Isn’t ice WONDERful? On a hot day, nothing goes down quite as well as lemonade poured over a glass full of ice cubes. In fact, ice makes so many things better. For example, we love to use ice to make homemade ice cream!

When Old Man Winter comes calling, falling temperatures can turn creeks, lakes, ponds and even rivers into frozen roads you can skate on. But what about the ocean? If you’ve ever been to the ocean in the winter, you’ve probably noticed that it doesn’t freeze like a small pond might.

So does the ocean ever freeze? If you’ve seen pictures of the North Pole or the South Pole, you know that there are polar ice caps in those places. If the ocean freezes in those areas, why doesn’t the rest of the ocean freeze during the winter?

The freezing point of regular water is 0° Celsius or 32° Fahrenheit. The presence of salt in water, though, reduces the freezing point of water. The more salt in the water, the lower the freezing point will be.

When regular water freezes, hydrogen and oxygen molecules have to bond together. The presence of salt makes it harder for these molecules to bond, because salt doesn’t naturally bond with ice.

When salt particles replace water particles, the freezing rate slows down. This is why salt is often used on icy roads to slow down freezing and make them safer to travel upon.

Normal ocean water usually has about 35 grams of salt for every 1,000 units of water. This lowers the freezing point of ocean water to about -1.8° C or 28.8° F. So ocean water will freeze. It just needs to reach a lower temperature.

Another factor that affects the freezing of ocean water is its movement. Unlike ponds, ocean waves move around constantly. This helps ocean water retain heat. As a result, only really cold areas, such as the North Pole or South Pole, usually get cold enough for ocean water to freeze.

When ocean water freezes, though, only the water part freezes. The salt molecules are pushed below the surface of the ice. As a result, polar ice ends up being freshwater ice that can be melted for drinking water!

About 15% of the ocean contains sea ice for at least part of the year. That might not sound like a lot, but that amounts to about 10 million square miles of sea ice!

44 Join the Discussion

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    • Thanks for sharing your comment, GM! We’re glad you picked out your favorite part of today’s Wonder, we’re so glad you are here today! :)

  1. You need a lot more calories in the cold, an average grown up needs about 3,000 calories a day but someone in the South Pole 7,000 calories! I want to go to the North Pole to study the penguins.

    • Thanks for sharing your comment, Grace! We’re so glad you enjoyed WONDERing about the chemistry of freezing today! We sure hope you get to the North Pole, too! Keep up the great work! :)

    • How great, Sheyla! We’re so happy to hear that our Wonder goes well with what you’re learning in class! WOOHOO for science! :)

  2. First of all today’s WONDER was so cool when I said it to my mom we both said WOW!!!

    When I just started to read this WONDER I said to myself I don’t think salt water freezes because of all the salt that in the water.

    And I’m pretty sure that im right. I think this was my favorite WONDER!!!!

    THANK YOU! :)

    • Hi there, Cate! We’re SUPER happy to hear that you and your mom enjoyed our science Wonder today! HOORAY! :)

      Water with a high concentration of salt prevents freezing– we LOVE WONDERing about chemistry together! Thanks for sharing your awesome comment! See you soon, Cate! :)

    • We’re glad you enjoyed today’s Wonder, Yeniffer, and learned something new, too! HOORAY for WONDERing with you! :)

  3. I really like this wonder, but I thought the salt would freeze! I wonder if there could still be bacteria inside of the ice even though it is made out of freshwater? I think the next Wonder will be about zooplankton. My mom and I are really enjoying the ocean themed Wonders!

    • We’re so glad you learned something new, Gavin! Chemistry is lots of fun to Wonder about! :-)

      Thanks for sharing your guess for tomorrow– we hope you and your mom are having loads of fun! :)

    • We’re so glad to hear how much you enjoyed our science Wonder, Morat! WOHOO! Thanks for joining the fun and sharing your comment! Have a SUPER day! :)

  4. We all learned new information about how salt water freezes. We think it is interesting that salt stops water from making ice. We also agree that ice can be fun to play with, is refreshing and useful.

