RACER: Temporal and spatial distribution of phytoplankton ...
Platt, T., W.G. Harrison, B. Irwin, E.P. Home, and C.L. Gallegos. 1982. Photosynthesis and photoadaptation of marine phytoplankton in the Arctic. Deep-Sea Research, 29, 1159-1170. Sakshaug, E., and 0. Holm-Hansen. 1986. Photoadaptation in Antarctic phytoplankton: Variations in growth rate, chemical composition and P versus I curves. Journal of Plankton Research, 8, 459-473.
Tilzer, M.M., B. von Bodungen, and V. Smetacek. 1985. Light-dependence of phytoplankton photosynthesis in the Antarctic Ocean: Implications for regulating productivity. in W.R. Siegfried, P.R. Condy, and R.M. Laws (Eds.), Antarctic nutrient cycles and food webs. Berlin: Springer-Verlag.
RACER: Temporal and spatial distribution of phytoplankton biomass and primary production
rophyll a were extremely variable, ranging over two orders of magnitude from 0.2 to 20 milligrams per cubic meter. The deep waters to the northwest of the South Shetland Islands were low in chlorophyll a (less than 0.5 milligrams per cubic meter). Highest levels of phytoplankton pigments were found in protected embayments and in the vicinity of islands as predicted by the central hypotheses of RACER. (See Huntley et al., Antarctic Journal, this issue.) Furthermore, a pronounced seasonal trend is evident with the peak occurring in December and decreasing progressively from January through March. Preliminary examination of approximately 300 profiles of chlorophyll a concentration and of water density (-t) as recorded in the upper 200 meters of the water column by our profiling unit showed, first, that chlorophyll a is fairly uniformly distributed throughout the entire upper mixed layer and, second, that concentrations decrease rapidly below the pycnocline. Extracted chlorophyll a values from standard depths confirmed these observations, and are in agreement with similar conclusions first reported by Dustan, Olson, and Holm-Hansen (1979). Distribution maps of chlorophyll a in surface waters (figure 1) will thus show the same general patterns as maps showing spatial distribution of integrated chlorophyll a for the upper 200 meters. Hart (1942) first documented the rapid increase in phytoplankton biomass in antarctic waters during austral spring, followed by a rapid decline. Our time series from December 1986 to March 1987 of integrated water column production at five stations in the RACER grid is presented in figure 2a. The pronounced seasonality of these data emphasizes the importance of high-resolution sampling through a seasonal cycle. Peak bloom conditions were already evident in mid-December. This is considerably earlier than the phytoplankton peak reported near the South Orkney Islands by Home et al. (1969). During RACER we found that within our 25,000-square-kilometer study area, surface pigments and integrated production varied over a range equal to previous reports for the world's oceans. This is summarized in figure 2b where the data from RACER are superimposed upon a summary plot of integrated production as a function of surface phytoplankton pigments compiled by Eppley etal. (1985). Understanding the underlying mechanism of such dynamic range within antarctic coastal ecosystems is one of the goals of RACER. The rate of primary production will be a function of both the phytoplankton standing stock and phytoplankton specific growth rates. Of the major factors which affect phytoplankton growth rates, available data indicate that light is the most important. One focus of RACER is that high productivity in the area of the Antarctic Peninsula is caused by high mean light levels experienced by the phytoplankton due to relatively shallow and stable upper water mixed layers.
