Isotopic and micropaleontological record of sediments of the Baffin Bay

The oxygen and carbon isotopic compositions of the planktonic foraminifer, Neogloboquadrina pachyderma (sinistral), were determined at 20-cm intervals through the 'composite' top ~ 22 m of sediments at ODP Site 645 (Holes 645B, 645C, 645F, and 645G) and at 10-cm intervals through a 9-m piston core (85-027-016) collected during the Hudson site survey. Quantitative analyses of palynomorphs, notably dinocysts, and of planktonic foraminifers were performed. Organic and nitrogen contents and isotopic composition of nitrogen and carbon in organic matter also were determined. These data provide a high-resolution record of changes that occurred in surface-water masses during the last glacial cycle in Baffin Bay. The basin experienced low planktonic productivity during most of the late Pleistocene, either from dilution in surface water by meltwater discharges from the surrounding ice-sheet or from the presence of a relatively dense sea-ice cover. Peaks of meltwater discharge are indicated by d18O values as low as about 1.5 per mil, correlative d13C- d18O shifts, low concentration of planktonic foraminifers, high concentrations of glacially reworked pre-Quaternary palynomorphs, and low-salinity dinocyst assemblages. As a whole, d18O values ranging between 4.5 and 2.5 per mil allow the establishment of an 18O stratigraphy spanning isotopic stages 5 to 1. Because of the poor core recovery, the general paucity of microflora and microfauna, and the possible occurrence of slumping or debris flow at Site 645, further interpretation remains problematic.

Phytoplankton of the southwest Kara Sea on August 9-12, 2007

A research was carried out along a transect from the Yamal Peninsula coast towards the outer shelf of the southwestern the Kara Sea in September 2007. 130 phytoplankton species were identified, among which 63 were found in the area for the first time. Total phytoplankton abundance varied from of 0.2 x10**9 to 11.3x10**9 cells/m**2, while biomass from 43 to 1057 mgC/m**2. A well pronounced cross-shelf zoning in phytoplankton communities was ascertained. The inner shelf zone about 30 km wide with depths down to 30 meters was characterized by predominance of diatoms (up to 80% of total algal abundance and biomass). The second group by value was dinoflagellates. Seaward in the area of depth increase from 30 to 140 m, the zone of the Yamal Current was located, which was 40 km wide and notable for its active water dynamics. Total abundance in the zone was maximal for the entire investigated area: up to 11.3x10**9 cells/m**2. Autotrophic flagellates were the leading group in phytoplankton, their share in total abundance reached 56-82%. Further than 70 km from the shore, the outer shelf zone was found with the water column rigidly stratified. The highest for the whole area phytoplankton biomass was identified here (up to 1.06 gC/m**2), 80% of which concentrated above the halocline. Diatoms dominated in phytoplankton abundance (up to 92%) and biomass (up to 90%) that resulted from mass development of two species: Chaetoceros diadema and Leptocylindrus danicus.

Sea surface temperature reconstruction based on dinoflagellates from the North Atlantic

The application of quantitative and semiquantitative methods to assemblage data from dinoflagellate cysts shows potential for interpreting past environments, both in terms of paleotemperature estimates and in recognizing water masses and circulation patterns. Estimates of winter sea-surface temperature (WSST) were produced by using the Impagidinium Index (II) method, and by applying a winter-temperature transfer function (TFw). Estimates of summer sea-surface temperature (SSST) were produced by using a summer-temperature transfer function (TFs), two methods based on a temperature-distribution chart (ACT and ACTpo), and a method based on the ratio of gonyaulacoid:protoperidinioid specimens (G:P). WSST estimates from the II and TFw methods are in close agreement except where Impagidinium species are sparse. SSST estimates from TFs are more variable. The value of the G:P ratio for the Pliocene data in this paper is limited by the apparent sparsity of protoperidinioids, which results in monotonous SSST estimates of 14-26°C. The ACT methods show two biases for the Pliocene data set: taxonomic substitution may force 'matches' yielding incorrect temperature estimates, and the method is highly sensitive to the end-points of species distributions. Dinocyst assemblage data were applied to reconstruct Pliocene sea-surface temperatures between 3.5-2.5 Ma from DSDP Hole 552A, and ODP Holes 646B and 642B, which are presently located beneath cold and cool-temperate waters north of 56°N. Our initial results suggest that at 3.0 Ma, WSSTs were a few degrees C warmer than the present and that there was a somewhat reduced north-south temperature gradient. For all three sites, it is likely that SSSTs were also warmer, but by an unknown, perhaps large, amount. Past oceanic circulation in the North Atlantic was probably different from the present.

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.

Palynomorph concentrations in ODP Hole 105-645B samples (Table 1)

Significant changes in terrestrial and marine environments of Baffin Bay occurred throughout the late Pliocene to Holocene. Upper Pliocene and lowermost Pleistocene sediments contain abundant pollen and spores, which indicates the existence of open, coniferous, boreal forest to forest tundra in areas surrounding Baffin Bay. The late Pliocene-earliest Pleistocene also is characterized by relatively rich, dinoflagellate cyst and acritarch assemblages of boreal character, in which the dominance of Cymatiosphaera and Peridiniaceae may indicate neritic influx of sediments. In contrast, the late-early Pleistocene to Holocene interval is marked by a sparse terrestrial and marine palynoflora, with rare productive intervals. The general paucity of the Pleistocene palynoflora suggests low primary productivity, both on land and offshore, probably caused by cold, dry, high arctic conditions.

