Lohmann, H. 1911. On the nanoplankton and the centrifugation ofvery small water samples to obtain nanoplankton in an alive con-dition. Internationale Revue der Gesamten Hydrobiologie und Hydrogra-phie, 4, 1-38.

Marchant, H.J., A.T. Davidson, and S.W. Wright. 1987. The distri-bution and abundance of cyanobacteria in the Southern Ocean. Pro-ceedings of the National institute of Polar Research Symposium on PolarBiology, 1, 1-9.

Murphy, L.S., and E.M. Haugen. 1985. The distribution and abun-dance of ultraplankton in the North Atlantic. Limuology and Ocean-ography, 30, 47-58.

Platt, T., D.V. Subba Rao, and B. Irwin. 1983. Photosynthesis of pi-coplankton in the oligotrophic ocean. Nature, 301, 702-704.

Porter, KG., and Y.S. Feig. 1980. The use of DAPI for identifying andcounting aquatic microflora. Liinnology and Oceanography, 25, 943-948.

Waterbury, J.B., S.W. Watson, R.R.L. Guillard, and L.E. Brand. 1979.Widespread occurrence of a unicellular, marine, planktonic, cyano-bacterium. Nature, 277, 293-294.

Wright, S.W., and H.R. Burton. 1981. The biology of Antarctic marinelakes. Hydrobiologia, 82, 319-338.

Spectral light absorptioncharacteristics

of individual sea-ice microalgaefrom McMurdo Sound, Antarctica

R. ITURRIAGA and C.W. SULLIVAN

Marine Biology Research SectionDepartment of Biological SciencesUniversity of Southern California

Los Angeles, California 90089-0371

Sea-ice microalgae are known to reach high abundances incongelation and platelet ice layers covering McMurdo Sound.Concentrations as high as 10 to 1010 cells per square meter (3milligrams chlorophyll a per liter) have been reported (Sullivanet al. 1983; Grossi et al. 1987). Substantial cell densities notonly affect the amount of photosynthetically active radiationavailable to the underlying ice algae communities, they alsoaffect the spectral composition of the incident irradiance alongits path through the ice. Thus, ice algae are the prime biologicaldeterminants of the quantity and quality of light that is avail-able to the water-column phytoplanktonic and epibenthic mi-croalgal communities that occur under land-fast sea ice. Theonly available information regarding spectral characteristics ofice algae is derived from measurements of the whole com-munity collected from different locations in McMurdo Sound(SooHoo et al. 1987) and in the Weddell Sea (Lizotte et al.Antarctic Journal, this issue). Such determinations provide anaverage of the in vivo absorption properties of all particulatespresent in the ice; however, information about the spectralabsorption characteristics of individual algal cells of such com-munities is not possible with such measurements. We haveapplied a microphotometric technique to study the spectralabsorption characteristics of individual sea-ice microalgae andtheir taxonomic identification during early summer at threelocations in McMurdo Sound.

Samples of ice microalgae were collected at three differentsites in McMurdo Sound during December of 1986: Erebus IceTongue, Granite Harbor, and Hut Point. Small core sectionsof sea ice collected by drilling with an ice auger were dilutedin 2 times volumes of filtered seawater (0.45 micrometer Mil-lipore) and kept in darkness at 0°C. Samples of ice meltwaterwere pepared for microphotometric analysis as described byIturriaga, Mitchell, and Kiefer (1988) and Iturriaga and Siegel

(1988). Briefly, this technique consists of concentrating thesample at very low vacuum pressure (<5 millimeters of mer-cury) or gravity to minimize cell rupture. Cells concentratedon the upper face of a 0.4-micrometer pore-size Nuclepore filterare then transferred to a microscope slide coated with a gelatinmixture containing preservative. The sample is covered withone or two drops of a glycerol solution and cover slip, thenstored at - 20°C unless measurements are performed imme-diately.

