UV climate over the Southern Ocean south of Australia, and its biological impact - 1994 data

• Other Authors: AADC (originator), AU/AADC > Australian Antarctic Data Centre, Australia (resourceProvider)
• Format: Dataset
• Language: unknown
• Published: Australian Ocean Data Network
• Subjects: climatologyMeteorologyAtmosphere; oceans; ULTRAVIOLET RADIATION; EARTH SCIENCE; ATMOSPHERE; ATMOSPHERIC RADIATION; ULTRAVIOLET RADIANCE; SPECTRAL/ENGINEERING; ULTRAVIOLET WAVELENGTHS; PROTISTS; BIOLOGICAL CLASSIFICATION; BACTERIA/ARCHAEA; PLANKTON; BIOSPHERE; AQUATIC ECOSYSTEMS; UV; wavelength; Macam spectral radiometer; RADIOMETERS; FIELD SURVEYS; GROUND-BASED OBSERVATIONS; FIELD INVESTIGATION; AMD/AU; CEOS; AMD; ACE/CRC; OCEAN > SOUTHERN OCEAN; CONTINENT > ANTARCTICA > Vestfold Hills; GEOGRAPHIC REGION > POLAR; Antarctic; Southern Ocean; The Antarctic; Vestfold; Davis Station; Davis-Station; Lever; Antarc*; Antarctica; Sea ice
• Online Access: https://researchdata.ands.org.au/uv-climate-southern-impact-1994/686410; https://data.aad.gov.au/metadata/records/ASAC_2210_94; https://data.aad.gov.au/eds/1525/download; https://secure3.aad.gov.au/proms/public/projects/report_project_public.cfm?project_no=2210; http://data.aad.gov.au/aadc/metadata/citation.cfm?entry_id=ASAC_2210_94

Issues The University of Tasmania purchased the Macam radiometer in 1992 as a field instrument. It was marketed as a field-adapted version of an instrument that was originally designed for laboratory use. During this campaign (and subsequent deployments) a number of problems and shortcomings emerged with respect to the desired use of the Macam. a) Operation in cold conditions The specifications of the Macam suggested that it would not function reliably when used in an ice/snow environment without protection. A wooden box lined with polystyrene foam was manufactured to transport, protect and insulate the Macam. In addition, a heating unit was installed inside the Macam (via the bottom of its standard case) driven by a battery that could be recharged. These adaptations were on the whole very successful. b) Sensitivity to motion The Macam operated as a double grating spectral radiometer, so that light collected by the sensor and transferred along the light pipe was directed on to a diffraction grating. The angle of the grating was adjusted to direct the appropriate section of the UV/visible spectrum onto a second grating. This grating was also steered to direct a (finer) portion of the spectrum onto detectors. The problem that emerged with time was that, while the mounts and drive mechanisms for the gratings were designed to work reliably in a comfortable, stable laboratory environment, they were less able to cope with disturbances as a result of transport by ship, Hagglund and helicopter. The result was a lack of confidence in the wavelength stability of the instrument. c)Fragility of light pipe The field measurements used a quartz fibre light pipe, twenty-five metres in length, which transmitted light in the ultraviolet regions as well as visible / near-infrared (operating specifications of Macam: 240 - 820 nm). The light pipe could not be bent in a radius less than 20 cm. In order to protect the light pipe from bending and from other damage, a rubber hose was placed surrounding the light pipe along its whole length - this necessitated splitting the hose and then taping it back around the light pipe. The rigidity of the hose made it very difficult to bend the light pipe in too tight a curve. However, it became clear even in this first field deployment that the light pipe was deteriorating even when used with great care. The light pipe was composed of many small fibres of quartz glass, and small breaks in the fibres would have the effect of slightly reducing the transmission of the light pipe. The high cost of the quartz light pipe also precluded replacing the light pipe or having spares on hand (cost at time of purchase was ~ A$1000 per metre). d) Difficulty of calibration The measurements from the Macam were only useful when the instrument was well calibrated. The calibration process consisted of viewing a pair of standard lamps (one UV, one visible) and setting the gains at each wavelength. The gain values were stored on disk in a file called 25M.CAL for operation of the Macam with the 25-m light pipe. A set of calibrations was accurate only as long as nothing changed with the characteristics of the whole radiometer system. Therefore small changes in the transmissivity