not a runaway situation because of proccvgrade inland slope and largely inconsequential buttressing of its floating shelf. (Jakobshavn, Humboldt and major ice streams in Northeast Greenland are seriously retrograde, beds deepening inland.)

However the study implies that numerous less-studied west side glaciers to the south will be melting much faster than thought, indeed sooner because the warmer tidal waters reaches them earlier.

Rignot told reporters this newly finding about tidal activity going km under grounded ice - if applicable too to West Antarctica collapse - could potentially double projected global melt.

To the extent models don't include these km-size inland tidal cycle melt intrusions along preexisting subglacial channels, they are seriously underestimating future sea level rise according to glaciologist R Alley.

Overall, sea level rise from western Greenland alone will be worse, sooner. The tidal situation adds to the zombie ice commitment resulting from a rising snow line (where melt is offset by fresh snowfall) and to increasing summer run-off.

The language of crossing thresholds of tipping points to new states seems only marginally applicable here. For example, a grounding line (a km wide zone for Petermann) can be stationary, advancing or retreating.

The authors make a distinction between 'grounding zone migration during the tidal cycle' and 'tidal flexure zone'. Previous evidence for tidal melt intrusion has been explicitly disparaged by the modeling community.

Here Petermann's grounding line has been retreating slowly since 2016 so that the tipping point changeover meant nothing catastrophic. That rate, like that of cavity melt, may still be linear per this new study, just with a larger constant related to the influx of warmer seawater.

The PNAS article by E Rignot et al is free full text; newspapers are reprinting S Borenstein's open AP account behind their pay walls. Jason Box has provided multiple youtubes explaining zombie ice.

The 74,348 sq km Petermann drainage has some 434 billion metric tons of ice already committed to melting according to Box's determination of the current snow line. A time frame is not provided by this concept alone.

Rignot once spent a summer camped by himself on Petermann which is very difficult to reach even today, with helicopters needing two fuel caches to return. He is headed back now with acoustic technology to better study the tidal-induced cavity.

Previous remote sensing of the grounding zone used interferometric radar, roughly speaking precision altimetry. This study needed a time-resolved study of the tidal cycle provided by the TanDEM-X, COSMO-SkyMed and ICEYE satellites. (None are US.)

We find that the grounding line of Petermann Glacier migrates over a zone considerably wider than anticipated, 2-6 km instead of a few 100 m, while deviating little from hydrostatic equilibrium.... the GZ experiences the highest melt rates anywhere on the ice shelf, with values averaging from 60 m/y at the glacier center to 90 at the sides.

We recommend revisions in the representation of ice melt rates at grounding lines in numerical ice sheet models, adopting subshelf melt schemes that include melting on elements at and upstream of the grounding line which will cause adjustments of the basal friction at and upstream of the grounding line, with implications for glacier sensitivity to forcing.

The revisions will likely produce higher projections of mass loss from glaciers and higher rates of sea level rise from ice sheets, possibly by up to a factor of two. We recommend further studies to examine the physical processes taking place in the grounding zone due to its critical role in glacier evolution.

https://www.pnas.org/doi/10.1073/pnas.2220924120

https://apnews.com/article/greenland-glacier-melt-climate-change-ice-e2aaad18722a355030e0d3162c7e0bf1

[sidd]

Thanks for the link. I seem to remember a glacier in WAIS (Wilkins?) that had large tidal intrusion under the ice behind the grounding line also ...

sidd

[A-Team]

glacier in WAIS (Wilkins?) that had large tidal intrusion

Right. Petermann is much studied despite the incredibly inconvenient location because it is one of the few in Greenland still having an ice shelf, thus possibly serving as a model for more civilization-critical Antarctic shelves.

(Rydberg Glacier, draining into the Lincoln Sea, has a bathymetric sill protecting its shelf in Osborn Fjord from warming water. https://www.nature.com/articles/s43247-020-00043-0)

However unlike the Wilkins Ice Shelf (and Thwaites) which Rignot has also studied, the free-floating portion of Petermann is not a buttressing cork in a bottle whose loss would result in an unstoppable catastrophic acceleration of glacier flow with subsequent rapid ocean iceberg melt dramatically raising sea level.

At least that is what's claimed for Petermann. Its ice shelf is already floating and semi-detached, meaning further calving and melt out in Baffin Bay would not significantly contribute to accelerated glacier flow and sea level rise. I favor wait-and-see on the effects of loss of buttressing (ie major calving).

Is tidal undercutting with warming waters in narrow Petermann Fjord 80.5ºN actually applicable to broad Antarctic ice shelves like in Wilkins Sound 70.0ºS? The PNAS authors seem to think so, meaning modeling paradigms - and climate risk - need drastic adjustment.

The response of Petermann Glacier  to large calving events and its future stability in the context of atmospheric and oceanic warming
FM Nick et al 2012
https://tinyurl.com/32yths45

This study assesses the impact of a large 2010 calving event on the current and future stability of Petermann Glacier, Greenland, and ascertains the glacier’s interaction with different components of the climate and ocean system.

We use a numerical ice-flow model that captures the major aspects of the glacier’s mass budget, the resistive forces controlling glacier flow, and includes dynamic calving.

Satellite observations and model results show that the recent break-off of 25% of the floating tongue did not result in a significant glacier speed-up due to the low lateral resistance of this relatively wide and thin ice tongue.

We demonstrate that seasonal speed-up at Petermann Glacier is mainly driven by meltwater lubrication rather than freeze-up conditions in the fjord. Results also show that sub-shelf ocean melt may have a profound effect on the future stability of Petermann Glacier.

Calving Induced Speedup of Petermann Glacier
M Rückamp et al 2019
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JF004775

Petermann's terminus position was considered to be stationary between 1876 and 2010, that is, glacial re-advance rates roughly equaled calving on decadal time scales.

This study assesses the response on ice dynamics of Petermann Glacier to the 2012 and a possible future calving event. So far Petermann Glacier has been believed to be dynamically stable as another large calving event in 2010 had no significant impact on flow velocity or grounding line retreat.

By analyzing a time series of remotely sensed surface velocities, we find an average acceleration of 10% between winter 2011/2012 and winter 2016/2017.

This increase in surface velocity is not linear but can be separated into two parts, starting in 2012 and 2016 respectively. By conducting modeling experiments, we show that the first speedup can be directly connected to the 2012 calving event, while the second speedup is not captured.

However, on recent remote sensing imagery newly developing fractures are clearly visible ∼12 km upstream from the terminus, propagating from the eastern fjord wall to the center of the ice tongue, indicating a possible future calving event.

By including these fracture zones as a new terminus position in the modeling domain, we are able to reproduce the second speedup, suggesting that surface velocities will remain on the 2016/2017 level after the anticipated calving event. This indicates that, from a dynamical point of view, the terminus region has already detached from the main ice tongue.

