Planktonic foraminifera in the latest Maastrichtian of Walvis Ridge, South Atlantic

An abrupt global warming of 3-4°C occurred near the end of the Maastrichtian at 65.45-65.10 Ma. The environmental effects of this warm event are here documented based on stable isotopes and quantitative analysis of planktonic foraminifera at the South Atlantic DSDP Site 525A. Stable isotopes of individual species mark a rapid increase in temperature and a reduction in the vertical water mass stratification that is accompanied by a decrease in niche habitats, reduced species diversity and/or abundance, smaller species morphologies or dwarfing, and reduced photosymbiotic activity. During the warm event, the relative abundance of a large number of species decreased, including tropical-subtropical affiliated species, whereas typical mid-latitude species retained high abundances. This indicates that climate warming did not create favorable conditions for all tropical-subtropical species at mid-latitudes and did not cause a massive retreat in the local mid-latitude population. A noticeable exception is the ecological generalist Heterohelix dentata Stenestad that dominated during the cool intervals, but significantly decreased during the warm event. However, dwarfing is the most striking response to the abrupt warming and occurred in various species of different morphologies and lineages (e.g. biserial, trochospiral, keeled globotruncanids). Dwarfing is a typical reaction to environmental stress conditions and was likely the result of increased reproduction rates. Similarly, photosymbiotic activity appears to have been reduced significantly during the maximum warming, as indicated by decreased delta13C values. The foraminiferal response to climate change is thus multifaceted resulting in decreased species diversity, decreased species populations, increased competition due to reduced niche habitats, dwarfing and reduced photosymbiotic activity.

Ostracoda in sediment core CRP-3 from the Ross Sea, Antarctica

A total of eighteen species of marine ostracods, in at least twelve genera, have been recovered from Early and Late Oligocene glacio-marine sediments from boreholes CRP-3 and CRP-2/2A in the Victoria Land Basin, Ross Sea, Antarctica. Faunas are sparse and generally moderately-well preserved. Previously, three species or closely related species have been recorded only from glacial settings (Kuiperiana meridionalislain (Müller), Australicythere polylyca (Müller), Hemicytheridea aff. H. kinggeorgeensis Blaszyk), but palaeotemperatures somewhat higher than at present in the Ross Sea are suggested by the presence of Austrocythere reticulotuberculata Hartmann, Cluthia aff. C. antiqua Ayress & Drapala and Cytherella? sp. 4796. Majungaella sp. 4471 is an enigmatic component, representing a genus previously known only from warm Cretaceous and Eocene, and relatively warm interglacial Pliocene habitats in southern Gondwana and the Antarctic Peninsula. Palaeobiogeographical considerations indicate that during Early Oligocene times, the Ross Sea area had faunal links with both Antarctic Peninsula/South America and southern Australasia. Three species present in the Early Oligocene glacial environments at Cape Roberts have survived to the Recent in the cool-cold Antarctic/Sub-Antarctic region: Austrocythere reticulotuberculata Hartmann, Australicythere polylyca (Müller), and Kuiperiana meridionalis (Müller).

Early and Middle Miocene calcareous nannofossil distribution in the North Atlantic Ocean

Deep Sea Drilling Project Site 563, located on the west flank of the northern Mid-Atlantic Ridge, recovered a long Miocene section from which magnetostratigraphic and isotopic stratigraphy are available. Quantitative analyses of calcareous nannofossil assemblages have been performed in the Lower and Middle Miocene sediments from Site 563. The abundance patterns of the identified species allow us to determine several bioevents for this time interval. The recognized biohorizons, related to the available magnetostratigraphy, provide new data on the biostratigraphic value of many species and on the synchroneity of the events over a wide geographic area. Relations with the oxygen isotope stratigraphy are also reported. Sphenolith distribution is examined in particular detail due to their biostratigraphic importance in the Early Miocene. In particular the recently described species Sphenolithus procerus, Sphenolithus tintinnabulum and Sphenolithus multispinatus can be useful to subdivide the Lower Miocene zones NN2 and NN3. A large variety of Reticulofenestra pseudoumbilicus has been identified within zones NN6 and NN7.

