Total phytoplankton abundance and biomass in the surface and fluorescence maximum layers and contributions of dominant species to their values in the Werstern Arctic in July-August 2003

Phytoplankton community was studied in the Bering Strait and over the shelf, continental slope, and deep-water zones of the Chukchi and Beaufort Seas in the middle of the vegetative season (July-August 2003). Its structure was analyzed in relation to ice conditions and seasonal patterns of water warming, stratification, and nutrient concentrations. Overall variations in phytoplankton abundance from 200 to 6000000 cells/l and biomass from 0.1 to 444.1 µg C/l.were estimated. The bulk of phytoplankton cells concentrated in the seasonal picnocline at depths 10-25 m. The highest values of cell abundance and biomass were recorded in regions influenced by inflow of Bering Sea waters or characterized by intense hydrodynamics, such as the Bering Strait, Barrow Canyon, and the outer shelf and slope of the Chukchi Sea. In the middle of the vegetative season, phytoplankton in the study region of the Western Arctic proved to comprise three successional (seasonal) assemblages: early spring, late spring, and summer assemblages. Their spatial distribution was dependent mainly on local features of hydrological and nutrient regimes rather than on general latitudinal trends of seasonal succession characteristic of arctic ecosystems.

Uppermost Jurassic to lower Cretaceous benthic foraminifera from ODP Hole 123-765C

Benthic foraminifers were studied in 99 samples collected from the lower 200 m of Hole 765C. The studied section ranges from the Tithonian to Aptian, and benthic foraminifers can be subdivided into five assemblages on the basis of faunal diversity and stratigraphic ranges of distinctive species. Compared with deep-water assemblages from Atlantic DSDP sites and Poland, assemblages from the Argo Abyssal Plain display a higher diversity of agglutinated forms, which comprise the autochthonous assemblages. Assemblages at the base of Hole 765C are wholly composed of agglutinated forms, reflecting deposition beneath the carbonate compensation depth (CCD). Most calcareous benthic species are found in turbidite layers, and the presence of an upper Valanginian Praedorothia praehauteriviana Assemblage may indicate deposition at or just below the CCD. The P. praehauteriviana Assemblage from Hole 765C is the temporal equivalent of similar assemblages from DSDP Holes 534A, 416A, 370, 105, and 101 in the Atlantic Ocean and Hole 306 in the Pacific Ocean. Stratigraphic ranges of cosmopolitan agglutinated species at Site 765 generally overlap with their reported ranges in the Atlantic and in the bathyal flysch sequences of the Carpathians; however, several species from Hole 765C have not been previously reported from Uppermost Jurassic to Lower Cretaceous abyssal sediments.

(Table 1) Geochemistry of upper Paleocene and upper Eocene glass particles at DSDP Hole 80-549

Two ash horizons have been identified in Hole 549, one in the upper Paleocene (basal NP9), the other in the upper Eocene (NP18); both are mixed lithic crystal tuffs of rhyolitic composition. These tuffs are absent in Hole 550 owing to unconformities, but the basal Eocene (NP10) of Hole 550 includes a series of over 50 thin bentonite layers. Intermediate plagioclase associated with these bentonites indicates that the original ash was of basaltic to andesitic composition. The bentonites are absent in Hole 549, probably because of an unconformity, but they have been identified in Hole 401 (Leg 48, Bay of Biscay). Two of the pyroclastic phases can be matched with phases previously reported for the North Sea Basin. The bentonites of Site 550 are probably equivalent to the widespread "ash series" of northwestern Europe, which may therefore be regarded as being lower Eocene in terms of Martini's calcareous nannoplankton zonation.

