AMLR program: Depletion of inorganic nutrients in the ...
in the UML (0 to 50 m; figure 3A). The high phytoplankton biomass below the UML was also reflected in the rate at which instantaneous production decreased with depth. In contrast to data in figures 1 and 2, the rates of primary production between 25 to 75 m remained relatively high as compared to values in the upper 25 m of the water column (figure 3B). Evidence for high phytoplankton biomass between 50 and 100 m is also seen in the increased rates of attenuation of solar radiation with depth. The 1 percent light level for this station was about 95 m. The above results are consistent with other data acquired throughout the AMLR sampling grid on the distribution of phytoplankton as determined by microscopic methods (Villafane et al., Antarctic Journal, in this issue) and on rates of primary production as estimated by radiocarbon techniques (Holm-Hansen, Villafañe, and Heibling 1994). It has been suggested (Holm-Hansen et al. 1994) that this dramatic difference in distribution of phytoplankton in the upper water column between Drake Passage and Bransfield Strait waters is due to iron limitation in the UML of stations in Drake Passage waters. This work was supported by National Oceanic and Atmospheric Administration (NOAA) Cooperative Agreement number NA47FR0030. We thank the officers and crew of the NOAA ship Surveyor for excellent support during the field operations. We also thank Virginia Villafane, Humberto DIaz, Christian Bonert, Pedro BarOn, and Marcel Ramos for help
onboard ship. Shipboard personnel included E. Walter Helbling (13 January to 9 February) and Osmund Holm-Hansen (14 February to 15 March).
References Amos, A.F., and M.K. Lavender. 1992. AMLR program: Dynamics of the summer hydrographic regime at Elephant Island. Antarctic Journal of the U.S., 27(5), 228-230. Chamberlin, W.S., C.R. Booth, D.A. Kiefer, J.H. Morrow, and R.C. Murphy. 1990. Evidence for a simple relationship between natural fluorescence, photosynthesis and chlorophyll in the sea. Deep-Sea Research, 37(6), 951-973. Holm-Hansen, 0., A.F. Amos, N. Silva S., V.E. Villafañe, and E.W. Helbling. 1994. In situ evidence for a nutrient limitation of phytoplankton growth in pelagic antarctic waters. Antarctic Science, 6(3), 315-324. Holm-Hansen, 0., V.E. Villafane, and E.W. Helbling. 1994. AMLR program: Photobiological characteristics of phytoplankton around Elephant Island, Antarctica. Antarctic Journal of the U.S., 29(5). Rosenberg, J.E., R.P. Hewitt, and R.S. Holt. 1994. The U.S. Antarctic Marine Living Resources (AMLR) program: 1993-1994 field season activities. Antarctic Journal of the U.S., 29(5). Silva S., N., E.W. Helbling, V.E. Villafane, A.F. Amos, and 0. HolmHansen. In press. Variability in nutrient concentrations around Elephant Island, Antarctica, during 1991-1993. Polar Research. Villafañe, V.E., E.W. Helbling, 0. Holm-Hansen, and H. DIaz. 1994. AMLR Program: Phytoplankton distribution and species composition around Elephant Island, Antarctica, January to March 1994. Antarctic Journal of the U.S., 29(5).
