Physical properties and neutron texture measuerments of deep-sea carbonates of DSDP Holes 62-463 and 62-465A

In weakly indurated, nannofossil-rich, deep-sea carbonates compressional wave velocity is up to twice as fast parallel to bedding than normal to it. It has been suggested that this anisotropy is due to alignment of calcite c-axes perpendicular to the shields of coccoliths and shield deposition parallel to bedding. This hypothesis was tested by measuring the preferred orientation (fabric) of calcite c-axes in acoustic anisotropic, calcareous DSDP sediment samples by X-ray goniometry, and it was found that the maximum c-axis concentrations are by far too low to explain the anisotropies. The X-ray method is subject to a number of uncertainties due to preparatory and technical shortcomings in weakly indurated rocks. The most serious weaknesses are: sample preparation, volume of measured sample (fraction of a mm3), beam defocusing and background intensity corrections, combination of incomplete pole figures, and necessity of recalculation of the c-axis orientations from other crystallographic directions. Goniometry using thermal neutrons overcomes most of these difficulties, but it is time consuming. We test the interferences made about velocity anisotropy by X-ray studies about the concentration of c-axes in deep-sea carbonates by employing neutron texture goniometry to eight DSDP samples comprising mostly nannofossil material. Fabric and sonic velocity were determined directly on the core specimens, thus from the same rock volume and requiring no preparation. The c-axis orientation is obtained directly from the [0006] calcite diffraction peak without corrections. The fabrics are clearly defined, but weak (1.1 to 1.86 times uniform) with the maximum about normal to bedding. They have crudely orthorhombic symmetry, but are not axisymmetric around the bedding normal. The observed c-axis intensities, although higher than determined by the X-ray method on other samples, are by far too low to explain the observed acoustic anisotropies.

Physical properties and geochemical pore-water analysis of sediment core GeoB16423-1

Several studies indicate that the 2011 Tohoku-Oki earthquake (Mw 9.0) off the Pacific coast of Japan has induced slip to the trench and triggered landslides in the Japan Trench. In order to better understand these processes, detailed mapping and shallow-coring landslides at the trench as well as Integrated Ocean Drilling Program (IODP) deep drilling to recover the plate boundary décollement (Japan Trench Fast Earthquake Drilling Project, JFAST) have been conducted. In this study we report sediment core data from the rapid response R/V SONNE cruise (SO219A) to the Japan Trench, evidencing a Mass Transport Deposit (MTD) in the uppermost section later drilled at this JFAST-site during IODP Expedition 343. A 8.7 m long gravity core (GeoB16423-1) recovered from ~7,000 m water depth reveals a 8 m sequence of semi-consolidated mud clast breccias embedded in a distorted chaotic sediment matrix. The MTD is covered by a thin veneer of 50 cm hemipelagic, bioturbated diatomaceous mud. This stratigraphic boundary can be clearly distinguished by using physical properties data from Multi Sensor Core Logging and from fall-cone penetrometer shear strength measurements. The geochemical analysis of the pore-water shows undisturbed linear profiles measured from the seafloor downcore across the stratigraphic contact between overlying younger background-sediment and MTD below. This indicates that the investigated section has not been affected by a recent sediment destabilization in the course of the giant Tohoku-Oki earthquake event. Instead, we report an older landslide which occurred between 700 and 10,000 years ago, implying that submarine mass movements are dominant processes along the Japan Trench. However, they occur on local sites and not during each megathrust earthquake.

Physical properties, compressional-wave velocity and consolidation characteristics of ODP Holes 133-815B and 133-817B

Sites 815 and 817 were drilled near the Townsville Trough during Leg 133 of the Ocean Drilling Program. The physical properties, compressional-wave velocity, and consolidation characteristics indicate that the periplatform carbonate sediments maintain more water content and lower compressional velocity near the Queensland Plateau than the clayey hemipelagic sediments, which have a clay content of up to 60%. Bulk density, void ratio or porosity, water content, and compressional-wave velocity are shown to have a linear relationship with burial depth. Between 3.5 and 5 Ma (about 100-500 mbsf), these physical properties maintained a constant rate vs. the depth in core because of the fast sedimentation-rate effect at Site 815. However, compressionalwave velocity still increases downward in this section. The clay content in this section causes an increase of bulk modulus and compaction effect. At Site 817, scarce terrigenous mud content and abundant carbonate content (88%-97%) cause a straight line relationship between physical properties and burial depth. During the consolidation test, we show that dominant micritic particles may cause faster acoustic velocity than sediments composed mainly of coccoliths. The bulk modulus ratio increasing rate in the clay-rich carbonate sediments is almost 4.5 times higher than in the clay-free periplatform carbonate sediments.