[johnm33]

I'm convinced that the residual current that flows deep through to Baffin has connected to incoming deep tidal penetration through Fram. If the Atlantic waters Icyseas indicates causing the melt were from the 'naturalised' Atlantic layer in the Arctic then I would expect them to flow south on the Ellesmere side. I suspect the connection in the past was erratic, that's now changed to variable, and as the tidal forces overcome the inertia of the Arctic ocean it will increase and become a driving force in it's own right.
Copernicus and Mercator both indicate an unbroken thread of salinity between Baffin and Fram.

[A-Team]

I sent a note to forum academic poster Andreas Muenchow hoping for a reaction to the Rignot tidal intrusion paper. He has extensive first-hand experience with tidal water circulation under the Petermann ice shelf. There's no commentary yet at his blog site https://icyseas.org/; he last posted here in March 2022 on the complexity of regional tides.

He can perhaps explain what can be learned about the tidal interaction with the grounding zone from this summer's acoustic sampling expedition. That was briefly mentioned in an interview with Rignot.

The ice shelf is said to be very noisy from constant internal ice fracturing. How that translates into acoustic tomography, say imaging the giant cavity (204 m tall, 21 sq km in area) in the grounding zone, isn't clear (passive seismography, receiver deployment?). Perhaps something can be learned about the glacier bed.

I don't think Petermann is currently set up for seismic distributed acoustic sensing using fiber optics which requires a borehole (and the equipment to make it). https://tinyurl.com/49jb98aw

Back on the matter of irreversible tipping points and state change, it's argued below that if the rest of the ice shelf broke off, Petermann might never recover it, even if the preindustrial ocean and atmosphere returned:

Petermann ice shelf may not recover after a future breakup
H Akesson et al  2022
https://www.nature.com/articles/s41467-022-29529-5

Floating ice shelves buttress inland ice and curtail grounded-ice discharge. Climate warming causes melting and ultimately breakup of ice shelves, which could escalate ocean-bound ice discharge and thereby sea-level rise. Should ice shelves collapse, it is unclear whether they could recover, even if we meet the goals of the Paris Agreement.

Here, we use a numerical ice-sheet model to determine if Petermann Ice Shelf in northwest Greenland can recover from a future breakup. Our experiments suggest that post-breakup recovery of confined ice shelves like Petermann’s is unlikely, unless iceberg calving is greatly reduced.

Ice discharge from Petermann Glacier also remains up to 40% higher than today, even if the ocean cools below present-day temperatures. A new retreated high-discharge state which may be exceedingly difficult to recover from.

Earth could eventually permit a return to a colder climate, reminiscent of that of the pre-industrial period. How marine outlet glaciers and their ice shelves would respond to a cooling climate has, however, been difficult to study due to a pervasive lack of data from historical analogues of such climate transitions over the recent past.

We have few modern observations of outlet-glacier growth, grounding-line advance and floating ice shelves that thicken and expand.  Therefore it remains unknown whether a return to the climate that prevailed in the pre-industrial period will permit ice sheets and glaciers to recover after decades to centuries of mass loss and retreat.

Note that Petermann’s ice shelf is confined in a fjord in contrast to many topographically unconfined ice shelves in Antarctica. We show that once a confined ice shelf has been lost, the glacier feeding it may get locked into a new stable regime of sustained mass loss even if the climate cools again.

[Andreas Muenchow]

There is also a pretty detailed write-up in the Washington Post by Chris Mooney on this new study at

https://www.washingtonpost.com/climate-environment/2023/05/08/sea-level-rise-greenland-glacier-melt/

When asked for comment, I read the paper twice last week and downloaded some of the data that, I hope, will be useful for my own research that involves how tides may vary across the grounding line/zone of Petermann. My most positive comments on this paper were included, but I had some more critical ones also. I am not entirely sure, for example, if the double of sealevel rise due to this "tidal heartbeat" is actually supported by the data presented in this new study. The paper says "potentially," but this is true always. Even highly unlikely events - like the world coming to an end next week - are potentially possible. The tricky and hard part is to assign both probabilities (how likely is this event?) as well as the uncertainty in the prediction. Science is fun, always.

Edit: LandSat from 2015 with 1992-2022 grounding lines at Petermann from Ciraci et al. (2023) as red point cloud with some selected grounding lines as black lines (1992 is thick, thinner ones are from May 2015, 2016, and 2018). The triangles are my fancy GPS locations with mm-scale tidal time series for 10 days in August of 2015 when the Swedish icebreaker Oden was working the fjord and glacier. Ocean stations (now defunct) are the cyan circles that were placed after holes were drilled through the glacier for sediment coring. I just "recycled" the holes by adding cabled sensors to them that were frozen in and reported data via satellite until Oct.-2017. Prof. Rignot may revisit some of these stations later this month to perhaps recover data loggers or SD-cards with additional data that did not make it through the satellite to my office ;-)

[A-Team]

The tricky and hard part is to assign both probabilities (how likely is this event?) as well as the uncertainty in the prediction.

Still, it might be worth assuming that the data accurately depicts the situation and fix the models which are really at the low end in terms of  convenient but contrafactual assumptions.

This cavity hollowed out by sea water is said to be 208 m high and 20.7 sq km in extent so about 4 cubic km in volume. That alone is too much melt and unsuspected substructure to brush off.

The Rignot paper takes a dim view of current Petermann (and Antarctic) modeling:

"Such high melt rates concentrated in kilometer-wide grounding zones contrast with the traditional plume model of grounding line melt which predicts zero melt.

"Despite [earlier grounding line melt] modeling studies, the physical processes driving melt under the grounded portion of an ice sheet are still represented in their simplest forms in many ice sheet models, i.e., a grounding line with no melt.

"Most ice sheet models employ parameterization of ice melt that assumes zero melt at a grounding line that does not migrate with tides (7, 8). It has been especially recommended not to apply melt in model mesh elements that cross the grounding line (9)."

8 H. Seroussi et al., ISMIP6 Antarctica: A multi-model ensemble of the Antarctic ice sheet evolution over the 21st century. Cryosphere 14, 3033–3070 (2020).
 
9. H. Seroussi, M. Morlighem, Representation of basal melting at the grounding line in ice flow models. Cryosphere 12, 3085–3096 (2018).

Curiously, the WaPo reporter relayed several comments from the lead author of references 8 and 9, notably that we are "many years away" from taking the experimental evidence into account in numerical models.

"More studies are needed" - they always are. However we have to go forward based on the best information that we have now. Not wait until every last scientist says no more studies are needed.

Actually I predict the appropriate numerical models will be published within the current calendar year by other scientists. "Many years" of delay on something this important is utterly unacceptable in terms of IPCC-type policy given a decades-long pattern of low-balling climate change risk and response.