    • That’s WONDERful news, Wonder Friends in Ms. Kilpatrick’s 5th grade class! We sure are happy to hear that you learned about the science of water, ice and salt. Whenever we’re extra thirsty, we toss some ice cubes in our glass of water– so refreshing! ahhhh! :-)

  5. My prediction is for Why doesn’t salt water freeze.

    Well I learned in science that ice can melt in water. And also my family sometimes uses salt to unfreeze the ice.

    So salt water can unfreeze ice pretty fast.

    - Duyen Quang .

    • Thanks for sharing your comment, Ky Duyen Quang! We’re so glad you have a connection to our science Wonder, too! How clever that your family uses salt to melt ice! :-)

  6. I love this website! Thanks Wonderopolis! I have this paper due on Friday and I just stumbled across this wonder and it was perfect !I will still continue to use this website. Thanks.

    -Ryan

    • We’re so glad you’re here, Ryan! Thanks for stopping by! We hope your paper is great, and we hope to see you soon, Wonder Friend! :)

    • We’re sorry to hear this Wonder wasn’t one of your favorites, Lilly. We Wonder: what’s your favorite topic to Wonder about? :)

  7. Dear Wonderopolis,

    I really like the video and I really like science, that’s why I picked this. I wonder what the next science article will be.

    • It sounds like you have learned all about frozen rivers, lakes and ponds today Devon! Nice work! Science is a lot of fun, especially when you can Wonder with your friends! Thanks for visiting us today! :)

  8. I love all the interesting articles and videos I had learned something new and hope to learn some more new things.

    • HOORAY, we’re so glad you’ve enjoyed WONDERing about the science behind salt, Bernadine! :) We look forward to more WONDERing with you– we’ll see you soon, Wonder Friend! :)

    • Hey Claudine! Salt is one cool ingredient, if we do say so ourselves! We love WONDERing about how it salt affects the temperature of water and other types of liquids, solids and even food! :)

    • That’s music to our ears, Wonder Friend Anthony! Thanks for telling us about what you learned today– we hope you’re staying cool after this chilly Wonder! :)

    • That’s an awesome thing to know, Wonder Friend Serenity, especially if you live in an area where it snows and ices! It’s so great that you learned something new with us today! HOORAY for WONDERing! :)

  9. The article was amazing. This month in class I am learning about lakes, rivers, ponds, and oceans. “About 15% of the ocean contains sea ice for at least part of the year.”

    • WOW, what a SUPER connection to your lessons in school, Monica! We hope you will come back to Wonder with us again soon– thanks for sharing what you learned today! :)

    • What a WONDERful connection, Sierra! Glaciers and water and freezing– oh my! :) Thanks for sharing your comment with us– we’re so glad you’re here today! :)

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Have you ever wondered…

  • Does salt water freeze?
  • At what temperature does ocean water freeze?
  • Is polar ice freshwater or salt water?

Wonder Gallery

Salt Water FreezeVimeo Video

Try It Out

Ready to see for yourself how salt affects the freezing point of water? Grab a friend or family member and try this easy science experiment at home.

You’ll need just a few simple supplies: two empty plastic bottles (clear water bottles work great!), salt, water and a freezer. Fill both plastic bottles with water. Add two tablespoons of salt to one bottle. Shake or stir to dissolve the salt. Be sure to mark the bottles “plain water” and “salt water.” When you’re finished marking the bottles, put them in the freezer.

After an hour or two, check on your bottles. Can you see that the plain water bottle is frozen more solidly than the salt water bottle? In a similar way, ocean water takes more time and lower temperatures to freeze solid. How cool is that?

Still Wondering

In Science NetLinks’ Water 3: Melting and Freezing lesson, children will investigate how melting and freezing impact three everyday items: water, chocolate and margarine.

Wonder What’s Next?

Tomorrow’s Wonder of the Day takes a look at some tiny aquatic creatures!

Upload a Photo or Paste the URL of a YouTube or SchoolTube Video.