Geochemical investigations of volcanic ash layers from ODP Leg 119

Geochemical investigations were carried out on 19 discrete ash layers and on 42 dispersed ash accumulations in Oligocene to Pleistocene sediments from Sites 736, 737, 745, and 746 of ODP Leg 119 (Kerguelen Plateau in the southern Indian Ocean). The chemical data obtained from more than 500 single-grain glass analyses allow the characterization of two dominant petrographic rock series. The first consists of transitional- to alkali-basalts, the second mainly of trachytes with subordinated alkali-rhyolites and rhyolites. Chemical correlation with possible source areas indicates that the tephra layers from the northern Kerguelen Plateau Sites 736 and 737 were probably erupted from the nearby Kerguelen Islands. The investigated ash layers clearly reflect the Oligocene to recent changes in the composition of the volcanic material recorded from the Kerguelen Islands. The dispersed ashes from Sites 745 and 746 in the Australian-Antarctic Basin display almost the same range in chemical compositions as those from the north. Heard Island and other sources may have contributed to their formation, in addition to the Kerguelen Islands. Dispersed ash of calc-alkaline composition is most probably derived from the South Sandwich island arc, indicating sea-ice rafting as an important mechanism of transport.

Geochemistry of marin ash layers and epiclastic rocks from the Kerguelen Plateau

Epiclastic volcanogenic rocks recovered from the Kerguelen Plateau during Ocean Drilling Program Legs 119 and 120 comprise (pre-)Cenomanian(?) claystones (52 m thick, Site 750); a Turonian(?) basaltic pebble conglomerate (1.2 m thick, Site 748; Danian mass flows (45 m thick, Site 747); and volcanogenic debris flows of Quaternary age at Site 736 (clastic apron of Kerguelen Island). Pyroclastic rocks comprise numerous Oligocene to Quaternary marine ash layers. The epiclastic sediments with transitional mid-ocean-ridge basalt (T-MORB) origin indicate weathering (Site 750) and erosion (Site 747) of Early Cretaceous T-MORB from a then-emergent Kerguelen Plateau, connected to Late Cretaceous tectonic events. The basal pebble conglomerate of Site 748 has an oceanic-island basalt (OIB) composition and denotes erosion and reworking of seamount to oceanic-island-type volcanic sources. The vitric- to crystal-rich marine ash layers are a few centimeters thick, have rather uniform grain sizes around 60 ± 40 µm, and are a result of Plinian eruptions. Crystal-poor silicic vitric ashes may also represent co-ignimbrite ashes. The ash layers have bimodal, basaltic, and silicic compositions with a few intermediate shards. The basaltic ashes are evolved high-titanium T-MORB; a few grains in a silicic pumice lapilli layer have a low-titanium basaltic composition. The silicic ashes comprise trachytic and rhyolitic glass shards belonging to a high-K series, except for a few low-K glasses admixed to a basaltic ash layer. Feldspar and clinopyroxene compositions fit the glass chemistry: high-Ti tholeiite-basaltic glasses have Plagioclase of An40-80 and pigeonite to augite clinopyroxene compositions. Silicic ashes have K-rich anorthoclase and minor Plagioclase around An20 and ferriaugitic to hedenbergitic clinopyroxene compositions. The line of magmatic evolution for the glass shards is not compatible with simple two-end member (high-Ti T-MORB and high-K rhyolite) mixing, but favors successive Ca-Mg-Fe pyroxene, Ti magnetite, and apatite fractionation, and K-rich alkali feldspar fractionation in trachytic magmas to yield rhyolitic compositions. Plagioclase fractionation occurs throughout. This qualitative model is in basic accordance with the observed mineral assemblage. However, as the time span for explosive volcanism spans >30 m.y., this basic model cannot comply with fractional crystallization in a single magma reservoir. The ash layers resulted from highly explosive eruptions on Kerguelen and, with less probability, Heard islands since the Oligocene. The explosive history starts with widespread Oligocene basaltic ash layers that indicate sea-level or subaerial volcanism on the Northern Kerguelen Plateau. After a hiatus of 24 m.y.(?), explosive magmatic activity was vigorously renewed in the late Miocene with more silicic eruptions. A peak in explosive activity is inferred for the Pliocene-Pleistocene. The composition and evolution of Kerguelen Plateau ash layers resemble those from other hotspot-induced, oceanic-island realms such as Iceland and Jan Mayen in the North Atlantic, and the Canary Islands archipelago in the Central Atlantic.

