AMLR program: Ultraviolet and visible solar irradiance ...
AMLR program: Ultraviolet and visible solar irradiance around Elephant Island, Antarctica, January to March 1993 E. WALTER HELBLING and OSMUND HOLM-HANSEN, Polar Research Program, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92093-0202 PATRICI0 MORAN, Universidad Nacional del Sur, (8000) Bahia Blanca, Argentina
UV-A region of the spectrum) were 35.3 and 28.4 IAW cm-2 nm' for Legs I and II, respectively (figure 1B). The irradiances at 320 and 340 nm showed the same pattern of variations as the above wavelengths, with the mean daily values being 12.4 and 9.5[LW cm-2 nm- 1 (for 320 nm) and 25.2 and 20.1 RW CM-2 nm' (for 340 nm) for Legs I and II, respectively. The mean daily PAR (figure 1C) had means of 787 and 651 microeinsteins per square meter per second (tEinst m- 2 s_') for Legs I and II, respectively. The observed length of the solar day, sunrise to sunset, decreased continuously during the time of our cruise (solid line in figure 1 Q. The irregular nature of this line is due to changes in latitude as the ship steamed in north-south directions within the survey grid. Because the region around Elephant Island is characterized by prolonged cloud cover, most of the daily PAR values are much less than the values that would prevail under a cloud-free atmosphere. The mean irradiance for PAR at 61°S on a cloud-free day in early January would be approximately 1,500 iEinst m-2 -• The attenuation of solar irradiance in the water column at two representative stations, one with high and the other with low chlorophyll-a concentrations, is shown in figure 2. At station A43, which had low chlorophyll-a values (figure 20, the attenuation coefficients for the four UVR wavelengths and for PAR were 0.124, 0.119, 0.069, 0.042, and 0.036, respectively (see figure 2A). The 1 percent light level for PAR was at approximately 128 m. Solar radiation was attenuated much more rapidly (see figure 2B) at station A77, which had much higher chlorophyll-a concentrations (figure 2C). The attenuation coefficients for UVR at 308, 320, 340, and 380 nanometers and for PAR were 0.242, 0.23, 0.192, 0.154, and 0.144, respectively. The 1 percent light level for PAR was at approximately 32 m. Data in figure 3 show the relationship between the diffuse attenuation coefficients (K) in the upper mixed layer, obtained with the cosine collector on the rosette, and chlorophyll-a concentrations in the upper mixed layer. There was a good correlation between KpAR values and chlorophyll-a concentrations (figure 3), with the equation for the relationship being K=0.0374 * chl-a+0.038 (r2=0.85, n=91). Because this relationship is good, it enables one to estimate the depth of the euphotic zone on the basis of chlorophyll-a concentrations in the upper water column. This would be useful when stations are occupied at night or when no PAR sensor is available for use in profiling studies. This research was supported by NOAA Cooperative Agreement No. NA37FR0001-01. We thank the officers and crew of NOAA ship Surveyor for excellent support during field operations, and also Alternative Fluorocarbon Environmental
ince the discovery of the seasonal ozone hole over AntarcS tica (Farman, Gardiner, and Shanklin 1985), great efforts have been made in measuring incident ultraviolet radiation (UVR) at high latitudes in the Southern Hemisphere (for example, the National Science Foundation UVR monitoring program), as well as the impact that enhanced UV-B radiation [280 to 320 nanometers (nm)] could have on the terrestrial and aquatic environments (see Weiler and Penhale in press). As one component of the Antarctic Marine Living Resources (AMLR) program, our phytoplankton group has been measuring total and spectral UVR, as well as photosynthetically available radiation (PAR, 400 to 700 nm), reaching the surface of the ocean and its attenuation in the