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.

(Table 3) Aeolian component of North Pacific pelagic sediments

Isolation and analysis of the eolian component of late Cenozoic pelagic sediments from the North Pacific provides direct information concerning changes in atmospheric circulation. A 50% increase in intensity of both the prevailing westerlies and the tradewinds coincides with increasing pole-to-equator temperature gradients resulting from the onset of northern hemisphere glaciation. At the same time, the mass flux of dust from continents to the North Pacific increased by a factor of 4.5, apparently reflecting significantly increased continental aridity associated with the late Cenozoic glacial ages.

Radiocarbon datings of Upper Quaternary bottom sediments from the Mediterranean Sea

Bottom sediment samples were collected in the Central Mediterranean, Southern Adriatic, Tyrrhenian, Algerian-Provencal, and Alboran basins of the Mediterranean Sea. Fifty-six datings were done for 12 sediment cores. The lowest sedimentation rates during Holocene were found on the abyssal plain of the Algerian-Provencal basin (2.4-4.0 cm/ky). In the Southern Adriatic, Tyrrhenian, and Alboran basins sedimentation rates were somewhat higher (6-12 cm/ky). On slopes of the Southern Adriatic and Tyrrhenian basins during Late Würm glaciation rates of "normal" sedimentation were within the range 11.8-26.8 cm/ky.

Diatom abundance in sediments from ODP Leg 167 sites

The Pliocene and Pleistocene periods are known for the onset and consequent amplification of glacial-interglacial cycles. The California margin, situated in the mid-latitudes of the northern Pacific Ocean, is expected to be one of the most interesting regions for Pliocene to Pleistocene paleoceanography because this area occupies a unique position in the ocean-atmosphere system over the region. In this study, we investigated paleoceanographic history, using fossil diatoms, since the Brunhes/Matuyama (B/M) paleomagnetic boundary in which glacial and interglacial periods began to alternate in 100-yr cycles. In Hole 1018A, to a depth corresponding to the beginning of Northern Hemisphere glaciation (late Pliocene), we investigated the responses of the ocean-atmosphere system to stepwise cooling in the California margin. Although the work is still continuing, this data report shows that fossil diatoms of Pliocene and Pleistocene sediments significantly changed both in quality and quantity and implies a possible relationship to global climatic changes.

Sedimentation rates and foraminiferal assemblages from ODP Site 162-184

Sedimentological and faunal records from the transitional period marking the onset of widespread northern hemisphere glaciation have been investigated at Ocean Drilling Program Site 984. The late Pliocene interglacial sediments of the northeast Atlantic are carbonate rich and show evidence of vigorous bottom water circulation at intermediate water depths. Contrasting this, the late Pliocene glacial sediments are characterised by carbonate dissolution and slower bottom current velocities. Weak or "leaky" Norwegian Sea overflows, undersaturated with respect to carbonate, influenced this region during the late Pliocene glacials. The early Pleistocene pattern of intermediate water circulation appears to have changed radically in the northeast Atlantic. At this time, interglacial carbonate values and inferred bottom current velocities are low. This suggests slow-flowing, undersaturated Norwegian Sea water bathing the site. The overflow increased during the early Pleistocene interglacials as the exchange between the Atlantic and Norwegian-Greenland Seas improved. The most significant feature of the early Pleistocene glacials is the increase in inferred bottom current velocity. These changes reflect a switch in deep North Atlantic convection to shallower depths during glacial periods, possibly in a manner similar to the increasing contribution of glacial intermediate water to the North Atlantic during the late Pleistocene glacials. Our results suggest that the late Pleistocene climate variability of the North Atlantic is a pervasive feature of the late Pliocene-early Pleistocene record.

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.