National Science Foundation
The effects of decreased protection from ultraviolet (UV) radiation are as troubling as the continuing depletion of stratospheric ozone. Already, evidence exists that clearly links the ozone hole to changes in the antarctic marine environment. In two Science papers published in 1992, U.S. scientists supported by the National Science Foundation (NSF) reported that enhanced exposure to mid-range UV radiation (280 to 320 nanometers) was affecting marine ecosystems. Near the Antarctic Peninsula, biologists in October 1991 recorded a 6- to 12-percent reduction in primary productivity, directly related to the ozone layer depletion. Using data from the McMurdo Sound region, a second research team has developed a model indicates that the ozone hole could reduce near-surface photosynthesis by as much as 12 to 15 percent.
To learn how much UV radiation may be reaching the Earth's surface during the austral spring, NSF established in 1988 a UV-radiation monitoring network with instruments at the three U.S. antarctic stations (Palmer, McMurdo, and Amundsen-Scott South Pole Station), Argentina's Centro Austral de Investigaciones (CADIC) at the tip of South America, and an arctic site. The table shows the location of the monitors and the period during which they operate.
The amount of UV light that reaches the ground depends on the angle of the sun, cloud cover, and atmospheric gas concentration. While the amount of stratospheric ozone has only negligible effects on UV wavelengths longer than 330 nanometers, decreasing amounts of ozone do increase the amount of shorter- wavelength UV radiation, particularly between 295 and 330 nanometers. This range of UV radiation, known as UV-B, can adversely affect living organisms, include humans.
This network, the first automated UV-scanning spectroradiometer system in world, provides data for researchers assessing the impact of ozone depletion on terrestrial and marine biological systems. These data have confirmed that ozone depletion does change the amount short wavelength UV light reaching the earth's surface.
| Sites of UV-monitors and periods of operation | ||
|---|---|---|
| Site | Date installed | Operating season |
| McMurdo | March 1988 | Aug to Apr |
| Palmer | May 1988 | Year round |
| South Pole | February 1988 | Sep to Mar |
| Ushuaia Arg. | November 1988 | Year round |
| San Diego* | October 1992 | Year round |
| Barrow, AK** | December 1990 | Jan to Nov |
The NSF UV monitoring system uses a spec- troradiometer. This device makes hourly, high-resolution measurements of the distribution of UV surface irradiance, which is the sum of direct and diffuse solar radiation encountering a horizontal plane. The network is maintained by Biospherical Instruments Inc. of San Diego, California, under contract to NSF's contractor Antarctic Support Associates. Biospherical Instruments also distributes the acquired data to the science community, according to instructions provided by NSF.
The system, designed to be operated unattended, only requires human attention for data transfer, periodic calibration, and maintenance. The hardware is divided into two sections. The first consists of the irradiance collector, monochromator, a 28-mm-diameter photomultiplier tube, and calibration sources; these are housed in a roof box. The second, located up to 15.5 meters from the roof box, includes power supplies, temperature controllers, electronic interfaces, and a personal computer.
The software developed by Biospherical Instruments, manages calibration, displays processed data, and creates databases. Calculated values include solar zenith and azimuthal angles, spectral integrals, weighted doses, and standard meteorological spectral integrals.
Data obtained via the NSF network show that ozone depletion has significantly increased the amount of UV-B reaching the surface at the five monitor-sites. For example, data from the monitor at McMurdo Station showed irradiance in the UV-B range increased 1,000 percent in 1989, above levels recorded in 1988 when ozone above the station was more abundant. Using the uv-monitoring data, scientists have discovered that ozone-driven changes in irradiance can occur in periods as short as 24 hours.
These data on UV levels also mirror changes in the ozone hole. In 1990, the ozone hole last longer than in the past, persisting until early December. During this period the UV network recorded highest UV levels in December as the days grew longer. In 1991 the movement of the ozone hole over the Antarctic Peninsula brought increased UV exposure to Palmer and Ushuaia in October, while at the South Pole and McMurdo--where ozone deple- tion levels were not as great--the highest UV levels were recorded near the summer solstice.
Data sets for 1989 to early 1993 (volumes 1 to 3) are available in CD-ROM format; data obtained before Volume 1 was published is available through the authors on special request. These are readable by a variety of platforms including IBM or IBM-compatible PCs, MacIntosh computers, and a variety of other work stations. Information concerning the data sets or the distribution of data can be obtained from Charles R. Booth (Biospherical Instruments, Inc.; 4901 Moena Blvd., San Diego, California 92117; 619/270-1315) or Dr. Polly Penhale (Manager, Polar Biology and Medicine, Office of Polar Programs], National Science Foundation, 4201 Wilson Boulevard; Arlington, Virginia 22230; 703/306-1033).
