Phytoplankton distribution, biomass, and activity in the
References
Amos, A. F. 1975. Physical oceanography from the arctic pack ice: Project A1DJEX STD programs. In W. R. Danielson (Ed.), Proceedings of the Third STD Conference and Workshop (San Diego, California, 2-5 February 1975). San Diego: Plessey Environmental Systems, Plessey
Publications.
Amos, A. F. 1982. Physical oceanography of the southwestern Ross Sea, January 1982. Antarctic Journal of the U.S., 17(5). Biggs, D. C. 1982. Ross Sea ammonium flux experiment. Antarctic Journal of the U.S., 17(5). Jacobs, S. S., Gordon, A. L., and Ardai, J. L. 1979. Circulation and melting beneath the Ross Ice Shelf. Science, 203, 439-443. Johnson, M. 1981. Pumped profiles of a tit moniii in and chlorophyll fluorescence from the upper 120 meters of the western Gulf of Mexico and the southwest Scotia Sea. Unpublished master's thesis, Texas A&M University.
Phytoplankton distribution, biomass, and activity in the southwest Ross Sea
STATION NO.
0
24 25
26 27 28 29
40
0. HOLM-HANSEN, A. NE0RI, and I. K0IKE*
80 E
Scripps Institution of Oceanography University of California La Jolla, California 92093
I0 LLJ
20 160 200
Our work on the USCGC Glacier in January 1982 had three basic objectives: to obtain data relevant to the ammonium flux experiment as described by Biggs (Antarctic Journal, this issue); to continue our investigation of physiological adaptations of phytoplankton to environmental conditions; and to increase our understanding of the dynamics of the initial stages of the food web in antarctic waters. Water samples were obtained at 26 stations in open water northeast of Ross Island; in addition, samples were taken from the surface to 130 meters, by means of a profiling pump system, at eight locations along the drift track of a drogued surface buoy (see Biggs, figure 1, for station locations). Phytoplankton distribution and biomass. Recent work (Glibert, Biggs, and McCarthy 1982; Koike, Rönner, and Holm-Hansen 1981; Olson 1980) has shown that 50 to 90 percent of the nitrogen assimilated by phytoplankton in the Antarctic is derived from ammonia. Most of the remainder is furnished by nitrate, but urea, nitrite, and dissolved organic compounds also are used. Although ammonia is the preferred nitrogenous nutrient for antarctic phytoplankton, it is not known if ammonia has a significant effect on either the rate of primary production or species composition. During the ammonium flux experiment, we wanted to determine the distribution, biomass, and species composition of the phytoplankton crop relative to the availability of ammonia.
*Permanent address: Ocean Research Institute, University of Tokyo, Nakamo, Tokyo 164, Japan. 150
240
0
5 4
40 80 120 160 200
240 50 40 30 20 10 0 DISTANCE (km)
Figure 1. Contours of chlorophyll a (micrograms per liter) along transects centered on 1 69°E longitude (upper section) and on 1730E longitude (lower section). Arrows to the right of each section indicate approximate depth of the Ross Ice Shelf, which was a few hundred meters to the south of stations 1 and about 16 kilometers from station 29. Shaded area denotes absence of bottle samples.
ANTARCTIC JOURNAL
Chlorophyll and phaeophytin were determined by fluorometric techniques at 12 depths at all of the stations. Phytoplankton biomass was highest at the two eastern transects and lowest at the westernmost transect. From east to west, the average chlorophyll a concentration in the upper 60 meters of the water column of the four transects averaged 0. 9, 1.1, 0.5, and 0.25 microgram per liter. Chlorophyll concentrations in the upper 250 meters for two of these sections (stations 1-7 and 24-29) are shown in figure 1. Data for stations 1-7 (figure 1, lower section) and 8-15 revealed a zone of high chlorophyll concentration centered at a depth of about 150 meters; this was well below the euphotic zone, which averaged 30-40 meters for these sections. Water samples were preserved with Lugol's iodine solution at many of our stations for floristic analysis by inverted microscope techniques. The biomass and species composition of the
phytoplankton crop will be anlayzed with regard to the distribution of nutrients and to physical data from the four sections (see Amos, Antarctic Journal, this issue). Carbon and nitrogen metabolism. Water samples were obtained at stations 8, 10, 23, 29, and at both "pump" stations (stations 16-18 and 30-34) for metabolic studies using both radiocarbon ( 14C) and the stable isotope of nitrogen ( 15 N). Sampling depths were approximately 2 meters, 10-20 meters (10 percent light level), and 30-50 meters (3 percent light level). Water samples for 15 N and 14 C studies were obtained from the same 30-liter Niskin bottle. Experiments were done in identical incubation vessels (either 1.0-liter borosilicate glass or 4.0-liter polycarbonate bottles) and incubated together in temperature- and lightcontrolled incubation units on the forward deck of the ship. Solar radiation (400 to 700 nanometers) was monitored
0.7
0.7
0.6
0.6
0
1\
FLU 0 z
(DARK)
AIN
0.5
LU
0
(1)
Ui
0 -J Li
\
TIME 0 0.4
\ / \ /
0.4
—\O
\/
20 40 60 80 100
(DARK)
03I I I 1 I I 0 20 40 60 80 100
DEPTH (m) I I I I 102 10' I 10' 102
l(
10 2 10' I 10' 102 10-3
