Planktonic foraminifera of sediment core T89-40 on the Walvis Ridge, South Atlantic

Core T89-40, eastern Walvis Ridge between the subtropical gyre and Benguela coastal upwelling system, contains three types of levels of abundant left-coiled Neogloboquadrina pachyderma, a cold, eutrophic species, next to subtropical species. Type A peaks (362, 110 and 53-43 ky BP) are accompanied with high percentages of other eutrophic species. They are attributed to intensified upwelling in the Northern Benguela region. Type B peaks (129 and 92 ky BP) are accompanied by moderate (<48%) contributions of other eutrophic species and increased numbers of subtropical species. These suggest intensified upwelling in the Northern Benguela cells and may reflect increased seasonal contrasts between the winter upwelling and the subtropical summer conditions. The highest C-peaks, up to 38%, are associated with strongly reduced percentages of other eutrophic species and with abundant subtropical species (Marine Isotopic Stage 11.3 (401 ky) and 9.3 (326 ky)). The subtropical species preceeded the C-peaks by ca 8 ky. We argue that the C-peaks were not produced by local reproduction but expatriated from the Northern Benguela upwelling cells. Here more nutrient-rich waters may have produced a mono-specific Neogloboquadrina pachyderma (left) fauna during strong polewards shifts of the frontal systems in the South Atlantic, which could have been transported 700 km offshore to the core location, unadmixed with eutrophic species from the surrounding waters. We propose meandering shelf-edge jets, strong contour jets, as a mechanism for the transport. The timing of the C-peaks and associated subtropical peaks agrees with the known precessional cyclicity of the SE Atlantic front movements and zonality of the trade winds, which supports the shelf-edge jet hypothesis.

Distribution of benthic foraminifera in lower Cretaceous sediments of the Cuvuer Abyssal Plain in the Indian Ocean

Analysis of 66 samples from DSDP Site 263 (Cores 263-4R-4 to 263-29R-4) reveals a unique faunal composition with a predominance of agglutinated taxa, many of them previously unrecorded from any other DSDP and ODP Indian Ocean sites. A total of 66 agglutinated and 31 calcareous taxa are documented and five new species are described: Hippocrepina gracilis n.sp., "Textuluriopsis" elegans n.sp., Aaptotoichus challengeri n.sp., "Gaudryinopsis" pseudobettenstaedti n.sp. and "Gaudryina" cuvierensis n.sp. Three assemblages are recognized based on changes in the composition of dominant taxa and occurrences of stratigraphically important species: (1) a high-diversity Valanginian to Barremian Bulbobaculites-Recurvoides Assemblage (Cores 263-29R to - 18R), comprised of numerous elongate agglutinated forms, rare nodosariids, and variable numbers of tubes and ammodiscids; (2) a moderately diverse Aptian to Albian Rhizammina-Ammodiscus-Glomospira Assemblage (Cores 263-18R to -7R) with highly fluctuating numbers of the nominate taxa and Haplophragmoides, Trochammina, Verneuilinoides spp., and Verneuilina howchini; (3) a very low diversity Albian or younger Assemblage (Cores 263-6R to -4R) containing sparse agglutinated foraminifera, rare nodosariids and rotaliids. We interpret the assemblages as shelf to lower slope and consider them to reflect a deepening palaeobathymetry as the Cuvier margin subsided after the initial breakup of East Gondwana during the Valanginian. Our interpretation is in sharp contrast with initial palaeodepth estimates of less than 100 m, as well as with original chronostratigraphic interpretations based on foraminifera and nannofossils which correlated the base of the recovered interval with the Aptian. The absence of many cosmoplitan forms, despite high diversity suggests strong faunal differentiation in the Austral realm or endemisn within the Cuvier Basin during the Early Cretaceous.