"The melt rates reported are very large, much larger than anything we suspected in this region,” said Hélène Seroussi, a glaciologist at Dartmouth College who uses models to study glaciers and sea level rise.

"However, Seroussi said, the models that researchers use to project sea level rise — complex suites of equations that are used to predict how glaciers all over the world will respond to warmer oceans and air — would not immediately change based on the results of the current study.

“We are many years away from implementing these processes correctly in numerical models,” Seroussi said. “It is important to understand that there are always long delays between the discovery of a new process and its inclusion in numerical models as these processes need to be perfectly understood from a physical point of view,” requiring more research.

"In particular, Seroussi said, the process in question is generally not included because the scale over which it operates is not fully understood. Until that happens, some models could show too much ice loss because of it, simply because they represent the process as playing out over too large of a region."

[A-Team]

The Petermann article is not really about Petermann other than it being the best Greenland proxy for the precarious Antarctic ice shelves.

Field observations can be made at Petermann during the 'off-season' for Antarctica. We don't know at this time what supporting data will emerge from the summer 2023 acoustic studies.

The supplemental pdf for the current article is just an additional figure. Be great if someone would make a youtube illustrating a whole tidal cycle inside the grounding zone.

The abstract says that "vigorous ice-ocean interaction in kilometer-wide grounding zone will make projections of sea level rise from glaciers potentially double" and briefly reviews the grounding zone literature for Pine Island, Thwaites, Ross and Getz ice shelves.

However the article already has its hands full with the Petermann situation and does not delve into specific calculations on Antarctic grounding lines nor tidal circulations there to support a doubling of sea level rise.

This being PNAS and submitter Rignot an elected member, it's worth looking at reviewers who let the distracting doubling go through. BR Parizek has published on far-reaching oceanic influences at Thwaite (cited in ref 10) and A Robel on layered seawater intrusion (cited in ref 13). 

I don't see anything unusual or inappropriate here in PNAS terms; anonymous referees chosen by an editor instead of author is the norm elsewhere but that sometimes degenerates into rivalry hostilities and long delays in publication.

I chased down the article's critique of no-melt modeling (ref 9):

Representation of basal melting at the grounding line in ice flow models
Hélène Seroussi and Mathieu Morlighem
https://tc.copernicus.org/articles/12/3085/2018/

While a lot of attention has been given to the numerical implementation of grounding lines and basal friction in the grounding zone, little has been done about the impact of the numerical treatment of ocean-induced basal melting in this region.

Several strategies are currently being employed in the ice sheet modeling community, and the resulting grounding line dynamics may differ strongly, which ultimately adds significant uncertainty to the projected contribution of marine ice sheets to sea level rise.

We investigate here several implementations of basal melt parameterization on partially floating elements in a finite-element framework, based on the Marine Ice Sheet–Ocean Model Intercomparison Project (MISOMIP) setup: (1) melt applied only to entirely floating elements, (2) melt applied over all elements that are crossed by the grounding line, and (3) melt integrated partially over the floating portion of a finite element using two different sub-element integration methods.

All methods converge towards the same state when the mesh resolution is fine enough. However, (2) and (3) will systematically overestimate the rate of grounding line retreat in coarser resolutions, while (1) converges faster to the solution in most cases.

The differences between sub-element parameterizations are exacerbated for experiments with high melting rates in the vicinity of the grounding line and for a Weertman sliding law. As most real-world simulations use horizontal mesh resolutions of several hundreds of meters at best, and high melt rates are generally present close to the grounding lines, we recommend not using (3) to avoid overestimating the rate of grounding line retreat and to carefully assess the impact of mesh resolution and sub-element melt parameterizations on all simulation results.

Here it might be far better computationally to use Iverson's sliding law which, incredibly, is lab based and applicable both to a bedrock and sedimentary till.

Glacier-in-a-freezer. Till deformed by laboratory ice experiments
https://www.news.iastate.edu/news/2020/04/02/slip-law Apr 2, 2020

“The potential collapse of the West Antarctic Ice Sheet is the single largest source of uncertainty in estimations of future sea-level rise, and this uncertainty results, in part, from imperfectly modeled ice-sheet processes.”

Iverson started experiments with the 9-foot-tall ring-shear device inside his laboratory’s walk-in freezer in 2009. At the center of the device is a ring of ice about three feet across and eight inches thick. Below the ring is a hydraulic press that can put as much as 100 tons of force on the ice and simulate the weight of a glacier 800 feet thick. Above the ring are motors that can rotate the ice at speeds of 1 to 10,000 feet per year.

The ice is surrounded by a tub of temperature-controlled, circulating fluid that keeps the ice ring right at its melting temperature so it slides on a thin film of water – just like all fast-flowing glaciers."

Future Projections of Petermann Glacier Under Ocean Warming Depend Strongly on Friction Law
H Akessonet et al   04 May 2021
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020JF005921

Inferring forms of glacier slip laws from estimates of ice-bed separation during glacier slip
Woodard, Zoet, NR Iverson Helanow 
https://tinyurl.com/4wtbc3f5  05 August 2022

A slip law for hard-bedded glaciers derived from observed bed topography
Same authors  14 May 2021
https://leap.columbia.edu/wp-content/uploads/2023/01/zoet_iverson_2020.pdf

[Andreas Muenchow]

I forgot that the tidal oscillations across the grounding zone of Petermann are published at

http://muenchow.cms.udel.edu/papers/Muenchow2016-TOS.pdf

both for the vertical oscillations and horizonal velocities that can be estimated from observed displacements measured every 30 seconds for 13 days. Lots of other stuff on ice-ocean interactions from Petermann.

[A-Team]

both for vertical oscillations and horizontal velocities measured every 30 seconds for 13 days.

The pdf does not show the horizontal displacements. Do you have a nice graph of that posted somewhere else? It's not made explicit from the PNAS paper what should be expected or indeed if the two data sets synergize being from different years.

First off, station GZ-00 of 2015 needs to be located graphically relative to the PNAS fringes and subglacial channels.

"The observed full range of vertical glacier displacements diminishes from almost 2 m about 26 km seaward of the grounding zone (GZ+26) to 0.6 m in the grounding zone (GZ-00) to nil (within the uncertainty) at GZ-20, about 20 km landward of the grounding zone." -  pdf

"The reduced vertical and increased horizontal (not shown) tidal oscillations at GZ-00 reflect active flexing of the glacier."-  pdf

In view of the Ciracì paper distinguishing between grounding zone migration and tidal flexure, which is the pdf referring to?

It seems that Fig.4 could be re-drawn for GZ-00 providing elevation with respect to that of the fixed underlying bedrock of the grounding line, rather than mean sea level.