0. HOLM-HANSEN, R. LETELIER, and B.C. MITCHELL Polar Research Program Scripps Institution of Oceanography University of California at San Diego La Jolla, California 92093
The RACER program (Research on Antarctic Coastal Ecosystem Rates) is an interdisciplinary study which seeks to understand the dynamic mechanisms controlling the planktonic ecosystem structure of the Antarctic Peninsula coastal environment (see Huntley et al., Antarctic Journal, this issue). The photobiology component of this program is concerned with temporal and spatial dynamics of phytoplankton populations, especially in relation to physical mixing processes and the environmental factors influencing growth rates. At each "fast" grid station our physical-optical-biological profiling unit was deployed from 0 to 200 meters to give continuous recording of depth, temperature, conductivity, 2-'rr irradiance (400-700 nanometers), seven channels downwelling irradiance, five channels upwelling radiance, beam attenuation (transmissometer), and chlorophyll a fluorescence (fluorometer with pulsed blue activating light). Water samples were obtained in 5.0-liter, polyvinyl chloride Niskin bottles at eight standard depths during the "up" cast of the profiling unit, and the water was used for determination of chlorophyll a, particulate organic carbon and nitrogen, inorganic nutrient concentrations, and floristic examination. Surface water samples were also obtained by "bucket" in conjunction with the microbiology program and used to measure chlorophyll a in nanoplankton (less than 20 micrometers in diameter) and microplankton (more than 20 micrometers). During the "slow" grid stations the above measurements were supplemented with studies concerned with photoadaptational status of the phytoplankton, as well as with in situ primary productivity measurements using radiocarbon incorporation. During the in situ incubations (12-24 hours) numerous profiles of light attenuation in the upper 100 meters of the water column were obtained with our profiling unit so that total light flux at various depths could be calculated and used in quantum efficiency calculations. The reults of our time series of fast-grid surface chlorophyll distributions are presented in figure 1. Concentrations of chlo142
ANTARCTIC JOURNAL
7
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Figure 1. Spatial distribution of chlorophyll a concentrations (in milligrams per cubic meter) in surface waters throughout the RACER grid of 69 stations for four surveys between December 1986 and March 1987. The concentrations ranged from over 20 milligrams per cubic meter (Gerlache Strait) to 0.2 milligram per cubic meter (Drake Passage). 1987 REVIEW
143
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DEC JAN FEB MAR Figure 2. Rates of primary production at RACER stations: A. Integrated daily production at individual stations from December, 1986, through March, 1987. ("N.D." denotes "no data," due to bad weather or ice. 11 gCIm 2 ;s,day" denotes "grams of carbon per square meter per day:' "St" denotes "station:') B. Integrated primary production (rr) from RACER stations (shown as solid squares) as a function of surface concentrations of chlorophyll a plus phaeopigment concentrations (C k). All other data shown in block B were compiled by Eppley el al. (1985) from data of the world's oceans reported in the literature. The open circle in the upper right represents the calculated limit value. (Tr is expressed as milligrams carbon per square meter per day, while C,, is expressed as milligrams of chlorophyll-a plus phaeopigment per cubic meter.)
Nutrients and temperature are generally ignored as controlling variables of antarctic primary production (Hayes, Whitaker, and Fogg 1984). Recent reports, however, indicate that temperature may play an important role in regulating primary production (Neori and Holm-Hansen 1982; Tilzer and Dubinsky 1987). The relationship between these observed temperature effects and rates of pelagic production is poorly understood. Data collected during RACER suggest that the range of ambient water temperatures within our study area (-1.8 to +3.5°C) may lead to twofold variations in the chlorophyll a specific rates of production (figure 3). It may not be coincidental that the highest water temperatures observed during RACER correspond to the stations with highest phytoplankton biomass. Although nutrients in antarctic waters are generally considered to be in excess for phytoplankton requirements, during the RACER study nitrate concentrations as low as 1.0 micromole and ammonium concentrations as high as 10 micromoles were observed at stations with high biomass and high rates of production. Sustained levels of production at such localities may be possible only as a consequence of nutrient recycling through the combined effects of micro- and macrozooplankton grazing as discussed by Hewes, Holm-Hansen, and Sakshaug (1985). The implications of this component of the food web must be considered when extrapolating gross primary production to food resources available to macrozooplankton or krill. The field work was divided into period 1(6 December 1986 to 8 February 1987) and period II (8 February to 6 April 1987). RACER personnel on board ship included B.C. Mitchell, A.F. 144
Amos, R. Letelier, J . Price, and C. Stallings during period I, and 0. Holm-Hansen, D. Menzies, A. Olea, and P. Wade during period II. This research was supported by National Science Foundation grant DPP 85-19908. 3.8 3.6 3.4 3.2
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Figure 3. Maximum rate of photosynthesis over the temperature range encountered in the RACER study area. Data based on incorporation of carbon-14-bicarbonate over a 2-hour photosynthesisirradiance experiment. ("Pmax" denotes "maximum photosynthesis:' "mgC/mgChl;s,Hr" denotes "milligrams of carbon per milligram of chlorophyll per hour:') ANTARCTIC JOURNAL
References Dustan, P., R.J. Olson, and 0. Holm-Hansen. 1979. Phytoplankton studies in the Scotia Sea. Antarctic Journal of the U.S., 14(5), 158-159. Eppley, R.W., E. Stewart, M.R. Abbott, and U. Heyman. 1985. Estimating ocean primary production from satellite chlorophyll: Introduction to regional differences and statistics for the Southern California Bight. Journal of Plankton Research, 7, 57-70.