LIGHT INTENSITY (% INCIDENT) Figure 2. Physiological adaptation of phytoplankton cells to varying light intensities as indicated by relative effectiveness of blue and green light in activating in vivo chlorphyll a fluorescence. The ordinate (fluorescence ratio) is defined as the fluorescence induced by green light (475-575 nanometers) divided by the fluorescence induced by blue light (350-450 nanometers). A: The fluorescence ratio of cells pumped from the upper 100 meters (continuous line), and that determined on discrete samples taken from Niskin bottles (dashed line). B: Time response of the change in the fluorescence ratio of cells (surface sample) when exposed to varying light intensities.
1982 REVIEW
151
continuously with a deck-mounted scalar irradiance quantum meter; the light flux within the experimental bottles was measured with a small, integrating irradiance meter. Total particulate organic carbon and nitrogen were measured in all water samples by CHN gas chromatographic techiques. Experiments with 13N-enriched substrates included (1) absolute nitrogen uptake rates from ammonia, nitrate, and urea as a function of light intensity, (2) time sequence of assimilation between 6 and 80 hours, and (3) uptake rates in size-fractionated samples (less than 10 micrometers, less than 75 micrometers, and unfractionated sample). The radiocarbon experiments were identical to the nitrogen experiments except that 14C-bicarbonate was used instead of the 15N-enriched nitrogen substrates. Chlorophyll also was measured in all samples, so that carbon and nitrogen assimilation rates can be expressed as a function of both chlorophyll concentration and absolute light flux incident upon the cells. All 15N samples will be processed by mass spectrometry at the University of Tokyo (by I. Koike) in late 1982. Phytoplankton adaptation to varying light intensity. The upper mixed layer in antarctic waters often extends much deeper than the euphotic zone. Hasle (1956) suggested that this limits phytoplankton biomass and primary production, since cells will be mixed below the euphotic zone. To assess the importance of this phenomenon, it is necessary to know something about the rate at which cells are "circulating" within the mixed layer. We have measured the in vivo action spectra for chlorophyll a fluorescence of cells from various depths in the water column to help determine both residence time at depth and physiological adaptations to the existing light fields. Previous experiments in the Scotia Sea and in coastal California waters (Neori et al. 1982) have indicated that cells from deep in the euphotic zone use green light for photosynthesis more effectively than do cells from surface waters. During the two "pump" stations in the Ross Sea, we passed the pumped water (0 to 130 meters depth) through two fluorometers, one having excitation light peaking in the blue portion of the spectrum (about 440 nanometers) and the other, in the green portion of the spectrum (about 550 nanometers). Data from both instruments were recorded and processed by a desktop computer to give us an index of how efficiently blue and green light activate chlorophyll a fluorescence. Cells from 20-50 meters depth show much more chlorophyll a fluorescence by green light than do cells from surface waters, (figure 2A, page 151, solid line). During the pumped profile, water samples were taken at six depths, filtered onto glass fiber filters, frozen, and returned to our laboratories at Scripps Institution of Oceanography for determination of corrected action spectra for chlorophyll a fluorescence in a recording spectrofluorometer. The results (figure 2A, dashed line) also show increasing use of green light by deeper samples, followed by a decline at depths below the light-compensation point. We do not know how long it takes for cells to show this "green light" adaptation in regard to activation of chlorophyll fluores-
152
cence. As a start on this problem, we took surface water from the first pump station and incubated subsamples at five different light intensities as well as at "no light." After 9 and 43 hours in the deck incubators, samples were filtered and the action spectra for chlorophyll fluorescence were determined in the same manner as were the discrete samples shown in figure 2A. A significant response was detected after 9 hours of incubation, but the response was much greater after 43 hours (see figure 2B). Data from such culture experiments, coupled with data on the action spectra for cells in the upper water column, should provide some limits for the rate at which phytoplankton cells are "circulating" in the mixed layer. Microzooplankton sampling. One of the unanswered questions regarding the food web structure and nutrient cycling in the Antarctic is the role of microzooplankton. To define microzooplankton abundance and population structure, samples were collected by the method used by Beers, Reid, and Stewart (1975) at 10- or 25-meter intervals from the surface to 100 meters at the two "pump" stations. These samples have been delivered to John R. Beers at Scripps Institution of Oceanography for analysis. Participants on the ship included 0. Holm-Hansen, I. Koike, A. Neori, and C. D. Hewes. We thank Texas A&M University personnel for processing the computer-drawn plots in figure 1. This research was supported by National Science Foundation grant DPP 80-20242.
