Radiocarbon ages, diatom abundance and laminae description of sediment core MD03-2597

Laminated sediments are unique archives of palaeoenvironmental and palaeoceanographic conditions, recording changes on seasonal and interannual timescales. Diatom-rich laminated marine sediments are examined from Dumont d'Urville Trough, East Antarctic Margin, to determine changes in environmental conditions on the continental shelf from 1136 to 3122 cal. yr BP. Scanning electron microscope backscattered electron imagery (BSEI) and secondary electron imagery are used to analyse diatom assemblages from laminations and to determine interlamina relationships. Diatom observations are quantified with conventional assemblage counts. Laminae are primarily classified according to visually dominant species identified in BSEI and, secondarily, by terrigenous content. Nine lamina types are identified and are characterized by: Hyalochaete Chaetoceros spp. resting spores (CRS); CRS and Fragilariopsis spp.; Fragilariopsis spp.; Corethron pennatum and Rhizosolenia spp.; C. pennatum; Rhizosolenia spp.; mixed diatom assemblage; Stellarima microtrias resting spores (RS), Porosira glacialis RS and Coscinodiscus bouvet; and P. glacialis RS. Formation of each lamina type is controlled by seasonal changes in sea ice cover, nutrient levels and water column stability. Quantitative diatom assemblage analysis revealed that each lamina type is dominated by CRS and Fragilariopsis sea ice taxa, indicating that sea ice cover was extensive and persistent in the late Holocene. However the lamina types indicate that the sea ice regime was not consistent throughout this period, notably that a relatively warmer period, ~3100 to 2500 cal. yr BP, was followed by cooling which resulted in an increase in year round sea ice by ~1100 cal. yr BP.

Vegetation in the coastal area of East Greenland

This paper deals with the syntaxonomy and ecology of debris, scree and alluvium vegetation of the Ammassalik district, Southeast Greenland, on more or less moist soil. The Oxyria digyna- and Chamaenerion latifoliumvegetation types are classified as Saxifrago-Oxyrietum digynae (Böcher 1933 ap. Nordh. 1943) Gjaerevoll 1950 respectively Chamaenerietum latifolii Böcher 1933 in the class Thlaspietea rotundifolii Br.-BI. ap. Br.-BI. et al. 1947. The chionophytic Saxifrago-Oxyrietum digynae and the Chamaenerietum latifolii occurring on river-banks are classified in the alliance Saxifrago stellaris-Oxyrion digynae Gjaerevoll 1950. This alliance belongs to the order Androsacetalia alpinae Br.-BI. ap. Br.-BI. & Jenny 1926, Thlaspietea rotundifolii Br.-BI. ap. Br.-BI. et al. 1947. The following syntaxa are described as new: Saxifrago-Oxyrietum digynae stellarietosum humifusae and typicum with two variants and one variant of the subassociation inops De Molenaar 1976, and the Chamaenerietum latifolii typicum with two variants and salicetosum herbaceae with three variants.

Biostratigraphy of sediment core CRP-3 from the Ross Sea, Antarctica

Early Oligocene siliceous microfossils were recovered in the upper c. 193 m of the CRP-3 drillcore. Although abundance and preservation are highly variable through this section, approximately 130 siliceous microfossil taxa were identified, including diatoms, silicoflagellates, ebridians, chrysophycean cysts, and endoskeletal dinoflagellates. Well-preserved and abundant assemblages characterize samples in the upper c. 70 m and indicate deposition in a coastal setting with water depths between 50 and 200 m. Abundance fluctuations over narrow intervals in the upper c. 70 mbsf are interpreted to reflect environmental changes that were either conducive or deleterious to growth and preservation of siliceous microfossils. Only poorly-preserved (dissolved, replaced, and/or fragmented) siliceous microfossils are present from c. 70 to 193 mbsf. Diatom biostratigraphy indicates that the CRP-3 section down to c. 193 mbsf is early Oligocene in age. The lack of significant changes in composition of the siliceous microfossil assemblage suggests that no major hiatuses are present in this interval. The first occurrence (FO) of Cavitatus jouseanus at 48.44 mbsf marks the base of the Cavitatus jouseanus Zone. This datum is inferred to be near the base of Subchron C12n at c. 30.9 Ma. The FO of Rhizosolenia antarctica at 68.60 mbsf marks the base of the Rhizosolenia antarctica Zone. The FO of this taxon is correlated in deep-sea sections to Chron C13 (33.1 to 33.6 Ma). However, the lower range of R. antarctica is interpreted as incomplete in the CRP-3 drillcore, as it is truncated at an underlying interval of poor preservation: therefore, an age of c. 33.1 to 30.9 Ma is inferred for interval between c. 70 and 50 mbsf. The absence of Hemiaulus caracteristicus from diatom-bearing interval of CRP-3 further indicates an age younger than c. 33 Ma (Subchron C13n) for strata above c. 193 mbsf. Siliceous microfossil assemblages in CRP-3 are significantly different from the late Eocene assemblages reported CIROS-1 drillcore. The absence of H. caracteristicus, Stephanopyxis splendidus, and Pterotheca danica, and the ebridians Ebriopsis crenulata, Parebriopsis fallax, and Pseudoammodochium dictyoides in CRP-3 indicates that the upper 200 m of the CRP-3 drillcore is equivalent to part of the stratigraphic interval missing within the unconformity at c. 366 mbsf in CIROS-1.

