Late Cretaceous dinoflagellate cysts of ODP Hole 120-748C

At Ocean Drilling Program Hole 748C in the Southern Indian Ocean, a total of 171 Late Cretaceous dinoflagellate taxa were encountered in 38 productive samples from Cores 120-748C-27R through 120-748C-62R (407-740 mbsf). Four provisional dinoflagellate assemblage zones and five subzones were recognized based on the character of the dinoflagellate flora and the first/last occurrences of some key species. Isabelidinium korojonense and Nelsoniella aceras occur in Zone A together with Oligosphaeridium pulcherrimum and Trithyrodinium suspect urn. Zone B was delineated by the total range of Odontochitina cribropoda. Zone C was separated from Zone B by the presence of Satyrodinium haumuriense, and Zone D is dominated by new taxa. The dinocyst assemblages bear a strong affinity to Australian assemblages. Paleoenvironmental interpretations based mainly on dinocysts suggest that during the ?Santonian-Campanian to the Maestrichtian this portion of the Kerguelen Plateau was a shallow submerged plateau, similar to nearshore to offshore to upper slope environments with water depths of tens to hundreds of meters, but isolated from the major continents of the Southern Hemisphere. Starting perhaps in the late Cenomanian (Mohr and Gee, 1992, doi:10.2973/odp.proc.sr.120.196.1992), the Late Cretaceous transgression over the plateau reached its maximum during the late Campanian. The plateau may have been exposed above sea level and subjected to weathering during the latest Maestrichtian. The studied dinocyst assemblages characterized by species of Amphidiadema, Nelsoniella, Satyrodinium, and Xenikoon together with abundant Chatangiella (the large-size species) and Isabelidinium suggest that a South Indian Province (tentatively named the Helby suite) may have existed during the Campanian-Maestrichtian in comparison with the other four provinces of Lentin and Williams. One new genus, three new species, and two new subspecies of dinocysts are described.

Cretaceous planktonic foraminifera of the Kerguelen Plateau

An almost complete Upper Cretaceous sedimentary sequence recently recovered on the Kerguelen Plateau (southern Indian Ocean) during ODP Leg 183 was analysed for planktonic foraminifera in order to refine and integrate the zonal schemes previously proposed for the Southern Ocean area. Detailed biostratigraphic analysis carried out on holes 1135A, 1136A and 1138A (poleward of 50°S palaeolatitude during Late Cretaceous time) has allowed recognition of low and mid-high latitude bioevents, useful for correlation across latitudes, in addition to known Austral bioevents. The low latitude biozonation can be applied to Turonian sediments, because of the occurrence of Helvetoglobotruncana helvetica, which marks the boundary between Whiteinella archaeocretacea and Helvetoglobotruncana helvetica zones. The base of the Whiteinella archeocretacea Zone falls within the uppermost Cenomanian-Turonian black shale level in Hole 1138A. The stratigraphic interval from upper Turonian to uppermost Santonian can be resolved using bioevents recognized in the mid-high latitude sections. They are, in stratigraphic order: the last occurrence of Falsotruncana maslakovae in the Coniacian, the first occurrence of Heterohelix papula at the Coniacian/Santonian boundary, the extinction of the marginotruncanids in the late Santonian, and the first occurrence of Globigerinelloides impensus in the latest (?) Santonian. The remainder of the Late Cretaceous fits rather well in the Austral zonal scheme, except that Globigerinelloides impensus exhibits a stratigraphic range in agreement with its record at the mid-high latitude sections and extends further downwards than previously recorded at southern sites. Therefore, despite the poor recovery in certain intervals and the presence of several hiatuses of local and regional importance as revealed by correlation among holes, a more detailed zonal scheme has been obtained (mainly for the less resolved Turonian-Santonian interval). Remarks on some species often overlooked in literature are also provided.

