New paper using RADARSAT data: Antarctic ice shelves slowed down – "…have not been changed in a significant way in the past 12 years"

A new paper published May 15th in the the journal The Cryosphere utilizes 12 years worth of RADARSAT data to determine the rate at which some well known ice shelves in Antarctica have been moving and changing, and the answer is: “not much”. In fact it appears there has been a slowing down. First a map of Antarctica and the most worrisome Ross Ice Shelf (marked by the red x) is in order:

If you follow the alarmosphere and MSM related to the Ross Ice Shelf and others, you get these kinds of stories:

• West Antarctic ice sheet collapse even more catastrophic for U.S. coasts
• West Antarctic ice shelf – a nudge and a push from collapse?
• Antarctic ice shelves ‘tearing apart’, says study
• Antarctic Ice Shelf Disintegration Underscores a Warming World

Clearly, there’s lots of gloom and doom surrounding Antarctic ice shelves for the worry that they’ll cause catastrophic sea level rise if they cut loose.

This study Twelve years of ice velocity change in Antarctica observed by RADARSAT-1 and -2 satellite radar interferometry (Full paper here) with radar data seems to indicate there not much change in the past 12 years, the authors write:

Overall, however, the observed changes have little impact on the mass balance of the region. We therefore conclude that in contrast with their counterparts in the Amundsen and Bellingshausen Seas (Rignot et al., 2008) the ice streams and ice shelves in the broad region under investigation herein have not been changed in a significant way in the past 12 yr, which suggests that the ice dynamics of the entire region does not have a strong impact on the mass budget of the Antarctic continent.

That’s quite a statement compared to the news headlines. To paraphrase NSIDC’s Dr. Mark Serreze famous “The Arctic is screaming” quote, I suggest that from the perspective of the data presented in this paper, I’ll say “The Antarctic is snoring”.

Here are some highlights and graphics from the paper:

Fig. 2. Ice surface velocity maps for Central Antarctica for 1997 (a) and 2009 (b) overlaid on MOA. (c) shows the velocity difference dv (2009–1997) for the entire region. Superimposed on (c) are velocity contour lines taken from the IPY ice velocity map (Rignot et al., 2011b). Blue tones indicate a slow down. The two dark red regions on the ice shelf edges (Ross Ice Shelf near Roosevelt Island and Filchner Ice Shelf) indicate pre-calving events.

Twelve years of ice velocity change in Antarctica observed by RADARSAT-1 and -2 satellite radar interferometry

B. Scheuchl1, J. Mouginot1, and E. Rignot1,2

1University of California Irvine, Department of Earth System Science, Irvine, California, USA

2Jet Propulsion Laboratory, Pasadena, California, USA

Received: 13 April 2012 – Accepted: 29 April 2012 – Published: 15 May 2012

Abstract

We report changes in ice velocity of a 6.5 million km2 region around South Pole encompassing the Ronne/Filchner and Ross Ice Shelves and a significant portion of the ice

streams and glaciers that constitute their catchment areas. Using the first full interfero-

metric synthetic-aperture radar (InSAR) coverage of the region completed in 2009 and

partial coverage acquired in 1997, we process the data to assemble a comprehensive

map of ice velocity changes with a nominal precision of detection of ±3–4myr−1.

The largest observed changes, an increase in speed of 100myr−1 in 12 yr, are near the

frontal regions of the large ice shelves and are associated with the slow detachment of

large tabular blocks that will eventually form icebergs. On the Ross Ice Shelf, our data

reveal a slow down of Mercer and Whillans Ice Streams with a 12 yr velocity difference

of 50myr−1 (16.7 %) and 100myr−1 (25.3 %) at their grounding lines. The slow down

spreads 450 km upstream of the grounding line and more than 500 km onto the shelf,

i.e., far beyond what was previously known. Also slowing in the Ross Ice Shelf sector

are MacAyeal Ice Stream and Byrd Glacier with a 12 yr velocity difference near their

grounding lines of 30myr−1 (6.7 %) and 35myr−1 (4.1 %), respectively.

Bindschadler Ice Stream is faster by 20myr−1 (5 %). Most of these changes in glacier speed extend on the Ross Ice Shelf along the ice streams’ flow lines. At the mouth of the Filchner/Ronne Ice Shelves, the 12 yr difference in glacier speed is below the 8% level.

