(Table 1) Age determination of western North Atlantic sediment cores

Foraminiferal abundance, 14C ventilation ages, and stable isotope ratios in cores from high deposition rate locations in the western subtropical North Atlantic are used to infer changes in ocean and climate during the Younger Dryas (YD) and Last Glacial Maximum (LGM). The d18O of the surface dwelling planktonic foram Globigerinoides ruber records the present-day decrease in surface temperature (SST) of ~4°C from Gulf Stream waters to the northeastern Bermuda Rise. If during the LGM the modern d18O/salinity relationship was maintained, this SST contrast was reduced to 2°C. With LGM to interglacial d18O changes of at least 2.2 per mil, SSTs in the western subtropical gyre may have been as much as 5°C colder. Above ~2.3 km, glacial d13C was higher than today, consistent with nutrient-depleted (younger) bottom waters, as identified previously. Below that, d13C decreased continually to -0.5 per mil, about equal to the lowest LGM d13C in the North Pacific Ocean. Seven pairs of benthic and planktonic foraminiferal 14C dates from cores >2.5 km deep differ by 1100 ± 340 years, with a maximum apparent ventilation age of ~1500 years at 4250 m and at ~4700 m. Apparent ventilation ages are presently unavailable for the LGM < 2.5 km because of problems with reworking on the continental slope when sea level was low. Because LGM d13C is about the same in the deep North Atlantic and the deep North Pacific, and because the oldest apparent ventilation ages in the LGM North Atlantic are the same as the North Pacific today, it is possible that the same water mass, probably of southern origin, flowed deep within each basin during the LGM. Very early in the YD, dated here at 11.25 ± 0.25 (n = 10) conventional 14C kyr BP (equal to 12.9 calendar kyr BP), apparent ventilation ages <2.3 km water depth were about the same as North Atlantic Deep Water today. Below ~2.3 km, four YD pairs average 1030 ± 400 years. The oldest apparent ventilation age for the YD is 1600 years at 4250 m. This strong contrast in ventilation, which indicates a front between water masses of very different origin, is similar to glacial profiles of nutrient-like proxies. This suggests that the LGM and YD modes of ocean circulation were the same.

Late Eocene to early Oligocene carbonate and barite accumulation rates in the Pacific Basin

The late Eocene through earliest Oligocene (40-32 Ma) spans a major transition from greenhouse to icehouse climate, with net cooling and expansion of Antarctic glaciation shortly after the Eocene/Oligocene (E/O) boundary. We investigated the response of the oceanic biosphere to these changes by reconstructing barite and CaCO3 accumulation rates in sediments from the equatorial and North Pacific Ocean. These data allow us to evaluate temporal and geographical variability in export production and CaCO3 preservation. Barite accumulation rates were on average higher in the warmer late Eocene than in the colder early Oligocene, but cool periods within the Eocene were characterized by peaks in both barite and CaCO3 accumulation in the equatorial region. We infer that climatic changes not only affected deep ocean ventilation and chemistry, but also had profound effects on surface water characteristics influencing export productivity. The ratio of CaCO3 to barite accumulation rates, representing the ratio of particulate inorganic C accumulation to Corg export, increased dramatically at the E/O boundary. This suggests that long-term drawdown of atmospheric CO2 due to organic carbon deposition to the seafloor decreased, potentially offsetting decreasing pCO2 levels and associated cooling. The relatively larger increase in CaCO3 accumulation compared to export production at the E/O suggests that the permanent deepening of the calcite compensation depth (CCD) at that time stems primarily from changes in deep water chemistry and not from increased carbonate production.

(Table 1) Stratigraphic distribution and abundances of Cretaceous radiolarians from ODP Holes 130-803D and 130-807C

Among the five sites drilled during Ocean Drilling Program Leg 130, two deep holes (8O3D and 807C) penetrated Cretaceous sediments overlying the basaltic pillows, flows, and possibly basement rocks. Abundant, poorly preserved radiolarians with limited diversity were recovered from a few horizons within the sediments proximal to the basalt. At Site 803, three thin layers of radiolarites interbedded with claystone and clayey siltstone yielded radiolarian assemblages of late Albian age. At Site 807, several layers of radiolarian siltstones were recovered proximal to the basalt. Among them the most significant radiolarian assemblage is an Aptian fauna, located approximately 7 m above the basaltic flows. The Aptian radiolarian age for Site 807 is at least in accord with those suggested by planktonic foraminifer and paleomagnetic evidence. These Cretaceous radiolarians are the oldest assemblages recorded from the Ontong Java Plateau region.

(Table T1) Abundance of silicoflagellates in sediments of ODP Hole 199-1219A

Silicoflagellates ranging from middle Eocene to middle Miocene in age are present in Ocean Drilling Program Hole 1219A. The hole was drilled 250.8 meters below seafloor of which an ~120 m section primarily composed of nannofossil ooze with variable radiolarian and clay content is early Miocene and Oligocene in age, and a 95-m section is Eocene radiolarian and zeolithic clays, radiolarian and diatom oozes, and nannofossil oozes and chalks. A total of 150 samples were studied at a sample interval of one per section. Diversity of silicoflagellates is moderate, and the preservation is good. Abundance is generally low, with many samples barren of silicoflagellates, but 31 species and subspecies were identified. One new species, Naviculopsis trigeminus, is described.