Early to middle Miocene radiolarian stratigraphy of the Kerguelen Plateau, Southern Ocean

Early to middle Miocene radiolarian assemblages were examined at three sites (747, 748, and 751) that were cored during Ocean Drilling Program Leg 120 south of the present polar frontal zone on the Kerguelen Plateau (Indian sector of the Southern Ocean). The radiolarian biostratigraphic study relies on a radiolarian zonation recently developed on Leg 113 materials in the Atlantic sector of the Southern Ocean, which is correlated with the geomagnetic time scale. New radiolarian biostratigraphic data also considering the established geomagnetic polarity record were used to improve and emend the age calibration of some lower Miocene radiolarian zones and a redefined middle Miocene radiolarian zonation is proposed. Based on these results, a revised age assignment of the lower Miocene sections drilled at Leg 113 Sites 689 and 690 is proposed.

Paleocene radiolarian distribution and biostratigraphy from offshore eastern New Zealand

A 100-m-thick Paleocene sequence of mainly pelagic sediments at ODP Site 1121, on the eastern flanks of the Campbell Plateau, contains few to common radiolarians of relatively low diversity in the lower 40 m (Early to early Late Paleocene) and abundant, diverse radiolarian assemblages in the upper 60 m (mid-Late Paleocene). The 150 taxa recorded from the entire Paleocene interval are thought to under-represent the actual species diversity by at least one half as many morphotypes have not been differentiated below the level of genus. Assemblages in the lower 40 m are similar to those described from onland New Zealand and DSDP Site 208 (northern Lord Howe Rise); they are correlated with South Pacific radiolarian zones RP4 and RP5. Assemblages in the upper 60 m differ from other known Late Paleocene assemblages in the great abundance of plagiacanthids and cycladophorids. Similarities are noted with later Cenozoic cool-water assemblages. This upper interval is correlated with South Pacific zone RP6, as revised herein, based on comparison with faunas from Site 208 and Marlborough, New Zealand. The interval is also correlated with the upper part of North Atlantic zone RP6 (RP6b-c) based on the presence of Aspis velutochlamydosaurus, Plectodiscus circularis and Pterocodon poculum. Other species, such as Buryella tetradica and Buryella pentadica, are valuable for local correlation but exhibit considerable diachroneity between the Pacific, Indian and Atlantic Oceans. An age model for the Paleocene interval at Site 1121, based on well-constrained nannofossil and radiolarian datums, indicates that the rate of compacted sediment accumulation doubles from 15 to 30 mm/ka at the RP5/RP6 zonal boundary. In large part this is due to a sudden and pronounced increase in accumulation rates for all siliceous fossils; radiolarians and larger diatoms increase from <100 to >10 000 specimens/cm2/ka. This apparent increase in biosiliceous productivity is age-equivalent to a mid-Paleocene cooling event (57-59 Ma) identified from global stable isotope records that is associated with the heaviest delta13C values for the entire Cenozoic.

Late middle Eocene to late Oligocene radiolarian biostratigraphy of ODP Hole 113-689B of Maud Rise, Southern Ocean

We propose a new biostratigraphic scheme comprising the Eucyrtidium spinosum, Eucyrtidium antiquum (new), Lychnocanoma conica (emended), Clinorhabdus robusta (emended) and Stylosphaera radiosa (emended) Zones, in ascending order, in Eocene to Oligocene sediments drilled on Maud Rise in Southern Atlantic Ocean (Site 689, Ocean Drilling Program Leg 113). The bases of these zones are defined by the lowermost occurrences of E. spinosum, E. antiquum, L. conica, C. robusta and the uppermost occurrence of Axoprunum irregularis (?), respectively. From correlation to the magnetostratigraphic data, the E. spinosum, E. antiquum, L. conica, C. robusta and S. radiosa Zones are assigned to the late middle Eocene through late Eocene (Subchrons C17n2 to C13r), earliest Oligocene (C13n to C11n), late early Oligocene (C11n to C10n2), early late Oligocene (C10n1 to C8r) and latest Oligocene (C8r to C7An), respectively. The four boundary datum levels and supplementary datum levels such as the lowermost occurrences of A. irregularis (?), Dicolocapsa microcephala and Lithomelissa challengerae may be recognized in other ODP sites in the Southern Ocean. The first occurrence of E. antiquum approximates the Eocene-Oligocene boundary in Southern Ocean but the last occurrences of many species such as Periphaena decora, D. microcephala and the Lithomelissa sphaerocephalis group are commonly diachronous between high latitude sites. Two new species, Theocyrtis (?) triapenna and Spirocyrtis parvaturris, are described.

