Earth's Frozen Oceans

Part C: Arctic Sea Ice Extent

As the Earth orbits the sun, the seasons change, and so does the amount of sea ice floating in the oceans. As air and sea temperatures get warmer in the summer months, ice melts, and when colder autumn and winter temperatures return, so does the ice cover. The extent to which sea ice grows and melts each year varies depending on how extreme air and water temperatures become and how much ice (if any) survived the last year's melt season. At any given time during the year, millions of square kilometers of ocean are covered by floating sea ice. Scientists keep a close eye on sea ice coverage and how it changes with time because it helps regulate the planet's heat, moisture, and salinity exchange in the polar oceans. Sea ice is also an important animal habitat, which in turn, affects human communities.

Sea ice extentsea ice extent: the total area covered by some amount of ice, including open water between ice floes; sea ice extent is typically measured in square kilometers. is a measurement of the area of ocean (usually given in units of km² or mi²) where there is at least some sea ice. As you go through this module, you may also come across the term sea ice concentrationsea ice concentration: the fraction of an area that is covered by sea ice.. Sea ice concentration is the proportion of a given area of the ocean that is covered by ice, and is usually stated as a percentage ranging from 0% (open water) to 100% (totally ice-covered). Scientists' measurements of sea ice extent include only areas where sea ice concentration is at least 15%. Arctic sea ice is considered to be a key indicator of global climate conditions. In this part of the investigation, you'll explore how Arctic sea ice extent changes over different timescales.

1. Open the National Snow and Ice Data Center's Sea Ice Animation Tool.
2. Set the parameters to show sea ice extent in the northern hemisphere, beginning in January, 2008.
3. Explore how Arctic sea ice extent changes over the course of a full year. Use the "next" arrows in the animation control bar to advance the animation one month at a time.
   1. [item]
      [question]During what month was the Arctic sea ice at its minimum extent?[end question]
      [choice incorrect]March[end choice]
      [choice incorrect]May[end choice]
      [choice incorrect]July[end choice]
      [choice correct]September[end choice]
      [end item]
   2. [item]
      [question]During what month was the Arctic sea ice at its maximum extent?[end question]
      [choice incorrect]January[end choice]
      [choice correct]March[end choice]
      [choice incorrect]September[end choice]
      [choice incorrect]December[end choice]
      [end item]
   3. [item]
      [question]True or False? Arctic sea ice completely disappeared during the summer of 2008?[end question]
      [choice incorrect]True [end choice]
      [choice correct]False [feedback]That's right! Even at its minimum (in September), Arctic sea ice still covered 4.7 million square kilometers in 2008.[end feedback][end choice]
      [end item]
4. Now, set the parameters to show sea ice extent in the northern hemisphere, beginning in January of the last full year before you started this lab (e.g., if today is October 17, 2019, set your start date at January, 2018).
5. Use the "next" arrow in the animation control bar to advance the animation one month at a time through the entire year. As you examine each frame, write down the total extent (in square kilometers) of sea ice for that month and how it compares to the median ice edge shown as a pink/purple line. This line allows you to see how the sea ice extent during a given month compares to the typical extent for that month.
6. Using graph paper or a spreadsheet program such as Microsoft Excel, make a plot of Arctic sea ice extent (y-axis) vs. time in months for the year you are studying (x-axis).
7. Repeat steps 4 and 5 for the 4 years before the year you just plotted.
8. Combine all of your data and create a 5-year plot of sea ice extent.