A universal microscope equipped with a type 03 photometer(Carl Zeiss, West Germany), interfaced to a tungsten-halogenlight source and a scanning monochromator was used for thisstudy. Determination of the spectral absorption of individualcells requires direct determination of the spectral transmittanceof the sample (is) compared to a blank (1 0(X)), which is deter-mined by focusing on the targeted cell and then on an adjacentarea with no particles, respectively. Such determinations en-abled us to calculate the absorption efficiency factor (Q ,1 (X)) forobserved cells.

Qa('\) = 1 - (1/I)The absorption efficiency factor is defined as the ratio of theenergy absorbed by the cell to the energy impingent upon itsgeometrical cross-sectional area (Morel and Bricaud 1981; Bri-caud, Morel, and Prieur 1983). The microphotometric tech-nique allowed us to measure the spectral shapes and magnitudeof Qa(X). These methods enable us to determine for individualalgal cells the major in vivo absorption bands correspondingto the photosynthetic pigments present, as well as to determinethe taxonomic position of cells.

The variation in spectral shape and magnitude of Q ,1 (X) wasstudied in several ice algae from different locations of Mc-Murdo Sound. The cells selected for analysis constituted themost representative species at each location. Examples of Qa(X)spectra for the following species: Nitzschia ste/Iota (1), Amp/u-prora kufferathii (2), Pinnularia quadratarea (3), and Nitzschia ker-gue/ensis (4) are shown in figure 1. The spectral resolution ofthese measurements allows discrimination of major absorptionbands corresponding to algal pigments: chlorophyll a at 435and 675 nanometers, chlorophyll c at 465 and 630 nanometers,as well as the accessory pigments such as fucoxanthin from470 to 550 nanometers. Individual diatoms appear to havespecies specific absorption spectral features. In addition, spec-tral variability within the clones of colonial algal species, suchas Nitzschia kergue/ensis or Amphiprora kufferathii, were mea-sured. Figure 2 shows a family of spectra derived from a clonalchain of 10 cells of Nitzschia kerguelensis. The variability of theabsorption efficiency factor Qa(X), in shape and magnitude, is

188 ANTARCTIC JOURNAL

0.9

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0.6

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0.1

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Figure 1. Absorption efficiency factor spectra [Qa(X)] for some in-dividual ice algae.

being statistically analyzed within clones of several species thatbuild colonies. Such clones offer the possibility of analyzing a

population of cells all of which contain an identical genomeand which share the same light history on a spatial scale ofmicrometers. This approach permits us to understand the rangeof natural optical variability among cells of the same speciescollected from a variety of sea-ice micro-environments as wellas a variety of species from the same environment.

Preliminary microphotometric measurements on individualcells indicate that optical properties of ice algae are subject tovariability on several scales. Statistical tests are being designedto rigorously define the variability at the level of clones of onespecies, among different species from the same environment,and among cells of the same species from different environ-ments. We will interpret this data in terms of the ability ofcells to adapt their biochemical composition (pigments) to theprevailing spectral irradiance field. Definition of the opticalvariability of species will tell us much about the photophy-siology of algae and the bio-optical characteristics of sea ice.Interestingly, these same cells contribute substantially to thecharacteristics of the prevailing in-ice and under-ice irradiancefields which may influence the sources of energy available toother photoautotrophic organisms and the visual response ofheterotrophic organisms at all trophic levels.

This research was supported by National Science Founda-tion grant DPP 87-17692.

Qa

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WAVELENGTHFigure 2. Absorption efficiency factor spectra [O a(X)] for individual cells determined on a chain of 10 cells of Nitzschia kerguelensis.

1989 REVIEW 189

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References

Bricaud, A., A. Morel, and L. Prieur. 1983. Optical efficiency factorsof some phytoplankters. Limnology and Oceanography, 28, 816-832.

Grossi, S.M., S.T. Kottmeier, R.L. Moe, G.T. Taylor, and C.W. Sul-livan. 1987. Sea ice microbial communities. VI. Growth and pro-duction in bottom ice under graded snow cover. Marine EcologyProgress Series, 35, 153-164.

Iturriaga, R., B.G. Mitchell, and D. Kiefer. 1988. Microphotometricanalysis of individual particle absorption spectra. Limnology andOceanography, 33, 128-135.