Radiolarians from ODP Leg 134 sites

In the cores obtained during Leg 134 of the Ocean Drilling Program, radiolarians occur intermittently and usually in a poor state of preservation, apparently as a result of the region having been at or near the boundary between the equatorial current system and the south-central Pacific water mass during most of the Cenozoic. A few well-preserved assemblages provide a record of the Quaternary forms, and some displaced middle and lower Eocene clasts preserve a record of radiolarians near that subepochal boundary. There are less satisfactory records of middle Miocene and early Miocene to late Oligocene forms.

Diatom stratigraphy of ODP Leg 150 holes

Diatoms are present in middle to lower upper Miocene sections of all holes examined during Leg 150, but are generally absent or in low abundance in Pleistocene to middle upper Miocene sediments. An exception is the alternating diatom-rich, diatom-poor intervals in upper Quaternary sediments. Five new diatom zones, covering an interval from near the lower/middle Miocene boundary to the lower upper Miocene, are proposed. Some of the taxon used to define these zones are also used in zonal schemes for the East Coast of the United States, and allow for correlations to be drawn between this region and Leg 150 sites. Lower Miocene and older levels are not included in this study. Although older Tertiary diatoms are present at some of the sites, dissolution has largely compromised their usefulness as zonal markers.

Radiolarian fauna of sediment core MD96-2089 off Lüderitz, Namibia

The study of radiolarian assemblages from Core MD 962086 provides new information on the variability in the upwelling intensity and origin of upwelled water masses over the past 350 ky in one of the major filamentous regions of the Benguela Upwelling System (BUS), located off Lüderitz, Namibia. The use of key radiolarian species to trace the source of upwelled waters, and the use of a radiolarian-based upwelling index (URI) to reconstruct the upwelling intensity represent the first use of radiolarians for paleoceanographic reconstructions in the BUS. These radiolarian-based proxies indicate strongest upwelling during Marine Isotope Stages (MIS) 3, 5, and 8, which compares well with other studies. While during MIS 3 and 8, the radiolarian-based proxies indicate the influx of waters of Southern Ocean origin, they also point to the increased influence of tropical waters during the lower portion of MIS 5. During MIS 2, 4 and 6 the radiolarian assemblages indicate generally lower upwelling intensities, although this signal is complicated by the increased occurrence of organic carbon in the sediments during these intervals. During MIS 2 there appears to be less of an input of Southern Ocean waters to the BUS, although during the also glacial MIS 4 and 6, there is evidence for an increased influence of cold Antarctic waters. The comparison of the results from Core MD 962086 with other studies in the BUS area indicates a non-uniform pattern of upwelling intensity and advection of cold, southern waters into this system during MIS 2. Weaker upwelling signaled by the radiolarian-based proxy in MIS 4 is in contrast to other studies that indicate higher productivity during this time period. In general, the data show that there is a strong spatiotemporal complexity in upwelling intensity in the BUS and that the advection of water into it is not strongly tied to glacial-interglacial variations in climate.

Siliceous microfossil assemblage and accumulation rate variations across the Middle Eocene Climatic Optimum at ODP Site 171-1051