Hart, T.J. 1942. Phytoplankton periodicity in Antarctic surface waters. Discovery Reports, 21, 261-365.
Hayes, P., T. Whitaker, and C. Fogg. 1984. The distribution and nutrient status of phytoplankton in the Southern Ocean between 200 and 70°W. Polar Biology, 3, 153-165.
Hewes, C.D., 0. Holm-Hansen, and E. Sakshaug. 1985. Alternate car-
RACER: Optical prediction of photobiological properties B.C. MITCHELL and 0. HOLM-HANSEN Polar Research Program Scripps Institution of Oceanography University of California at San Diego La Jolla, California 92093
C. STALLINGS and D.A. KIEFER Department of Biological Sciences University of Southern California Los Angeles, California 90089-0377
Several hypotheses of the Research on Antarctic Coastal Ecosystem Rates (RACER) program require data on phytoplankton biomass and photosynthetic activity throughout the upper water column over a relatively large and heterogeneous area extending from shallow, inshore locations to deep, oceanic stations. (See Huntley et al. Antarctic Journal, this issue.) During our fieldwork in 1986-1987, we employed conventional techniques to document rates of primary production and phytoplankton biomass (see Holm-Hansen, Letelier, and Mitchell, Antarctic Journal, this issue) and also explored alternative methods to provide comparable data more synoptically and with less ship time. Optical sensors provide a powerful tool to monitor quantitatively phytoplankton properties in natural waters. Previous work in temperate and tropical waters (Mitchell 1987) indicates that optical properties are good predictors of phytoplankton chlorophyll a and the photoadaptative state of the phytoplankton. In order reliably to apply optical algorithms for biomass estimates or primary production to the antarctic coastal regions, traditional algorithms must be tested and verified. Several important aspects of the optical properties may be different from those in temperate waters, including the fraction of detrital absorption, the presence of glacial sediments, and pigment complements of cells. 1987 REVIEW
bon pathways at lower tropic levels in the Antarctic food web. In W. R. Siegfried, P.R. Condy, and R.M. Laws (Eds.), Antarctic nutrient cycles and food webs. Berlin: Springer-Verlag. Home, A., G. Fogg, and D. Eagle. 1969. Studies in situ of the primary reproduction of an area of inshore Antarctic sea. Journal of the Marine Biological Association of the United Kingdom, 49, 393-405.
Huntley, ME., D.M. Karl, P. Niiler, and 0. Holm-Hansen. 1987. RACER: An interdisciplinary field study. Antarctic Journal of the U.S., 22(5).
Neon, A., and 0. Holm-Hansen. 1982. Effect of temperature on rate of photosynthesis in Antarctic phytoplankton. Polar Biology, 1, 33-38. Tilzer, M., and A. Dubinsky. 1987. Effects of temperature and day length on the mass balance of Antarctic phytoplankton. Polar Biology, 7, 35-42.
