Tag Archives: Salinity

Happy International Polar Bear Day!


Everyone loves those cute cuddly polar bears that we see on TV commercials that look like the most harmless white puffballs. Well unfortunately, that portrayal is far from the truth. Polar bears are the largest terrestrial carnivores alive today and have some extreme adaptations to their extreme environment. Unfortunately, this extreme environment, the arctic, is losing much of its ice that is the polar bears prime hunting ground and habitat. Luckily polar bear international has installed International Polar Bear Day on February 27th so that we can all save our furry friends. 

The Basics

Like stated before Ursus maritimus, the polar bear, is the largest land carnivore alive today, males can weigh up to 1,760 pounds! These ferocious predators live all around the arctic on the annual ice near the mainland during the winter months then during summer months head to the land where they rest and wait for the ice to reform (Figure1). Polar bears mate from late March to late May and give birth from November to January about every three years. Polar bears are mostly solitary except for females with their cubs. They are almost strictly carnivorous feeding on ringed and bearded seals.

The Hunting

  1. maritimus is one of the most radical hunters on the entire planet. These extreme predators rely on the sea ice to catch their prey. Ringed seals, their preferred prey, carve breathing holes through the ice so they can catch a breathe after diving for their own hunting treks. The polar bears have adapted to recognizing these breathing holes by sniffing them out with their powerful sense of smell and waiting for the unsuspecting seal to pop up. They have to be incredibly patient and wait for hours to days before they get their meal. Another tactic is the sneak-up approach. Polar bears rely on their white coat to sneak up on the seal, freezing in place whenever the seal raises its head. Then once they are close enough, about 20 feet away, they use their explosive speed and suction cup like paws to skate on the ice and pounce on their blubbery feast.

Interesting Adaptations

Believe it or not polar bears fur is not actually white. Their fur coat is incredibly dense and each hair is pigment-free and transparent with a hollow core that reflects visible light similar to the white snow or ice. Their fur is actually so dense that adult males can quickly overheat when running on land. Under their pigment-free fur they have black skin covering a thick layer of blubber to keep them warm in water. Their paws they have suction cup like holes that prevent slippage on the ice. Their front paws are also very large and paddle like so they can swim very well! (Figure 2)

Dangers to Polar Bears

Polar bears heavily rely on sea ice to hunt during the winter months and struggle when there isn’t any ice to find and catch prey. With global climate change warming the earth more and more sea ice is disappearing creating huge difficulties to polar bears survival. This forces polar bears to swim long distances to find food essentially exhausting them and making their lives a whole lot harder

What Can You Do?!

International Polar Bear Day is designed to build awareness to our incredible furry friends. Polar Bear International is urging you to lower your thermostat to lower your carbon emissions and make less of an impact that day and into the future. To spread the word post a picture of you lowering your thermostat or cuddling up under some blankets with #PolarBearDay #ThermostatChallenge and #Hygge the Danish word for coziness! So embrace your inner polar bear and put on a dense fur coat while your lowering your thermostat to help save our wonderfully beautiful bear friends.


Hydrometers: Measuring Oceans Salinity

Hydrometers are used to measure the oceans salinity, or how “salty” the ocean is. To use a hydrometer you must fill up the tool with saltwater and then observe how much the lever is raised by the salinity. We like to use the measurement PPT or Parts per Thousand. PPT is a measure of salinity in the units of thousands, for instance if we had 1000 buckets of freshwater and then added 1 bucket of salt water to it we would have 1 PPT. Here on Catalina Island our PPT ranges from around 32 and 34 PPT. To make more sense of these numbers we like to break them down into percentages. If we were to do that our PPT in percentages would range from about 3.2 to 3.4 percent salt!


There are many other tools we can use to study Oceanography. We will use Secchi Disks to measure the visibility of the ocean, lead lines to measure the depth and plankton tows to measure what exactly is in our water column! Plankton tows work by towing a net with a jar attached to the bottom. The net will siphon through the excess water not allowing the plankton to escape. At the end hopefully you will have a jar full of microscopic plankton!

Why You Gotta Be So Dense

Cooking 101: What happens when you put oil into a pot of water? Well, as any pasta lover should know, the oil floats to the surface creating its own layer that rests right above the still water beneath. But why is that?

The answer to this question, my friends, is density.

density.Density, in the simplest of terms, is how much of something an object has. More technically, it represents how much mass an object contains, with respect to its overall volume. Most of us are familiar with the mathematical formula for density, D=M/V, which helps to visually show us this relationship. Typically, larger, heavier objects hold more mass, where as smaller, lighter ones hold less. Comparing that to the size, or volume, of the object will determine its overall density. This will also help to judge how they may react in different mediums, such as water.

density2If we cycle back to our original question as to why oil floats above water, we can see that the oil must be lighter than the water for it to rest on the surface. In fact, oil is lighter, or less dense, than our medium, which is more dense, thus explaining the phenomenon that we observe when cooking.

Within the marine world, this concept applies to all objects that come in contact with the water. If it contains more mass than its overall volume, the object will sink and vice versa. If you drop a strawberry into the water, which actually weighs less in comparison to the amount of space it takes up for itself, it will float! As for a piece of clay, its mass is heavier, meaning that it will sink. On a more complex scale, these objects might react differently within the oceans that surround us. Because marine waters contain a higher salinity than freshwater, our strawberry and piece of clay will decrease in density, as salt water is more dense. As a result, our strawberry will continue to float to the top while our piece of clay may surface as well instead of sink.

Written by: John Cornett

Salinity and Water Density

When swimming in salt water you can make observations on more than just the salty taste. An observation you may have made is that you are more buoyant, or you float more, in salt water than in fresh water. This is a result of the oceans salinity, the amount of salt in the water. Density is the amount of matter in a given space or area. When a volume of water is replaced by an item of greater density than the water, the object will sink. Likewise, if a volume of water is replaced with an object that is less dense than the water, it will float towards the surface.

This physical happening can be observed when pouring fresh water into a pitcher of salt water. The fresh water, when poured slowly, will remain on the top of the salt water. A small layer forms where the two bodies of water meet, called a Halocline. You can also observe the difference in density by using an egg. Place an egg in fresh water and watch as it sinks to the bottom. When placed in salt water it will float. The egg was denser than the space it replaced in the fresh water causing it to sink and was less dense than the salt water causing it to float. When placing the egg into the pitcher that had the fresh and salt water the egg floated right at the Halocline.


We would like to thank you for visiting our blog. Catalina Island Marine Institute is a hands-on marine science program with an emphasis on ocean exploration. Our classes and activities are designed to inspire students toward future success in their academic and personal pursuits. This blog is intended to provide you with up-to-date news and information about our camp programs, as well as current science and ocean happenings. This blog has been created by our staff who have at least a Bachelors Degree usually in marine science or related subjects. We encourage you to also follow us on Facebook, Instagram, Google+, Twitter, and Vine to see even more of our interesting science and ocean information. Feel free to leave comments, questions, or share our blog with others. Please visit www.cimi.org for additional information. Happy Reading!