Culture experiments to evaluate CO2 effects on growth and morphology of the coccolithophore Pleurochrysis cf. pseudoroscoffensis

In the framework of the Italian project CO2 Monitor, two culture experiments were carried out in vertical closed photobioreactors with Pleurochrysis cf. pseudoroscoffensis Gayral & Fresnel 1983, a coccolithophore isolated from the Gulf of Trieste (North Adriatic Sea). The aim of this study was to investigate the effects induced by pH variations due to CO2 emissions on its growth and morphology. Two experiments were carried out with two different CO2 concentrations (1 and 2%). Growth and cell size in light microscopy, morphology and coccolith size in scanning electron microscopy, particulate nitrogen (PN) and particulate inorganic and organic carbon (PIC and POC) content of the coccolithophore were investigated during the light and dark phases. Dissolved inorganic nutrient (nitrate and phosphate) concentrations and pH of the medium and the presence of heterotrophic prokaryotes (HP) were monitored as well.

Calcareous nannofossil biostratigraphy of ODP Leg 108 sediments

Calcareous nannofossils were examined from the 400 cores recovered at 12 sites during Ocean Drilling Program Leg 108 in the eastern equatorial Atlantic Ocean and along the northwest African margin, representing a transect spanning 24° of latitude. Thirty calcareous nannofossil biohorizons were recognized in the Neogene and Quaternary sequences; only Site 661, located in water depths of 3500 m, contains a fossiliferous record older than the Oligocene. At Site 661, a 200-m-thick sequence of Upper Cretaceous sediments yielded Maestrichtian and uppermost Campanian nannofossils, yet a continuous Cretaceous/Tertiary boundary was not recovered. Widespread sediment slumps and turbidites deposited at many sites interrupted the pelagic sedimentation. A careful study of calcareous nannofossil and foraminifer assemblages correlated to paleomagnetic records suggests that "slumped" units at most sites were added as extra sediments to rapidly deposited pelagic sediments, with minor disturbance of the surrounding layers. Nannofossils are generally common to abundant and moderately preserved at all sites except for those located in two upwelling areas, where placoliths are etched and discoasters overgrown. Typical low-latitudinal zonal markers were used during this study, yet some of them were considered to be of little biostratigraphic value because of their inconsistent stratigraphic ranges and low abundances. This is especially apparent for the intervals representing the Miocene/Pliocene and Oligocene/Miocene boundaries. Characteristic nannofossils of cool-water conditions and low discoaster abundances occur at the coastal African upwelling and along the south equatorial divergence sites, signifying a stronger advection of cold waters toward the equator within the Canary and Benguela eastern boundary currents.

Paleogene and early Neogene planktonic foraminifera of ODP sites 119-738 and 119-744

A virtually complete composite history of Cenozoic pelagic sedimentation was recovered from ODP Sites 738 (62°43' S) and 744 (61°35' S), drilled during Leg 119 on the Kerguelen Plateau. An excellent magnetobiochronologic record was obtained from upper Eocene through Holocene sediments at Site 744, and an expanded lower Paleocene through lower Oligocene sequence was cored at Hole 738. Analysis of the stratigraphic distribution of over 125 planktonic foraminifer taxa from these sites reveals changes in species composition that were strongly influenced by the climatic evolution of Antarctic water masses. Early Paleocene planktonic foraminifer assemblages are nearly identical in species composition to coeval assemblages from low and middle latitude sites, showing the same patterns of post-extinction recovery and taxonomic radiation. Biogeographic isolation, revealed by the absence of tropical keeled species, became apparent by late early Paleocene time. Diversity increased near the Paleocene/Eocene boundary when keeled morozovellids immigrated to the Kerguelen Plateau. Greatest diversity (23 species) was achieved by early Eocene time, corresponding to a Cenozoic warming maximum that has been recognized in lower Eocene deep sea and terrestrial sediments worldwide. A gradual decline in diversity from the late early through middle Eocene, primarily due to the disappearance of acarininids, parallels the record of cooling paleotemperatures in Southern Ocean surface waters. Chiloguembelina-dominated assemblages appeared in the late middle Eocene and persisted through the early Oligocene as Antarctic surface waters became thermally isolated. Late Eocene and early Oligocene assemblages exhibit considerably lower diversity than the older Eocene faunas, and were dominated by chiloguembelinids, subbotinids, and catapsydracids during a time of pronounced climatic cooling and development of continental glaciation on East Antarctica. The small foraminifer Globigerinit? juvenilis replaced chiloguembelinids as the dominant taxon during the late Oligocene. Diversity increased slightly toward the end of the late Oligocene with new appearances of several tenuitellid, globoturborotalitid, and globigerinid species. The trend toward diminishing planktonic foraminifer diversity was renewed during the late early Miocene as siliceous productivity increased in the Antarctic surface waters, culminating with the reduction to nearly monospecific assemblages of Neogloboqu?drin? p?chyderm? that occur in Pliocene-Holocene biosiliceous sediments. An Antarctic Paleogene zonal scheme previously devised for ODP Sites 689 and 690 in the Weddell Sea is used to biostratigraphically subdivide the Kerguelen Plateau sequence. The definition of one Antarctic Paleogene biozone is modified in the present study to facilitate correlation within the southern high latitudes. The ages of 13 late Eoceneearly Miocene datum events are calibrated based on a magnetobiochronologic age model developed for Site 744.