During the RACER cruises in 1986-1987, in situ optical properties in the upper 200 meters of the water column were determined as described in Mitchell, Menzies, and Holm-Hansen (Antarctic Journal, this issue) and included downwelling irradiance (7 wavelengths), 2-'Tr downwelling irradiance (also termed photosynthetically available radiation), upwelling radiance (5 wavelengths), beam attenuation, and induced chlorophyll a fluorescence. Particulate optical properties included spectral absorption coefficients and excitation spectra of chlorophyll a fluorescence determined according to the procedures of Mitchell and Kiefer (1984). Extracted photosynthetic pigments were also measured by high-performance liquid chromatography techniques as described by Vernet (1983). Detailed spatial and temporal mapping of primary production is essential to test the central RACER hypotheses (Huntley et al., Antarctic Journal, this issue), but the traditional in situ radiocarbon techniques require long periods of ship time at each station. Recently, a few workers (Topliss and Platt 1986; Kiefer and Booth 1986) have begun examining and testing a new optical technique for measuring primary production. This technique involves determining the relationship between natural fluorescence or solar-induced fluorescence of chlorophyll a and gross primary production. Based on theoretical and laboratory studies on the relationship between natural fluorescence and photosynthesis, Kiefer and Booth (1986) have formulated equations which permit calculation of daily gross primary production at any depth from measurements of natural fluorescence at 683 nanometers and the flux of photosynthetically available radiation. The equations they have developed include terms for the quantum yields for photosynthesis and fluorescence. Preliminary studies suggest that the ratio of these quantum yields is fairly constant, in which case absolute values for these terms need not be derived for each sampling depth. Kiefer and Booth (1986) found a good correlation between measurements of L,,683 (upwelling radiance at 683 nanometers) throughout the euphotic zone and calculated gross primary production in tropical waters (Kiefer unpublished data). During the RACER studies, we measured all the essential parameters which are needed to evaluate this approach for future application in antarctic waters. Data in figure 1 indicate that the rate of measured primary production is linear with the natural fluorescence over the broad range of production rates observed. The linear regression fit to the data is significant (r2 = 0.8; n = 50; P < 0.05) but much variance is left 145
Tilzer, M.M., B. von Bodungen, and V. Smetacek. 1985. Light-dependence of phytoplankton photosynthesis in the Antarctic Ocean: Implications for regulating productivity. in W.R. Siegfried, P.R. Condy, and R.M. Laws (Eds.), Antarctic nutrient cycles and food webs. Berlin: Springer-Verlag.
RACER: Temporal and spatial distribution of phytoplankton biomass and primary production
rophyll a were extremely variable, ranging over two orders of magnitude from 0.2 to 20 milligrams per cubic meter. The deep waters to the northwest of the South Shetland Islands were low in chlorophyll a (less than 0.5 milligrams per cubic meter). Highest levels of phytoplankton pigments were found in protected embayments and in the vicinity of islands as predicted by the central hypotheses of RACER. (See Huntley et al., Antarctic Journal, this issue.) Furthermore, a pronounced seasonal trend is evident with the peak occurring in December and decreasing progressively from January through March. Preliminary examination of approximately 300 profiles of chlorophyll a concentration and of water density (-t) as recorded in the upper 200 meters of the water column by our profiling unit showed, first, that chlorophyll a is fairly uniformly distributed throughout the entire upper mixed layer and, second, that concentrations decrease rapidly below the pycnocline. Extracted chlorophyll a values from standard depths confirmed these observations, and are in agreement with similar conclusions first reported by Dustan, Olson, and Holm-Hansen (1979). Distribution maps of chlorophyll a in surface waters (figure 1) will thus show the same general patterns as maps showing spatial distribution of integrated chlorophyll a for the upper 200 meters. Hart (1942) first documented the rapid increase in phytoplankton biomass in antarctic waters during austral spring, followed by a rapid decline. Our time series from December 1986 to March 1987 of integrated water column production at five stations in the RACER grid is presented in figure 2a. The pronounced seasonality of these data emphasizes the importance of high-resolution sampling through a seasonal cycle. Peak bloom conditions were already evident in mid-December. This is considerably earlier than the phytoplankton peak reported near the South Orkney Islands by Home et al. (1969). During RACER we found that within our 25,000-square-kilometer study area, surface pigments and integrated production varied over a range equal to previous reports for the world's oceans. This is summarized in figure 2b where the data from RACER are superimposed upon a summary plot of integrated production as a function of surface phytoplankton pigments compiled by Eppley etal. (1985). Understanding the underlying mechanism of such dynamic range within antarctic coastal ecosystems is one of the goals of RACER. The rate of primary production will be a function of both the phytoplankton standing stock and phytoplankton specific growth rates. Of the major factors which affect phytoplankton growth rates, available data indicate that light is the most important. One focus of RACER is that high productivity in the area of the Antarctic Peninsula is caused by high mean light levels experienced by the phytoplankton due to relatively shallow and stable upper water mixed layers.