Mid-Cretaceous planktonic foraminifera off central Morocco

Sites 545 and 547 collectively penetrated 629 m of mid-Cretaceous strata (upper Aptian to upper Cenomanian) off central Morocco during Leg 79 of the Deep Sea Drilling Project. Site 545, at the base of the steep Mazagan Escarpment, records a virtually complete succession of hemipelagic sediments of early late Aptian to middle Cenomanian age. Minor faunal recycling occurred throughout much of the upper Aptian to middle Albian part of the sequence (Cores 55 through 41), reflecting bottom currents along the Mazagan Escarpment. This may be related to the strong upwelling regime and high surface water productivity over Site 545 during the latest Aptian through middle Albian. The upwelling system ceased rather abruptly in this area in late middle Albian time. Recycling of older strata by bottom currents also ceased in the late middle Albian and resulted in a slower average accumulation rate in the upper Albian to middle Cenomanian section of Site 545 (Cores 40 through 28). However, intervals of pebbly claystone conglomerates in Cores 40 and 34 record sporadic instability in the slope adjacent to Site 545. Site 547, located only about 15 km seaward, is situated in a small sub-basin adjacent to the basement block drilled by Site 544. It contains an expanded upper Albian to upper Cenomanian sequence as a result of the numerous conglomeratic intervals throughout much of the section. In contrast to Site 545, the conglomerates were not derived from older strata cropping out on the Mazagan Escarpment; rather, they originated penecontemporaneously from a local unstable slope. A detailed biostratigraphic framework based on planktonic foraminifers is established for the mid-Cretaceous sections of Sites 545 and 547 and a new composite zonal scheme is proposed for the early late Aptian through early late Cenomanian interval. Fifty-five species are recognized and illustrated

Megabenthic communities in the waters around Svalbard during POLARSTERN cruise ARK-VIII/2 (EPOS II)

Composition and distribution of megabenthic communities around Svalbard were investigated in June/July 1991 with 20 Agassiz trawl and 5 bottom trawl hauls in depths between 100 and 2100 m. About 370 species, ranging from sponges to fish, were identified in the catches. Species numbers per station ranged from 21 to 86. Brittle stars, such as Ophiacantha bidentata, Ophiura sarsi and Ophiocten sericeum, were most important in terms of constancy and relative abundance in the catches. Other prominent faunal elements were eunephthyid alcyonarians, bivalves, shrimps, sea stars and fish (Gadidae, Zoarcidae, Cottidae). Multivariate analyses of the species and environmental data sets showed that the spatial distribution of the megabenthos was characterized by a pronounced depth zonation: abyssal, bathyal, off-shore shelf and fjordic communities were discriminated. However, a gradient in sediment properties, especially the organic carbon content, seemed to superimpose on the bathymetric pattern. Both main factors are interpreted as proxies of the average food availability, which is, hence, suggested to have the strongest influence in structuring megabenthic communities off Svalbard.

(Table 3) Stable isotope composition of sof t tissues of specimens from the Sea of Okhotsk

We discovered and investigated several cold-seep sites in four depth zones of the Sea of Okhotsk off Northeast Sakhalin: outer shelf (160-250 m), upper slope (250-450 m), intermediate slope (450-800 m), and Derugin Basin (1450-1600 m). Active seepage of free methane or methane-rich fluids was detected in each zone. However, seabed photography and sampling revealed that the number of chemoautotrophic species decreases dramatically with decreasing water depth. At greatest depths in the Derugin Basin, the seeps were inhabited by bacterial mats and bivalves of the families Vesicomyidae (Calyptogena aff. pacifica, C. rectimargo, Archivesica sp.), Solemyidae (Acharax sp.) and Thyasiridae (Conchocele bisecta). In addition, pogonophoran tubeworms of the family Sclerolinidae were found in barite edifices. At the shallowest sites, on the shelf at 160 m, the seeps lack chemoautotrophic macrofauna; their locations were indicated only by the patchy occurrence of bacterial mats. Typical seep-endemic metazoans with chemosynthetic symbionts were confined to seep sites at depths below 370 m. A comparative analysis of the structure of seep and background communities suggests that differences in predation pressure may be an important determinant of this pattern. The abundance of predators such as carnivorous brachyurans and asteroids, which can invade seeps from adjacent habitats and efficiently prey on sessile seep bivalves, decreased very pronouncedly with depth. We conclude from the obvious correlation with the conspicuous pattern in the distribution of seep assemblages that, on the shelf and at the upper slope, predator pressure may be high enough to effectively impede any successful settlement of viable populations of seep-endemic metazoans. However, there was also evidence that other depth-related factors, such as bottom-water current, sedimentary regimes, oxygen concentrations and the supply of suitable settling substrates, may additionally regulate the distribution of seep fauna in the area. As a consequence of the pronounced pattern in the distribution of seep communities, their ecological significance as food sources of surrounding background fauna increased with water depth. Isotopic analyses suggest that in the Derugin Basin seep colonists feed on chemoautotrophic seep organisms, either directly or by preying on metazoans with chemosynthetic symbionts. In contrast, seep organisms apparently do not contribute to the nutrition of the adjacent background fauna on the shelf and at the slope. In this area, elevated epifaunal abundances at seep sites were caused primarily by the availability of suitable settling substrates rather than by an enrichment of food supply.

