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How icebergs ‘really’ melt?

  • Posted By
    10Pointer
  • Categories
    Geography
  • Published
    18th Feb, 2021
  • Context

    Icebergs are melting faster than current models describe, according to a new study at the University of Sydney. The researchers have proposed a new model to more accurately represent the melting speed of icebergs into oceans.

  • Background

    • Today, several million icebergs are floating on the oceans of all sizes and shapes. They are formed in the Arctic and Antarctic and, once detached, follow the currents (ocean) until they melt and disappear.
    • Iceberg melt is responsible for about half the freshwater entering the ocean from the Antarctic and Greenland ice sheets.
    • However, current models wrongly assume icebergs melt uniformly.
    • Thus, accurately modeling how it enters is important for understanding the potential impact on ocean circulation.
  • Analysis

    Understanding the geography of Icebergs

    • Icebergs are pieces of ice that formed on land and float in an ocean or lake.
    • Icebergs come in all shapes and sizes, from ice-cube-sized chunks to ice islands the size of a small country.
      • The term "iceberg" refers to chunks of ice larger than 5 meters (16 feet) across.
      • Smaller icebergs are known as bergy bitsand growlers. They can be especially dangerous for ships because they are harder to spot.
    • The North Atlantic and the cold waters surrounding Antarctica are home to most of the icebergs on Earth.

    Difference between icebergs, glaciers, and other ice trivia

    • Glaciers and icebergs represent two of the most important facets of Earth's ecosystem. 
    • The glaciers, icebergs, ice sheets, and permanent areas of snow in the polar regions (the Arctic and Antarctica) comprise 1.7% of the total water on the planet.
    • Glaciers are large sheets of ice that can extend for miles.
      • Larger glaciers are referred to as continental glaciers, which start at a central point and spread out as they accumulate more ice and other debris like dirt and rock.
      • Glaciers are located in the Arctic and Antarctica, with the largest glaciers appearing in Antarctica.
    • Icebergs, on the other hand, are smaller pieces of ice that have broken off (or calved) from glaciers and now drift with the ocean currents.
      • Only the larger continental glaciers create icebergs, as it typically does not happen that a mountain glacier releases an iceberg into the sea.
  • How do they form? Where do they go?

    • Icebergs calve from glaciers when direct sunlight or rising air temperature causes the glacier's surface ice to become more brittle.
    • Once an iceberg has calved off a glacier it is already floating and, by the principle known since Archimedes, raises the oceans' volume.  

    Archimedes’ principle and melting of sea ice and ocean water level

    • Archimedes' principle is used to understand why there's no change in water level when the ice that is floating in the water melts.
    • The principle states that a body immersed in a fluid is subjected to an upwards force equal to the weight of the displaced fluid.
      • For example, a ship that is launched sinks into the ocean until the weight of the water it displaces is just equal to its own weight. As the ship is loaded, it sinks deeper, displacing more water, and so the magnitude of the buoyant force continuously matches the weight of the ship and its cargo.
    • Application: The applications of Archimedes' principle are:
      • Archimedes' principle is used in designing ships and submarines
      • Lactometers based on Archimedes' principle is used to measure the purity of a sample of milk
    • Icebergs travel with ocean currents, sometimes smashing up against the shore or getting caught in shallow waters.
    • When an iceberg reaches warm waters, the new climate attacks it from all sides.
    • On the iceberg surface, warm air melts snow and ice into pools called melt pondsthat can trickle through the iceberg and widen cracks.
    • At the same time, warm water laps at the iceberg edges, melting the ice and causing chunks of ice to break off.
    • On the underside, warmer waters melt the iceberg from the bottom up.
    • Impacts: Icebergs have two main impacts on climate
      • Iceberg production affects the mass balance of the parent ice sheets
      • melting icebergs influence both ocean structure and global sea level
  • What were the assumptions made in the current model?

    • Current models, which are incorporated into the methodology used by the Intergovernmental Panel on Climate Change, assume that icebergs melt uniformly in ocean currents.
      • The IPCC is the gold standard for climate science.
    • However, this recent research has shown that icebergs do not melt uniformly and melt at different speeds depending on their shape.

    The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) to assess climate change based on the latest science.

  • What is the proposed method?

    The results, published in Physical Review Fluids, have implications for oceanographers and climate scientists.

    • The new research proposes a very simple model that accounts for iceberg shape, as a prototype for an improved model of iceberg melting.
    • To test these models, the researchers developed the first realistic small-scale simulations of melting ice in saltwater.
    • The old models assumed that stationary icebergs didn't melt at all, whereas the latest experiments show melting of about a millimeter every minute.
    • In icebergs moving in oceans, the melting on the base can be up to 30 percent faster than in old models.
    • The research shows that iceberg shape is important. Given that the sides melt faster, wide icebergs melt more slowly but smaller, narrower icebergs melt faster.
    • The sides of icebergs melt about twice as fast as their base.
    • For icebergs that are moving in the ocean, melting at the front can be three or four times faster than what the old models predicted.
  • Conclusion

    While icebergs are only one part of the global climate system, the improved model provides scientists with a dial that they can tune to better capture the reality of Earth's changing climate.

    These methods can also be applied to many other systems, including glaciers melting or the melting of frozen, saline sea ice. Moreover, these methods could be used by astrobiologists to better understand ice moons like Saturn's Enceladus, a candidate for finding life elsewhere in the Solar System.