0. HOLM-HANSEN, R. LETELIER, and B.C. MITCHELL Polar Research Program Scripps Institution of Oceanography University of California at San Diego La Jolla, California 92093
The RACER program (Research on Antarctic Coastal Ecosystem Rates) is an interdisciplinary study which seeks to understand the dynamic mechanisms controlling the planktonic ecosystem structure of the Antarctic Peninsula coastal environment (see Huntley et al., Antarctic Journal, this issue). The photobiology component of this program is concerned with temporal and spatial dynamics of phytoplankton populations, especially in relation to physical mixing processes and the environmental factors influencing growth rates. At each "fast" grid station our physical-optical-biological profiling unit was deployed from 0 to 200 meters to give continuous recording of depth, temperature, conductivity, 2-'rr irradiance (400-700 nanometers), seven channels downwelling irradiance, five channels upwelling radiance, beam attenuation (transmissometer), and chlorophyll a fluorescence (fluorometer with pulsed blue activating light). Water samples were obtained in 5.0-liter, polyvinyl chloride Niskin bottles at eight standard depths during the "up" cast of the profiling unit, and the water was used for determination of chlorophyll a, particulate organic carbon and nitrogen, inorganic nutrient concentrations, and floristic examination. Surface water samples were also obtained by "bucket" in conjunction with the microbiology program and used to measure chlorophyll a in nanoplankton (less than 20 micrometers in diameter) and microplankton (more than 20 micrometers). During the "slow" grid stations the above measurements were supplemented with studies concerned with photoadaptational status of the phytoplankton, as well as with in situ primary productivity measurements using radiocarbon incorporation. During the in situ incubations (12-24 hours) numerous profiles of light attenuation in the upper 100 meters of the water column were obtained with our profiling unit so that total light flux at various depths could be calculated and used in quantum efficiency calculations. The reults of our time series of fast-grid surface chlorophyll distributions are presented in figure 1. Concentrations of chlo142
ANTARCTIC JOURNAL
7
TON ISLAND
9NGST N ISLAND
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Figure 1. Spatial distribution of chlorophyll a concentrations (in milligrams per cubic meter) in surface waters throughout the RACER grid of 69 stations for four surveys between December 1986 and March 1987. The concentrations ranged from over 20 milligrams per cubic meter (Gerlache Strait) to 0.2 milligram per cubic meter (Drake Passage). 1987 REVIEW
143
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DEC JAN FEB MAR Figure 2. Rates of primary production at RACER stations: A. Integrated daily production at individual stations from December, 1986, through March, 1987. ("N.D." denotes "no data," due to bad weather or ice. 11 gCIm 2 ;s,day" denotes "grams of carbon per square meter per day:' "St" denotes "station:') B. Integrated primary production (rr) from RACER stations (shown as solid squares) as a function of surface concentrations of chlorophyll a plus phaeopigment concentrations (C k). All other data shown in block B were compiled by Eppley el al. (1985) from data of the world's oceans reported in the literature. The open circle in the upper right represents the calculated limit value. (Tr is expressed as milligrams carbon per square meter per day, while C,, is expressed as milligrams of chlorophyll-a plus phaeopigment per cubic meter.)