"Note here that grounding zone refers to the zone of migration of the grounding line during the tidal cycle. It should not be confused with the zone of tidal flexing of an ice shelf, previously called a grounding zone (17, 18), but more appropriately named the tidal flexure zone. - pnas

We find that the grounding line migrates at tidal frequencies over a kilometer-wide (2 to 6 km) grounding zone, which is one order of magnitude larger than expected for grounding lines on a rigid bed." - pnas

It seems nil vertical displacement at  GZ-20 is unfortunate as it does not allow much of a flexure decay function to be determined, ie GZ-5 might also be nil but not GZ-3. GZ-00 was somewhere else back then as it moved 3800 m inland in the last four years.

Sometimes fourier analysis can pull a signal out when there seems to be just instrument noise -- here we know the tidal driving frequency, phase and relative vertical weighting in advance, plus the averaging outcome might receive internal validation from discernable major and minor high tide peaks.

In terms of horizontal motion, Petermann Glacier is sliding forward at about 1180 m per year which is 3 m per 24 hr tidal cycle or 12 cm/hr (5 inches/hr).

Presumably this forward velocity is strictly uniform only in the average. Seasonally, melt water in subglacial channels may briefly reduce friction at the grounding line, peaking variably in early August in high melt years.

On a daily tidal scale, horizontal motion may proceed in the form of lurches coordinated with the reduction in friction as the tide lifts the grounding zone 0.6 m (less farther back depending on flexure). The GPS deployed in 2015 can easily resolve this:

"Our final glacier speed estimate originates from three dual frequency geodetic GPS receivers that provide centimeter accuracy at 30-second intervals; however, we only have time series for the 13 day numbers 223-236 that the instruments were deployed during 11-23 August 2015." - pdf

"For the 13 days of measurements, we find the glacier moving a total of 26 m 20 km landward of the grounding line, 44 m at the grounding line, and 43 m at the site seaward for speeds of 732, 1,235 and 1,208 ± 1 m yr–1, with maximum speed at the grounding line." - pdf

"As the glacier lifts and migrates, the water can rush in for over a mile, thinning the ice by as much a 250 feet (76 m) a year in some places. You have this constant flushing of seawater going many kilometers below the glacier and melting the ice,” said Eric Rignot in a WaPo interview.

What determines how far the seawater rushes in with the tide - and how would this change after another major caving? The shelf itself is already floating in approximate hydrodynamic equilibrium but ice upstream of the (retreating) grounding line must be lifted.

[A-Team]

This PNAS paper, which is complicated enough by itself, has reams of data and code that didn't make it into the article or its supplemental. It's stored at a non-profit data warehouse called Dryad which can issue a doi whether or not there is an associated publication.

Some of these same authors including Rignot are also using Dryad to store data from yet another Petermann paper.

The idea is admirable ... scientific reproducibility. Or maybe to do away with field notes scribbled in never-transcribed paper notebooks. Provide all the tools, data and installations to allow bubba to recreate every aspect of the papers including figures. I ask myself though how many people actually do. Petermann would have to be the entire focus of your professional and personal life.

I struggled even to download the Dryad data zip @ home. Fortunately, a linked site Zenodo shows a preview of the code content.

https://datadryad.org/stash/dataset/doi:10.7280/D1XT4G
https://zenodo.org/record/7853454

April 25, 2023 Software Open Access
Ice shelf basal melt rate estimation in a Lagrangian framework
Ciracì, Enrico

We present a dense record of glacier ice dynamics and ice melt rate at the boundary between grounded ice and ocean - or grounding line - of Petermann Glacier, a major outlet glacier in Northwest Greenland. The traditional view of grounding lines implemented in physical models in charge of projecting sea level rise is a fixed grounding line with zero ice melt. Instead, the satellite record reveals kilometer-size grounding line migrations - or grounding zones - during tidal cycles, with preferential intrusions of 6 km along pre-existing subglacial channels. The highest melt rates of ice are recorded within the grounding zone. Kilometer-wide grounding zone with vigorous ice-ocean interaction will make projections of sea level rise from glaciers potentially double.

Data for: Seasonal acceleration of Petermann Glacier from changes in subglacial hydrology
S Ehrenfeucht, Morlighem, Rignot, Dow, Mouginot, Jeremie
https://datadryad.org/stash/dataset/doi:10.7280%2FD1Z69G 20 Dec 2022
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GL098009

Petermann Glacier, a major outlet glacier of Northern Greenland, drains a marine-based basin vulnerable to destabilization. Using satellite radar interferometry data from the Sentinel-1a/b missions, we observe a seasonal glacier acceleration of 15% in the summer, from 1,250 m/yr to 1,500 m/yr near the grounding line, but the physical drivers of this seasonality have not been elucidated. [[The speed of a glacier can vary along its length because of rheology (slow cold flow, thinning without crevassing]]

Here, we use a subglacial hydrology model coupled one-way to an ice sheet model to evaluate the role of subglacial hydrology as a physical mechanism explaining the seasonality in speed. We model the basal effective pressure using the Glacier Drainage System model which then forces the Ice-sheet and Sea-level System Model. We find an excellent agreement between the observed and modeled velocity in terms of magnitude and timing, and conclude that seasonal changes in subglacial hydrology are sufficient to explain the observed seasonal speed up of Petermann Glacier.

This data publication provides all of the scripts and data necessary to initialize and run the subglacial hydrology model and ice sheet model used in this work (Manuscript number 2022GL098009). We also provide the model output and the scripts used to create the figures in the manuscript and the animations in the supplemental document.

Several data sets are also made available here, including integrated melt water runoff derived from the regional climate model, MAR (Modèle Atmosphérique Régional), which is used to force the hydrology model, and daily average effective pressure derived from the hydrology model output, which is used to force the ice sheet model. These files combined are sufficient to reproduce all results and figures presented in this w

[Andreas Muenchow]

I discover more old stuff that perhaps should be published, but life happens, too. Here is a slide from a Jan.-2017 talk that shows both vertical and horizontal motions as well as more detail. My GPS reference station on the bedrock at Kap Schoubye (SCBY in GNET parlance) at 80.260 N and 59.594 W is about 18 km, 33 km, and 58 km from this base on the glacier. For "error estimation" I compared the bedrock station at Kap Schoubye with another bedrock station (KMOR about 133 km away at the entrance of the fjord). It took me all day trying to figure out what I did why some 6 years ago ... but here is the abstract that goes with the slide deck.

Ocean impacts on glacier motions at Petermann Gletscher in North-Greenland
Andreas Münchow, University of Delaware, Newark, DE
muenchow@udel.edu

A cabled, real time ocean observatory was established in August 2015. It continues reports hourly recordings of GPS position, wind vector, air temperature, air pressure, and ocean temperature and salinity below the floating ice shelf of Petermann Gletscher. During its installation, we placed three dual-frequency GPS systems at 25-km spacing along the glacier centered on the grounding line for 13 days. High-precision vertical and horizontal glacier motions were obtained by referencing data to GNET station data at Kap Schoubye and Kap Morton and using GAMIT/TRACK software for data processing. Preliminary results indicate that the floating ice shelf oscillates vertical with the ocean tide with little horizontal motion at tidal frequencies. Near the grounding line, however, tidal motions in the vertical are reduced while those in the horizontal are enhanced. Upstream of the grounding line we observe no tidal oscillations at diurnal or semi-diurnal periods. In contrast, ocean sea level signals at longer than 10-day periods propagate past the grounding line into the section of the glacier that is grounded on bed-rock and cause horizontal motions that are coherent with ocean perturbations of similar magnitude.

