(Figure 1) Silicoflagellates at DSDP Hole 69-504

Diverse and abundant late Miocene to Pleistocene silicoflagellates at DSDP Site 504 can be correlated by tropical biostratigraphic zones and relative paleotemperature values to eastern tropical Pacific reference site DSDP 503A farther to the west. Early Pliocene assemblages, which were poorly known until now, are present and can be correlated locally between DSDP Holes 504, 503A, and 495, using species events associated with the new Dictyocha pulchella Subzone and Dictyocha angulata Subzone. Silicoflagellate relative paleotemperature values show major warming at 4.7 to 5.0 Ma (Cores 45-48), 3.4 to 3.8 Ma (Cores 32-33), 1.5 to 1.7 Ma (Cores 12-16), and 0.5 to 0.8 Ma (Cores 3-6). Major coolings occurred at 5.0 to 5.1 Ma (Core 51), 3.9 to 4.4 Ma (Cores 38-44), and 1.0 to 1.3 Ma (Cores 8-10). The appearance of Dictyocha longa is proposed to replace the asperoid/fibuloid ratio reversal as the bottom of the Dictyocha fibula Zone, because the non-evolutionary ratio reverses several times in the upper Miocene of Hole 503A, and at least once in Hole 504. Three new Pliocene silicoflagellates are defined: Dictyocha concinna Bukry, n. sp., D. helix Bukry, n. sp., and D. tamarae Bukry, n. sp.

Plant species, biomass and environmental characteristics of relevés along the North America Arctic bioclimate gradient

Question: How do interactions between the physical environment and biotic properties of vegetation influence the formation of small patterned-ground features along the Arctic bioclimate gradient? Location: At 68° to 78°N: six locations along the Dalton Highway in arctic Alaska and three in Canada (Banks Island, Prince Patrick Island and Ellef Ringnes Island). Methods: We analysed floristic and structural vegetation, biomass and abiotic data (soil chemical and physical parameters, the n-factor [a soil thermal index] and spectral information [NDVI, LAI]) on 147 microhabitat releves of zonalpatterned-ground features. Using mapping, table analysis (JUICE) and ordination techniques (NMDS). Results: Table analysis using JUICE and the phi-coefficient to identify diagnostic species revealed clear groups of diagnostic plant taxa in four of the five zonal vegetation complexes. Plant communities and zonal complexes were generally well separated in the NMDS ordination. The Alaska and Canada communities were spatially separated in the ordination because of different glacial histories and location in separate floristic provinces, but there was no single controlling environmental gradient. Vegetation structure, particularly that of bryophytes and total biomass, strongly affected thermal properties of the soils. Patterned-ground complexes with the largest thermal differential between the patterned-ground features and the surrounding vegetation exhibited the clearest patterned-ground morphologies.

Absolute abundances of benthic foraminifers and stable isotopes from the Alvin dives 3709-3712

The presence of gas hydrates on the Blake Ridge diapir, northeastern Atlantic Ocean, offers an opportunity to study the impact of methane seepage on the ecology and geochemistry of benthic foraminifera in the late Holocene. Three push cores, covering a time span of ~ 1000 yrs, were retrieved from three distinct microhabitats at the top of the diapir at a water depth of ~ 2150 m: (i) sediments away from seepage (control core), (ii) sediments overlain by clusters of methanotrophic and thiotrophic bivalves, and (iii) chemoautotrophic microbial mats. The foraminiferal assemblages at the two seep sites are marked by a reduction in benthic foraminiferal species diversity, coupled with a near-absence of agglutinated species. However, an opportunistic population rise in CH4- or H2S-tolerant calcareous species (e.g., Globocassidulina subglobosa and Cassidulina laevigata) that utilize the abundant trophic resources at the seeps has led to an increase in the overall assemblage density there. The delta18O and delta13C values of three species of benthic foraminifera - Gyroidinoides laevigatus, Globocassidulina subglobosa, and Uvigerina peregrina - and the planktonic species Globorotalia menardii were acquired from all three cores. The benthic species from methane seeps yield delta13C values of 0.1 to - 4.2 (per mil VPDB), that are distinctly more 13C-depleted relative to the delta13C of 0.4 to - 1.0 (per mil VPDB) at the control (off seep) site. The species from a mussel-bed site exhibit more negative delta13C values than those from microbial mats, possibly reflecting different food sources and higher rate of anaerobic oxidation of methane. The positive delta13C values in the paired planktonic species suggest that authigenic carbonate precipitation did not overprint the observed 13C depletions. Hence the probable cause of negative delta13C of benthic foraminifera is primary calcification from Dissolved Inorganic Carbon (DIC) containing mixed carbon fractions from (a) highly 13C-depleted, microbially-oxidized methane and (b) a seawater source.