water column throughout the AMLR study area in the vicinity of Elephant Island. The measurements described in this article were conducted on board the National Oceanic and Atmospheric Administration (NOAA) ship Surveyor, a description of operations and a listing of the station locations are given in Rosenberg, Hewitt, and Holt (Antarctic Journal, in this issue). Ultraviolet radiation at four wavelengths (308, 320, 340, and 380 nm) and PAR were measured using a spectroradiometer (PUV-500/5 10, Biospherical Instruments, Inc.), which was mounted in a shade-free area on the helicopter deck close to the stern of the ship. The irradiance values for each channel were recorded on a 386 computer every minute throughout the entire cruise. A profiling underwater unit (with the same five channels mentioned above) and sensors for temperature, pressure, and 683-nm upwelling light were deployed down to 50-100 meters (m) at all stations when weather conditions permitted. The signals from all sensors on this unit were recorded on the same computer, at a rate of once per second. A 2-pi collector (model QSR 240, Biospherical Instruments, Inc.) for PAR and an Eppley radiometer (TUVR) for total U\TR from 295 to 385 nm, were mounted in a shade-free area on the ship's superstructure. Signals from these sensors were recorded every minute on a Data World computer. To determine the attenuation of PAR in the upper water column, a PAR sensor (model QCP-200L, Biospherical Instruments, Inc.) with a cosine response was mounted on the rosette that was lowered at every station to 750-m depth or to within 10-m of the bottom at the shallower stations. The incident solar radiation during both legs of the cruise is shown in figure 1. The mean daily irradiance at 308 nm (in the UV-B region of the spectrum) had values of 0.45 and 0.3 microwatts per square centimeter per nanometer (iW cm-2 nm') for Legs I and II, respectively, with a range of 0.23-0.79 tW cm-2 nm- 1 for Leg I and 0.09-0.63 tLW cm-2 nm- 1 for Leg II (figure 1A). The mean daily irradiance values at 380 nm (in the
ANTARCTIC JOURNAL - REVIEW 1993 189
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Figure 2. Spectral attenuation of solar irradiance in the water column and pigment content at two stations within the AMLR study area. A. Station A43. B. Station A77. C. Chlorophyll-a concentrations at stations A43 and A77.
Figure 1. Mean daily incident solar radiation reaching the surface of the ocean during the AMLR cruise in January-March 1993, and duration of the solar day. A. Radiation at 308 nm. B. Radiation at 380 nm. C. PAR and solar day length in hours.
ANTARCTIC JOURNAL - REVIEW 1993 190
Acceptability Study for furnishing of essential equipment. Grateful acknowledgment is also made to Aldo Aguilera, Samuel Hormazabal, Sandra Rivera, and Livio Sala for their generous help on board ship. Shipboard personnel included E. Walter Helbling (11 January to 9 February), Patricio Moran (11 January to 15 March), and Osmund Holm-Hansen (14 February to 15 March).
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References
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Farman, J.C., B.G. Gardiner, and J.D. Shanklin. 1985. Large losses of total ozone in Antarctica reveal seasonal CIO/NO interaction. Nature, 315(6016), 207-210. Rosenberg, J.E., R.P. Hewitt, and R.S. Holt. 1993. The U.S. Antarctic Marine Living Resources (AMLR) program: 1992-1993 field season activities. Antarctic Journal of the U.S., 28(5). Weiler, S., and P. Penhale (Eds.). In press. Ultraviolet Radiation and Biological Research in Antarctica (Antarctic Research Series). Washington, D.C.: American Geophysical Union.
0.04 0.02
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Chlorophyll-a (mg/m3)
Figure 3. Relationship between the diffuse attenuation coefficient K PAR and chlorophyll-a concentration. The line indicates the mean square fit of the data.
