Tracking Arctic sea ice

This exercise is a part of Educator Guide: The Case of the Arctic’s Missing Ice / View Guide

Directions: After your students read the article “The case of the Arctic’s missing ice,” have them answer the questions below. Questions are organized by story section with summary questions at the end.


1. What was unusual about the Bering Sea in the winter of 2017–2018? Why are scientists concerned?

Sea ice never appeared in the Bering Sea, and a large mass of cold, salty water that’s associated with the ice never formed near the seafloor. This development concerns scientists because sea ice is important to the Arctic ecosystem. Its absence could disrupt every part of the Arctic food web.

Open waters

2. Describe the typical pattern of winter sea ice formation in the Bering Sea. What factors contributed to a different scenario in the winter of 2017–2018?

Most years, ice forms in the Bering Sea or migrates south from the Chukchi Sea through the Bering Strait. In the winter of 2017–2018, strong winds from the south not only kept the sea ice in the Chukchi Sea but also brought warmer waters into the sea, limiting sea ice formation. Higher-than-normal air temperatures in the Chukchi meant less ice was available to drift through the Bering Strait. Both of these factors contributed to record-low winter sea ice cover in the Bering Sea.

3. What does Peggy, or mooring M2, do? What unexpected data did Peggy collect in the summer of 2018?

Peggy, or mooring M2, tracks the temperature, salinity and other properties of water at one spot in the southern Bering Sea. In the summer of 2018, Peggy detected that the temperatures near the seafloor never dropped below zero.

4. According to the graph titled “Deep warming” on Page 23 of the article, how did Peggy’s data from the summer of 2018 compare with previous years? Based on the caption and the text of the “Open waters” section, what explains the summer 2018 data?

Though there is yearly variation, water temperatures near the seafloor typically average below zero degrees Celsius in the summer. But in 2018, the average temperature was much higher — about 1.5 degrees Celsius. The data suggest that no cold pool formed in 2018. Cold pools are by-products of sea ice formation, so the fact that the Bering Sea didn’t “freeze up” in the winter of 2017–2018 is likely responsible for the cold pool’s absence.

Arctic in transition

5. What effects has sustained warming already had on the Arctic ecosystem? Be sure to frame your answer in terms of a “cascade of changes,” the terminology used in the opening of the article.

Warming has triggered changes in the lower levels of the Arctic food web, which has impacted species higher up in the web. Bivalves — which are food for walruses, seals and a kind of sea duck called a spectacled eider — have moved north. Less nutritious marine worms have taken the bivalves place to the detriment of other species. Populations of small copepods have increased while larger copepods, which juvenile fish depend on to survive the winters, have declined. Changes at the lower level of the food web have affected the distribution and types of fish populations, which in turn impacts seabirds. The summer of 2018 was the third year in a row with a massive seabird die-off.

The heat is on

6. What factors affect the timing, location and size of phytoplankton blooms in the Arctic? Provide an example from the article.

Sea ice and sunlight both play a major role in where and when phytoplankton bloom. Other factors such as nutrient availability and water temperatures can affect the size of blooms. In 2018, more light penetrating early in the year meant more phytoplankton blooms, and the blooms came earlier in the northern waters.

7. Phytoplankton make up the base of the Arctic food web and animals depend on the food, but sometimes the blooms are problematic. Why?

Blooms can turn toxic, akin to the deadly red tides that have blossomed along Florida’s coast. Toxic blooms can kill wildlife and make people ill.

Summary questions

8. Do you think the relatively iceless Arctic winter was a one-time fluke or is it likely to happen again? Cite evidence from the article to explain your answer.

Students’ answers will vary. An argument for a one-time fluke includes the fact that the combination of southerly winds and warm temperatures that led to the record-low sea ice was unusual and scientists don’t yet have enough data to say whether the Bering Sea is increasingly likely to be ice-free in winter. Students might also cite natural variability from year to year. An argument for the iceless winter happening again includes the fact that the Arctic is warming twice as fast as the rest of the planet — the five years since 2014 are the five warmest scientists have ever measured in the Arctic. That temperature increase has led to a sharp decline in summer sea ice cover. It wouldn’t be that surprising if warming conditions affected winter sea ice cover, too.

9. What questions do researchers still hope to answer about the interplay of ice, temperature and life in the Arctic?

Questions could include: How warm will it be in the future Arctic? How typical will southerly winds be? How are toxic phytoplankton responding to changing Arctic conditions?