AMLR program: Depletion of inorganic nutrients in the area around Elephant Island, Antarctica NELSON SILVA S. and MARCEL RAMOS, Escuela de Ciencias del Mar, Universidad Católica de Valparaiso, Valparaiso, Chile
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
shaken, and discarded two times. The 60-milliliter bottles were then filled approximately three-fourths full with water from the 10-liter Niskin bottles and frozen (-20°C) immediately. The samples were kept frozen until analyses (1-2 months after collection), which were performed at the Universidad CatOlica de Valparaiso, Chile, using an autoanalyzer and employing the technique described by Atlas et al. (1971). Nitrate concentrations at 5 meters depth were high during Survey A: values ranged from about 22.3 to more than 29 micromolar (tM) (figure 1A). During Survey D, nitrogen values decreased in the area to the south and southeast of King George Island and also in the area between King George Island and Elephant Island (figure 1B), but nitrate concentrations increased in coastal waters around King George Island, as well as in deep waters to the north of the island. Nitrate concentrations during Survey D ranged from 20 to 34 tiM. Phosphate concentrations at 5 meters depth varied from 1.65 to more than 2.1 tM during Survey A (figure 2A). Rela-
norganic nutrient concentrations are generally high in I antarctic waters, but significant depletions of nitrogen, phosphorus, and silicic acid have been documented in coastal areas where large phytoplankton blooms occurred (Nelson and Smith 1986; Holm-Hansen and Mitchell 1991). In this paper, we report the concentrations of these inorganic nutrients from January to March 1994 in a large sampling grid around Elephant Island. The grid included both coastal and pelagic stations. The cruise track and station positions are given in Rosenberg, Hewitt, and Holt (Antarctic Journal, in this issue). As one component of the phytoplankton studies of the Antarctic Marine Living Resources (AMLR) program, samples for determination of nutrient concentrations were obtained at each station, during both Legs I and II, using 10-liter Niskin bottles mounted on the rosette profiling system. Water from the Niskin bottles was poured directly into 60-milliliter, clean (soaked in 1.0 normal hydrochloric acid) polyethylene bottles,
ANTARCTIC JOURNAL - REVIEW 1994
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60
A
23-24.6
-
60.5
61
V a)
24.626.9
61.5
4 26.9-'
26.929 62 62.5k 5958
57 56 55 54 53
Longitude (W)
rigure 1. Nitrate concentrations (IJ.M) at 5 meters depth in waters around Elephant Island. A. Data from Survey A (17-28 January 1994). B. Data from Survey D (25 February to 9 March 1994).
t-igure z. 1-'riospFiate concentrations (riM) at 5 meters depth in waters around Elephant Island. A. Data from Survey A (17-28 January 1994). B. Data from Survey D (25 February to 9 March 1994). tively high values were found around King George, Elephant, and Clarence Islands. There was a general decrease in phosphate concentrations between Legs I and II over most of the sampling grid, with the most dramatic decrease being in the area south of King George Island, where concentrations ranged from 1.2 to 1.35 tM. This area with maximum phosphate depletion was, in general, similar to the area with maximum nitrate depletion (figure 1B). Silicic acid concentrations were generally low in Drake Passage waters, with values less than 30 i.tM (figure 3). Highest concentrations of silicic acid were observed in the southern portion of the sampling grid. Although the ranges of concentrations of silicic acid were quite similar between Surveys A and D, less than 30 to 80 tM, a general decrease in concentrations was observed between Legs I to II over most of the sampling grid (figures 3A and 3B).
The molar ratios of silicic acid/nitrogen/phosphate for all the data obtained at 5 meters depth were 31.2/13.7/1 for Survey A and 34.4/16.1/1 for Survey D, with the nitrogen/phosphate ratio being close to the theoretical value of 16 (Redfield, Ketchum, and Richards 1963, pp. 26-77). The general distribution of inorganic nutrients is in agreement with previous studies in the area (Silva et al. in press). Silicic acid concentrations during AMLR 1994, however, showed a smaller range than the concentrations found during the AMLR 1993 field season (20 to 108 Silva et al. 1993). The nitrogen/phosphate ratio did not show any significant difference between the two seasons. Although a general decrease in nutrient concentrations was observed throughout the sampling grid for all three nutrients analyzed, the relative depletion was greater in phosphate and silicic acid concentrations than for nitrate. This suggests
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Figure 3. Silicic acid concentrations (iA at 5 meters depth in waters around Elephant Island. Data from Survey D (25 February to 9 March 1994). that other forms of nitrogen, such as ammonium, could have an important role in the nutrient uptake by phytoplankton as suggested by Koike, Holm-Hansen, and Biggs (1986). The decrease in nutrient concentrations between Legs I and II, throughout such a large sampling area, is thought to be related to a general increase of phytoplankton biomass, because Villafañe et al. (Antarctic Journal, in this issue) have reported an extensive bloom of phytoplankton during Leg II. This large bloom has integrated values of chlorophyll-a (chl-a) (0 to 100 meters) of more than 200 milligrams chl-a per square meter (mg chl-a rn-2). Our complete nutrient data set will be analyzed together with other information such as phytoplankton biomass and rates of primary production to obtain estimates of rates of nutrient assimilation and recycling in the AMLR study area. This work was supported by National Oceanic and Atmospheric Administration (NOAA) Cooperative Agreement number NA47FR0030. We thank the officers and crew of the NOAA ship Surveyor for excellent support during the field operations. We also thank Noé Cáceres and Maria Angdlica Varas for their help on chemical analyses and data processing and Virginia Villafane, Humberto DIaz, Pedro BarOn, and Christian Bonert for help onboard ship. Shipboard personnel included E. Walter Heibling (13 January to 9 February), Marcel Ramos (13 January to 15 March), and Osmund HolmHansen (14 February to 15 March).
