Recent diatom distributions in theAmundsen Sea

D.E. KELLOGG and T.B. KELLOGG

Institute for Quaternary Studiesand

Department of Geological SciencesUniversity of MaineOrono, Maine 04469

We summarize here the results of diatom analyses of water,sediment, and sea-ice samples collected during a cruise of theU.S. Coast Guard icebreaker Glacier to the Amundsen Sea inJanuary of 1985 (T. Kellogg, D. Kellogg, and Hughes 1985). Thiswork, described in greater detail by D. Kellogg and T. Kellogg(in preparation) is the first study of modern Amundsen Seamicrofossil distributions and will serve as the basis for inter-pretation of sediment cores in terms of past oceanographic,glacial, and climatic fluctuations (D. Kellogg and T. Kellogg,Antarctic Journal, this issue). Sample locations are shown in acompanion paper in this volume (D. Kellogg and T. kellogg,Antarctic Journal, this issue, figure 1).

Marine diatoms in sediments. Fifty-seven marine taxa wereidentified in the core-top samples (42 to the species level), butmost of these taxa occur only rarely (1-5 specimens per sample).Species that were present consistently in most samples, often inmoderate to high abundance (more than 10 specimens persample) include: Actinocyclus actinochilus, Chactoceros sp. spores,Eucampia antarctica, Paralia sol, Nitzschia curta, N. kerguelensis, N.vanheurckii, N. obliquecostata, N. sublineata, and Thalassiosira gra-cilis. Present in lower abundance were various species of thegenra Cocconeis and Thalassiosira. All but two of the marinespecies recorded are extant in modern antarctic waters or occurin Recent antarctic sediments (e.g., Fenner, Schrader, andWienigk 1976; Truesdale and Kellogg 1979). These species aretypical of McCollum's (1975) Thalassiosira lentiginosa (formerlyCoscinodiscus lentiginosus) Parital Range Zone. The two excep-tions are Denticulopsis hustedtii and Trinacria pileolus, both ofwhich occur as single specimens in DF85-111 and DF85-96,respectively. These species have stratigraphic ranges intheMiocene (McCollum 1975) to Pliocene (Ciesielski 1983; Burcklepersonal communication). Their presence in Amundsen Seacore-top samples suggests either reworking or the exposure ofolder sediment on the sea floor. Reworking is more likely forboth samples because they contain the Quaternary species N.curta and the Quaternary/upper Pliocene species A. actinochilusin abundance (D. Kellogg and T. Kellogg 1986b).

Nonmarine diatoms in sediments. Nonmarine diatoms are pres-ent in most sediment samples, but abundances are generallymuch lower than those of marine species and usually consist ofonly one or two specimens of each species. Taxa recorded in-clude Melosira distans, and species of Cyclotella, Diploneis,Navicula, and Tabellaria. The nonmarine species appear to bedistributed nearly uniformly throughout the Amundsen Seacore tops, with slightly higher abundances in cores DF85-95 andDF85-99.

Our report of nonmarine diatoms in Amundsen Sea sedi-ments is not anomalous. Many of these same species occur, incomparable abundances, in Ross Sea sediments (T. Kellogg andTruesdale 1979; Truesdale and Kellogg 1979; T. Kellogg and D.

Kellogg 1981). These nonmarine species are widespread in lakesand melt ponds throughout the ice-free valleys of southernVictoria Land (D. Kellogg et al. 1980), on the McMurdo Ice Shelf(D. Kellogg and T. Kellogg 1984, in press), and in the VestfoldHills (Setty, D. Kellogg, and T. Kellogg 1984). Melt pools occur-ring on antarctic sea ice could also provide a suitable habitat fornonmarine diatoms throughout the circumantarctic sea-icezone. Introduction of nonmarine diatoms to marine sedimentsrequires only melting of the pack ice. Once they are introducedto the water column, currents may carry diatoms even beneathice shelves and floating glacier tongues, such as Pine IslandGlacier.

