Major element and cadmium contents in phosphorites from Pacific seamounts

Cadmium contents in studied rocks from Pacific seamounts usually lower than both in biogenic-diagenetic shelf phosphorites and in pelagic sedimentatary-diagenetic Fe-Mn nodules. In general, the behavior of Cd in phosphorites, phosphatized rocks and iron-manganese-phosphate crusts from the seamounts shows that phosphorus, iron, and manganese are apparently of normal sedimentary origin.

Late Miocene development of the western Pacific warm pool: Planktonic foraminifer and oxygen isotopic evidence

The disappearance at ~10 Ma of the deep dwelling planktonic foraminifer Globoquadrina dehiscens from the western Pacific including the South China Sea was about 3 Myr earlier than its final extinction elsewhere. Accompanying this event at ~10 Ma was a series of faunal turnover characterized by increase in mixed layer, warm-water species and decrease to a minimum in deepwater species. Paleobiological and isotopic evidence indicates sea surface warming and a deepened local thermocline that we interpret as related to the development of an early western Pacific warm pool. The stepwise decline of G. dehiscens and other deep dwelling species from the NW and SW Pacific suggests more intensive warm water pileup than equatorial localities where surface bypass flow through the narrowing Indonesia seaway appears to remain efficient during the late Miocene. Planktonic delta18O values from the South China Sea consistently lighter than the tropical western Pacific during the Miocene also suggest, similar to today, more variable hydrologic conditions along the periphery than in the core of the warm pool. Stronger hydrologic variability affected mainly by monsoons and increased thermal gradient along the western margin of the late Miocene warm pool may have contributed to the decline of deep dwelling planktonic species including the early extinction of G. dehiscens from the South China Sea region. The late Miocene warm pool became influential and paleobiologically detectable from ~10 Ma, but the modern warm pool did not appear until about 4 Ma, in the middle Pliocene.

Description of two mass species of Pacific copepods in terms of two polymorphic loci

Population genetics of two species of mass copepods Undinula darwini and Calanus australis, with different range types, is investigated. Both species exhibit considerable genetic diversity, especially C. australis (observed heterozygoticity = 0.36), which inhabits a variable biotope in the zone of the Peru current. Samples of both species exhibited highly significant genetic heterogeneity as well as heterozygote deficiency compared with the situation expected from the Hardy-Weinberg law. Contribution of distance isolation to genetic differentiation of populations is estimated. Gene drift is discussed as a source of heterogeneity in populations of planktic copepods. Possible aspects of population genetic research on marine plank-tic crustaceans are discussed.

Pollen and spores record, and paleotemperature reconstructions for mid-Holocene sediments of the Northwest Pacific

Sannai-Maruyama is one of the most famous and best-researched mid-Holocene (mid-Jomon) archaeological sites in Japan, because of a large community of people for a long period. Archaeological studies have shown that the Jomon people inhabited the Sannai-Maruyama site from 5.9-4.2 +/- 0.1 cal. kyr B.P. However, a continuous record of the terrestrial and marine environments around the site has not been available. Core KT05-7 PC-02, was recovered from Mutsu Bay, only 20 km from the site, for the reconstruction of high-resolution time series of environmental records, including sea surface temperature (SST). C37 alkenone SSTs showed clear fluctuations, with four periods of high (8.4-7.9, 7.0-5.9, 5.1-4.1, and 2.3-1.4 cal. kyr B.P.) and four of low (-8.4, 7.9-7.0, 5.9-5.1, and 4.1-2.3 cal. kyr B.P.) SST. Thus, each SST cycle lasted 1.0-2.0 kyr, and the amplitude of fluctuation was about 1.5-2.0 °C. Total organic carbon (TOC) and C37 alkenone contents, and the TOC/total nitrogen ratio indicate that marine biogenic production was low before 7.0 cal. kyr B.P., but was clearly increased between 5.9 and 4.0 cal. kyr B.P., because of stronger vertical mixing. During the period when the community at the site prospered (between 5.9 and 4.2 +/- 0.1 cal. kyr B.P.), the terrestrial climate was relatively warm. The high relative abundance of pollen of both Castanea and Quercus subgen. Cyclobalanopsis supports the interpretation that the local climate was optimal for human habitation. Between 5.9 and 5.1 cal. kyr B.P., in spite of warm terrestrial climates, the C37 alkenone SST was low; this apparent discrepancy may be attributed to the water column structure in the Tsugaru Strait, which differed from the modern condition. The evidence suggests that at about 5.9 cal. kyr B.P, high productivity of marine resources such as fish and shellfish and a warm terrestrial climate led to the establishment of a human community at the Sannai-Maruyama site. Then, at about 4.1 +/- 0.1 cal. kyr B.P., abrupt marine and terrestrial cooling, indicated by a decrease of about 2 °C in the C37 alkenone SST and an increase in pollen of taxa of cooler climates, led to a reduced terrestrial food supply, causing the people to abandon the site. The timing of the abandonment is consistent with the timing (around 4.0-4.3 cal. kyr B.P.) of the decline of civilizations in north Mesopotamia and along the Yangtze River. These findings suggest that a temperature rise of ~2 °C in this century as a result of global warming could have a great impact on the human community and especially on agriculture, despite the advances of contemporary society.

