Chronostratigraphic summary and raw counts of selected dinoflagellate cysts and architarch taxa of ODP Hole 151-907A

A detailed dinoflagellate cyst investigation of the almost continuous Middle Miocene through Pliocene of Ocean Drilling Program Hole 907A in the Iceland Sea has been conducted at 100-kyr resolution. The investigated section is well constrained by magnetostratigraphy, providing for the first time an independent temporal control on a succession of northern high-latitude dinoflagellate cyst bioevents. Based on the highest/lowest occurrences (HO/LO) and highest common occurrence (HCO) of 20 dinoflagellate cyst taxa and one acritarch species, 26 bioevents have been defined and compared with those recorded at selected DSDP, ODP, and IODP sites from the North Atlantic and contiguous seas, and in outcrops and boreholes from the onshore and offshore eastern U.S.A., and the North Sea and Mediterranean basins. Comparisons reveal near-synchronous HOs of the dinoflagellate cysts Batiacasphaera micropapillata (3.8-3.4 Ma, mid-Pliocene) and Reticulatosphaera actinocoronata (4.8-4.2 Ma, Lower Pliocene) across the Nordic Seas and North Atlantic, highlighting their value on a supraregional scale. This probably applies also to Hystrichosphaeropsis obscura (upper Tortonian), when excluding ODP Hole 907A where its sporadic upper stratigraphic range presumably relates to cooling in the early Tortonian. Over a broader time span within the upper Tortonian, the HO of Operculodinium piaseckii likely also permits correlation across the Nordic Seas and North Atlantic, and the HO of Labyrinthodinium truncatum appears useful in the Labrador and Nordic Seas. Biostratigraphic markers useful for regional rather than supraregional correlation are the HOs of Batiacasphaera hirsuta (c. 8.4 Ma, upper Tortonian) and Unipontidinium aquaeductus (c. 13.6-13.9 Ma, upper Langhian), the HCO of the acritarch Decahedrella martinheadii (c. 6.7-6.3 Ma, Messinian), and possibly the LO of Cerebrocysta irregulare sp. nov. (c. 13.8 Ma, uppermost Langhian) across the Nordic Seas. Since Habibacysta tectata, B. micropapillata, R. actinocoronata and D. martinheadii have been observed in the Arctic Ocean, they are potentially useful for high latitude correlations in the polar domain. The LOs of Habibacysta tectata and Unipontidinium aquaeductus suggest a mid- to late Langhian age (15.1-13.7 Ma) for deposits at the base of Hole 907A, thus providing new constraints on the age of basalts at the base of ODP Hole 907A. The stratigraphically important dinoflagellate cysts Cerebrocysta irregulare sp. nov., and Impagidinium elongatum sp. nov. are formally described.

Late Miocene and Pliocene dinoflagellate cysts, acritarchs and terrestrial palynomorphs from ODP Hole 642B, Vøring Plateau, Norwegian Sea

The globally warm climate of the early Pliocene gradually cooled from 4 million years ago, synchronous with decreasing atmospheric CO2 concentrations. In contrast, palaeoceanographic records indicate that the Nordic Seas cooled during the earliest Pliocene, before global cooling. However, a lack of knowledge regarding the precise timing of Nordic Seas cooling has limited our understanding of the governing mechanisms. Here, using marine palynology, we show that cooling in the Nordic Seas was coincident with the first trans-Arctic migration of cool-water Pacific mollusks around 4.5 million years ago, and followed by the development of a modern-like Nordic Seas surface circulation. Nordic Seas cooling precedes global cooling by 500,000 years; as such, we propose that reconfiguration of the Bering Strait and Central American Seaway triggered the development of a modern circulation in the Nordic Seas, which is essential for North Atlantic Deep Water formation and a precursor for more widespread Greenland glaciation in the late Pliocene.

