Calcareous nannofossil stratigraphy and datums of sediments from ODP Leg 198 sites

During Ocean Drilling Program Leg 198, Sites 1207, 1208, 1212, 1213, and 1214 were drilled on Shatsky Rise, coring Lower to mid-Cretaceous successions of nannofossil chalk, porcellanite, and chert. Although recovery was poor, these sites yielded an outstanding record of calcareous nannoplankton, providing valuable data concerning the evolutionary succession and paleobiogeography of the largest Cretaceous marine habitat. Mid-Cretaceous sections (Aptian-Cenomanian) were recovered at all sites, and Site 1213 includes an apparently complete Berriasian-Hauterivian section. Biostratigraphic dating is problematic in places because of the absence or rarity of zonal fossils of both Boreal and Tethyan affinity. The majority of nannofossil assemblages are relatively typical of this age, but there are clear differences that set them apart from coeval epicontinental assemblages: for example, Lithraphidites carniolensis is common to abundant throughout and was most likely an oceanic-adapted taxon; the cold- to temperate-water species Crucibiscutum salebrosum, Repagulum parvidentatum, and Seribiscutum primitivum are entirely absent, indicating the persistence of tropical, warm surface water temperatures; and the warm-water species Hayesites irregularis is common. Most striking, however, is the virtual absence of Nannoconus and Micrantholithus, both taxa that were conspicuous and often common components of many Tethyan and Atlantic nannofloras. These forms were almost certainly neritic adapted and usually absent in deep open-ocean settings away from guyots and platforms. Other Tethyan taxa are also absent or rare and sporadically distributed (e.g., Calcicalathina oblongata, Conusphaera spp., Tubodiscus verenae, and Lithraphidites bollii), and factors related to neritic environments presumably controlled their distribution. Site 1213 also records extended Early Cretaceous ranges for species previously thought to have become extinct during the Late Jurassic (e.g., Axopodorhabdus cylindratus, Hexapodorhabdus cuvillieri, and Biscutum dorsetensis), suggesting these species became Pacific-restricted prior to their extinction. Watznaueria britannica may also have been a species with Pacific affinities before reexpansion of its biogeography in the early Aptian. One new genus (Mattiolia) and thirteen new species (Zeugrhabdotus clarus, Zeugrhabdotus petrizzoae, Helicolithus leckiei, Rhagodiscus amplus, Rhagodiscus robustus, Rhagodiscus sageri, Rhagodiscus adinfinitus, Tubodiscus bellii, Tubodiscus frankiae, Gartnerago ponticula, Haqius peltatus, Mattiolia furva, and Kokia stellata) are described from the Shatsky Rise Lower Cretaceous section.

Chaetoceros resting spores in Quaternary sediments of ODP Leg 119 sites

During Leg 119 of the Ocean Drilling Program (ODP), Quaternary sediments of the Southern Ocean were examined for the presence and abundance of Chaetoceros resting spores. Six drill sites were occupied along the Kerguelen Plateau. An additional five drill sites were clustered within Prydz Bay, Antarctica. Chaetoceros resting spores were present at all sites examined. These resting spore assemblages were comprised primarily of Chaetoceros neglectus and several unidentified Chaetoceros species. Resting spore assemblages accounted for approximately 20% of the total diatom assemblage (ranging from 0% to 91.4% of any given sample). Quantitative estimates of resting spores demonstrated considerable downcore abundance fluctuations, ranging from 0 to 1.82*10*9 valves/g sediment. The highest spore production rates (3.75*10**12 spores/cm/yr) were found on the northern Kerguelen Plateau (Sample 119-736B-1H-3,35-37 cm). A lack of adequate chronological control at all sites prevented proper between-core comparisons. Mean resting spore abundance, however, appeared highest within the sediments of Prydz Bay and across the northern Kerguelen Plateau. Deep-water stations of the southern Kerguelen Plateau demonstrated the lower spore abundances and a reduction in the percentage contribution of spore to the total diatom assemblage.