Iturriaga, R., and D. Siegel. 1988. Microphotometric distinction ofphytoplankton and detrital absorption properties. Proceedings of theSociety of Photo-Optical Instrumentation Engineers, 925, Ocean OpticsIX, 277-287.

Lizotte, M.P., W.S. Chamberlin, R.A. Reynolds, and C.W. Sullivan.1989. AMERIEZ 1988: Photobiology of microalgae in the sea ice andwater column of the Weddell-Scotia Sea during winter. AntarcticJournal of the U.S., 24(5).

Morel, A., and A. Bricaud. 1981. Theoretical results concerning lightabsorption in a discrete medium, and application to specific ab-sorption of phytoplankton. Deep Sea Research, 28, 1,375-1,393.

SooHoo, J.B., A.C. Palmisano, M.P. Lizotte, S.T. Kottmeier, S.L.SooHoo, and C.W. Sullivan. 1987. Spectral light absorption andphotosynthetic quantum yield of sea ice algae from McMurdo Sound,Antarctica. Marine Ecology Progress Series, 39, 175-189.

Sullivan, C.W., A.C. Palmisano, S. Kottmeier, S. McGrath-Grossi, R.Moe, and G.T. Taylor. 1983. The influence of light on developmentand growth of sea ice microbial communities in McMurdo Sound.Antarctic Journal of the U.S., 18(5), 177-179.

Chemical characteristicsof aquatic fulvic acid

isolated from Lake Fryxell,Antarctica

G.R. AIKEN, D.M. MCKNIGHT, and R.A. HARNISH

U.S. Geological SurveyArvada, Colorado 80002

The lakes in the McMurdo Dry Valleys of Victoria Land,Antarctica, present a unique opportunity to study the internalproduction and degradation of organic material in lake eco-systems. These lakes are located in one of the most and andbarren desert environments on Earth, where in addition to theabsence of plants, the microflora of the soils is quite sparse(Cameron, King, and David 1970) and the organic content ofthe soils is less than 0.1 percent (Horowitz, Cameron, andHubbard 1972). Within the lakes, organic compounds derivedfrom higher plants are absent (Matsumoto, Toni, and Hanya1984), and the dissolved organic carbon is limited to thosecompounds produced by algae and bacteria. Because of thisunique situation, these lakes represent a group of endmemberecosystems that are ideal natural laboratories to study pro-cesses related to the chemistry of microbially derived organicmatter in the absence of factors that complicate the interpre-tation of data obtained from other aquatic systems. The sci-entific objectives of our research on lakes in the McMurdo DryValleys are to determine the distinctive chemical characteristicsof the major fractions of dissolved organic material in lakeswhere the only source of organic material is autochthonousmicrobial productivity, and determine the chemical and bio-logical pathways and rates of formation of dissolved organiccarbon in one lake ecosystem.

Lake Fryxell located in the Taylor Valley was chosen forstudy because it is one of the more productive Dry Valley lakes(Vincent 1981). Lake Fryxell is amictic with a highly stablewater column due to the year round ice cover. Depth profilesfor a number of chemical constituents within Lake Fryxell havebeen presented by McKnight et al. (1988). Despite the low lightintensities caused by the 4.5-meter-thick ice cover, abundantalgal populations develop in the oxic zone of the water column

above the 9.5-meter depth, as demonstrated by in vivo fluo-rescence data (figure 1), which is an indirect estimate of phy-toplanton abundance. The depth profile for dissolved organiccarbon in Lake Fryxell, however, is quite different from thedepth profile for in vivo fluorescence (figure 2). The dissolvedorganic carbon concentration increases with depth throughoutthe oxic and anoxic zones to a maximum concentration of 25milligrams of carbon per liter at the bottom of the lake (18meters). This profile is generally similar to the depth profiles

In Vivo Fluorescence (IVF)051015202530

Dissolved Oxygen (mg/L)Figure 1. In vivo fluorescence and dissolved oxygen depth profilesfor Lake Fryxell as determined in December 1987. (mg/L denotesmilligrams per liter.)

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