[gerontocrat]

Another technical study (open access) on an apparently limited scope, i.e. the Petermann Glacier, that has a sting in its tail, i.e.

... will make projections of sea level rise from glaciers potentially double
Extracts from https://www.pnas.org/doi/10.1073/pnas.2220924120 below (my italics)

Melt rates in the kilometer-size grounding zone of Petermann Glacier, Greenland, before and during a retreat
Enrico Cira

cì, Eric Rignot, Bernd Scheuchl , and Luigi Dini - Authors[/i]
Significance
We present a record of glacier ice dynamics and ice melt rate at the boundary between grounded ice and ocean—or grounding line—of Petermann Glacier, a major outlet glacier in Northwest Greenland. The traditional view of grounding lines implemented in ice sheet models in charge of projecting sea level rise is that they not migrate during the tidal cycle and experiences no ice melt. Instead, the satellite record reveals kilometer-size grounding line migrations—or grounding zones—with preferential intrusions along preexisting subglacial channels. The highest melt rates of ice are recorded within the grounding zone. Vigorous ice-ocean interaction in kilometer-wide grounding zone will make projections of sea level rise from glaciers potentially double.

Abstract
Warming of the ocean waters surrounding Greenland plays a major role in driving glacier retreat and the contribution of glaciers to sea level rise. The melt rate at the junction of the ocean with grounded ice—or grounding line—is, however, not well known. Here, we employ a time series of satellite radar interferometry data from the German TanDEM-X mission, the Italian COSMO-SkyMed constellation, and the Finnish ICEYE constellation to document the grounding line migration and basal melt rates of Petermann Glacier, a major marine-based glacier of Northwest Greenland. We find that the grounding line migrates at tidal frequencies over a kilometer-wide (2 to 6 km) grounding zone, which is one order of magnitude larger than expected for grounding lines on a rigid bed. The highest ice shelf melt rates are recorded within the grounding zone with values from 60 ± 13 to 80 ± 15 m/y along laterally confined channels. As the grounding line retreated by 3.8 km in 2016 to 2022, it carved a cavity about 204 m in height where melt rates increased from 40 ± 11 m/y in 2016 to 2019 to 60 ± 15 m/y in 2020 to 2021. In 2022, the cavity remained open during the entire tidal cycle. Such high melt rates concentrated in kilometer-wide grounding zones contrast with the traditional plume model of grounding line melt which predicts zero melt. High rates of simulated basal melting in grounded glacier ice in numerical models will increase the glacier sensitivity to ocean warming and potentially double projections of sea level rise.

2. Discussion
Our results have vast implications for the modeling of glaciers terminating in ocean waters. Prior attempts at estimating melt rates using DEMs from optical data excluded the area within 5-km downstream of the grounding line and reported lower melt rates with peak values of 50 m/y at Petermann Glacier (28). Here, we are able to extend these calculations to the grounding zone because we document the full extent of the grounding line migration and verify with precision DEMs that the ice surface remains close to flotation in the GZ. We exclude from our calculations a narrow band where the ice transits from grounded to floating within the time separation of the DEMs, which is one year (limit of viability about 700 m in width or 1/2 y of ice motion in Figs. 2 and 3). The results reveal that the melt rates continue to increase within the GZ and are, in fact, the highest anywhere on the ice shelf. We are confident that the vertical motion of the ice in the GZ is caused by seawater intrusion and not, for instance, by flexural bending upstream of a fulcrum located at a fixed grounding line because such ice motion above the fulcrum would be of the opposite sign compared to the tide (12).
The traditional plume model for ice shelf melt (31, 32) predicts peak melt about 10 to 15 km from a fixed grounding line, which is not observed here. The grounding line migrates over considerable distances in response to tidal forcing, which brings a large amount of ocean heat, at high speed, beneath grounded ice. The speed of transfer may be approximated by the width of the GZ divided by the tidal cycle, or 6 h. Thermodynamics dictates that the ice melt rate is the product of the heat capacity of water, Cp, times the ocean thermal forcing, T − Tf, and the entrainment speed, e, of the water along the ice boundary. The entrainment speed of pressurized water in the GZ is the rate of opening of the cavity, i.e., 6 km in 6 h, or 28 cm/s. Such a water speed matches peak values observed in meltwater plumes of Greenland tidewater glaciers (33) and ice shelf channels beneath Petermann Ice Shelf (34). The high flow speed will be conducive to vigorous melt and justify a posteriori high melt rates in the GZ. This situation contrasts with zero melt at fixed grounding lines used in some ice sheet models. Other ice sheet models use depth-dependent melt parameterizations (7) which predict the largest melt at the grounding line. These models however differ in how they implement melt on elements that cross the grounding line (9). Models that have zero melt on model elements crossed by the grounding line, called No-Melt Parameterization (NMP), have been recommended by ref. 9, but these models are not consistent with our observations. As suggested by refs. 8–10 and 13, the implications of wet, broad grounding zones for sea level rise projections are significant, especially as more groups adopt full-melt parameterization (FMP) or subelement melt (SEM) for representing basal melt grounding lines as in ref. 35.
Tidal flushing in kilometer-size GZ will progressively reduce basal resistance to flow if the ocean gets warmer. A prior study of ephemeral grounding of ice shelves revealed that the effect is most efficiently felt once the ungrounding of grounded ice is permanent during the tidal cycle (36). The cavity that developed at the center of Petermann’s GZ over the time period 2016 to 2022 is about 20 square km in size. Assuming a spatially averaged basal drag of 1 bar or 100 kPa (Pascal), the ungrounding removed a force of 2TN (Tera Newton). For comparison, assuming a uniform lateral drag of 1 bar along the ice shelf sides (two sides) and an ice shelf thickness of 500 m, the removal of a 20-km long ice shelf would reduce the buttressing force by the same 2 TN. Hence, the grounding line retreat at the glacier center is equivalent to the hypothetical removal of the entire ice shelf in terms of changes in buttressing force. The loss of basal resistance yielded a readjustment in stress balance at the grounding line region and beyond, which was accompanied by a glacier speed up of 15% between 2015 and 2021 (22).

Several modeling studies have indicated that a wide GZ with high melt rates could double the projections of glacier loss (10, 12, 13, 37). This increase in ice sheet sensitivity may help explain the inability of previous models to reproduce rapid rates of sea level rise during past warm periods (38) and the generally too-low ice loss simulated during the recent historical period by ISMIP models (39).