Pacific Neogene carbonate accumulation rates

I have compiled CaCO3 mass accumulation rates (MARs) for the period 0-25 Ma for 144 Deep Sea Drilling Project and Ocean Drilling Program drill sites in the Pacific in order to investigate the history of CaCO3 burial in the world's largest ocean basin. This is the first synthesis of data since the beginning of the Ocean Drilling Program. Sedimentation rates, CaCO3 contents, and bulk density were estimated for 0.5 Myr time intervals from 0 to 14 Ma and for 1 Myr time intervals from 14 to 25 Ma using mostly data from Initial Reports volumes. There is surprisingly little coherence between CaCO3 MAR time series from different Pacific regions, although regional patterns exist. A transition from high to low CaCO3 MAR from 23-20 Ma is the only event common to the entire Pacific Ocean. This event is found worldwide. The most likely cause of lowered pelagic carbonate burial is a rising sea-level trend in the early Miocene. The central and eastern equatorial Pacific is the only region with adequate drill site coverage to study carbonate compensation depth (CCD) changes in detail for the entire Neogene. The latitude-dependent decrease in CaCO3 production away from the equator is an important defining factor of the regional CCD, which shallows away from the equatorial region. Examination of latitudinal transects across the equatorial region is a useful way to separate the effects of changes in carbonate production ('productivity') from changes in bottom water chemistry ('dissolution') upon carbonate burial.

Description of, and 238U, 234U, 232Th and 230Th measurements on a nodule from R/V Sonne station SO79_62KD, Central East Pacific Ocean

Two diagenetic manganese nodules from the Peru Basin were investigated by thermal ionization mass spectrometry and high resolution alpha spectrometry for uranium and thorium. The TIMS concentrations for nodule 62KD (63KG) vary as follows: 0.12-1.01 ppb (0.06-0.59) 230Th, 0.51-1.98 ppm (0.43-1.40) 232Th, 0.13-0.80 ppb (0.09-0.49) 234U, and 1.95-13.47 ppm (1.66-8.24) 238U. Both nodules have average growth rates of ~110 mm per million years. However, from the variations of excess 230Th with depth we estimate partial accumulation rates which range from 50 to 400 mm per million years. The 234U dating method cannot be applied due to remobilization of U from the sediment and subsequent incorporation into the nodules' crystal lattice, reflected by decay corrected 234U values far above the ocean water value. Sections of fast nodule growth are related to those layers having high Mn/Fe ratios (up to 200) and higher densities. As a possible explanation we develop a scenario that describes similar glacial/interglacial trends in both nodules as a record of regional changes of sediment and/or deep water chemistry.

Planktic foraminiferal assemblages in sediments of four ODP Leg 198 holes

A pulse of intense carbonate dissolution occurred during the early late Paleocene at 58.4 Ma. A prominent 5 to 25 cm-thick dark brown clay-rich calcareous nannofossil ooze was found on Shatsky Rise at Sites 1209, 1210, 1211, and 1212 during Ocean Drilling Program Leg 198. The layer corresponds to the lower part of planktonic foraminiferal Zone P4 and coincides with the evolutionary first occurrence of the nannolith Heliolithus kleinpellii, an important component of late Paleocene assemblages and a marker for the base of Zone CP5. The clay-rich layer contains common crystals of phillipsite, fish teeth, and phosphatic micronodules and corresponds to a prominent peak in magnetic susceptibility that probably reflects these high amounts of detrital and authigenic materials. Detailed quantitative analysis of planktonic foraminiferal assemblages across the clay-rich nannofossil ooze layer shows that fundamental changes in faunal composition occurred before, during, and after deposition of the clay-rich ooze. Planktonic foraminifers in the clay-rich layer are characterized by a low-diversity, largely dissolved assemblage dominated by representatives of the genus Igorina (mainly Igorina tadjikistanensis and Igorina pusilla). Conversely, Igorina albeari, morozovellids, acarininids, globanomalinids, subbotinids, and chiloguembelinids are common below the clay-rich layer, almost disappear within it, and reappear in low abundances above the clay-rich layer. These changes in faunal compositions are likely a response to a change in carbonate saturation that caused increased dissolution on the seafloor owing to the shoaling of the lysocline and the carbonate compensation depth.

New calibration of Neogene radiolarian events in the North Pacific

New age models for twelve Deep Sea Drilling Project sites in the North Pacific have been produced, based on (in order of importance in our dataset) a recompilation of previously published diatom, calcareous nannofossil and foraminifer first and last occurrences, and magnetostratigraphy. The projected ages of radiolarian first and last occurrences derived from the line of correlation of the age/depth plots have been computed from these sites, and 28 radiolarian events have thereby been newly cross calibrated to North Pacific diatom and other stratigraphy. Several of the North Pacific radiolarian events are older than in previously published equatorial Pacific calibrations, and some may be diachronous within the North Pacific. These patterns may be due to complex latitudinal patterns of clinal variation in morphotypes within lineages, or to migration events from the North Pacific towards the Equator.

Sea surface temperature reconstruction of a combined sediment record of the midlatitude North Pacific

Suborbital climate variability during the last glacial period is suggested to have involved a 1500-year pacing cycle, but the expression and spatial distribution of the ~1500-year oscillation during interglacials remains unclear. We generated a multidecade resolution record of alkenone sea surface temperature (SST) in the northwestern Pacific off central Japan during the Holocene. The SST record showed centennial and millennial variability with an amplitude of ~1 °C throughout the entire Holocene. Spectral analysis for SST variation revealed a statistically significant peak with 1470-year periodicity. The SST variation partly correlated with the variations of ice-rafted hematite-stained grain content in North Atlantic sediments. These findings indicate that the mean latitude of the Kuroshio Extension has varied on a 1500-year cycle, and suggest that a climatic link exists between the North Pacific gyre system and the high-latitude North Atlantic thermohaline circulation. The regular pacing at 1500-year intervals seen throughout both the Holocene and the last glacial period suggests that the oscillation was a response to external forcing.