The Middle Eocene Climatic Optimum (MECO; ~ 40 million years ago [Ma]) is one of the most prominent transient global warming events in the Paleogene. Although the event is well documented in geochemical and isotopic proxy records at many locations, the marine biotic response to the MECO remains poorly constrained. We present new high-resolution, quantitative records of siliceous microplankton assemblages from the MECO interval of Ocean Drilling Program (ODP) Site 1051 in the subtropical western North Atlantic Ocean, which are interpreted in the context of published foraminiferal and bulk carbonate stable isotope (d18O and d13C) records. High diatom, radiolarian and silicoflagellate accumulation rates between 40.5 and 40.0 Ma are interpreted to reflect an ~ 500 thousand year (kyr) interval of increased nutrient supply and resultant surface-water eutrophication that was associated with elevated sea-surface temperatures during the prolonged onset of the MECO. Relatively low pelagic siliceous phytoplankton sedimentation accompanied the peak MECO warming interval and the termination of the MECO during an ~ 70 kyr interval centered at ~ 40.0 Ma. Following the termination of the MECO, an ~ 200-kyr episode of increased siliceous plankton abundance indicates enhanced nutrient levels between ~ 39.9 and 39.7 Ma. Throughout the Site 1051 record, abundance and accumulation rate fluctuations in neritic diatom taxa are similar to the trends observed in pelagic taxa, implying either similar controls on diatom production in the neritic and pelagic zones of the western North Atlantic or fluctuations in sea level and/or shelf accommodation on the North American continental margin to the west of Site 1051. These results, combined with published records based on multiple proxies, indicate a geographically diverse pattern of surface ocean primary production changes across the MECO. Notably, however, increased biosiliceous accumulation is recorded at both ODP Sites 1051 and 748 (Southern Ocean) in response to MECO warming. This may suggest that increased biosiliceous sediment accumulation, if indeed a widespread phenomenon, resulted from higher continental silicate weathering rates and an increase in silicic acid supply to the oceans over several 100 kyr during the MECO.

Radiolarian assemblages of the late Neogene North Pacific

Radiolarian census and abundance data were collected from three deep-sea cores drilled by the Ocean Drilling Program Sites 884, 887 and 1151 to investigate patterns of ecologic changes in space and time during the last 16 million years for the mid-latitude to subarctic North Pacific. High concentrations of radiolarians occurred between 9.0 and 2.7 Ma. Radiolarian species richness was highest in the early middle Miocene at each site and gradually decreased up to about 7 Ma, coinciding with a well-established global cooling trend. A degree of overlap index calculated for radiolarian assemblages revealed 11 faunal change events, of which 8 corresponded to global cooling events and expansions of polar ice sheets. Three of the faunal change events were observed within the peak of radiolarian accumulation rate and were ascribed to changes in primary productivity in the North Pacific rather than global climatic changes. Our assemblage analyses revealed that north-south differentiation in radiolarian assemblages in the northwestern Pacific has existed since 16 Ma and became more distinct via major steps at 6.8 Ma and 2.7 Ma, coinciding with major glaciation events, and that east-west faunal contrasts in the subarctic region became obvious beginning at 11.7 Ma and changed to a different mode around 6.8 Ma. The observed east-west faunal differences possibly reflect east to west climate differences that were characterized by cooler temperatures in the east than the west during the late Miocene (11.7-6.8 Ma) and then by the opposite temperature trend (6.8 Ma-Recent). A severe glaciation at 2.7 Ma played a large role, particularly in temporal changes in radiolarian accumulation rate and assemblage composition.

The Global Plankton Database: an inventory and data from the Former Soviet Union expeditions

At present time, there is a lack of knowledge on the interannual climate-related variability of zooplankton communities of the tropical Atlantic, central Mediterranean Sea, Caspian Sea, and Aral Sea, due to the absence of appropriate databases. In the mid latitudes, the North Atlantic Oscillation (NAO) is the dominant mode of atmospheric fluctuations over eastern North America, the northern Atlantic Ocean and Europe. Therefore, one of the issues that need to be addressed through data synthesis is the evaluation of interannual patterns in species abundance and species diversity over these regions in regard to the NAO. The database has been used to investigate the ecological role of the NAO in interannual variations of mesozooplankton abundance and biomass along the zonal array of the NAO influence. Basic approach to the proposed research involved: (1) development of co-operation between experts and data holders in Ukraine, Russia, Kazakhstan, Azerbaijan, UK, and USA to rescue and compile the oceanographic data sets and release them on CD-ROM, (2) organization and compilation of a database based on FSU cruises to the above regions, (3) analysis of the basin-scale interannual variability of the zooplankton species abundance, biomass, and species diversity.