On the fine structure of oxygen distribution in surface water layers in the area between Iceland and Faroe Islands

During the international "Overflow-Expedition'' 1973 on R.V. "Meteor" oxygen concentrations in surface layers were measured in order to determine the oxygen gradients within the first two meters and to add some informations to the mechanisms of oxygen exchange at the air-sea interface. These investigations may be interesting also with regard to longterm- observations of the oxygen distribution in the Atlantic, especially the problem of the A.O.U. (apparent oxygen utilization) determination. To measure oxygen gradients a special sampler was built which is able to take water samples each 20 cm of the first 2 meters. These data were supplemented by further samples down to 150 m, taken by conventional water samplers, from which samples were also taken to measure N2/O2-relations. By comparing these relations with theoretical relations in air-saturated water the influence of biological production and consumption on the oxygen contents in water could be estimated. A simple glass apparatus was built to extract gas from the water samples, and hereafter the N2/O2-relations were determined by mass spectrometry. Most distributions of the oxygen anomaly show a negative oxygen balance which varies largely, probably due to strong mixing processes in the Iceland-Faroe ridge area. The distribution of surface oxygen saturation values are of two different types. The values of the stations 260, 262 and 270 stem from mixed water and show homogeneous supersaturations, as can be found instantly when whitecaps appear. The values of 9 other stations are from water, sampled during calm periods which has been mixed and supersaturated before. They show a decreasing oxygen saturation towards the sea surface and often undersaturation in the upper decimeters up to 98 % and even 91 %. So at the air-sea interface even less initial oxygen saturation than 100 % can be found after supersaturation during heavy weather periods.

Dinoflagellates and pollen of the Brito-Arctic Igneous Province flora, ODP Hole 104-642E

Palynological studies of the intrabasaltic sediment layers in the lower volcanic series from ODP Leg 104 outer Voring Plateau Hole 642E Cores 102 through 109 indicated abundant pollen and rarer dinoflagellate cysts. The dinoflagellates belong to the Apectodinium hyperacanthum Zone and indicate an age equivalent to nannoplankton Zones NP9-lower NP10 around the Paleocene/Eocene boundary. The pollen and spore assemblage found here in 12 of the samples from the lower volcanic series is of well- preserved and distinctive specimens and contains unusual forms of pollen from the Taxodiaceae and the Hamamelidae. It has not been transported far from vegetation that was dominated by conifer forest with some ferns and deciduous arborescent angiosperms. Nearly identical assemblages are found elsewhere in the Brito-Arctic Igneous Province, in intrabasaltic sediments from eastern Greenland, the Faeroe Islands, the Isle of Mull, and Antrim (Northern Ireland), and above basalt at the Rockall Plateau. The assemblage is also present in sediments around the Paleocene/Eocene boundary in Spitsbergen. This pollen and spore flora is also associated with dinoflagellate cysts of the Apectodinium hyperacanthum Zone in the deposits from eastern Greenland, the Rockall Plateau, and Spitsbergen, suggesting that these are correlative. Assemblages of the same age from the North Sea, Denmark, and the London and Paris Basins are different. Paleobotanical evidence suggests a short survival of the intrabasaltic flora, and that all the deposits considered here are of about the same age. We propose that at around the Paleocene/Eocene boundary a distinct flora, named here as the Brito-Arctic Igneous Province (BIP) flora, occurred on the line of volcanicity stretching from Rockall to the Greenland Sea, and even to Spitsbergen. Geophysical evidence supports our view that the Rockall to East Greenland intrabasaltics are more or less contemporaneous, at about the Paleocene/Eocene boundary. However, the comparable pollen and spore assemblage in the Hebridean province, at Mull and Antrim, is from pyroclastics that may be a little older.