Aptian to Cenomanian dinoflagellate cysts from the Mazagan Plateau

Eighty-eight samples of Aptian to lower Cenomanian sediments of Sites 545 and 547, DSDP Leg 79, from the Mazagan Plateau area (offshore Northwest Africa) were analyzed for palynomorphs. The very rich dinoflagellate cyst assemblages make it possible to narrow shipboard age determinations and to correlate Sites 545 and 547. The distribution of 174 dinoflagellate cyst taxa is tabulated in this study and the biostratigraphic value of selected dinoflagellate cysts is discussed. Additional taxonomic remarks are made about some species. The new dinoflagellate cyst species Aptea almohadensis, Occisucysta hinzü, O. mazaganensis, and the subspecies Maghrebinia perforata (Clarke and Verdier, 1967) Below, 1981 ssp. mirabilis are described.

(Table 1) Dinoflagellate cysts and acritarchs in upper Pliocene and Pleistocene sediments from ODP Hole 151-911A

Pliocene and Pleistocene sediments from Ocean Drilling Program Leg 151, Hole 911 A, drilled on the innermost Yermak Plateau (Eastern Arctic Ocean), were studied for their dinoflagellate cyst content. Three assemblage zones were tentatively defined, characterized by the predominance of few species. The composition of the assemblages changed markedly, even within single assemblage zones, during the last 2.6 to 2.8 m.y., reflecting the variable influence of warmer water from the Norwegian Sea, fluctuations in the influence of cold polar water masses, and the extent of sea-ice cover. Polar to subpolar surface water masses prevailed on the Yermak Plateau during the late Pliocene, when the eastern Arctic Ocean was probably isolated from the Norwegian-Greenland Sea. Intrusions of warmer water are recorded since the latest Pliocene, alternating with colder periods and a prolonged seasonal sea-ice cover. The composition of the dinoflagellate cyst assemblages has also changed considerably since the middle Pleistocene, reflecting the establishment of stronger fluctuations in surface water mass conditions than before at Yermak Plateau.

Dinoflagellate cyst records from the East Greenland continental margin

Late Weichselian and Holocene dinoflagellate cyst assemblages have been investigated at two stations situated close to the modern Polar Front at the continental margin oft East Greenland. Both the concentrations of dinoflagelate cysts and the assemblage composition reflect changes in the surface water conditions, occurring in distinct steps during the past 15,000 years. Low concentrations of dinoflagellate cysts during Termination Ia suggest harsh environmental conditions, most probably caused by an extensive sea-ice cover and/or a high influx of low salinity meltwater. A surface water warming was recorded from 13,000 - 12,000 years BP, related to the inflow of warmer water trom the North Atlantic into the western Norwegian-Greenland Sea. The interval between Terminations la and Ib was characterized by a strong seasonality with an extensive sea-ice cover in winter and relatively warm surface waters in summer. At the transition to the Holocene, a reorganisation of the hydrography resulted in surface water conditions characteristic for the Holocene with three well-defined major water masses and oceanographic fronts The modern water mass conditions at both stations were established at the end of Termination Ib, around 6,400 to 6,800 years BP. In general, the influence of colder surface waters was more pronounced at the location off Scoresby Sund throughout the Holocene. Arctic water had the strongest influence at both stations in the middle Holocene. A progressive cooling with an increase in sea-ice cover is time-transgressivelyrecorded at both stations during the Holocene, indicating that the Polar Front moved to its present position or that branches of the zonal currents expanded from the East Greenland shell eastward during tlie last 3,000 years.

Dinoflagellate cysts analyses from sediment cores of the Po River discharge plume over the last two centuries

To obtain insight into the natural and/or human-induced changes in the trophic state of the distal portion of the Po River discharge plume over the last two centuries, high temporal resolution dinoflagellate cyst records were established at three sites. Cyst production rates appear to reflect the natural variability in the river's discharge, whereas cyst associations reflect the trophic state of the upper waters, which in turn can be related to agricultural development. The increased abundances of Lingulodinium machaerophorum and Stelladinium stellatum found as early as 1890 and 1920 correspond to the beginning of the industrial revolution in Italy and the first chemical production and dispersion of ammonia throughout Europe. After 1955, the increased abundances of these species and of Polykrikos schwartzii, Brigantedinium spp. and Pentapharsodinium dalei correspond to agriculturally induced alterations of the hypertrophic conditions. A slight improvement in water quality can be observed from 1987 onward.