Diatoms in ice and water samples. Additional material was col-lected for comparison of fossil and living diatom distributions.Sea-water samples were obtained routinely at each coring sta-tion, and ice samples were collected intermittently. All ice ana-lyzed was stained green or red by algal material. Sea water andmelted ice were filtered to extract diatoms. Filters (cleared withacetic acid) were mounted on slides using Hyrax.

All our ice and water samples contained abundant marinediatoms and were dominated by large to very large numbers ofN. cylindrus, Nitzchia curta, N. vanheurckii, and N. obliquecostata,in varying proportions, were subdominants in most samples.These four species together usually comprised over 95 percentof each sample in our quantitative analyses, and a total of 300specimens was almost always obtained after analyzing only asmall portion of each slide.

The overwhelming dominance in ice and water samples of N.cylindrus may be attributed to a seasonal bloom, because allthese samples were collected within 1 week and because theycover almost the entire north-south extent of the easternAmundsen Sea. Other species which are known to spend partof their life cycle attached to the underside of the sea ice (e.g., N.curta, N. kerguelensis, and N. vanheurckii are, predictably,subdominants.

More than half of the sea-ice and sea-water samples con-tained occasional specimens of nonmarine diatoms. One sam-ple (DF85-73-55) had nearly 50 specimens of a small delicatespecies of Navicula which we have not encountered previouslybut which we suspect is nonmarine, as are most members ofthat genus. Nonmarine diatoms in sea-ice samples may repre-sent populations that inhabit small melt pools or occur at thebase of the snow layer (i.e., in situ assemblages), or they mayhave been carried from some terrestrial location by winds. Thelow abundances of nonmarine diatoms in our ice samples (ex-cept DF85-73-55) suggest that they represent a contaminant andwere probably introduced by winds. Scattered occurrences ofnonmarine diatoms in surface water samples probably also re-sult from distribution by winds.

We also sampled melt ponds on islands in the AmundsenSea, to determine if nonmarine species present in this area aresimilar to those in the Ross Sea sector and elsewhere. Sampleswere collected from open water in ponds on the Lindsey andEdwards Islands. Both these samples were dominated by themarine species N. cylindrus, although nonmarine species com-prised 22.4 percent of the diatom flora at the Lindsey Islands.We suspect that marine species are introduced to these pondsby storm waves and spray, an hypothesis that is supported bythe lower percentage of marine species at the higher elevationLindsey Islands site. Nonmarine diatoms at the Lindsey Islandsare dominated by formae of the species Navicula muticopsis,which occur commonly in similar melt ponds in the ice-freevalleys of southern Victoria Land and on the McMurdo Ice Shelf(D. Kellogg et al. 1980; D. Kellogg and T. Kellogg in press). The

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same small delicate Navicula species we noted in the ice sampleat DF85-74-55 was also found in both terrestrial ponds samples.We conclude that both these sites are situated too close to the seato give an accurate representation of a typical nonmarine diatomflora for the area surrounding the Amundsen Sea.

We thank Captain W. Hewell and the officers and crew of U.S.Coast Guard icebreaker Glacier, Terence Hughes, and John An-derson and his students, who assisted with our coring projectin January 1985. Dennis Cassidy assisted with sampling thecores. David Thompson and Stephanie Staples assisted withsample preparation. This work was supported by National Sci-ence Foundation grant DPP 80-20000.

References

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McCollum, D.W. 1975. Diatom stratigraphy of the Southern Ocean.Initial Reports of the Deep Sea Drilling Project, Vol. 28 Washington, D.C.:U.S. Government Printing Office.

Setty, M.G.A.P., D.E. Kellogg, and T.B. Kellogg. 1984. Preliminaryreport on diatoms from the Deep Lake terraces, Vestfold Hills, Ant-arctica. Antarctic Journal of the U.S., 19(5), 88-90.

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