Nutrients and temperature are generally ignored as controlling variables of antarctic primary production (Hayes, Whitaker, and Fogg 1984). Recent reports, however, indicate that temperature may play an important role in regulating primary production (Neori and Holm-Hansen 1982; Tilzer and Dubinsky 1987). The relationship between these observed temperature effects and rates of pelagic production is poorly understood. Data collected during RACER suggest that the range of ambient water temperatures within our study area (-1.8 to +3.5°C) may lead to twofold variations in the chlorophyll a specific rates of production (figure 3). It may not be coincidental that the highest water temperatures observed during RACER correspond to the stations with highest phytoplankton biomass. Although nutrients in antarctic waters are generally considered to be in excess for phytoplankton requirements, during the RACER study nitrate concentrations as low as 1.0 micromole and ammonium concentrations as high as 10 micromoles were observed at stations with high biomass and high rates of production. Sustained levels of production at such localities may be possible only as a consequence of nutrient recycling through the combined effects of micro- and macrozooplankton grazing as discussed by Hewes, Holm-Hansen, and Sakshaug (1985). The implications of this component of the food web must be considered when extrapolating gross primary production to food resources available to macrozooplankton or krill. The field work was divided into period 1(6 December 1986 to 8 February 1987) and period II (8 February to 6 April 1987). RACER personnel on board ship included B.C. Mitchell, A.F. 144
Amos, R. Letelier, J . Price, and C. Stallings during period I, and 0. Holm-Hansen, D. Menzies, A. Olea, and P. Wade during period II. This research was supported by National Science Foundation grant DPP 85-19908. 3.8 3.6 3.4 3.2
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Figure 3. Maximum rate of photosynthesis over the temperature range encountered in the RACER study area. Data based on incorporation of carbon-14-bicarbonate over a 2-hour photosynthesisirradiance experiment. ("Pmax" denotes "maximum photosynthesis:' "mgC/mgChl;s,Hr" denotes "milligrams of carbon per milligram of chlorophyll per hour:') ANTARCTIC JOURNAL
References Dustan, P., R.J. Olson, and 0. Holm-Hansen. 1979. Phytoplankton studies in the Scotia Sea. Antarctic Journal of the U.S., 14(5), 158-159. Eppley, R.W., E. Stewart, M.R. Abbott, and U. Heyman. 1985. Estimating ocean primary production from satellite chlorophyll: Introduction to regional differences and statistics for the Southern California Bight. Journal of Plankton Research, 7, 57-70.
Hart, T.J. 1942. Phytoplankton periodicity in Antarctic surface waters. Discovery Reports, 21, 261-365.
Hayes, P., T. Whitaker, and C. Fogg. 1984. The distribution and nutrient status of phytoplankton in the Southern Ocean between 200 and 70°W. Polar Biology, 3, 153-165.
