Paleoenvironmental analysis of the Mawaki archaeological site,central Japan,in relation to the stratigraphic position of dolphin bones

In order to elucidate the paleoenvironment associated with the early Holocene Mawaki archaeological site on the Noto Peninsula of central Japan, a high‐resolution stratigraphic study was conducted of 17 boreholes drilled at the archaeological site. We selected three boreholes for which lithological and/or chronological data are reported. Initial magnetic susceptibility was utilized for correlation of clastic core samples with the assistance of 26 radiocarbon dates. Four lithological units (A, B, C, and D in ascending order) were identified and interpreted as a sequence in a cycle of marine transgression and regression. Dated coastal horizons were chosen to indicate former sea levels. A Holocene relative sea level curve was generated on the basis of the geological data, and a rapid rise from 8000cal. yr B.P. to 7000cal. yr B.P. and a succeeding minor sea level fall represent the basic eustatic trend around the Sea of Japan because hydroisostatic and tectonic effects are moderate in the study area. Abundant dolphin bones lay just above the top of the marine sequence (boundary between Units C and D), located in the seashore environment. Cultural artifacts are found in a subaerial deposit (Unit D) near the dolphin bone level that is assigned to a period of high, stable sea level after the post‐glacial eustatic highstand. Dolphin bones are associated with stone artifacts (arrowheads, knives, and scrapers) and ritual wood columns, indicating the presence of a longstanding fishery during the early Holocene on the Sea of Japan coast. © 2011 Wiley Periodicals, Inc.     

A possible Caledonide arm through the Barents Sea imaged by OBS data

The assembly of the crystalline basement of the western Barents Sea is related to the Caledonian orogeny during the Silurian. However, the development southeast of Svalbard is not well understood, as conventional seismic reflection data does not provide reliable mapping below the Permian sequence. A wide-angle seismic survey from 1998, conducted with ocean bottom seismometers in the northwestern Barents Sea, provides data that enables the identification and mapping of the depths to crystalline basement and Moho by ray tracing and inversion. The four profiles modeled show pre-Permian basins and highs with a configuration distinct from later Mesozoic structural elements. Several strong reflections from within the crystalline crust indicate an inhomogeneous basement terrain. Refractions from the top of the basement together with reflections from the Moho constrain the basement velocity to increase from 6.3 km s⁻¹ at the top to 6.6 km s⁻¹ at the base of the crust. On two profiles, the Moho deepens locally into root structures, which are associated with high top mantle velocities of 8.5 km s⁻¹. Combined P- and S-wave data indicate a mixed sand/clay/carbonate lithology for the sedimentary section, and a predominantly felsic to intermediate crystalline crust. In general, the top basement and Moho surfaces exhibit poor correlation with the observed gravity field, and the gravity models required high-density bodies in the basement and upper mantle to account for the positive gravity anomalies in the area. Comparisons with the Ural suture zone suggest that the Barents Sea data may be interpreted in terms of a proto-Caledonian subduction zone dipping to the southeast, with a crustal root representing remnant of the continental collision, and high mantle velocities and densities representing eclogitized oceanic crust. High-density bodies within the crystalline crust may be accreted island arc or oceanic terrain. The mapped trend of the suture resembles a previously published model of the Caledonian orogeny. This model postulates a separate branch extending into central parts of the Barents Sea coupled with the northerly trending Svalbard Caledonides, and a microcontinent consisting of Svalbard and northern parts of the Barents Sea independent of Laurentia and Baltica at the time. Later, compressional faulting within the suture zone apparently formed the Sentralbanken High.     

Basin-Scale Geographic Patterns of Bacterioplankton Biomass and Production in the Subarctic Pacific, July–September 1997

Bacterial biomass and production rate were measured in the surface (0–100 m) and mesopelagic layers (100–1,000 m) in the subarctic Pacific and the Bering Sea between July–September, 1997. Depth profiles were determined at stations occupied in oceanic domains including the subarctic gyres (western, Bering Sea, and Gulf of Alaska) and a boundary region south of the gyres. In the surface layer (0–100 m), both bacterial biomass and production were generally high in the western and Bering Sea gyres, with the tendency of decrease toward east. This geographic pattern was consistent with the dominant regime of phytoplankton biomass at the time of our survey. A significant portion of variation in bacterial production was explained by the concentration of chlorophyll a (r ² = 0.340, n = 60, P < 0.001) and, to the greater extent, by the concentration of semilabile total organic carbon (SL-TOC = TOC at a given depth—TOC at 1,000 m, r ² = 0.488, n = 59, P < 0.0001). Temperature significantly improved the regression model: temperature and chlorophyll jointly explained 60% of variation in bacterial production. These results support the hypothesis that bacteiral growth is largely regulated by the combination of temperature and the supply of dissolved organic carbon in subarctic surface waters. In the mesopelagic layer (100–1,000 m), the geographic pattern of bacterial production was strikingly different from the surface phytoplankton distribution: the production was high in the boundary region where the phytoplankton biomass was lowest. Bacterial growth appeared to be largely controlled by the supply of organic carbon, as indicated by the strong dependency of bacterial production on SL-TOC (r ² = 0.753, n = 75, P < 0.0001). The spatial uncoupling between surface phytoplankton and mesopelagic bacterial production suggests that the supply rate of labile dissolved organic carbon in the mesopelagic zone does not simply reflect the magnitude of the particulate organic carbon flux in the subarctic Pacific.     

Vertical Distributions of Phyllosoma Larvae of Palinurid and Scyllarid Lobsters in the Western North Pacific

Vertical distributions of phyllosoma larvae were examined in waters east of the Philippines or west of the Mariana Islands (18°56′ N to 19°04′ N; 129°10′ E to 129°35′ E) based on zooplankton samples collected with an Isaacs-Kidd Midwater Trawl on September 22–24, 1986. Phyllosoma larvae belonged to the two families Scyllaridae and Palinuridae comprising 4 genera and 9 species. Of the collected phyllosoma larvae, those of Scyllarus cultrifer and Panulirus longipes were most abundant and showed similar vertical distributions: (1) both species were collected from the mixed layer at night but not in the day, (2) their vertical distributions did not change with their stages, and (3) the upper limit of their vertical distributions during the day accorded with the base of mixed layer. Furthermore, their vertical distributions were similar to those of lepthocephalus larvae which were collected using the same sampling stations and gear in the present study. Vertical distributions of phyllosoma larvae were discussed in relation to their horizontal distributions. This revised version was published online in August 2006 with corrections to the Cover Date.     

T waves from deep earthquakes generated exactly at the bottom of deep-sea trenches

T waves (seismic water waves), which were generated by deep-focused earthquakes, have been found by an array of sensitive ocean-bottom seismographic observations depolyed on the western Pacific basin. The points of generation of T waves have been exactly located by use of the accurate velocity of water waves which were known from explosions. The positions obtained are at the bottom of deep-sea trenches; however, the positions are slightly (10–35 km) ocean-side of the trench. T waves have been known to be generated by seismic waves which were transmitted from the focus to the trench bottom along the descending lithosphere. The intensity of the observed T waves implies that the Q value along the descending lithosphere is more than 4000. The positions of T-wave generation are consistent with the 8.2- to 8.6-km/s stratified structure of the oceanic lithosphere. T waves from shallow earthquakes beneath the lower continental slope are also clearly observed by bottom seismography.     

Crustal structure between the Knipovich Ridge and the Van Mijenfjorden (Svalbard)

Marine Geophysical Research - The Alfred Wegener Institute of Polar and Marine Research, the University of Bergen and Hokkaido University acquired new seismic refraction data along a transect from...