Taoufik Radi

Dinocyst distribution in surface sediments from the northeastern Pacific margin (40–60°N) in relation to hydrographic conditions, productivity and upwelling

Seventy-six surface marine sediment samples from the northwest margin of North America, between 40°N and 60°N, were analysed for their palynological content in order to document the regional distribution of dinocyst assemblages and their relationships with environmental conditions (sea-surface temperature and salinity, productivity and upwelling). The results illustrate a high concentration of dinocysts, notably in the neritic area (up to 34 000 cysts cm−3) and a relatively high species diversity with 32 taxa identified. The assemblages include cysts of both autotrophic and heterotrophic species. Brigantedinium spp. accompanied by other heterotrophic taxa such as Votadinium spp., Quinquecuspis concreta, Trinovantedinium variabile and Lejeunecysta spp. dominate in the nearshore areas influenced by seasonal upwelling. The offshore sites are dominated by autotrophic taxa represented mainly by Operculodinium centrocarpum, Pyxidinopsis reticulata, Nematosphaeropsis labyrinthus and Impagidinium aculeatum in the south, and by O. centrocarpum, Pentapharsodinium dalei, Spiniferites ramosus and Spiniferites elongatus in the Gulf of Alaska. Principal component analysis demonstrates that the regional distribution of dinocyst assemblages is controlled by the primary productivity and upwelling, and by the winter temperature gradient.

Reconstructing Sea Ice Conditions in the Arctic and Sub-Arctic Prior to Human Observations

Sea ice is a sensitive parameter characterized by a high variability in space and time that can be reconstructed from paleoclimatological archives. The most direct indication of past sea ice cover is found in marine sediments, which contain various tracers or proxies ofenvironments characterized by sea ice. They include sedimentary tracers of particles entrained and dispersed by sea ice, biogenic remains associated with production under/within sea ice or with ice-free conditions, in addition to geochemical and isotopic tracers of brine formation linked to sea ice growth. Reconstructing the extent of past sea ice is, however, difficult because proxies are only indirectly related to sea ice and require the use of transfer functions having inherent uncertainties. In particular, we have to assume a correspondence between sea ice cover values from modern observations and the sea ice proxies from surface sediment samples, which is a source of bias since the time intervals represented by modern observations (here 1954-2000) and surface sediments (10 0 ―10 3 years) are not equivalent. Moreover, suitable sedimentary sequences for reconstructing sea ice are rare, making the spatial resolution of reconstructions very patchy. Nevertheless, although fragmentary in time and space and despite uncertainties, available reconstructions reveal very large amplitude changes of sea ice in response to natural forcing during the recent geological past. For example, during the early Holocene, about 8000 years ago, data from dinocyst assemblages suggest reduced sea ice cover as compared to present in some subarctic basins (Labrador Sea, Baffin Bay, and Hudson Bay), whereas enhanced sea ice cover is reconstructed along the eastern Greenland margin and in the western Arctic, showing a pattern not unlike the dipole anomaly that was observed during the 20th century.

A new heterotrophic dinoflagellate from the North-eastern Pacific, Protoperidinium fukuyoi: cyst–theca relationship, phylogeny, distribution and ecology

The cyst–theca relationship of Protoperidinium fukuyoi n. sp. (Dinoflagellata, Protoperidiniaceae) is established by incubating resting cysts from estuarine sediments off southern Vancouver Island, British Columbia, Canada, and San Pedro Harbor, California, USA. The cysts have a brown‐coloured wall, and are characterized by a saphopylic archeopyle comprising three apical plates, the apical pore plate and canal plate; and acuminate processes typically arranged in linear clusters. We elucidate the phylogenetic relationship of P. fukuyoi through large and small subunit (LSU and SSU) rDNA sequences, and also report the SSU of the cyst‐defined species Islandinium minutum (Harland & Reid) Head et al. 2001. Molecular phylogenetic analysis by SSU rDNA shows that both species are closely related to Protoperidinium americanum (Gran & Braarud 1935) Balech 1974. Large subunit rDNA phylogeny also supports a close relationship between P. fukuyoi and P. americanum. Three subgroups in total are further characterized within the Monovela group. The cyst of P. fukuyoi shows a wide geographical range along the coastal tropical to temperate areas of the North‐east Pacific, its distribution reflecting optimal summer sea‐surface temperatures of ~14–18 °C and salinities of 22–34 psu.

Paleoenvironments of the Strait of Georgia, British Columbia during the last deglaciation: microfaunal and microfloral evidence

The Strait of Georgia is situated between Vancouver Island and the western Canadian mainland. It was deglaciated quickly, around 12,500 14C yr BP, by in situ downwasting. The subsequent marine invasion has left glacimarine sediments with foraminifers, diatoms and dinocysts characterizing successive paleoenvironments recognizable basinwide. The first paleoenvironment represents near-ice conditions under the influence of the turbid meltwater plume marked by low algal productivity and few foraminifers, mostly Elphidium excavatum. Just off the plume, the second environment shows a peak of Nonionellina labradorica possibly resulting from an observed sudden increase in diatom numbers, mostly ice-dwelling forms implying a long annual sea-ice cover. Further away, Cassidulina reniforme increases, N. labradorica decreases while other calcareous foraminifer species colonize the area; there are fewer ice diatoms, more marine planktonic diatoms and dinocysts become more abundant. Finally, after 12,000 14C yr BP, calcareous foraminifers are gradually replaced because of dissolution of calcium carbonate by a low-diversity arenaceous assemblage. At the same time, abundant planktonic diatoms and dinocysts indicate warmer surface temperature. The succession of fossils and environments compares well with modern, horizontal, off-glacier successions observed in fjords of the European Arctic.

PALEOCEANOGRAPHY, BIOLOGICAL PROXIES | Dinoflagellates

Dinoflagellates occur in most aquatic environments and constitute an important part of primary productivity. During their life cycle, some dinoflagellates produce organic-walled cysts (or dinocysts) that fossilize in sediment and are prepared for microscopic observation following palynological procedures. The dinoflagellates producing fossilizable cysts include autotrophic and heterotrophic species that belong either to the phytoplankton or to the microzooplankton. The study of dinocysts on the sea floor has revealed relatively diverse assemblages from the equator to polar environments, with particularly high fluxes in marine environments of the continental margins. The geographical distribution of dinocyst assemblages suggests relationships with sea-surface temperature, salinity, sea-ice cover, and productivity. Qualitative and quantitative approaches permit the reconstruction of past sea-surface conditions.