Assemblages and isotopic signals of modern ostracodes and host waters from Patagonia, Argentine

Ostracode species assemblages and stable oxygen and carbon isotope ratios of living and recent ostracodes, together with delta18O and delta13C_DIC values of host water samples, provide a first data set that characterizes a wide range of modern aquatic environments in the Laguna Cari-Laufquen (41°S, 68 - 69°W) and the Lago Cardiel area (48 - 49°S, 70 - 71°W) in Patagonia, Argentina. This data set will ultimately be used to interpret and calibrate data acquired from lake sediment cores with the goal of reconstructing past climate. Species assemblages and isotope values can be assigned to three groups; (1) springs, seeps and streams, (2) permanent ponds and lakes, and (3) ephemeral ponds and lakes. Springs, seeps and streams are characterized by Darwinula sp., Heterocypris incongruens, Eucypris fontana, Amphicypris nobilis and Ilyocypris ramirezi. Ostracode and water isotope values range between -13 and -5 per mil for oxygen, and between -15 and -3 per mil for carbon. They are the most negative of the entire sample set, reflecting ground water input with little or no evaporative enrichment. Limnocythere patagonica, Eucypris labyrinthica, Limnocythere sp. and Eucypris aff. fontana are typical species of permanent ponds and lakes. Isotope values indicate high degree of evaporation of lake waters relative to feeder springs and streams and range between -7 and +5 per mil for oxygen, and -5 and +4 per mil for carbon. Limnocythere rionegroensis is the dominant species in ephemeral ponds and lakes. These systems display the most enriched isotope values in both ostracodes and host waters, extending from -5 to +7 per mil for oxygen, and from -5 to +6 per mil for carbon. Living ostracodes show a positive offset from equilibrium values of up to 2 per mil for oxygen. Carbon-isotope values are up to 6? more negative than equilibrium values in highly productive pools. Comparison of ostracode and host water isotope signals permits assessment of the life span of the aquatic environments. Valves from dead ostracodes collected from ephemeral ponds and lakes show a wide scatter with each sample providing a snapshot of the seasonal history of the host water. The presence of the stream species Ilyocypris ramirezi and a wide range of ostracode isotope values suggest that ephemeral ponds and lakes are fed by streams during spring run-off and seasonally dry. A temporary character is also indicated by Heterocypris incongruens, a drought-resistant species that occupies most springs and seeps. In addition, Limnocythere rionegroensis has adjusted its reproduction strategies to its environment. Whereas only females were collected in fresh host waters, males were found in ephemeral ponds and lakes with higher solute content. Sexual reproduction seems to be the more successful reproduction strategy in high and variable salinities and seasonal droughts. The temporary character of the aquatic environments shows that the availability of meteoric water controls the life span of host waters and underlines the sensitivity of the area to changes in precipitation.

(Table 2) Radiolaria species in nodule samples from the Clarion-Clipperton province, Pacific Ocean

Radiolaria were studied in 19 manganese nodules raised from the bottom. The nodules occurred mainly on the surface of thin Quaternary sediments covering Tertiary deposits of various ages (Middle Eocene to Early Miocene). Radiolaria in nodule cores and in inner and surface layers were studied. We found 85 radiolaria species and groups of species. Usually 1-4 to 6-19 radiolaria species were detected in each of the samples. Species belonging to Middle Eocene, Late Miocene to Early Oligocene, and Oligocene to Early Miocene were found. Rare Neogene species were revealed only in fractured surface layers. Age of the nodules is mainly Oligocene. Seismic waves cause sediment vibration, loosening disintegration, and removal of suspension by bottom currents. The vibration effect causes ancient nodules to float up to the surface of Quaternary sediment. This hypothesis suggests the reason for characteristics of the Clarion-Clipperton zone: regional stratigraphic hiatus, accumulation of residual fields of nodules, and the ''floating up'' of nodules to the surface of the Quaternary sediments.

Lower Cretaceous planktonic foraminifer stratigraphy of sediments from ODP Leg 171B sites

During Ocean Drilling Program Leg 171B, an Aptian to Turonian sedimentary succession yielding exceptionally well-preserved planktonic foraminiferal faunas was recovered at Sites 1049, 1050, and 1052. Most of the standard Tethyan planktonic foraminiferal zones have been recognized within the mid-Cretaceous section, with the exception of two Albian zones not reached by any of the drilled holes. In addition, some emphasis is brought here on the current problems concerning the definition of the Aptian/Albian and Albian/Cenomanian boundaries.