A.
Data from Survey A (17-28 January 1994).
B.
References Atlas, E.L., L.I. Gordon, S.W. Hager, and P.K. Park. 1971. A practical
manual for the use of the Technicon Autoanalyzer in seawater nutrient analyses, rev. ed. (Technical Report 71-22). Corvallis: Ore-
gon State University, Department of Oceanography. Holm-Hansen, 0., and B.G. Mitchell. 1991. Spatial and temporal distribution of phytoplankton and primary production in the western Bransfield Strait region. Deep-Sea Research, 38(8/9), 961-980. Koike, I., 0. Holm-Hansen, and D.C. Biggs. 1986. Inorganic nitrogen metabolism by antarctic phytoplankton with special reference to ammonium cycling. Marine Ecology Progress Series, 30(2), 105-116. Nelson, D.M., and W.O. Smith. 1986. Phytoplankton bloom dynamics of the Ross Sea ice edge. II. Mesoscale cycling of nitrogen and silicon. Deep-Sea Research, 33(10), 1389-1412. Redfield, A.C., B.H. Ketchum, and F.A. Richards. 1963. The influence of organisms on the composition of seawater. In M.N. Hill (Ed.), The sea (Vol. II.). New York: Interscience. Rosenberg, I.E., R.P. Hewitt, and R.S. Holt. 1994. The U.S. Antarctic Marine Living Resources (AMLR) program: 1993-1994 field season activities. Antarctic Journal of the U.S., 29(5). Silva S., N., E.W. Helbling, V.E. Villafañe, A.F. Amos, and 0. HolmHansen. In press. Variability in nutrient concentrations around Elephant Island, Antarctica, during 1991-1993. Polar Research. Silva S. N., S. Hormazábal F., E.W. Helbling, and 0. Holm-Hansen. 1993. AMLR program: Inorganic nutrient concentrations in nearsurface waters around Elephant Island, Antarctica, January to March 1993. Antarctic Journal of the U.S., 28(5), 196-198. Villafañe, V.E., E.W. Helbling, 0. Holm-Hansen, and H. DIaz. 1994. AMLR program: Phytoplankton distribution and species composition around Elephant Island, Antarctica, January to March 1994. Antarctic Journal of the U.S., 29(5).
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onboard ship. Shipboard personnel included E. Walter Helbling (13 January to 9 February) and Osmund Holm-Hansen (14 February to 15 March).
References Amos, A.F., and M.K. Lavender. 1992. AMLR program: Dynamics of the summer hydrographic regime at Elephant Island. Antarctic Journal of the U.S., 27(5), 228-230. Chamberlin, W.S., C.R. Booth, D.A. Kiefer, J.H. Morrow, and R.C. Murphy. 1990. Evidence for a simple relationship between natural fluorescence, photosynthesis and chlorophyll in the sea. Deep-Sea Research, 37(6), 951-973. Holm-Hansen, 0., A.F. Amos, N. Silva S., V.E. Villafañe, and E.W. Helbling. 1994. In situ evidence for a nutrient limitation of phytoplankton growth in pelagic antarctic waters. Antarctic Science, 6(3), 315-324. Holm-Hansen, 0., V.E. Villafane, and E.W. Helbling. 1994. AMLR program: Photobiological characteristics of phytoplankton around Elephant Island, Antarctica. Antarctic Journal of the U.S., 29(5). Rosenberg, J.E., R.P. Hewitt, and R.S. Holt. 1994. The U.S. Antarctic Marine Living Resources (AMLR) program: 1993-1994 field season activities. Antarctic Journal of the U.S., 29(5). Silva S., N., E.W. Helbling, V.E. Villafane, A.F. Amos, and 0. HolmHansen. In press. Variability in nutrient concentrations around Elephant Island, Antarctica, during 1991-1993. Polar Research. Villafañe, V.E., E.W. Helbling, 0. Holm-Hansen, and H. DIaz. 1994. AMLR Program: Phytoplankton distribution and species composition around Elephant Island, Antarctica, January to March 1994. Antarctic Journal of the U.S., 29(5).