References Amos, A. F. 1982. Physical oceanography of the southwestern Ross Sea, January 1982. Antarctic Journal of the U.S., 17(5). Beers, J. R., Reid, F. M. H., and Stewart, G. L. 1975. Microplankton of the North Pacific Central Gyre. Population structure and abundance, June 1973. International revue der gesamten hydrobiolagie, 60(5), 607-638. Biggs, D. C. 1982. Ross Sea ammonium flux experiment. Antarctic Journal of the U.S., 17(5). Glibert, P. M., Biggs, D. C., and McCarthy, J . J. 1982. Uptake of ammonium and nitrate during austral summer in the Scotia Sea. DeepSea Research, 29(7a), 837-850. Hasle, G. R. 1956. Phytoplankton and hydrography of the Pacific part of the antarctic ocean. Nature, 177, 616-617. Koike, I., Rönner, U., and Holm-Hansen, 0. 1981. Microbial nitrogen metabolism in the Scotia Sea. Antarctic Journal of the U.S., 16(5), 165-166. Neon, A., Mitchell, B. G., SooHoo, J . , Kiefer, D. A., and Holm-Hansen, 0. 1982. Increased efficiency of energy transfer from accessory pigments to chlorophyll-a in phytoplankton, with depth: An adaptation to changing light conditions or reaction to environmental stress? EOS, Transactions of the American Geophysical Union, 63(3), 96. (Abstract) Olson, R. J . 1980. Nitrate and ammonium uptake in antarctic waters. Limnology and Oceanography, 25(6), 1064-1074.
ANTARCTIC JOURNAL
Amos, A. F. 1975. Physical oceanography from the arctic pack ice: Project A1DJEX STD programs. In W. R. Danielson (Ed.), Proceedings of the Third STD Conference and Workshop (San Diego, California, 2-5 February 1975). San Diego: Plessey Environmental Systems, Plessey
Publications.
Amos, A. F. 1982. Physical oceanography of the southwestern Ross Sea, January 1982. Antarctic Journal of the U.S., 17(5). Biggs, D. C. 1982. Ross Sea ammonium flux experiment. Antarctic Journal of the U.S., 17(5). Jacobs, S. S., Gordon, A. L., and Ardai, J. L. 1979. Circulation and melting beneath the Ross Ice Shelf. Science, 203, 439-443. Johnson, M. 1981. Pumped profiles of a tit moniii in and chlorophyll fluorescence from the upper 120 meters of the western Gulf of Mexico and the southwest Scotia Sea. Unpublished master's thesis, Texas A&M University.
Phytoplankton distribution, biomass, and activity in the southwest Ross Sea
STATION NO.
0
24 25
26 27 28 29
40
0. HOLM-HANSEN, A. NE0RI, and I. K0IKE*
80 E
Scripps Institution of Oceanography University of California La Jolla, California 92093
I0 LLJ
20 160 200
Our work on the USCGC Glacier in January 1982 had three basic objectives: to obtain data relevant to the ammonium flux experiment as described by Biggs (Antarctic Journal, this issue); to continue our investigation of physiological adaptations of phytoplankton to environmental conditions; and to increase our understanding of the dynamics of the initial stages of the food web in antarctic waters. Water samples were obtained at 26 stations in open water northeast of Ross Island; in addition, samples were taken from the surface to 130 meters, by means of a profiling pump system, at eight locations along the drift track of a drogued surface buoy (see Biggs, figure 1, for station locations). Phytoplankton distribution and biomass. Recent work (Glibert, Biggs, and McCarthy 1982; Koike, Rönner, and Holm-Hansen 1981; Olson 1980) has shown that 50 to 90 percent of the nitrogen assimilated by phytoplankton in the Antarctic is derived from ammonia. Most of the remainder is furnished by nitrate, but urea, nitrite, and dissolved organic compounds also are used. Although ammonia is the preferred nitrogenous nutrient for antarctic phytoplankton, it is not known if ammonia has a significant effect on either the rate of primary production or species composition. During the ammonium flux experiment, we wanted to determine the distribution, biomass, and species composition of the phytoplankton crop relative to the availability of ammonia.