AMLR program: Rates of primary production around Elephant Island, Antarctica OSMUND HOLM-HANSEN, VIRGINIA E. VILLAFAIE, and E. WALTER HELBLING, Polar Research Program, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92093-0202 LIVI0 SALA, Universidad Nacional de la Patagonia, Facultad de Ciencias Naturales, Chubut, Argentina
683 nm as a function of depth and downwelling irradiance of PAR. Water samples obtained from eight depths between 5 to 75 m were dispensed into 120-milliliter (mL) borosilicate glass bottles (two light and one dark), which were inoculated with 5.0 microcuries (iCi) of carbon-14 ( 14 C) bicarbonate. The bottles were placed in a shade-free deck incubator, which was cooled with flowing sea water, and incubated for 8-10 hours (h) centered around local apparent noon. Neutral density filters were used to attenuate solar radiation so that the samples were exposed to eight different irradiance regimes, which ranged from 95 percent to 0.5 percent of incident radiation. Incident PAR was continuously recorded (every minute), so that the amount of carbon dioxide (G0 2) fixed during the incubation period could be extrapolated to estimate total daily primary production. Rates of photosynthesis as a function of mean irradiance during the incubation period are shown in figure 1. The photosynthesis-irradiance parameters as calculated by the equation of Platt and Jassby (1976) are as follows: • 1max=27 milligrams of carbon per milligram of chlorophyll-a per hour (mg C mg chl-a' h'); • 'k=945 microeinsteins per square meter per second (tEinst m-2 sec-1); • alpha=0.029 mg C (mg chl-a hour)-' (pEinst m- 2 sec')'. There were no significant differences in photosynthetic
n important goal of the U.S. Antarctic Marine Living esources (AMLR) program is to improve understanding of the temporal and spatial characteristics of primary production in the area around Elephant Island. Villafañe et al. (Antarctic Journal, in this issue) have described various features of the standing stock of phytoplankton throughout the AMLR study area during the period from January to March 1993. In this article, we report the daily rate of primary production in the AMLR study area and discuss various factors that influence rates of phytoplankton photosynthesis. The AMLR survey grid consisted of 91 stations, each of which was sampled once during Leg I and once during Leg II between January and March 1993. The station locations have been described by Rosenberg, Hewitt, and Holt (Antarctic journal, in this issue). Upper water column characteristics and water samples from 11 depths were obtained at every station with an instrumented profiling unit consisting of a rosette containing sensors for depth, temperature, and conductivity; a pulsed in situ fluorometer (Sea Tech); a 25-cm transmissometer (Sea Tech); a solar irradiance sensor (Biospherical Instruments, Inc.,) for photosynthetically available radiation (PAR) between 400 to 700 nanometers (nm); and 1110-liter (L) Niskin bottles equipped with Teflon-covered springs. A profiling PUV-510 unit (Biospherical Instruments, Inc.,) was also deployed at selected stations [surface to 100 meters (m)] to record upwelling radiance at
ANTARCTIC JOURNAL - REVIEW 1993 191
UV-A region of the spectrum) were 35.3 and 28.4 IAW cm-2 nm' for Legs I and II, respectively (figure 1B). The irradiances at 320 and 340 nm showed the same pattern of variations as the above wavelengths, with the mean daily values being 12.4 and 9.5[LW cm-2 nm- 1 (for 320 nm) and 25.2 and 20.1 RW CM-2 nm' (for 340 nm) for Legs I and II, respectively. The mean daily PAR (figure 1C) had means of 787 and 651 microeinsteins per square meter per second (tEinst m- 2 s_') for Legs I and II, respectively. The observed length of the solar day, sunrise to sunset, decreased continuously during the time of our cruise (solid line in figure 1 Q. The irregular nature of this line is due to changes in latitude as the ship steamed in north-south directions within the survey grid. Because the region around Elephant Island is characterized by prolonged cloud cover, most of the daily PAR values are much less than the values that would prevail under a cloud-free atmosphere. The mean irradiance for PAR at 61°S on a cloud-free day in early January would be approximately 1,500 iEinst m-2 -• The attenuation of solar irradiance in the water column at two representative stations, one with high and the other with low chlorophyll-a concentrations, is shown in figure 2. At station A43, which had low chlorophyll-a values (figure 20, the attenuation coefficients for the four UVR wavelengths and for PAR were 0.124, 0.119, 0.069, 0.042, and 0.036, respectively (see figure 