Planktonic foraminifera in Core ML2_66, North Atlantic

Evolution of approaches and methods for reconstruction of paleoenvironmental conditions from microfossils contained in bottom sediments is assessed. Authors elaborated a new actualistic basis for such reconstructions, consisting of a database on contents of tests of planktonic foraminifers in the surface layer of Atlantic sediments and a package of mathematical tools for computer data processing. Structure of the database is described. It contains data on test contents for 29 species and varieties of planktonic foraminifers in 381 samples. A mathematical model designed for reconstructions is based on factor analysis and multidimensional spline interpolation. The model allows one to deduce Quaternary hydrological parameters (paleotemperature, paleosalinity) for standard hydrological levels down to depth of 250 m for the four seasons of the year. Reconstructions are illustrated by an example of a sedimentary core from the North Atlantic representing a period of 300 ky. During the next to last and the last maxima of continental glaciation (oxygen isotope stages 8, 6, 4, and 2), the subarctic water mass was spread here. Winter and summer surface water temperatures comprised 1-5° and 5-7°C, respectively. During interglacials and in Holocene the conditions were close to present ones: winter and summer surface water temperatures comprised 10-12 and 15-17°C, respectively. Vertical paleohydrological profiles compiled for peaks of climatostratigraphic intervals suggest that during cold intervals water stratification was stronger than during the warm ones. At depth 50 m seasonal salinity oscillations did not exceed 0.4 per mil and commonly salinity was minimum in winter and maximum in summer.

Stable isotope ratios of foraminifera from ODP Hole 171B-1051B sediments

The primary aim of the this investigation was to examine the stability of subtropical sea-surface temperatures and reconstruct the surface-to-benthos thermal gradient. High-resolution stable isotopic analyses (18O and 13C) were conducted on late middle Eocene planktonic and benthic foraminifers recovered from Hole 1051B, Blake Nose, western North Atlantic. The sequence comprises a siliceous nannofossil and foraminifer ooze, with well-preserved calcareous microfossils. Isotopic examination was conducted on the mixed-layer dweller Morozovella spinulosa and the benthic foraminifer Nuttalides truempyi at this subtropical site.

Upper Turonian - lower Campanian planktonic foraminifera from Exmouth Plateau

A planktonic foraminiferal zonal scheme is presented for subdivision of the Upper Cretaceous pelagic carbonate sequence from southern mid-high latitudes. Definition of the zones is based on first and last occurrences of planktonic foraminifera from Ocean Drilling Program Holes 762C and 763B (Leg 122; Exmouth Plateau, south Indian Ocean). During the Late Cretaceous the studied holes were located close to 50°S and for the first time a complete sedimentary record for the mid-high latitudes was obtained. A detailed biostratigraphic analysis has allowed recognition of two new zones (Falsotruncana maslakovae Zone and Marginotruncana marianosi Zone) for the interval extending from the last occurrence of Helvetoglobotruncana helvetica to the first occurrence of Dicarinella asymetrica (upper Turonian - lower Santonian). From this study it is apparent that some low latitude (Globotruncana ventricosa, Hedbergella flandrini, Marginotruncana marianosi) and high latitude (Globigerinelloides impensus and Hedbergella sliteri) marker taxa display a vertical distribution at mid-high latitudes which is different from that known from low latitudes; moreover, one species (Heterohelix papula), overlooked at low latitudes, exhibits a restricted range that seems to be useful for chrono-biostratigraphic correlations: its appearance is suggested to coincide with the Coniacian/Santonian boundary. The proposed biozonation, which is integrated with calcareous nannofossil and magnetostratigraphic data available for the sections studied, is compared with both the low-latitude standard zonation and the planktonic foraminiferal zonal scheme for the circum-Antarctic region, in order to define a bio-chronostratigraphic scale that is useful for mid-high latitudes of the southern oceans.

Benthic foraminifera of ODP Leg 116 holes

Benthic foraminifers were examined from turbiditic sequences at Sites 717, 718, and 719. Three assemblages, 1, 2, 3, were identified and are interpreted as reflecting different bathymetric environments. Based on the distribution patterns of these assemblages, six paleontological intervals (a to f) were distinguished and correlated to the lithostratigraphic units and calcareous nannofossil biostratigraphy and biochronology. This relationship indicated three signals of climatic deterioration, the first in the late Pliocene (around 2.42 Ma) and two others in the Pleistocene (younger than 1.59 Ma and 0.93 Ma).