*Permanent address: Ocean Research Institute, University of Tokyo, Nakamo, Tokyo 164, Japan. 150
240
0
5 4
40 80 120 160 200
240 50 40 30 20 10 0 DISTANCE (km)
Figure 1. Contours of chlorophyll a (micrograms per liter) along transects centered on 1 69°E longitude (upper section) and on 1730E longitude (lower section). Arrows to the right of each section indicate approximate depth of the Ross Ice Shelf, which was a few hundred meters to the south of stations 1 and about 16 kilometers from station 29. Shaded area denotes absence of bottle samples.
ANTARCTIC JOURNAL
Chlorophyll and phaeophytin were determined by fluorometric techniques at 12 depths at all of the stations. Phytoplankton biomass was highest at the two eastern transects and lowest at the westernmost transect. From east to west, the average chlorophyll a concentration in the upper 60 meters of the water column of the four transects averaged 0. 9, 1.1, 0.5, and 0.25 microgram per liter. Chlorophyll concentrations in the upper 250 meters for two of these sections (stations 1-7 and 24-29) are shown in figure 1. Data for stations 1-7 (figure 1, lower section) and 8-15 revealed a zone of high chlorophyll concentration centered at a depth of about 150 meters; this was well below the euphotic zone, which averaged 30-40 meters for these sections. Water samples were preserved with Lugol's iodine solution at many of our stations for floristic analysis by inverted microscope techniques. The biomass and species composition of the
phytoplankton crop will be anlayzed with regard to the distribution of nutrients and to physical data from the four sections (see Amos, Antarctic Journal, this issue). Carbon and nitrogen metabolism. Water samples were obtained at stations 8, 10, 23, 29, and at both "pump" stations (stations 16-18 and 30-34) for metabolic studies using both radiocarbon ( 14C) and the stable isotope of nitrogen ( 15 N). Sampling depths were approximately 2 meters, 10-20 meters (10 percent light level), and 30-50 meters (3 percent light level). Water samples for 15 N and 14 C studies were obtained from the same 30-liter Niskin bottle. Experiments were done in identical incubation vessels (either 1.0-liter borosilicate glass or 4.0-liter polycarbonate bottles) and incubated together in temperature- and lightcontrolled incubation units on the forward deck of the ship. Solar radiation (400 to 700 nanometers) was monitored
0.7
0.7
0.6
0.6
0
1\
FLU 0 z
(DARK)
AIN
0.5
LU
0
(1)
Ui
0 -J Li
\
TIME 0 0.4
\ / \ /
0.4
—\O
\/
20 40 60 80 100
(DARK)
03I I I 1 I I 0 20 40 60 80 100
DEPTH (m) I I I I 102 10' I 10' 102
l(
10 2 10' I 10' 102 10-3
LIGHT INTENSITY (% INCIDENT) Figure 2. Physiological adaptation of phytoplankton cells to varying light intensities as indicated by relative effectiveness of blue and green light in activating in vivo chlorphyll a fluorescence. The ordinate (fluorescence ratio) is defined as the fluorescence induced by green light (475-575 nanometers) divided by the fluorescence induced by blue light (350-450 nanometers). A: The fluorescence ratio of cells pumped from the upper 100 meters (continuous line), and that determined on discrete samples taken from Niskin bottles (dashed line). B: Time response of the change in the fluorescence ratio of cells (surface sample) when exposed to varying light intensities.
