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The Oceans & Melting Glaciers
How can the OMG mission compliment the GRACE mission?
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How Greenland Loses Ice
The island of Greenland is covered by a sheet of ice nearly two miles thick. But as the planet warms, this ice is melting and being lost to the ocean, where it drives sea levels higher across the globe. But this ice doesn’t just melt because of the warming air. Around the edges, Greenland’s ice flows into the oceans by way of giant “rivers” of ice called glaciers. Most of these glaciers reach the oceans and interact with the ocean water directly. As ocean waters warm, they can melt glaciers from below and cause the ice to break off more quickly and the glaciers to speed up. This means that Greenland’s ice is being melted from below as much as it is being melted from above.
What is OMG?
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OMG Logo Source: PO.DAAC OMG Mission website
Oceans Melting Greenland (OMG) was a 6-year mission in Greenland that started in 2016 and ended in 2021, designed to answer the question, how much of Greenland’s ice loss is caused by the oceans? Each Summer, the OMG mission used airplanes to drop about 250 probes called Airborne eXpendable Conductivity Temperature Depth (AXCTD) instruments, which measured the temperature and salinity of the water from the surface down the sea floor in most cases. 1 These measurements helped scientists understand how the ocean temperatures were changing from one year to the next.
What is GRACE?
GRACE Satellites Source: GRACE website
The Gravity Recovery and Climate Experiment (GRACE) satellites originally launched on March 17, 2002 in collaboration with both NASA and DLR the German Aerospace Center. 2 It is a set of twin satellites that make detailed measurements of Earth's month-to-month changes of its gravity field. Because water is so heavy, when it moves from one place to another, it changes the pull of gravity in that location. So, GRACE is able to investigate how water moves between the land, the ice, and the ocean. GRACE ended its data collection in July 2017, but was succeeded by the GRACE Follow-On (GRACE-FO) mission which launched on May 22, 2018. 3 Just like GRACE did, GRACE-FO measures mass changes in the polar ice sheets, mountain glaciers, total water storage on land, deep ocean currents, as well as glacial isostatic adjustment and impacts from major earthquakes.
Working Together
How can the datasets from the GRACE and OMG missions help us understand how Greenland is losing ice? The GRACE and GRACE-Follow On missions tell us how much ice is lost from each region of the ice sheet every year, by literally weighing the ice from space. 4 The OMG mission tells us about ocean temperatures every year between 2016 and 2021, by looking at both the ocean temperature and the ice sheet changes. Together we can get a better idea of just how much the oceans are responsible for ice loss in Greenland.
Study Site
2019 saw a record year for ice melt in Greenland resulting in 532 billion tons of melt that broke previous records. 5 This water loss could cover the state of California with about 4 feet of water. On July 29th and 30th a heatwave occurred in Europe which resulted in warm air traveling to Greenland. This set record temperatures that led to 90 percent of the ice sheet surface melting from July 30th to August 3rd. 6 Particularly on August 1st, the ice sheet records were broken since record-keeping began in 1950 with 12.5 billion tons of water from the melt. 7
Greenland Ice Mass Loss 2002 - 2021 Source: NASA and JPL/Caltech
Preparing GRACE Data for Study
ArcGIS Pro is the latest Geographical Information System (GIS) software offering the capabilities of visualizing geospatial data. GRACE and OMG data comes in the file format called Network Common Data Form (NetCDF). NetCDF stores multidimensional scientific data variables such as temperature or time. 8 ArcGIS Pro offers the ability to visualize various scientific data formats with multidimensional analysis and geoprocessing tools.
This tutorial will be going through the steps of visualizing GRACE data in ArcGIS Pro . Particularly looking at August 2019 and August 2020 for comparison.
Resulting visualization of clipped Greenland layer August 2019/2020.
Preparing OMG data for Study
This tutorial will be going through the steps of visualizing OMG AXCTD point data in ArcGIS Pro.
Conclusion
These tutorials can be helpful in the visualization and exploration of understanding ice melt and salinity in the ocean. Below is an interactive map to toggle through the OMG AXCTD point data, Sea Surface Salinity, Sea Surface Temperature and GRACE datasets of August 2019/2020 for comparison. OMG AXCTD featuring salinity data measured at 3 different depths for this example; 10, 25 and 50 meters. Also, temperature data at depths of 100, 250, & 350 meters.
Greenland Surface Melt Extent Chart for years 2019/2020. Source: https://nsidc.org/greenland-today/greenland-surface-melt-extent-interactive-chart/
The tutorial can be replicated utilizing the tools mentioned for any other area of interest. ArcGIS Pro also offers the ability to create 3D Voxel layers or Multidimensional Raster layers with many different scientific data formats.
For more information please visit PO.DAAC and the PO.DAAC StoryMap Collection page to learn about other datasets.