2A). The 1 percent light level for PAR was at approximately 128 m. Solar radiation was attenuated much more rapidly (see figure 2B) at station A77, which had much higher chlorophyll-a concentrations (figure 2C). The attenuation coefficients for UVR at 308, 320, 340, and 380 nanometers and for PAR were 0.242, 0.23, 0.192, 0.154, and 0.144, respectively. The 1 percent light level for PAR was at approximately 32 m. Data in figure 3 show the relationship between the diffuse attenuation coefficients (K) in the upper mixed layer, obtained with the cosine collector on the rosette, and chlorophyll-a concentrations in the upper mixed layer. There was a good correlation between KpAR values and chlorophyll-a concentrations (figure 3), with the equation for the relationship being K=0.0374 * chl-a+0.038 (r2=0.85, n=91). Because this relationship is good, it enables one to estimate the depth of the euphotic zone on the basis of chlorophyll-a concentrations in the upper water column. This would be useful when stations are occupied at night or when no PAR sensor is available for use in profiling studies. This research was supported by NOAA Cooperative Agreement No. NA37FR0001-01. We thank the officers and crew of NOAA ship Surveyor for excellent support during field operations, and also Alternative Fluorocarbon Environmental
ince the discovery of the seasonal ozone hole over AntarcS tica (Farman, Gardiner, and Shanklin 1985), great efforts have been made in measuring incident ultraviolet radiation (UVR) at high latitudes in the Southern Hemisphere (for example, the National Science Foundation UVR monitoring program), as well as the impact that enhanced UV-B radiation [280 to 320 nanometers (nm)] could have on the terrestrial and aquatic environments (see Weiler and Penhale in press). As one component of the Antarctic Marine Living Resources (AMLR) program, our phytoplankton group has been measuring total and spectral UVR, as well as photosynthetically available radiation (PAR, 400 to 700 nm), reaching the surface of the ocean and its attenuation in the water column throughout the AMLR study area in the vicinity of Elephant Island. The measurements described in this article were conducted on board the National Oceanic and Atmospheric Administration (NOAA) ship Surveyor, a description of operations and a listing of the station locations are given in Rosenberg, Hewitt, and Holt (Antarctic Journal, in this issue). Ultraviolet radiation at four wavelengths (308, 320, 340, and 380 nm) and PAR were measured using a spectroradiometer (PUV-500/5 10, Biospherical Instruments, Inc.), which was mounted in a shade-free area on the helicopter deck close to the stern of the ship. The irradiance values for each channel were recorded on a 386 computer every minute throughout the entire cruise. A profiling underwater unit (with the same five channels mentioned above) and sensors for temperature, pressure, and 683-nm upwelling light were deployed down to 50-100 meters (m) at all stations when weather conditions permitted. The signals from all sensors on this unit were recorded on the same computer, at a rate of once per second. A 2-pi collector (model QSR 240, Biospherical Instruments, Inc.) for PAR and an Eppley radiometer (TUVR) for total U\TR from 295 to 385 nm, were mounted in a shade-free area on the ship's superstructure. Signals from these sensors were recorded every minute on a Data World computer. To determine the attenuation of PAR in the upper water column, a PAR sensor (model QCP-200L, Biospherical Instruments, Inc.) with a cosine response was mounted on the rosette that was lowered at every station to 750-m depth or to within 10-m of the bottom at the shallower stations. The incident solar radiation during both legs of the cruise is shown in figure 1. The mean daily irradiance at 308 nm (in the UV-B region of the spectrum) had values of 0.45 and 0.3 microwatts per square centimeter per nanometer (iW cm-2 nm') for Legs I and II, respectively, with a range of 0.23-0.79 tW cm-2 nm- 1 for Leg I and 0.09-0.63 tLW cm-2 nm- 1 for Leg II (figure 1A). The mean daily irradiance values at 380 nm (in the
ANTARCTIC JOURNAL - REVIEW 1993 189
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Figure 2. Spectral attenuation of solar irradiance in the water column and pigment content at two stations within the AMLR study area. A. Station A43. B. Station A77. C. Chlorophyll-a concentrations at stations A43 and A77.
Figure 1. Mean daily incident solar radiation reaching the surface of the ocean during the AMLR cruise in January-March 1993, and duration of the solar day. A. Radiation at 308 nm. B. Radiation at 380 nm. C. PAR and solar day length in hours.