of the light pipe would introduce systematic underestimations of the spectral irradiance data. In the long term, the Macam radiometer became useless as a precision instrument in the UV-B because of highly reduced sensitivity in those wavelengths because of accumulated damage to the light pipe. Where a spreadsheet contains little or no data, it is a reflection of problems with data collection or subsequent data quality. Ozone depletion over Antarctica increases UVB irradiances reaching the Earth's surface in the region. Marine microbes, that support the Antarctic food web and play an integral part in carbon cycling, are damaged by UVB. This research determines Antarctic UV climate, biological responses to UV from the molecular to community level, and combines these elements to predict UV-induced changes in Antarctic marine microbiology. A season of field work was undertaken over November and December 1994 based from Davis Station with the intention of making field measurements of ultraviolet radiation in the fast ice environment, as well as some of the lakes in the Vestfold Hills. Instrumentation The instrument for the measurements was a Macam spectral radiometer, owned by Geography and Environmental Studies, University of Tasmania. Field personnel were Dr Kelvin Michael (IASOS) and Mr Michael Wall (Honours student, Geography and Environmental Studies, UTas). The radiometer was equipped with a 25-metre quartz light pipe, with a cosine sensor attachment at the end. To make a measurement of ultraviolet irradiance, the sensor would be oriented so that its sensing surface was horizontal, and it would collect light which was then transmitted along the light pipe to the radiometer - a suitcase-sized unit which ran on battery power in the field. The radiometer was encased in a wooden box lined with polystyrene foam to provide protection from the elements and heat insulation. The radiometer was controlled via a laptop PC and the data were stored on the hard disk of the PC. Measurements Measurements of the attenuation of ultraviolet and visible radiation as a function of wavelength in water were made at the ice edge and lake measurement sites. At the ice edge, the light pipe was spooled over a wheel and lowered to preset depths (typically 1,2,4,8,16 and 32 m below the water surface). On a lake, a 25-cm augur hole was drilled, and the light pipe was lowered by hand to various depths, the exact depths chosen depended on the depth of the lake. Where the lake ice conditions permitted, a frame was lowered through the hole and used to lever the light pipe against the underside of the ice and a measurement of the ultraviolet and visible transmission of the sea ice was collected. In all cases, measurements of the ultraviolet and visible surface irradiance were collected before and/or after the sub-surface measurements. When the sky conditions were sufficiently clear, the direct and diffuse components of the ultraviolet and visible irradiance values were estimated, via the use of a shading apparatus. This would ensure that the radiometer would measure the diffuse component of the radiation field, allowing the direct component to be estimated by subtraction of the diffuse from the global (unshaded) measurement. On some occasions, the upwelling irradiance from the snow or ice surface was also measured, providing information on the spectral albedo of the surface. At each measurement, spectral irradiance values were generally collected for two spectral ranges: UV-B (280 - 400 nm, in 1-nm steps) and visible (400 - 700 nm, in 5-nm steps). In some cases, the wavelength boundaries were different - eg 280 - 350 nm for the UV-B, or 550 - 680 nm in the visible (corresponding to channel 1 of the NOAA AVHRR sensor). The data were stored by the PC as raw data files. The names of these files are automatically defined from the time on the logging PC as 'hhmmss.dti'. Note that the PC was operating on Australian Eastern Summer Time, 4 hours ahead of DLT. These data files were later read into Excel spreadsheets for manipulation. See the linked report for further information. The measurements are all in units of watts per metre squared per nanometre (Wm^-2 nm_-1) The heading UV-B refers to the fact that the data are collected in the ultraviolet part of the spectrum (280 - 400 nm) The heading AVHRR refers to the fact that the data are collected in the visible part of the spectrum (400 - 700 nm) The fields in this dataset are: UV Radiation Wavelength Depth AVHRR