Our results demonstrate that high melt rates should be applied in kilometer-size GZ instead of zero melt on Petermann Glacier. Several explanations are possible for a wide GZ. One is the presence of bending stresses (12), which relax as the grounding line retreats and enable greater penetration of seawater at the GZ wedge. Second, seawater is applied under pressure (40), which violates the assumption that water is at the hydrostatic pressure. Third, the bed may be deformable (41, 42), which facilitates seawater intrusion over greater distances. Fourth,
seawater may propagate in the till or through preexisting subglacial channels (11). Fifth, simulations of grounding line migration as the propagation of an elastic crack suggest the possibility of kilometer-size GZ (43). Finally, bed topography is not uniform beneath the glacier and may include roughness elements that will facilitate the infiltration of seawater at high tide or conversely will trap seawater intrusion at low tide (42).

Prior simulations of ice shelf melt beneath Petermann did not produce high melt rates (44), but the model resolution was 20 m in the vertical dimension and did not include a GZ. It would be of interest to extend the modeling of ice shelf melt with vigorous tidal flushing over a thin (about 1 m) GZ multiple kilometers in width. It will also be of interest to confirm these high ice melt rates in situ, e.g., using portable, coherent, radar sounding devices (45).

The glacier configuration of Petermann is not unique to Greenland. It may be representative of many other glaciers terminating into an ice shelf in other parts of Greenland and to glaciers and ice shelves in Antarctica. Wide, heterogeneous GZs have already been revealed in Antarctica (14–16). Wide GZ may be exposed to high melt rates from vigorous tidal flushing. Conversely, narrow GZ may experience limited tidal flushing and ice melt, as in ref. 46, or seawater may be trapped at low tide (47), which will limit heat exchange and ice melt.

3. Conclusions
Using a dense time series of satellite observations of ice surface elevation and millimeter-scale vertical motion of ice as it reaches flotation at tidal frequencies, we find that the grounding line of Petermann Glacier migrates over a zone considerably wider than anticipated, i.e., 2 to 6 km instead of a few 100 m, while deviating little (2 to 3 m) from hydrostatic equilibrium. Using a Lagrangian approach with precision DEM data, we find that the GZ experiences the highest melt rates anywhere on the ice shelf, with values averaging from 60 ± 15 m/y at the glacier center to 80 to 100 ± 15 m/y at the glacier sides. During the retreat and formation of a new cavity, the average melt rates dropped to 40 ± 11 m/y before increasing again to 60 ± 15 m/y as the cavity became fully formed. In light of these results, we recommend revisions in the representation of ice melt rates at grounding lines in numerical ice sheet models. We suggest that ice sheet models adopt subshelf melt schemes that include melting on elements at and upstream of the grounding line (13). Separately, this modification will cause adjustments of the basal friction at and upstream of the grounding line, which has implications for glacier sensitivity to forcing (43). The revisions will likely produce higher projections of mass loss from glaciers and higher rates of sea level rise from ice sheets, possibly by up to a factor of two. We recommend further studies to examine the physical processes taking place in the grounding zone due to its critical role in glacier evolution.

[Andreas Muenchow]

Yes, GerontoCrat, that paper was reported on by AP News, CNN, and the Washington Post. It very much motivated me (and A-Team) to dig in a bit. I am not entirely sure that the projections of sealevel rise will indeed double, if tidal processes at grounding zones of floating glaciers are included in models. Such  projections/modelings have not yet been done, so it is a bit speculative. Nothing wrong with speculation, but fact it is not yet ;-)

[gerontocrat]

There is a bit of confusion (at least in me) of what they actually mean by sea level rise doubling.

At the beginning of the paper the wording used is "Vigorous ice-ocean interaction in kilometer-wide grounding zone will make projections of sea level rise from glaciers potentially double".

In the Abstract the wording is High rates of simulated basal melting in grounded glacier ice in numerical models will increase the glacier sensitivity to ocean warming and potentially double projections of sea level rise

And finally, in Conclusions,  the wording is The revisions will likely produce higher projections of mass loss from glaciers and higher rates of sea level rise from ice sheets, possibly by up to a factor of two.

So are they claiming the doubling is just that part of sea level rise from basal melt at the GZ of marine-terminating glaciers, or are they meaning doubling of sea level rise from all sources of mass loss?

It is impossible (for me) not then to start thinking about consequences. Are there any papers planned on projections of the consequences of greatly increased basal melt, e.g. increased flow of glaciers to the ocean, AbruptSLR's Armada of icebergs invading the Southern Ocean and beyond? After all, what happens in Petermann is not confined to Petermann.

[A-Team]

doubling is just that part of sea level rise from basal melt at the GZ of marine-terminating glaciers, or are they meaning doubling of sea level rise from all sources of mass loss?

Neither. As explained over and over in the last dozen posts #863-#874, Rignot means more rapid loss of ice shelves from the giant Antarctic ice shelves listed above. Those are corks stopping the bottle unlike Petermann. Greenland is mostly a surface melt story.

Once the buttressing is broken off, the parent grounded retrograde glaciers will empty into the sea much faster. Future projections of sea level rise, say for 2100, then may double.

The PNAS article is strictly about Petermann, how the warming Atlantic Waters coming up the fjord are eating away at the grounding line base much farther and faster than conservative models had assumed.

The Petermann situation may imply that the warming ocean off the WAIS is eating away at the grounding lines much farther and faster than the zero conservative models assume.

As explained over and over, this doubling is just a throw-away line in a long complicated article about Petermann Glacier within a fifty year series of long complicated Petermann articles (which include important observational studies by Prof Muenchow).

Summer surface melt thins Petermann Gletscher Ice Shelf by enhancing channelized basal melt
https://tinyurl.com/muh2k9hs 2019

This is not a doubling forum; we are just trying to understand Petermann better and perhaps integrate information from the very latest articles to add value.

The PNAS article does not discuss Antarctic grounding line attack and makes no calculations of how models of ice shelves loss quantitatively accelerate glacier advance there, much less derive a doubling.

So yes it is speculation. Some would say informed speculation, worth a good look. I would call it exceedingly well informed speculation, worth serious scientific and climate policy consideration.

The thing is, we cannot wait until the ink is dry. We have to go forward with what we've got, even if "more studies are needed". Always taking the least inconvenient assumption like the IPCC introduces a very risky bias.

Six km of intrusive melt is very different from assuming zero. Occam's Razor is in a different place.

Have Petermann and Wais studies fully met the burden of proof? No, but the latest observations are very hard to ignore. Doubling is not an extraordinary claim (requiring extraordinary evidence) but a very plausible one given the surprising new support.