Physicochemical characteristics and protist occurrence at stations sampled in 2007/2008 in the eastern Beaufort Sea

This study documents, for the first time, the abundance and species composition of protist assemblages in Arctic sea ice during the dark winter period. Lack of knowledge of sea-ice assemblages during the dark period has left questions about the retention and survival of protist species that initiate the ice algal bloom. Sea-ice and surface water samples were collected between December 27, 2007 and January 31, 2008 within the Cape Bathurst flaw lead, Canadian Beaufort Sea. Samples were analyzed for protist identification and counts, chlorophyll (chl) a, and total particulate carbon and nitrogen concentrations. Sea-ice chl a concentrations (max. 0.27 µg/l) and total protist abundances (max. 4 x 10**3 cells/l) were very low, indicating minimal retention of protists in the ice during winter. The diversity of winter ice protists (134 taxa) was comparable to spring ice assemblages. Pennate diatoms dominated the winter protist assemblage numerically (averaging 77% of total protist abundances), with Nitzschia frigida being the most abundant species. Only 56 taxa were identified in surface waters, where dinoflagellates were the dominant group. Our results indicate that differences in the timing of ice formation may have a greater impact on the abundance than structure of protist assemblages present in winter sea ice and at the onset of the spring ice algal bloom.

List of plant species found on Victoria Island

While engaged in geoecological field work on Victoria Island, 277 new plants could be recorded for the vicinities of Holman, Cambridge Bay, Wellington Bay, Mt. Pelly, Richardson Islands, Hadley Bay, and Minto lnlet; 8 of them were new for Victoria Island, 6 for the western Canadian arctic archipelago.

Late Cretaceous dinoflagellate cysts of ODP Hole 120-748C

At Ocean Drilling Program Hole 748C in the Southern Indian Ocean, a total of 171 Late Cretaceous dinoflagellate taxa were encountered in 38 productive samples from Cores 120-748C-27R through 120-748C-62R (407-740 mbsf). Four provisional dinoflagellate assemblage zones and five subzones were recognized based on the character of the dinoflagellate flora and the first/last occurrences of some key species. Isabelidinium korojonense and Nelsoniella aceras occur in Zone A together with Oligosphaeridium pulcherrimum and Trithyrodinium suspect urn. Zone B was delineated by the total range of Odontochitina cribropoda. Zone C was separated from Zone B by the presence of Satyrodinium haumuriense, and Zone D is dominated by new taxa. The dinocyst assemblages bear a strong affinity to Australian assemblages. Paleoenvironmental interpretations based mainly on dinocysts suggest that during the ?Santonian-Campanian to the Maestrichtian this portion of the Kerguelen Plateau was a shallow submerged plateau, similar to nearshore to offshore to upper slope environments with water depths of tens to hundreds of meters, but isolated from the major continents of the Southern Hemisphere. Starting perhaps in the late Cenomanian (Mohr and Gee, 1992, doi:10.2973/odp.proc.sr.120.196.1992), the Late Cretaceous transgression over the plateau reached its maximum during the late Campanian. The plateau may have been exposed above sea level and subjected to weathering during the latest Maestrichtian. The studied dinocyst assemblages characterized by species of Amphidiadema, Nelsoniella, Satyrodinium, and Xenikoon together with abundant Chatangiella (the large-size species) and Isabelidinium suggest that a South Indian Province (tentatively named the Helby suite) may have existed during the Campanian-Maestrichtian in comparison with the other four provinces of Lentin and Williams. One new genus, three new species, and two new subspecies of dinocysts are described.

Species occurrence and richness of lichen, bryophytes and vascular plants near Abisko, Sweden and Toolik lake, Alaska

Little is known about the impact of changing temperature regimes on composition and diversity of cryptogam communities in the Arctic and Subarctic, despite the well-known importance of lichens and bryophytes to the functioning and climate feedbacks of northern ecosystems. We investigated changes in diversity and abundance of lichens and bryophytes within long-term (9-16 years) warming experiments and along natural climatic gradients, ranging from Swedish subarctic birch forest and subarctic/subalpine tundra to Alaskan arctic tussock tundra. In both Sweden and Alaska, lichen diversity responded negatively to experimental warming (with the exception of a birch forest) and to higher temperatures along climatic gradients. Bryophytes were less sensitive to experimental warming than lichens, but depending on the length of the gradient, bryophyte diversity decreased both with increasing temperatures and at extremely low temperatures. Among bryophytes, Sphagnum mosses were particularly resistant to experimental warming in terms of both abundance and diversity. Temperature, on both continents, was the main driver of species composition within experiments and along gradients, with the exception of the Swedish subarctic birch forest where amount of litter constituted the best explanatory variable. In a warming experiment in moist acidic tussock tundra in Alaska, temperature together with soil ammonium availability were the most important factors influencing species composition. Overall, dwarf shrub abundance (deciduous and evergreen) was positively related to warming but so were the bryophytes Sphagnum girgensohnii, Hylocomium splendens and Pleurozium schreberi; the majority of other cryptogams showed a negative relationship to warming. This unique combination of intercontinental comparison, natural gradient studies and experimental studies shows that cryptogam diversity and abundance, especially within lichens, is likely to decrease under arctic climate warming. Given the many ecosystem processes affected by cryptogams in high latitudes (e.g. carbon sequestration, N2-fixation, trophic interactions), these changes will have important feedback consequences for ecosystem functions and climate.