Tab. 1+2: C14-dates cf the older and younger emergence periods

In the neighbourhood of Oobloyah Bay various phenomena ean be eneountered whieh point to a ularge-seale uplift of shorelines, i.e. to an emergence of 200 m. Delta terraces, deltaic fan terraces and glacio-marine sands are regarded by the author as being the most reliable evidence of this. The marine limit documented by glacio-marine sand is to be found at ~170 m a.s.l. Hints of ancient shorelines located at a higher level exist only in the shape of badly preserved raised beaches. They were classified as less reliable records of past sea-levels, due to the lack of marine fossils and/or drift wood, and furthermore because those forms had been strongly influenced by periglacial processes. Deltaic deposits are of more importance in this context. The glacio-marine deltaic sands of several terrace levels contain terrestrial plant remnants which delivered C14dates. Using these dates und the relative elevations of terraces the emergenee of the area investigated could be recorded. This occured in a series of phases (and steps) which were summarized into two periods: an early period of emergenee which took place from at least 25 300 years B.P. to later than 17 340 years B.P. and a later one from at least 12 870 years B.P. up to the present day. The emergence seems to represent a discontinuous but regular sequence of relative sea level movements without intermittent submergence. Since the deltaic fans of the early emergence period were accumulated by sediments through glacio-fluvial channels of an adjacent glacier body the appropriate location of this glacial stage for one of the glaciers delivering meltwater (Nukapingwa Glacier) could be reconstructed. This stage of the glacier appears to belong to a retreating phase of the Mid-Wisconsin (?). The later period of emergence resulted in six rather glacio-marine delta terrace generations at the mouths of the main rivers with glaciofluvial regimen debouching into the Oobloyah Bay. A connection of this emergence with the glacial history of the field area is discussed. If one may rely on the age determinations of land derived plant fossils and their application for the climatic history of the area investigated, it must be concluded that the Heidelberg Valley, to a large extent, was alreaely deglaciated 25 000 years ago. The existence of a "Cockburn"-Phase in the sense of a major readvanee in Late Wisconsin times appears to be doubtful, or has been developed rather weakly.

Neogene calcareous nannofossils in ODP Leg 116 holes

The three sites (717, 718, and 719) drilled on the distal Bengal Fan during ODP Leg 116 cored turbidite sediments almost exclusively. Calcareous nannofossils were recovered sporadically and, although all of them probably have been redeposited, it is possible to date the sediments at all three sites with reasonable confidence. Site 717 penetrated the uppermost middle Miocene Catinaster coalitus highest occurrence datum and represents the most nearly continuous succession of turbidites. Site 718 penetrated the lower Miocene, well below the Helicosphaera ampliaperta highest occurrence datum, but this site contains a major late Pliocene to mid-Pleistocene hiatus. Site 719, the shallowest hole, penetrated only into the upper Miocene. Identification of several critical lowest occurrence datums allows using the poorly constrained but more numerous highest occurrence datums for comparison with the model succession (zonal markers) and thereby to derive a reasonably accurate time framework for the sediments.

(Table 2) Taxonomic composition of diatoms from bottom deposits of the Kronotsky Bay

Eocene diatom and silicoflagellate complexes from deposits of the Kronotsky Bay are presented. Pro tempore they are the most ancient finds of fossil phytoplankton with silica skeletons in the Northwest Pacific. More than 130 diatom species belonging to 59 genera and 24 silicoflagellate species belonging to 5 genera have been determined. Three Middle Eocene complexes (of the Lisitzinia kanayai, Lisitzinia inconspicua var. trilobata, and Praecymatosira monomembranaceae zones) and one presumably Middle-Late Eocene complex (of the zone with Rylandsia conniventa) of diatoms have been identified. For the first time a large silicoflagellate complex attributable to the Dictyocha hexacantha zone is presented. It is assumed that the complexes formed mainly in bathyal conditions at relatively high (close to sub-tropical) temperatures of surface waters.