Distribution of diatoms in Oligocene to Pleistocene sediments of the tropical Pacific

According to the drilling probes of the Deep Waier Drilling Project, Neogene sediments in a tropical area of the Pacific Ocean are divided into 15 zones based on diatoms. The author shows that a unique zonation may be applied for the entire region. Identification of diatoms zones boundaries was conducted through their direct correlation with nannoplancton, radiolarian and foraminiferal zonal sceals. Their ultra-structure and morphological relationship are being analysed. The mode of siliceous accumulation within the equatorial belt differed through the western central and eastern region since the early Miocene and the difference become more evident from the end of Middle Miocene. The distribution of Neogene diatomaceous silt in the tropical area is controlled by the character of gyre-water circulation and agrees with the modern geographical zonation.

Microfossils detected in a block of ancient dense clay coated with a ferromanganese crust, Clarion-Clipperton Province, East Equatorial Pacific

The area in study is characterized by a regional stratigraphic hiatus from Early Miocene to Quaternary. Deposits from Late Eocene to Early Miocene occur on the bottom surface or under a thin sedimentary cover. Ferromanganese nodules, mostly of Oligocene age, formed on surface layers of Tertiary or Quaternary sediments. A detailed micropaleontological study of a block of dense ancient clay coated with a ferromanganese crust was carried out. Composition of found radiolarian and diatomaceous complexes proved that the crust formed in Quaternary on an eroded surface of Late Oligocene clay. In Quaternary Neogene sediments were eroded and washed away by bottom currents. It is likely that the erosion began 0.9-0.7 Ma at the beginning of the "Glacial Pleistocene". The erosion could be initiated by loosening and resuspension of surface sediments resulting from seismic activity generated by strong earthquakes in the Central America subduction zone. The same vibration maintained residual nodules at the seafloor surface. Thus, for the area in study a common reason and a common Quaternary interval for formation of the following features is supposed: a regional stratigraphic hiatus, formation of residual nodule fields, and position of ancient nodules on the surface of Quaternary sediments.

Radiolarian events in the eastern Equatorial Pacific

The development of an orbitally tuned time scale for the ODP leg 138 sites provides biostratigraphers a very high resolution chronostratigraphic framework. With this framework we are better able to define which of the first and last appearances of species appear to be synchronous. In addition, the geographic distribution of sites provides the means with which the detailed spatial patterns of invasion of new species and the extinction of older species can be mapped. These maps not only provide information on the process of evolution, migration, and extinction, they can also be related to water mass distributions and near-surface circulation of the ocean. Of 39 radiolarian events studied at 11 sites in the eastern equatorial Pacific, 28 were found to have a minimum range in their estimated age that exceeded 0.15 m.y. The temporal pattern of first and last appearances of these diachronous events have coherent spatial patterns that indicate shifts in the areas of high oceanographic gradients over the past 10 Ma. These changes in the locations of high gradient regions suggest that the South Equatorial Current (SEC) was north of its present position prior to approximately 7 Ma. There was a southward shift in the northern boundary of this current between approximately 6 and 7 Ma, and the development of a relatively strong gradient between the northeastern and northwestern sites. Between approximately 3.7 and 3.4 Ma, there was a very slight northward shift in the northern boundary of the SEC and the steep gradients between the northeastern and northwestern sites may have disappeared. This change is thought to be associated with the closing of the Isthmus of Panama. The temporal-spatial patterns of diachronous events younger than 3.4 Ma are consistent with patterns of circulation in the modern ocean.