//
you're reading...

Book Review

Glacial crevasses: how deep do they go? What does it mean?

Morlighem, M., E. Rignot, J. Mouginot, H. Seroussi, and E. Larour, (2014). Deeply incised submarine glacial valleys beneath the Greenland ice sheet. Nature Geoscience. V.7, pp. 418-422. Doi: 10.1038/NGEO2167

Background

Greenland ice sheets are big and beautiful and breathtaking. They are also mysterious and there are major gaps in what is known about the ice thickness in Greenland, especially along the coast. The missing information would be a helpful key for understanding the relationship between sea level and glacial retreat.

Commonly, ice thickness is determined by airborne radar sounding. The technique has many caveats including the expense, the need for numerous surveys over a small area, limitations of depth, and limitations on accuracy. The technique has however proven to work well for interpreting inland ice thickness. In contrast, and perhaps expected based on the caveats, the method has not been usefully applicable to the coastal areas. In the research reviewed here the scientists thought that analyzing data sets of ice thickness and flow with respect to each other, and focusing on bed topography, would enable them to interpret glacial-ocean interaction in Greenland. Information gained could then be used to refine sea-ice and glacial retreat models.

Methods

In short, researchers input data into an algorithm and used the results to calculated bed topography along Greenland’s east, west, and north coasts. The two inputs used were ice thicknesses from airborne radar soundings and ice flow rates from high resolution ice motion data derived from satellite interferometric synthetic aperture radar (InSAR).  The information was input into a mass conservation algorithm to calculate ice thickness. Finally, bed topography was determined by subtracting the calculated ice thickness from an available digital ice-surface elevation data set.

The shaded boxes are the areas focused on in this study.

Figure 1: The shaded boxes are the areas focused on in this study. This map depicts bed topography elevation determined from the MC algorithm technique.

Results

Researchers identified previously undetected U-shaped crevasses extending below sea level from the terminus to tens to hundreds of kilometers (km) inland that house fast-flow ice. The features are evidence that the glacial motion has been consistent for some time because they are so large and very well shaped.

Observations varied depending on what section of Greenland studied (Figure 1). In West Greenland there were three troughs all below sea level and all cutting ~100 km inland.   Northern Greenland hosts troughs that extended 50 km inland and a couple hundred meters below sea level, and there were also submarine valleys that did not have ice cover. East Greenland had troughs but they did not extend below sea level, a phenomenon attribute to hard bedrock and colder ice sheets.

The study found that modeling the landscape in this fashion predicts between 100-300% more ice below sea level in Greenland than predicted in early investigations.

Conclusion/Significance

The real reason to care about the presence of a network of crevasses is because they are drains to the ocean; only 8% of the identified crevasse network contacts seawater, but it controls 88% of the ice discharged from Greenland. Increased contact of glaciers with the ocean implies Greenland’s ice retreat influenced by the oceans is more susceptible than previously understood; it is possible that a faster than expected retreat inward may occur.  For example retreat could be increased from ocean heat flow 300-400 m below the sea surface.   There is also potential for subtropical water from the North Atlantic to make its way into fjords and contribute to an accelerated retreat.

Investigations like this provide important improvements to existing predictions and models.   With each new study of this type region there is literally going to be a deepened knowledge of glacial dynamics, how scientists predict glaciers will be affected by environmental changes, and how their relationship with the ocean with evolve.

Similar approaches could be applied towards exploring unseen topography below ice sheets on our own planet, and maybe even Jupiter’s ice covered sixth moon, Europa!

Discussion

Trackbacks/Pingbacks

  1. […] time readers may have noticed how often acoustics comes up in the study of the ocean. This is no coincidence and there are a myriad of reasons why. The most basic, however, has […]

Post a Comment

Instagram

  • by oceanbites 2 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 3 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 4 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 5 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 7 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 8 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 8 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 9 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 9 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 10 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 11 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 11 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com