Planktonic foraminifera stratigraphy and datum events of ODP Leg 198 sites

During Leg 198 of the Ocean Drilling Program (ODP), Paleogene sediments were recovered form 10 holes at four sites along a bathymetric transect from the Southern High of Shatsky Rise. In terms of age, the Paleogene successions span from the Cretaceous/Paleocene boundary to the early Oligocene. Sediments are mainly composed of tan nannofossil ooze with scattered darker layers richer in clay. This data report concerns planktonic foraminiferal biostratigraphy from three holes, specifically Hole 1209A (water depth = 2387 m), Hole 1210A (water depth = 2573 m), and Hole 1211A (water depth = 2907 m). The thickness of Paleogene sediments is 105.90 m in Hole 1209A, 95.05 m in Hole 1210A, and 56.11 m in the deepest Hole 1211A. Preliminary investigations conducted on board revealed that at Site 1209 the succession was mostly complete, whereas the succession was more condensed at Site 1211.

Stable isotope record of benthic foraminifera from the Gulf of California

A high-resolution, accelerator radiocarbon dated climate record of the interval 8,000-18,000 years B.P. from Deep Sea Drilling Project site 480 (Guaymas Basin, Gulf of California) shows geochemical and lithological oscillations of oceanographic and climatic significance during deglaciation. Nonlaminated sediments are associated with cooler climatic conditions during the late glacial (up to 13,000 years B.P.), and from 10,300 to 10,800 years B.P., equivalent to the Younger Dryas event of the North Atlantic region. We propose that the changes from laminated (varved) to nonlaminated sediments resulted from increased oxygen content in Pacific intermediate waters during the glacial and the Younger Dryas episodes, and that the forcing for the latter event was global in scope. Prominent events of low delta18O are recorded in benthic foraminifera from 8,000 to 10,000 and at 12,000 years B.P.; evidence for an earlier event between 13,500 and 15,000 years B.P. is weaker. Maximum delta18O is found to have occurred 10,500, 13,500, and 15,000 years ago (and beyond). Oxygen isotopic variability most likely reflects changing temperature and salinity characteristics of Pacific waters of intermediate depth during deglaciation or environmental changes within the Gulf of California region. Several lines of evidence suggest that during deglaciation the climate of the American southwest was marked by increased precipitation that could have lowered salinity in the Gulf of California. Recent modelling studies show that cooling of the Gulf of Mexico due to glacial meltwater injection, which is believed to have occurred at least twice during deglaciation, would have resulted in increased precipitation with respect to evaporation in the American southwest during summertime. The timing of deglacial events in the Gulf of Mexico and the Gulf of California supports such an atmospheric teleconnection.

Benthic foraminifera and stable isotope record of ODP Leg 182 sites

Cores from Sites 1129, 1131, and 1132 (Ocean Drilling Program (ODP) Leg 182) on the uppermost slope at the edge of the continental shelf in the Great Australian Bight reveal the existence of upper Pleistocene bryozoan reef mounds, previously only detected on seismic lines. Benthic foraminiferal oxygen isotope data for the last 450,000 years indicate that bryozoan reef mounds predominantly accumulated during periods of lower sea level and colder climate since stage 8 at Sites 1129 and 1132 and since stage 4 at the deeper Site 1131. During glacials and interstadials (stages 2-8) the combination of lowered sea level, increased upwelling, and absence of the Leeuwin Current probably led to an enhanced carbon flux at the seafloor that favored prolific bryozoan growth and mound formation at Site 1132. At Site 1129, higher temperatures and downwelling appear to have inhibited the full development of bryozoan mounds during stages 2-4. During that time, favorable hydrographic conditions for the growth of bryozoan mounds shifted downslope from Site 1129 to Site 1131. Superimposed on these glacial-interglacial fluctuations is a distinct long-term paleoceanographic change. Prior to stage 8, benthic foraminiferal assemblages indicate low carbon flux to the seafloor, and bryozoan mounds, although present closer inshore, did not accumulate significantly at Sites 1129 and 1132, even during glacials. Our results show that the interplay of sea level change (eustatic and local, linked to platform progradation), glacial-interglacial carbon flux fluctuations (linked to local hydrographic variations), and possibly long-term climatic change strongly influenced the evolution of the Great Australian Bight carbonate margin during the late Pleistocene.