ANTARCTIC JOURNAL - REVIEW 1993 190
Acceptability Study for furnishing of essential equipment. Grateful acknowledgment is also made to Aldo Aguilera, Samuel Hormazabal, Sandra Rivera, and Livio Sala for their generous help on board ship. Shipboard personnel included E. Walter Helbling (11 January to 9 February), Patricio Moran (11 January to 15 March), and Osmund Holm-Hansen (14 February to 15 March).
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References
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Farman, J.C., B.G. Gardiner, and J.D. Shanklin. 1985. Large losses of total ozone in Antarctica reveal seasonal CIO/NO interaction. Nature, 315(6016), 207-210. Rosenberg, J.E., R.P. Hewitt, and R.S. Holt. 1993. The U.S. Antarctic Marine Living Resources (AMLR) program: 1992-1993 field season activities. Antarctic Journal of the U.S., 28(5). Weiler, S., and P. Penhale (Eds.). In press. Ultraviolet Radiation and Biological Research in Antarctica (Antarctic Research Series). Washington, D.C.: American Geophysical Union.
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Chlorophyll-a (mg/m3)
Figure 3. Relationship between the diffuse attenuation coefficient K PAR and chlorophyll-a concentration. The line indicates the mean square fit of the data.
AMLR program: Rates of primary production around Elephant Island, Antarctica OSMUND HOLM-HANSEN, VIRGINIA E. VILLAFAIE, and E. WALTER HELBLING, Polar Research Program, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92093-0202 LIVI0 SALA, Universidad Nacional de la Patagonia, Facultad de Ciencias Naturales, Chubut, Argentina
683 nm as a function of depth and downwelling irradiance of PAR. Water samples obtained from eight depths between 5 to 75 m were dispensed into 120-milliliter (mL) borosilicate glass bottles (two light and one dark), which were inoculated with 5.0 microcuries (iCi) of carbon-14 ( 14 C) bicarbonate. The bottles were placed in a shade-free deck incubator, which was cooled with flowing sea water, and incubated for 8-10 hours (h) centered around local apparent noon. Neutral density filters were used to attenuate solar radiation so that the samples were exposed to eight different irradiance regimes, which ranged from 95 percent to 0.5 percent of incident radiation. Incident PAR was continuously recorded (every minute), so that the amount of carbon dioxide (G0 2) fixed during the incubation period could be extrapolated to estimate total daily primary production. Rates of photosynthesis as a function of mean irradiance during the incubation period are shown in figure 1. The photosynthesis-irradiance parameters as calculated by the equation of Platt and Jassby (1976) are as follows: • 1max=27 milligrams of carbon per milligram of chlorophyll-a per hour (mg C mg chl-a' h'); • 'k=945 microeinsteins per square meter per second (tEinst m-2 sec-1); • alpha=0.029 mg C (mg chl-a hour)-' (pEinst m- 2 sec')'. There were no significant differences in photosynthetic
n important goal of the U.S. Antarctic Marine Living esources (AMLR) program is to improve understanding of the temporal and spatial characteristics of primary production in the area around Elephant Island. Villafañe et al. (Antarctic Journal, in this issue) have described various features of the standing stock of phytoplankton throughout the AMLR study area during the period from January to March 1993. In this article, we report the daily rate of primary production in the AMLR study area and discuss various factors that influence rates of phytoplankton photosynthesis. The AMLR survey grid consisted of 91 stations, each of which was sampled once during Leg I and once during Leg II between January and March 1993. The station locations have been described by Rosenberg, Hewitt, and Holt (Antarctic journal, in this issue). Upper water column characteristics and water samples from 11 depths were obtained at every station with an instrumented profiling unit consisting of a rosette containing sensors for depth, temperature, and conductivity; a pulsed in situ fluorometer (Sea Tech); a 25-cm transmissometer (Sea Tech); a solar irradiance sensor (Biospherical Instruments, Inc.,) for photosynthetically available radiation (PAR) between 400 to 700 nanometers (nm); and 1110-liter (L) Niskin bottles equipped with Teflon-covered springs. A profiling PUV-510 unit (Biospherical Instruments, Inc.,) was also deployed at selected stations [surface to 100 meters (m)] to record upwelling radiance at
ANTARCTIC JOURNAL - REVIEW 1993 191