Prof. Rignot is not an anonymous loony on twitter. His 884 publications include 262 on Antarctic glaciers, their ice shelves and grounding lines. Those have been cited 45,014 times by other scientists in peer-reviewed articles. That includes 20,673 from 2018 on. These are astronomic numbers. He is an active 61, not a demented NAS elder holding forth on race relations or whatever.

Rignot has long been alarmed about unwitting climate change commitments, writing in 2014 (based on Antarctic grounding line retreat) that the melting of glaciers in the Amundsen Sea is "unstoppable" and that these glaciers have "passed the point of no return."

https://scholar.google.com/citations?user=IEEkR3gAAAAJ&hl=en
https://en.wikipedia.org/wiki/Eric_Rignot

[nadir]

Shouldn’t the waters eroding Petermann glacier be affected by the weakening of AMOC and thus actually getting colder these recent years? In fact shouldn’t these water temperatures be directly affected by the increasing melting rate, acting as negative feedback rather than accelerator? These are honest questions, I don’t understand why Atlantic waters should be increasing glacier erosion when Atlantic waters are supposed to be reaching the glacier at a weakened rate.

[johnm33]

Shouldn’t the waters eroding Petermann glacier be affected by the weakening of AMOC and thus actually getting colder these recent years? In fact shouldn’t these water temperatures be directly affected by the increasing melting rate, acting as negative feedback rather than accelerator? These are honest questions, I don’t understand why Atlantic waters should be increasing glacier erosion when Atlantic waters are supposed to be reaching the glacier at a weakened rate.

The waters reaching the glacier are, I think, near the densest most saline fraction of waters passing north through Fram, thus they spend more time being warmed through insolaton and cooled by evaporation if the amoc slows, so probably a small net gain of temp.. They have some residual inertia so are affected by their passage N. of Greenland and the vortices generated close by the fjords they pass. I think the determining factors are the net flow of Atl. waters into the Nordic seas, the tidal forcings and current variations at Fram and the negative tidal pressure in N. Baffin which induces the Atl. waters to flow south. The simple fact that the water flows into this fjord indicates it has some residual 'eastbound' inertia and this kinetic energy will be translated to heat when forced to a halt, increasing melt above expectations from temps. alone. That said it's a huge ice tongue which is constantly being 'repaired' by the supply of freshwater emerging from any cracks that form, and the fjord itself channels bone dry air both down the glacier itself and from it's tributaries. Sometimes this air is warmed by the height loss so some melt can take place but as it progresses it causes rapid evaporative cooling in the emerging meltwater.
 Whilst the southern/western side seems to recieve little precipitation the north/eastern side still has glaciers which I'm assuming press the tongue fast against the opposite face preventing it's movement which is also inhibited by the curvature of the fjord. sentinel

[gerontocrat]

When I read the science paper on Petermann GZ melting I was in two minds as to whether to post it in the Petermann glacier thread or a thread on sea level rise / consequences, and this is why.

A-Team's Reply #878 on: May 12, 2023 from which I quote parts below (my italics).

The PNAS article is strictly about Petermann, how the warming Atlantic Waters coming up the fjord are eating away at the grounding line base much farther and faster than conservative models had assumed.

The Petermann situation may imply that the warming ocean off the WAIS is eating away at the grounding lines much farther and faster than the zero conservative models assume.

As explained over and over, this doubling is just a throw-away line in a long complicated article about Petermann Glacier within a fifty year series of long complicated Petermann articles (which include important observational studies by Prof Muenchow).

[/size]

I would suggest that the doubling effect is not just a throwaway line, and perhaps Eric Rignot and his co-authors discussed it before deciding to plant it several times throughout the text. If this comes to pass, it puts a very large spanner in all the works of mitigation and resilience planning and investments underway for the coastal areas and many inland low-lying lands. E.g.s UK  large parts of the East Coast, much of East Anglia, in the midlands the Somerset Levels and coastal cities including London. Bangladesh 70% of the country is less than 1m above sea level.

I have been a great admirer of Eric Rignot for a good few years - his papers manage to explain complicated processes in a way that even a non-climate scientist such as myself can extract great value. So I agree entirely with A-Team's asessment of the value of the warning on sea level rise, i.e.

The PNAS article does not discuss Antarctic grounding line attack and makes no calculations of how models of ice shelves loss quantitatively accelerate glacier advance there, much less derive a doubling.

So yes it is speculation. Some would say informed speculation, worth a good look. I would call it exceedingly well informed speculation, worth serious scientific and climate policy consideration.
The thing is, we cannot wait until the ink is dry. We have to go forward with what we've got, even if "more studies are needed". Always taking the least inconvenient assumption like the IPCC introduces a very risky bias.

Will the decision-makers take the warming seriously? Will it even get a mention at COP28? I doubt it.

[oren]

A well informed speculation indeed. And as opposed to many papers which are a result of simulations, this one is the result of direct and accurate observations of Petermann, which leads even more credence to the conclusions, IMHO.

Is there any time series of measurements of the water temperature at depth in the Petermann fjord?

[gerontocrat]

Some of the media have picked up the comment in the science paper on doubling sea level rise. I bet Eric Rignot et al have been receiving a good number of requests for info.

See google search result below

[nadir]

Shouldn’t the waters eroding Petermann glacier be affected by the weakening of AMOC and thus actually getting colder these recent years? In fact shouldn’t these water temperatures be directly affected by the increasing melting rate, acting as negative feedback rather than accelerator? These are honest questions, I don’t understand why Atlantic waters should be increasing glacier erosion when Atlantic waters are supposed to be reaching the glacier at a weakened rate.

The waters reaching the glacier are, I think, near the densest most saline fraction of waters passing north through Fram, thus they spend more time being warmed through insolaton and cooled by evaporation if the amoc slows, so probably a small net gain of temp.. They have some residual inertia so are affected by their passage N. of Greenland and the vortices generated close by the fjords they pass. I think the determining factors are the net flow of Atl. waters into the Nordic seas, the tidal forcings and current variations at Fram and the negative tidal pressure in N. Baffin which induces the Atl. waters to flow south. The simple fact that the water flows into this fjord indicates it has some residual 'eastbound' inertia and this kinetic energy will be translated to heat when forced to a halt, increasing melt above expectations from temps. alone. That said it's a huge ice tongue which is constantly being 'repaired' by the supply of freshwater emerging from any cracks that form, and the fjord itself channels bone dry air both down the glacier itself and from it's tributaries. Sometimes this air is warmed by the height loss so some melt can take place but as it progresses it causes rapid evaporative cooling in the emerging meltwater.
 Whilst the southern/western side seems to recieve little precipitation the north/eastern side still has glaciers which I'm assuming press the tongue fast against the opposite face preventing it's movement which is also inhibited by the curvature of the fjord. sentinel

From your response and Gerontocrat’s I believe that this is a problem caused more by sea level rise than water temperature or salinity itself, so this has little to do with AMOC strength. Sorry for the misunderstanding.