AMLR program: Depletion of inorganic nutrients in the area around Elephant Island, Antarctica NELSON SILVA S. and MARCEL RAMOS, Escuela de Ciencias del Mar, Universidad Católica de Valparaiso, Valparaiso, Chile
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
shaken, and discarded two times. The 60-milliliter bottles were then filled approximately three-fourths full with water from the 10-liter Niskin bottles and frozen (-20°C) immediately. The samples were kept frozen until analyses (1-2 months after collection), which were performed at the Universidad CatOlica de Valparaiso, Chile, using an autoanalyzer and employing the technique described by Atlas et al. (1971). Nitrate concentrations at 5 meters depth were high during Survey A: values ranged from about 22.3 to more than 29 micromolar (tM) (figure 1A). During Survey D, nitrogen values decreased in the area to the south and southeast of King George Island and also in the area between King George Island and Elephant Island (figure 1B), but nitrate concentrations increased in coastal waters around King George Island, as well as in deep waters to the north of the island. Nitrate concentrations during Survey D ranged from 20 to 34 tiM. Phosphate concentrations at 5 meters depth varied from 1.65 to more than 2.1 tM during Survey A (figure 2A). Rela-
norganic nutrient concentrations are generally high in I antarctic waters, but significant depletions of nitrogen, phosphorus, and silicic acid have been documented in coastal areas where large phytoplankton blooms occurred (Nelson and Smith 1986; Holm-Hansen and Mitchell 1991). In this paper, we report the concentrations of these inorganic nutrients from January to March 1994 in a large sampling grid around Elephant Island. The grid included both coastal and pelagic stations. The cruise track and station positions are given in Rosenberg, Hewitt, and Holt (Antarctic Journal, in this issue). As one component of the phytoplankton studies of the Antarctic Marine Living Resources (AMLR) program, samples for determination of nutrient concentrations were obtained at each station, during both Legs I and II, using 10-liter Niskin bottles mounted on the rosette profiling system. Water from the Niskin bottles was poured directly into 60-milliliter, clean (soaked in 1.0 normal hydrochloric acid) polyethylene bottles,
ANTARCTIC JOURNAL - REVIEW 1994
195
60
A
23-24.6
-
60.5
61
V a)
24.626.9
61.5
4 26.9-'
26.929 62 62.5k 5958
57 56 55 54 53
Longitude (W)
rigure 1. Nitrate concentrations (IJ.M) at 5 meters depth in waters around Elephant Island. A. Data from Survey A (17-28 January 1994). B. Data from Survey D (25 February to 9 March 1994).
t-igure z. 1-'riospFiate concentrations (riM) at 5 meters depth in waters around Elephant Island. A. Data from Survey A (17-28 January 1994). B. Data from Survey D (25 February to 9 March 1994). tively high values were found around King George, Elephant, and Clarence Islands. There was a general decrease in phosphate concentrations between Legs I and II over most of the sampling grid, with the most dramatic decrease being in the area south of King George Island, where concentrations ranged from 1.2 to 1.35 tM. This area with maximum phosphate depletion was, in general, similar to the area with maximum nitrate depletion (figure 1B). Silicic acid concentrations were generally low in Drake Passage waters, with values less than 30 i.tM (figure 3). Highest concentrations of silicic acid were observed in the southern portion of the sampling grid. Although the ranges of concentrations of silicic acid were quite similar between Surveys A and D, less than 30 to 80 tM, a general decrease in concentrations was observed between Legs I to II over most of the sampling grid (figures 3A and 3B).