Hewes, C.D., 0. Holm-Hansen, and E. Sakshaug. 1985. Alternate car-
RACER: Optical prediction of photobiological properties B.C. MITCHELL and 0. HOLM-HANSEN Polar Research Program Scripps Institution of Oceanography University of California at San Diego La Jolla, California 92093
C. STALLINGS and D.A. KIEFER Department of Biological Sciences University of Southern California Los Angeles, California 90089-0377
Several hypotheses of the Research on Antarctic Coastal Ecosystem Rates (RACER) program require data on phytoplankton biomass and photosynthetic activity throughout the upper water column over a relatively large and heterogeneous area extending from shallow, inshore locations to deep, oceanic stations. (See Huntley et al. Antarctic Journal, this issue.) During our fieldwork in 1986-1987, we employed conventional techniques to document rates of primary production and phytoplankton biomass (see Holm-Hansen, Letelier, and Mitchell, Antarctic Journal, this issue) and also explored alternative methods to provide comparable data more synoptically and with less ship time. Optical sensors provide a powerful tool to monitor quantitatively phytoplankton properties in natural waters. Previous work in temperate and tropical waters (Mitchell 1987) indicates that optical properties are good predictors of phytoplankton chlorophyll a and the photoadaptative state of the phytoplankton. In order reliably to apply optical algorithms for biomass estimates or primary production to the antarctic coastal regions, traditional algorithms must be tested and verified. Several important aspects of the optical properties may be different from those in temperate waters, including the fraction of detrital absorption, the presence of glacial sediments, and pigment complements of cells. 1987 REVIEW
bon pathways at lower tropic levels in the Antarctic food web. In W. R. Siegfried, P.R. Condy, and R.M. Laws (Eds.), Antarctic nutrient cycles and food webs. Berlin: Springer-Verlag. Home, A., G. Fogg, and D. Eagle. 1969. Studies in situ of the primary reproduction of an area of inshore Antarctic sea. Journal of the Marine Biological Association of the United Kingdom, 49, 393-405.
Huntley, ME., D.M. Karl, P. Niiler, and 0. Holm-Hansen. 1987. RACER: An interdisciplinary field study. Antarctic Journal of the U.S., 22(5).
Neon, A., and 0. Holm-Hansen. 1982. Effect of temperature on rate of photosynthesis in Antarctic phytoplankton. Polar Biology, 1, 33-38. Tilzer, M., and A. Dubinsky. 1987. Effects of temperature and day length on the mass balance of Antarctic phytoplankton. Polar Biology, 7, 35-42.
During the RACER cruises in 1986-1987, in situ optical properties in the upper 200 meters of the water column were determined as described in Mitchell, Menzies, and Holm-Hansen (Antarctic Journal, this issue) and included downwelling irradiance (7 wavelengths), 2-'Tr downwelling irradiance (also termed photosynthetically available radiation), upwelling radiance (5 wavelengths), beam attenuation, and induced chlorophyll a fluorescence. Particulate optical properties included spectral absorption coefficients and excitation spectra of chlorophyll a fluorescence determined according to the procedures of Mitchell and Kiefer (1984). Extracted photosynthetic pigments were also measured by high-performance liquid chromatography techniques as described by Vernet (1983). Detailed spatial and temporal mapping of primary production is essential to test the central RACER hypotheses (Huntley et al., Antarctic Journal, this issue), but the traditional in situ radiocarbon techniques require long periods of ship time at each station. Recently, a few workers (Topliss and Platt 1986; Kiefer and Booth 1986) have begun examining and testing a new optical technique for measuring primary production. This technique involves determining the relationship between natural fluorescence or solar-induced fluorescence of chlorophyll a and gross primary production. Based on theoretical and laboratory studies on the relationship between natural fluorescence and photosynthesis, Kiefer and Booth (1986) have formulated equations which permit calculation of daily gross primary production at any depth from measurements of natural fluorescence at 683 nanometers and the flux of photosynthetically available radiation. The equations they have developed include terms for the quantum yields for photosynthesis and fluorescence. Preliminary studies suggest that the ratio of these quantum yields is fairly constant, in which case absolute values for these terms need not be derived for each sampling depth. Kiefer and Booth (1986) found a good correlation between measurements of L,,683 (upwelling radiance at 683 nanometers) throughout the euphotic zone and calculated gross primary production in tropical waters (Kiefer unpublished data). During the RACER studies, we measured all the essential parameters which are needed to evaluate this approach for future application in antarctic waters. Data in figure 1 indicate that the rate of measured primary production is linear with the natural fluorescence over the broad range of production rates observed. The linear regression fit to the data is significant (r2 = 0.8; n = 50; P < 0.05) but much variance is left 145