Thanks.

[grixm]

The latest satellite image is a bit interesting.

There are a bunch of trails coming from the cracks in the glacier. I'm not sure what it is, snow being whirled up by the wind maybe. But it could give us some clues about the crack.

You can see a faint continuation of the crack that I've marked as 2. Originally I thought this was the weakest point, where the crack would continue to grow and calve.
However, the wind trails might actually tell a different story. There are trails coming from a different line perpendicular to the original crack direction, that I've marked as 1. There are many such white lines on the glacier (rivers during the melting season) and I believe this was there before the crack grew this far, and thus I thought it was just a coincidence.

However clearly this line is special. The wind trails appear to be very consistent: They show up on basically all proper cracks, but almost none of the other white lines. However they do show up on this particular white line (1), and not on what appears like the direct continuation of the crack (2). This could mean that below the snow in the white line, there has actually formed a proper crack connected to the main crack, and perhaps this is even where the calving will happen, not the straight continuation of the crack.

[Niall Dollard]

Nibbling at the NE Corner.

Click to run GIF

[grixm]

This poll is funny in retrospect: https://forum.arctic-sea-ice.net/index.php/topic,2862.50.html

Latest possible option was after August 2020. And here we are, three years later, and it *still* hasn't calved 

[John_the_Younger]

I agree with you, grixm.  But at least 5 voters got it right!

I think the 'sideways' pressure from the right (tributary glacier) ended (little icebergs floated away) leaving nothing to break off the last kilometer or so of ice near the left bank.  It is clear that some of the lateral crack has healed - it goes right through a lake that didn't drain this year.

[grixm]

Satellite images of Petermann Glacier have started coming in.

Here is a comparison of now and one year ago, aligned to the crack.

You can see that the main crack has actually all but stopped moving. There seems to be almost no forces acting on it anymore. I don't know why this is.

On the other hand, the crack behind it is actually growing significantly, you can see both an expansion and extension compared to last year. Would be funny if this crack ends up calving before the downstream one, though that probably remains unlikely.

[Espen]

Satellite images of Petermann Glacier have started coming in.

Here is a comparison of now and one year ago, aligned to the crack.

You can see that the main crack has actually all but stopped moving. There seems to be almost no forces acting on it anymore. I don't know why this is.

On the other hand, the crack behind it is actually growing significantly, you can see both an expansion and extension compared to last year. Would be funny if this crack ends up calving before the downstream one, though that probably remains unlikely.

The reason why the large crack in the glacier do not develop is because there is no resistance from the rock wall on the starboard side, which in reality was the cause of the 2 previous calvings in 2010 and 2012, the second crack will probably be the cause of the next large calving, provided that the ice material (starboard) is preserved as a Jemmy / Crow Bar.

[FredBear]

Satellite images of Petermann Glacier have started coming in.

Here is a comparison of now and one year ago, aligned to the crack.

You can see that the main crack has actually all but stopped moving. There seems to be almost no forces acting on it anymore. I don't know why this is.

On the other hand, the crack behind it is actually growing significantly, you can see both an expansion and extension compared to last year. Would be funny if this crack ends up calving before the downstream one, though that probably remains unlikely.

grixm - if you had aligned your images on the incoming glacier feeds on the right the motion of the main glacier would have shown its movement over the year and where the fractures are being worked out now. (It would not, however, show how little the old crack has changed!)

[kassy]

Grounding zone discovery explains accelerated melting under Greenland's glaciers

Researchers at the University of California, Irvine and NASA's Jet Propulsion Laboratory have conducted the first large-scale observation and modeling study of northwest Greenland's Petermann Glacier. Their findings reveal the intrusion of warm ocean water beneath the ice as the culprit in the accelerated melting it has experienced since the turn of the century, and their computer predictions indicate that potential sea level rise will be much worse than previously estimated.

For a paper published recently in Geophysical Research Letters, the UCI-led team used radar interferometry data from several European satellite missions to map the tidal motion of Petermann Glacier and the Massachusetts Institute of Technology's general calculation model to estimate the impact of climate change in a complex environment involving ice, seawater and land, all of which are under the influence of tides and climate change-driven temperature boosts.

"Satellite data revealed that the glacier shifts by several kilometers -- or thousands of feet -- as tides change," said lead author Ratnakar Gadi, UCI Ph.D. candidate in Earth system science.

"By factoring this migration into the MIT numerical ocean model, we were able to estimate roughly 140 meters [460 feet] of thinning of the ice between 2000 and 2020. On average, the melt rate has increased from about 3 meters per year in the 1990s to 10 meters per year in the 2020s."

Senior co-author Eric Rignot, UCI professor of Earth system science, said that this and other studies conducted by his team in recent years have caused a fundamental shift in polar ice researchers' thinking about ocean and glacier interactions.

"For a long time, we thought of the transition boundary between ice and ocean to be sharp, but it's not, and in fact it diffuses over a very wide zone, the 'grounding zone,' which is several kilometers wide," said Rignot, who is also a senior research scientist at NASA JPL.

"Seawater rises and falls with changes in oceanic tides in that zone and melts grounded ice from below vigorously."

Gadi said the model predicted that melt rates will be highest near the mouth of the grounding zone cavity and greater than anywhere else in the ice shelf cavity.

Warmer water and greater seawater intrusion beneath the ice explains the observed thinning along Petermann's central flowline.

According to the study, the elongated shape of the grounding zone cavity is a major contributor to accelerated ice melting.

In a run of the numerical model taking into account just warmer ocean temperature, the team found thinning of about 40 meters.

In a second modeling exercise, an increase in the grounding zone cavity from 2 to 6 kilometers was included, and in that case, ice thinning grew to 140 meters.

"These modeling results conclude that changes in grounding zone lengths increase melt more significantly than warmer ocean temperatures alone," Gadi said.

The researchers noted that grounding zone ice melt reduces the resistance glaciers experience when flowing toward the sea, speeding their retreat.

The researchers said this is a key factor used in projecting the severity of future sea level rise.

"The results published in this paper have major implications for ice sheet modeling and projections of sea level rise," Rignot said.

"Earlier numerical studies indicated that including melt in the grounding zone would double the projections of glacier mass loss. The modeling work in this study confirms these fears. Glaciers melt much faster in the ocean than assumed previously."

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https://www.sciencedaily.com/releases/2024/03/240313135328.htm

letter:

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023GL105869

[sidd]

Thanks for the paper. I beleive this kind of thing has been seen i west antarctica also, in the glaciers feeding the eastern bit of Ross.

sidd

[John_the_Younger]

I see a melt pond very near the end of the transverse crack that nearly broke off the end of the floating glacial tongue makes me think that crack is well and solidly frozen back up.  (I saw this melt pond in the 'same place' last year.) [image source]