Partial pressure of carbon dioxide along the Transatlantic section from 7 November till 19 December 2000

Along a transatlantic section from 57°N to 60°S that was carried out from November 7 till December 19, 2000 on board R/V Horizont II concentrations of CO2 were measured in the near-water layer of the air and differences between partial pressures in water and air in various climatic zones were calculated. It was shown that variations of CO2 concentrations in the near-water layer of air and those of values of water-air partial pressure difference were from 324x10**-6 to 426x10**-6 and from 150x10**-6 to 100x10**-6 atm, respectively. Maximum value of CO2 partial pressure in air in the near-water layer (426x10**-6 atm) was noted at 45°-47°N; minimum of 324x10**-6 atm was found in Antarctica at 59°S. During measurenents maximum value of CO2 partial pressure difference in water and air (150 x10**-6) was observed at 45°-48°N; maximum flux in this case was directed from the atmosphere to water. Maximum value of CO2 partial pressure difference in water and air for flux directed from the ocean to air (100 x10**-6) was observed at 59°-60°S. Comparison of calculated values of partial pressure difference in water and air with previous data points to more intense exchange of CO2 between the ocean and atmosphere during the survey period was considered. According to values of CO2 partial pressure difference in air and water as compared to 1975, exchange intensity in the Northern Hemisphere (absorption from the atmosphere) increased. A well-pronounced latitudinal effect of distribution of CO2 partial pressure in air was observed. Along the route variations in CO2 concentrations in zones of water divergence and convergence were registered.

Upper Cretaceous sediments of ODP Hole 122-762C

Well-developed Campanian to Maestrichtian pelagic cyclic sediments were recovered from Hole 762C on the Exmouth Plateau, off northwest Australia, during Ocean Drilling Program Leg 122. The cycles consist of nannofossil chalk (light beds) and clayey nannofossil chalk (dark beds). Both light and dark beds are strongly to moderately bioturbated, alternate on a decimeter scale, and exhibit gradual boundaries. Bioturbation introduces materials from a bed of one color into an underlying bed of another color, indicating that diagenesis is not responsible for the cyclicity. Differences in composition between the light and dark beds, revealed by calcium carbonate measurement and X-ray diffraction analysis, together with trace fossil evidence, indicate that the cycles in the sediments are a depositional feature. Diagenetic processes may have intensified the appearance of the cycles. Spectral analysis was applied to the upper Campanian to lower Maestrichtian cyclic sediments to examine the regularity of the cycles. Power spectra were calculated from time series using Walsh spectral analysis. The most predominant wavelengths of the color cycles are 34-41 cm and 71-84 cm. With an average sedimentation rate of 1.82 cm/k.y. in this interval, we found the time durations of the cycles to be around 41 k.y. and 21 k.y., respectively, comparable to the obliquity and precession periods of the Earth's rotation, which strongly suggests an orbital origin for the cycles. On the basis of sedimentological evidence and plate tectonic reconstruction, we propose the following mechanism for the formation of the cyclic sediments from Hole 762C. During the Late Cretaceous, when there was no large-scale continental glaciation, the cyclic variations in insolation, in response to cyclic orbital changes, controlled the alternation of two prevailing climates in the area. During the wetter, equable, and warmer climatic phases under high insolation, more clay minerals and other terrestrial materials were produced on land and supplied by higher runoff to a low bioproductivity ocean, and the dark clayey beds were deposited. During the drier and colder climatic phases under low insolation, fewer clay minerals were produced and put into the ocean, where bioproductivity was increased and the light beds were deposited.

Oxygen and carbon isotope measurements of North Atlantic from IODP Hole 307-U1317E

Recent deep-ocean exploration has revealed unexpectedly widespread and diverse coral ecosystems in deep water on continental shelves, slopes, seamounts, and ridge systems around the world. Origin and growth history of these cold-water coral mounds are poorly known, owing to a lack of complete stratigraphic sections through them. Here we show high-resolution oxygen isotope records of planktic foraminifers from the base to the top of Challenger Mound, southwest of Ireland, which was drilled during Integrated Ocean Drilling Program Expedition 307. Challenger Mound began to grow during isotope stage 92 (2.24 million years ago (Ma)), immediately after the onset of Northern Hemisphere glaciation and the initiation of modern stratification in the northeast Atlantic. Mound initiation was likely due to reintroduction of Mediterranean Outflow Water (MOW) and ensuing development of a density gradient with overlying northeastern Atlantic water (NEAW), where organic matter was prone to be stagnated and fueled the coral ecosystem. Coral growth continued for 11 glacial-interglacial cycles until isotopic stage 72 (1.82 Ma) with glacial siliciclastic input from the continental margin. After a long hiatus that separates the lower mound and the upper mound, coral growth restored for a short time in isotope stages 19-18 (0.8-0.7 Ma) in which sediments were either eroded or not deposited during a full glacial stage. The development pattern of the water mass interface between MOW and NEAW might have changed, because of the fluctuations of the MOW production which is responsible for the amplitude in ice volume oscillations from the low-amplitude 41 ka cycles for the lower mound to the high-amplitude 100 ka cycles for the upper mound. The average sedimentation and CaCO3 production rates of the lower mound were evaluated 27 cm/ka and 31.1 g/cm2/ka, respectively.