Ice 101 and the Living Arctic

September 17, 2008 · Filed Under Journey · Comment

Jessica Robertson, U.S. Geological Survey Public Affairs Specialist

In addition to the work to define the continental shelf during this expedition, there are several projects underway, such as sea ice observations and analysis of organisms in the ocean.

I spent the other day chatting about sea ice observations with Pablo Clemente-Colón, Chief Scientist of the National Ice Center and an oceanographer with NOAA. Pablo told me that we have already lost a record amount of multi-year (older) ice in the Arctic compared to last year. In fact, well over 60 percent of the old ice pack has disappeared since the 1980s. We have never observed such an advanced state of ice deterioration of the old ice pack in this location. It appears, though, that an overall seasonal freezing trend is now setting up for this part of the Arctic. Through this journey, we have observed a combination of new, first-year and multi-year ice all in one pack. In some cases, we have even witnessed new ice form overtop of heavily melted multi-year ice flows, creating ice-type concentration conditions difficult to assess and typically not observed or reported.

During this expedition, Pablo routinely monitors the ice coverage visually and records what types of ice are dominantly present. These data are used to validate satellite remote sensing observations of ice coverage in the area. Sea ice data from remote sensing analysis are used by various customers, including the National Weather Service, the Navy (particularly for submarine Arctic crossings), and the U.S. Coast Guard for safety of navigation, life, and property at sea. Data can also be used for fisheries support and research, oceanographic and atmospheric models, and much more.

Sea ice can be roughly categorized into three general groups, which I briefly mentioned above. There is new ice and nilas, which is the thinnest sea ice; young and first-year ice, which can grow from four inches to four feet in one season; and old or multi-year ice, which has survived at least one melting season. As ice ages, its thickness and color tone change. Water usually appears as a dark color surface and new to first year would typically go from dark to grey to a grey-white color. The youngest of the old ice, second-year ice, is seen as a greenish-blue color, and older multi-year ice has a deeper blue tone. Color alterations are due to the presence or absence of salt and air bubbles in the ice. Newer ice has more salt, while older ice has more air bubbles. In the absence of salt, more sunlight is available to scatter around and reflect off the air bubbles, providing the brighter blue tone appearance of the multi-year ice.

Other scientists onboard Healy are studying microorganisms in the Arctic Ocean to better understand processes such as the food chain, carbon cycle, and nutrient cycle. Over the last several decades, it has been recognized that microorganisms are more active and abundant in this area than previously thought, therefore playing a key role in the above processes. Research is being conducted by Rebecca Gast with Woods Hole Oceanographic Institution and Robert Sanders with Temple University. Becky and Bob are studying protists with a specific focus on the presence of mixotrophs, which are a type of algae that have not been studied much in this region. Mixotrophic algae eat bacteria as well as use sunlight for photosynthesis, potentially helping them thrive in the extreme polar environment.

To study these microorganisms, water samples are collected at various depths in the ocean. Samples are taken using a Conductivity Temperature Depth Profiler (CTD), which, as you can assume from the name, also measures conductivity and temperature as a function of water depth. I will discuss how we use that information for seafloor mapping in a later journal entry, but for now I will just focus on the water samples. Healy’s CTD has 24 bottles to collect water, each with an opening at the top and bottom (not all CTDs have this design). When it is placed in the ocean and reaches a desired depth, an electronic signal is sent from the ship that closes the bottles. They can be closed at various times and at different depths. After collection, the water is incubated with particles that the mixotrophs can eat, and the organisms are detected by microscopic analysis.

I also want to quickly point out my recent discovery of artwork on the ship’s aloft conn web camera. Many Healy crew members have been onboard intermittently for several years, so as you can imagine, they are always looking for means of entertainment. If you haven’t checked out the camera in awhile, take a glance through our slideshow of past images. You may find it amusing!

Until next time,

Jessica Robertson

: Preparing to send the CTD in the water.

: The CTD is lowered into the ocean to collect water samples and measure conductivity, temperature and depth.

: Setting the CTD’s bottles open before deployment.

: These are the lids both on top and below the water bottles. When triggered, they close and a water sample is collected.

: Bob Sanders collects water for microscopic analysis of microorganisms.

: Rebecca Gast counts cells at a microscope.

: USGS scientist Jonathan Childs and NOAA oceanographer Pablo Clemente-Colón, also Chief Scientist of the National Ice Center.

: This is an image of nilas, which is thin ice. As nilas comes together like fingers, which is known as finger rafting, it creates thicker ice called young ice.

: A piece of multi-year ice surfacing on its side after we break through. You can tell it is older ice as the color is a bright blue underneath. There is also a dusting of snow on the top.

: This image shows a combination of various ice types. There is multi-year ice in the left forefront, characterized by the brighter blue color. Nilas and new ice can be seen toward the middle, characterized by darker and grey colors. As you move up in the picture, you can see a large, smooth area of first-year ice covered with snow. The background is dominated by a combination of multi-year and first-year ice. Photograph by: Pablo Clemente-Colón, Chief Scientist of the National Ice Center and an oceanographer with NOAA.