New Vision Environmental Science Program
The New Vision Environmental Science Program provides an opportunity for students to explore many aspects of environmental science. This program emphasizes the social, economic, governmental, and political impacts upon the environment and is part of the ESF in the High School program. Cayuga-Onondaga BOCES in cooperation with the Cayuga County Natural Resource Center will provide an inside look at environmental issues while conducting field site research projects.
BOCES students communicated by email with ESF chemistry professor, David Kieber, as he pursued his research aboard the research vessel Nathaniel B. Palmer in Antarctica's Ross Sea. Questions and answers are posted below.
Questions for Professor Kieber
(Dr. Kieber's additions to the questions are in parentheses)
Wouldn't DMS (dimethyl sulfide) and other forms of (organic) sulfur be isolated in the polar region of the polar vortex? (sent 11/9)
Answer: NO. The polar vortex refers to the seasonally isolated air mass that occurs in the polar stratosphere, which is a region in the atmosphere whose lower boundary is about 8 km above the earth's surface in Antarctica. The stratosphere is where the depletion in ozone occurs in the austral spring time (which is our fall in the northern hemisphere). Any DMS (or most other organic sulfur compounds) that is emitted from the Antarctic Ocean into the atmosphere is too reactive to ever be transported into the stratosphere. Therefore, it will not be isolated in the polar vortex.
DMS is not very stable in the atmosphere. It is gone (through chemical reactions) after only a few days to at most weeks in the lower atmosphere. For a chemical to be transported to the stratosphere (and hence to the polar vortex) by air currents in an appreciable amount, that chemical has to have a lifetime in the lower atmosphere on the order of years. The only organic sulfur compound that is emitted from the oceans into the atmosphere with a long lifetime is a compound called carbonyl sulfide. This compound is significantly transported into the lower stratosphere where it is converted to sulfuric acid through reactions involving ultraviolet sunlight, forming the "Junge" aerosol (particle) layer.
Interestingly, it is exactly this air mass isolation, along with some interesting chemistry, that gives rise to the loss of stratospheric ozone in the spring in the Antarctic. This is because the main source of stratospheric ozone in the Antarctic stratosphere is through transport of ozone from its source region in temperate and tropical latitudes. If you stop this transport, then any chemical losses that occur will result in a drop in ozone concentrations, which is exactly what is observed in the spring until the polar vortex breaks up.
What effect does ozone depletion have on algae population? (sent 11/9)
Answer: This is at first glance a simple question, but its answer in fact is quite complicated. Ozone acts as an atmospheric filter for ultraviolet (UV) radiation. The less ozone there is, the more UV radiation that reaches the earth's surface. If there was nothing else to consider, then the answer would be a simple yes because UV inhibits the growth of and even can kill algae. Of course, the answer is not nearly this simple. Other factors need to be considered such as cloud cover, type of cloud, time of year, extent of ice cover, sea state (calm or choppy), type of algae present, the depth in the water column that the algae are living, and vertical mixing. Most investigators do not consider vertical mixing, which is very important because mixing keeps the organisms out of full sun light for long periods of time. If you do not consider mixing, then you have likely overestimated the effect of the ozone hole on algal growth. Then why have biologists generally not considered mixing in their experiments? Because it is very difficult to design an experiment at sea to look at the effect of the ozone hole on biological processes and at the same time consider mixing. Therefore, this question is still largely not answered.
However, there are three scientists on board our cruise who are considering mixing and trying to answer this question not only for algae but also for bacteria, which tend to be much more resistant to the damaging effects of UV radiation. The three scientists involved in this project are: Drs. Wade Jeffrey (a microbiologist, University of West Florida), Patrick Neale (a photobiologist, Smithsonian Environmental Research Center) and Ann Gargett (a physical oceanographer, Old Dominion University).
If DMS results in increased cloud production, would the algae population decrease (negative feedback)? (sent 11/9)
Answer: Good question! This question is really two questions in one. Does DMS affect cloud production, and do more clouds lower algal production? The first question has not been answered by scientists yet--some results indicate that DMS does affect the formation of clouds, while other studies have shown that DMS is not that important in cloud formation. For the second question, the answer is relatively straight forward. Clouds are the main attenuator of visible light in the atmosphere, which algae need to grow. However, under many circumstances, there is still plenty of light that passes through clouds allowing algae to grow well, and clouds can act to shade the algae from very bright light that can inhibit their growth. If there are too many clouds and not enough light, then of course the growth of the algae would decrease. The effect of clouds on algal growth is generally "overshadowed" by other factors such as time of year, water temperature and nutrients, which tend to be the main factors that affect algal growth in the water.
Of course the other important variable that I forgot to mention that controls algal growth is the amount of UV light that penetrates through the water. Clouds do not attenuate UV radiation nearly as well as visible light--that's why it's so easy to get a sunburn on a cloudy day! Too much UV will limit algal growth. The greatest inhibition of algal growth that is observed in the Antarctic (and in other oceanic regions) is when it is not windy and it is a sunny day. The light that penetrates into the sea during a sunny day will heat the surface mixed layer and the lack of winds will diminish vertical mixing. These conditions will "trap" the algae in the upper water layer and expose them to relatively high solar UV radiation for longer periods of time, which will likely inhibit their growth. To observe inhibition, you need to trap the algae near the sea surface because UV radiation is attenuated very rapidly in the sea (primarily by the dissolved organic matter), much more so than visible light. In the open ocean, UV radiation is completely attenuated by 20 m--the shorter the wavelength the more rapidly the UV is attenuated. By contrast, visible radiation can penetrate the sea more than 100 m, depending on the wavelength considered. In a lake, the attenuation of light is generally much more rapid because there's a lot more organic matter and particles in the water. In some organic-rich lakes, short wavelengths of UV radiation (e.g., 300-305 nm) may only penetrate the water a few cm!
Of course some algae are much more sensitive to UV light than others, and the inhibition that is observed will depend on the algal species that are present in the seawater. One important unanswered question related to this is: Has the dramatic seasonal ozone hole observed in the Antarctic for many years already changed the plankton community such that we are now only observing the more resistant species? Scientists have only been studying UV affects on algal growth in Antarctica since the mid 1980s, while the ozone hole has been around every spring much longer than this.