On day 4 of our trip across the Southern Ocean with Cheeseman’s Ecological Safaris and Quark Expeditions, we awoke to a calmness. I could hardly believe it was possible to have a reprieve from the constant rocking back and forth. I peeked out the window and saw a scene like the one above. I was excited beyond belief! I learned that we were going to be traveling through the Antarctic Sound for the next several hours. I rushed outside with my camera (and promptly went back in to layer up more) and began taking photos of the gorgeous scenes around the ship.
One of the expedition staff onboard the ship, a glaciologist named Colin Souness, educated us on sea ice during one of the daily presentations. I had never really thought about sea ice prior to this expedition, but I have since learned about its importance not only in the local Antarctic environment but also in the global one.
In order for sea ice to develop, ocean water must be below the freezing point of fresh water (0 degrees Celsius/32 degrees Fahrenheit) due to the salinity of the water that lowers the freezing point to -1.8 degrees Celsius/28.8 degrees Fahrenheit. Typically the top 100-150 m (300-450 ft) of ocean water must be at this freezing point before ice crystals begin to form. This form of ice is called frazil ice. In the image below, the top portion demonstrates this beginning stage.
In calm cold waters, the frazil ice crystals join together to form grease ice, aptly named due to the slick appearance of the thin layers of ice. As we were moving through the Antarctic Sound, I was able to capture a few images of the grease ice although it was less prevalent than other forms of ice due to it being the beginning of spring.
In rough ocean waters, the frazil ice crystals bump into each other and turn into a slushy round forms of ice called pancake ice. One of the identifying features of this ice is the raised perimeter of these circular ice forms.
As pancake or grease ice grows and accumulates in cold winter temperatures, it begins to form sheets of ice that thicken over time. If the ice is attached to the shoreline, it is called fast ice since it is fastened to land. We were able to see a lot of fast ice around Snow Hill, Seymour and James Ross Islands.
When the ice sheets remain mobile and move with the ocean currents, they are considered drift ice. As we were approaching the islands in the ship, there was a lot of evidence of this type of ice before we reached the fast ice.
When sheets of drift ice are large enough, (greater than 20 m or 65.6 ft across), they are known as floes. As the floes move over the ocean surface and ram into each other due to currents, they create pressure ridges such as the one shown below.
As I took photos of this stunning landscape, I had hoped to capture each form of ice described above. I was happy I succeeded at this from an artistic and aesthetic point of view, but having these visuals further helped me understand the importance of sea ice for the global climate. The white ice was very reflective of sunlight (as I learned the first day when I went without sunglasses) which in turn helps direct solar energy back into space. This allows the polar climates to stay colder than the rest of earth. When sea ice melts in an area or over a larger region, the dark ocean waters absorb that solar energy, causing temperatures to rise in the surrounding area. More sea ice begins to melt and a cycle of heating and melting begins. The arrival of winter can put a temporary pause in this cycle, but if overall temperatures remain higher, the polar environment will change drastically.
Sea ice and this process has important implications on the movement of ocean waters and in the maintenance of a proper balance in the temperature across earth. When sea ice forms, most of the salt in the ocean water gets pushed below the ice. This causes the salinity of the water below the ice to increase and thus the density of the water increases. When this happens, the denser, heavier, cooler water drops to the bottom of the ocean and moves towards the equator as hotter lighter water from the equator moves along the ocean surface towards the poles. This helps disperse heat from the equator to help maintain the temperature balance of earth. If there is less sea ice on the poles, the ability of earth to moderate heat lessens, thereby affecting the whole world. It was fascinating to learn that sea ice can have such an important effect on all of us, no matter where we are in this world.
Some of the information presented above came from Colin Souness’s presentation, but I wanted to learn more and read the National Snow and Ice Data Center’s website, located Here.
You can view these images individually in my portfolio located here. Stay tuned for more from this adventure as I continue wading through the images and wrapping my mind around what I saw and experienced.
If you are interested in one of my 2019 calendars that contains an image of sea ice in addition to penguins, puffins and more, please contact me at firstname.lastname@example.org by November 20, 2018. See my past post here for more details and examples of images I am using in the calendar.