Strontium-isotope stratigraphy and oxygen- and carbon-isotope record of Middle Jurassic to Early Cretaceous belemnites in the South Atlantic

87Sr/86Sr data of belemnites are presented from a Middle Jurassic-Early Cretaceous succession from the Falkland Plateau (Deep Sea Drilling Project Sites 511 and 330) that was deposited in a periodically anoxic, semi-enclosed shallow water basin. Diagenetically screened strontium-isotope values of 0.706789 rise to 0.707044 before increasing sharply to 0.707428 in the uppermost part of the sampled succession. Comparison with published strontium calibration curves suggests that the oldest samples were Callovian to Oxfordian in age, whilst the remainder of the Jurassic part of the succession consisted of Kimmeridgian and Early Tithonian age sediments. The nannofossil, dinoflagellate and molluscan assemblages provide comparable age determinations. The strontium-isotope analysis of the youngest belemnites points to a Hauterivian-Barremian age, whilst age interpretations based upon the fauna provide a wide age range from the Barremian to early Albian. Strontium-isotope stratigraphy of this succession hence offers increased age resolution providing data regarding the timing of episodes of bottom water anoxia which have been recorded throughout the South Atlantic Basin. Well-preserved belemnite specimens display an oxygen-isotope range between +0.08 and -2.22? (PDB, Peedee belemnite international standard) and a carbon-isotope range from +2.35 to -1.33? (PDB). Delta13C values become increasingly negative through the Late Jurassic-Early Cretaceous and in concert with the 87Sr/86Sr data reveal a trend that could be accounted for by increasing levels of weathering and erosion. The oxygen-isotope data if interpreted in terms of palaeotemperature are consistent with warm palaeotemperatures in the Kimmeridgian and slightly cooler temperatures for the Tithonian and Early Cretaceous parts of the succession. The proposed relative Kimmeridgian warmth (based upon strontium-isotope age assignments) is thus in good agreement with other published palaeotemperature records.

Paleomagnetic and rock magnetic properties of IODP Expedition 318 cores

The Integrated Ocean Drilling Program Expedition 318 to the Wilkes Land margin of Antarctica recovered a sedimentary succession ranging in age from lower Eocene to the Holocene. Excellent stratigraphic control is key to understanding the timing of paleoceanographic events through critical climate intervals. Drill sites recovered the lower and middle Eocene, nearly the entire Oligocene, the Miocene from about 17 Ma, the entire Pliocene and much of the Pleistocene. The paleomagnetic properties are generally suitable for magnetostratigraphic interpretation, with well-behaved demagnetization diagrams, uniform distribution of declinations, and a clear separation into two inclination modes. Although the sequences were discontinuously recovered with many gaps due to coring, and there are hiatuses from sedimentary and tectonic processes, the magnetostratigraphic patterns are in general readily interpretable. Our interpretations are integrated with the diatom, radiolarian, calcareous nannofossils and dinoflagellate cyst (dinocyst) biostratigraphy. The magnetostratigraphy significantly improves the resolution of the chronostratigraphy, particularly in intervals with poor biostratigraphic control. However, Southern Ocean records with reliable magnetostratigraphies are notably scarce, and the data reported here provide an opportunity for improved calibration of the biostratigraphic records. In particular, we provide a rare magnetostratigraphic calibration for dinocyst biostratigraphy in the Paleogene and a substantially improved diatom calibration for the Pliocene. This paper presents the stratigraphic framework for future paleoceanographic proxy records which are being developed for the Wilkes Land margin cores. It further provides tight constraints on the duration of regional hiatuses inferred from seismic surveys of the region.

Palynology of the Middle to Late Miocene from ODP Hole 175-1085A off the west coast of South Africa

Aim To test whether the radiation of the extremely rich Cape flora is correlated with marine-driven climate change. Location Middle to Late Miocene in the south-east Atlantic and the Benguela Upwelling System (BUS) off the west coast of South Africa. Methods We studied the palynology of the thoroughly dated Middle to Late Miocene sediments of Ocean Drilling Program (ODP) Site 1085 retrieved from the Atlantic off the mouth of the Orange River. Both marine upwelling and terrestrial input are recorded at this site, which allows a direct correlation between changes in the terrestrial flora and the marine BUS in the south-east Atlantic. Results Pollen types from plants of tropical affinity disappeared, and those from the Cape flora gradually increased, between 10 and 6 Ma. Our data corroborate the inferred dating of the diversification in Aizoaceae c. 8 Ma. Main conclusions Inferred vegetation changes for the Late Miocene south-western African coast are the disappearance of Podocarpus-dominated Afromontane forests, and a change in the vegetation of the coastal plain from tropical grassland and thicket to semi-arid succulent vegetation. These changes are indicative of an increased summer drought, and are in step with the development of the southern BUS. They pre-date the Pliocene uplift of the East African escarpment, suggesting that this did not play a role in stimulating vegetation change. Some Fynbos elements were present throughout the recorded period (from 11 Ma), suggesting that at least some elements of this vegetation were already in place during the onset of the BUS. This is consistent with a marine-driven climate change in south-western Africa triggering substantial radiation in the terrestrial flora, especially in the Aizoaceae.