The molar ratios of silicic acid/nitrogen/phosphate for all the data obtained at 5 meters depth were 31.2/13.7/1 for Survey A and 34.4/16.1/1 for Survey D, with the nitrogen/phosphate ratio being close to the theoretical value of 16 (Redfield, Ketchum, and Richards 1963, pp. 26-77). The general distribution of inorganic nutrients is in agreement with previous studies in the area (Silva et al. in press). Silicic acid concentrations during AMLR 1994, however, showed a smaller range than the concentrations found during the AMLR 1993 field season (20 to 108 Silva et al. 1993). The nitrogen/phosphate ratio did not show any significant difference between the two seasons. Although a general decrease in nutrient concentrations was observed throughout the sampling grid for all three nutrients analyzed, the relative depletion was greater in phosphate and silicic acid concentrations than for nitrate. This suggests
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Figure 3. Silicic acid concentrations (iA at 5 meters depth in waters around Elephant Island. Data from Survey D (25 February to 9 March 1994). that other forms of nitrogen, such as ammonium, could have an important role in the nutrient uptake by phytoplankton as suggested by Koike, Holm-Hansen, and Biggs (1986). The decrease in nutrient concentrations between Legs I and II, throughout such a large sampling area, is thought to be related to a general increase of phytoplankton biomass, because Villafañe et al. (Antarctic Journal, in this issue) have reported an extensive bloom of phytoplankton during Leg II. This large bloom has integrated values of chlorophyll-a (chl-a) (0 to 100 meters) of more than 200 milligrams chl-a per square meter (mg chl-a rn-2). Our complete nutrient data set will be analyzed together with other information such as phytoplankton biomass and rates of primary production to obtain estimates of rates of nutrient assimilation and recycling in the AMLR study area. This work was supported by National Oceanic and Atmospheric Administration (NOAA) Cooperative Agreement number NA47FR0030. We thank the officers and crew of the NOAA ship Surveyor for excellent support during the field operations. We also thank Noé Cáceres and Maria Angdlica Varas for their help on chemical analyses and data processing and Virginia Villafane, Humberto DIaz, Pedro BarOn, and Christian Bonert for help onboard ship. Shipboard personnel included E. Walter Heibling (13 January to 9 February), Marcel Ramos (13 January to 15 March), and Osmund HolmHansen (14 February to 15 March).
A.
Data from Survey A (17-28 January 1994).
B.
References Atlas, E.L., L.I. Gordon, S.W. Hager, and P.K. Park. 1971. A practical
manual for the use of the Technicon Autoanalyzer in seawater nutrient analyses, rev. ed. (Technical Report 71-22). Corvallis: Ore-
gon State University, Department of Oceanography. Holm-Hansen, 0., and B.G. Mitchell. 1991. Spatial and temporal distribution of phytoplankton and primary production in the western Bransfield Strait region. Deep-Sea Research, 38(8/9), 961-980. Koike, I., 0. Holm-Hansen, and D.C. Biggs. 1986. Inorganic nitrogen metabolism by antarctic phytoplankton with special reference to ammonium cycling. Marine Ecology Progress Series, 30(2), 105-116. Nelson, D.M., and W.O. Smith. 1986. Phytoplankton bloom dynamics of the Ross Sea ice edge. II. Mesoscale cycling of nitrogen and silicon. Deep-Sea Research, 33(10), 1389-1412. Redfield, A.C., B.H. Ketchum, and F.A. Richards. 1963. The influence of organisms on the composition of seawater. In M.N. Hill (Ed.), The sea (Vol. II.). New York: Interscience. Rosenberg, I.E., R.P. Hewitt, and R.S. Holt. 1994. The U.S. Antarctic Marine Living Resources (AMLR) program: 1993-1994 field season activities. Antarctic Journal of the U.S., 29(5). Silva S., N., E.W. Helbling, V.E. Villafañe, A.F. Amos, and 0. HolmHansen. In press. Variability in nutrient concentrations around Elephant Island, Antarctica, during 1991-1993. Polar Research. Silva S. N., S. Hormazábal F., E.W. Helbling, and 0. Holm-Hansen. 1993. AMLR program: Inorganic nutrient concentrations in nearsurface waters around Elephant Island, Antarctica, January to March 1993. Antarctic Journal of the U.S., 28(5), 196-198. Villafañe, V.E., E.W. Helbling, 0. Holm-Hansen, and H. DIaz. 1994. AMLR program: Phytoplankton distribution and species composition around Elephant Island, Antarctica, January to March 1994. Antarctic Journal of the U.S., 29(5).
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