1982 REVIEW
151
continuously with a deck-mounted scalar irradiance quantum meter; the light flux within the experimental bottles was measured with a small, integrating irradiance meter. Total particulate organic carbon and nitrogen were measured in all water samples by CHN gas chromatographic techiques. Experiments with 13N-enriched substrates included (1) absolute nitrogen uptake rates from ammonia, nitrate, and urea as a function of light intensity, (2) time sequence of assimilation between 6 and 80 hours, and (3) uptake rates in size-fractionated samples (less than 10 micrometers, less than 75 micrometers, and unfractionated sample). The radiocarbon experiments were identical to the nitrogen experiments except that 14C-bicarbonate was used instead of the 15N-enriched nitrogen substrates. Chlorophyll also was measured in all samples, so that carbon and nitrogen assimilation rates can be expressed as a function of both chlorophyll concentration and absolute light flux incident upon the cells. All 15N samples will be processed by mass spectrometry at the University of Tokyo (by I. Koike) in late 1982. Phytoplankton adaptation to varying light intensity. The upper mixed layer in antarctic waters often extends much deeper than the euphotic zone. Hasle (1956) suggested that this limits phytoplankton biomass and primary production, since cells will be mixed below the euphotic zone. To assess the importance of this phenomenon, it is necessary to know something about the rate at which cells are "circulating" within the mixed layer. We have measured the in vivo action spectra for chlorophyll a fluorescence of cells from various depths in the water column to help determine both residence time at depth and physiological adaptations to the existing light fields. Previous experiments in the Scotia Sea and in coastal California waters (Neori et al. 1982) have indicated that cells from deep in the euphotic zone use green light for photosynthesis more effectively than do cells from surface waters. During the two "pump" stations in the Ross Sea, we passed the pumped water (0 to 130 meters depth) through two fluorometers, one having excitation light peaking in the blue portion of the spectrum (about 440 nanometers) and the other, in the green portion of the spectrum (about 550 nanometers). Data from both instruments were recorded and processed by a desktop computer to give us an index of how efficiently blue and green light activate chlorophyll a fluorescence. Cells from 20-50 meters depth show much more chlorophyll a fluorescence by green light than do cells from surface waters, (figure 2A, page 151, solid line). During the pumped profile, water samples were taken at six depths, filtered onto glass fiber filters, frozen, and returned to our laboratories at Scripps Institution of Oceanography for determination of corrected action spectra for chlorophyll a fluorescence in a recording spectrofluorometer. The results (figure 2A, dashed line) also show increasing use of green light by deeper samples, followed by a decline at depths below the light-compensation point. We do not know how long it takes for cells to show this "green light" adaptation in regard to activation of chlorophyll fluores-
152
cence. As a start on this problem, we took surface water from the first pump station and incubated subsamples at five different light intensities as well as at "no light." After 9 and 43 hours in the deck incubators, samples were filtered and the action spectra for chlorophyll fluorescence were determined in the same manner as were the discrete samples shown in figure 2A. A significant response was detected after 9 hours of incubation, but the response was much greater after 43 hours (see figure 2B). Data from such culture experiments, coupled with data on the action spectra for cells in the upper water column, should provide some limits for the rate at which phytoplankton cells are "circulating" in the mixed layer. Microzooplankton sampling. One of the unanswered questions regarding the food web structure and nutrient cycling in the Antarctic is the role of microzooplankton. To define microzooplankton abundance and population structure, samples were collected by the method used by Beers, Reid, and Stewart (1975) at 10- or 25-meter intervals from the surface to 100 meters at the two "pump" stations. These samples have been delivered to John R. Beers at Scripps Institution of Oceanography for analysis. Participants on the ship included 0. Holm-Hansen, I. Koike, A. Neori, and C. D. Hewes. We thank Texas A&M University personnel for processing the computer-drawn plots in figure 1. This research was supported by National Science Foundation grant DPP 80-20242.
References Amos, A. F. 1982. Physical oceanography of the southwestern Ross Sea, January 1982. Antarctic Journal of the U.S., 17(5). Beers, J. R., Reid, F. M. H., and Stewart, G. L. 1975. Microplankton of the North Pacific Central Gyre. Population structure and abundance, June 1973. International revue der gesamten hydrobiolagie, 60(5), 607-638. Biggs, D. C. 1982. Ross Sea ammonium flux experiment. Antarctic Journal of the U.S., 17(5). Glibert, P. M., Biggs, D. C., and McCarthy, J . J. 1982. Uptake of ammonium and nitrate during austral summer in the Scotia Sea. DeepSea Research, 29(7a), 837-850. Hasle, G. R. 1956. Phytoplankton and hydrography of the Pacific part of the antarctic ocean. Nature, 177, 616-617. Koike, I., Rönner, U., and Holm-Hansen, 0. 1981. Microbial nitrogen metabolism in the Scotia Sea. Antarctic Journal of the U.S., 16(5), 165-166. Neon, A., Mitchell, B. G., SooHoo, J . , Kiefer, D. A., and Holm-Hansen, 0. 1982. Increased efficiency of energy transfer from accessory pigments to chlorophyll-a in phytoplankton, with depth: An adaptation to changing light conditions or reaction to environmental stress? EOS, Transactions of the American Geophysical Union, 63(3), 96. (Abstract) Olson, R. J . 1980. Nitrate and ammonium uptake in antarctic waters. Limnology and Oceanography, 25(6), 1064-1074.
ANTARCTIC JOURNAL