We detect the largest slow down with a 12 yr velocity difference of up to 30myr−1 on

Slessor and Recovery Glaciers, equivalent to 6.7% and 3.3 %, respectively. Foundation

Ice Stream shows a modest speed up (30myr−1 or 5 %). No change is detected on

Bailey, Rutford, and Institute Ice Streams. On the Filchner Ice Shelf proper, ice slowed

down rather uniformly with a 12 yr velocity difference of 50myr−1, or 5% of its ice

25 front speed, which we attribute to an 12 km advance in its ice front position. Overall,

we conclude that the ice streams and ice shelves in this broad region, in contrast with

their counterparts in the Amundsen and Bellingshausen seas, exhibit changes in ice

dynamics that have almost no impact on the overall ice balance of the region.

Introduction

Ice velocity is crucial information for estimating the mass balance of glaciers and ice

sheets and for studying ice dynamics. Satellite information has fundamentally changed

the way velocity information is collected today. Firstly, Global Positioning System (GPS)

5 has simplified the way ground measurements are made, allowing for high precision

measurements of key areas at dense temporal spacing. For detailed analyses of specific

motion patterns (i.e. Bindschadler et al., 2003), field measurements continue to be vital in glaciology (e.g. Aðalgeirsd ´ ottir et al., 2008). Secondly, spaceborne remote sensing satellites are a means to measure ice velocity without the necessity of ground campaigns. They allow data collection over vast areas, thereby providing information that would be practically impossible to collect in the field. Since the launch of the European ERS satellites in the early 1990’s, spaceborne Interferometric Synthetic Aperture Radar (InSAR) data have become the single most important means of measuring ice velocity. Projects and area coverage have evolved from single glaciers, over ice fields to most recently covering the vast ice sheets of Greenland and Antarctica (Rignot et al., 2011b; Joughin et al., 2011). InSAR satellite data coverage in Central Antarctica remains sparse. The first complete interferometric mapping campaign covering South Pole took place in 2009 as part of a coordinated acquisition campaign for the International Polar Year (IPY) (Jezek and Drinkwater, 2008).

In this paper, we present a new ice velocity map and a grounding line map based on

RADARSAT-2 InSAR data collected in fall 2009. We revisit and re-calibrate the InSAR

data collected by RADARSAT-1 in 1997. A difference map is created using the two data

sets to reveal for the first time changes in speed over a vast extent of Central Antarctica

in the 12 yr interim. After exposing the details of the data processing, we discuss the

25 changes observed along Siple Coast and the Filchner/Ronne sectors and conclude on

the ongoing evolution of glaciers and ice shelves in these regions.

Conclusions

We present a 12 yr change record in ice motion in Central Antarctica, covering the two

largest ice shelves and many major ice streams and glaciers. Data quality is excellent and provides ice motion results with a precision of ±2–3myr−1 on average and detection

of changes in speed with a precision of about ±3–4myr−1. Our change map provides new, important information about the evolution of this sector of Antarctica, or lack thereof. Filchner and Ross Ice Shelves exhibit signs of pre-calving events.

Other than those, the Filchner/Ronne sector shows few changes, with most ice streams slowing down slightly. The 12 yr velocity difference for all glaciers and ice streams in the region is below 8 %, which is of little consequence for the overall mass budget of the region. The most distinct signal, however, is a slight slow down of the Filchner Ice Shelf, consistent with an ice shelf advance, and a small slow down of Slessor Glacier over a large sector that warrants further study. On the Ross Ice Shelf, we confirm the slow down of Mercer and Whillans Ice Stream, with a 12 yr velocity difference of 16.7% and 25.3 %, respectively.

Our change map shows, for the first time, the entire spatial extent of the change. The slow down, extends hundreds of km upstream and onto the shelf. Regional variations in velocity changes on Ross Ice Shelf proper are defined by the ice streams and glaciers that constitute its catchment area.

Overall, however, the observed changes have little impact on the mass balance of the region. We therefore conclude that in contrast with their counterparts in the Amundsen

and Bellingshausen Seas (Rignot et al., 2008) the ice streams and ice shelves in the broad region under investigation herein have not been changed in a significant way in the past 12 yr, which suggests that the ice dynamics of the entire region does not have

a strong impact on the mass budget of the Antarctic continent.

Fig. 3. (comprising 5 graphs and 1 map above) Velocity Difference map (2009–1997) detail, 1997 and 2009 ice front, and flow line plots for Ross Ice Shelf overlaid on MOA. Each flow line includes markers every 100 km for easier orientation. The flow line graphs show the absolute velocities for 1997 and 2009 and the velocity difference. The vertical dashed line is the 2009 grounding line.

h/t to WUWT reader “HR”.