(Table 1) Results of measurements of production characteristics of phytoplankton and some physical parameters of the environment in the northeastern Norwegian Sea in July 1995

From July 4 to 18,1995 surface chlorophyll a concentrations (C_cs) and integral primary production (C_ps) were studied in the northeastern part of the Norwegian Sea (73°42'N; 13°16'E), over a test area where an accident of the nuclear submarine Komsomolets had taken place. It was found that during this interval C_cs decreased by factor of about 3.3 (from 0.78 to 0.24 mg/m**3); average chlorophyll concentration within the photo-synthetic layer (C_cl) decreased by factor of about 3.5 (from 0.97 to 0.28 mg/m**3). The value of C_ps in the water column varied slightly (from 445 to 539 mg C/m**2 per day), since decrease in C_cl was compensated both by 1.5-fold growth of the photosynthetic layer thickness (from 40 to 60 m) and by 2.1-fold increase in its average assimilation number (from 0.58 to 1.20 mg C/mg chl a per hour). Monthly averages of C_ps were obtained from published data on seasonal C_cs changes and on the level of incident solar irradiation. They were found to be less than 100 mg C/m**2 per day in March and October and 100-500 mg C/m**2 per day in April-June. Annual primary production calculated from above values was equal to 105 g C/m**2.

Physical properties nd chemistry of igneous rocks from the Pigafetta and East Mariana Basins

Physical properties of basalts from Ocean Drilling Program Sites 800 and 801 in the Pigafetta Basin and Site 802 in the East Mariana Basin, including porosity, wet-bulk density, grain density, compressional wave velocity, and thermal conductivity, were measured aboard JOIDES Resolution during Leg 129. The ranges for the properties are large, as typified by the velocity, which varies from 3.46 to 6.59 km/s. Extensively altered basalts immediately above and below a silicified hydrothermal deposit (60-69 m sub-basement depth) at Site 801 display the highest porosity, and lowest bulk density, velocity, and thermal conductivity, whereas the slightly altered rocks from Site 802 and the lowermost part of Site 801 represent the other extreme in physical properties variations. In order to better establish the relationship between physical properties and alteration of the rocks, the compressional wave velocities were compared with results from major and trace elemental analyses and petrographic examination of select samples. For the Leg 129 basalts, velocity displays a generally consistent decrease with increasing K2O, H2O+, loss on ignition, and Rb contents and the value of Fe3+/FeT and decreasing concentrations of SiO2, FeOT, CaO, MgO, and MnO. These trends are consistent with trends documented for the progressive alteration of oceanic crust and indicate that on a laboratory sample scale, basalt alteration is largely responsible for the variation of the physical properties of basalts sampled at Sites 800, 801, and 802.

Physical properties, pore water geochemistry, 210Pb-dating of sediment cores GeoB16426-1, GeoB16427-1, GeoB16429-1

We present differential bathymetry and sediment core data from the Japan Trench, sampled after the 2011 Tohoku-Oki (offshore Japan) earthquake to document that prominent bathymetric and structural changes along the trench axis relate to a large (~27.7 km**2) slump in the trench. Transient geochemical signals in the slump deposit and analysis of diffusive re-equilibration of disturbed SO4**2- profiles over time constrain the triggering of the slump to the 2011 earthquake. We propose a causal link between earthquake slip to the trench and rotational slumping above a subducting horst structure. We conclude that the earthquake-triggered slump is a leading agent for accretion of trench sediments into the forearc and hypothesize that forward growth of the prism and seaward advance of the deformation front by more than 2 km can occur, episodically, during a single-event, large mega-thrust earthquake.

Physical properties and AMS characteristics of ODP Site 185-1149 sediments

During Ocean Drilling Program Leg 185, we studied progressive changes of microfabrics of unconsolidated pelagic and hemipelagic sediments in Holes 1149A and 1149B in the northwest Pacific at 5818 m water depth. We paid particular attention to the early consolidation and diagenetic processes without tectonic deformation before the Pacific plate subduction at the Izu-Bonin Trench. Shape, size, and arrangement of pores were analyzed by scanning electron microscope (SEM) and were compared to anisotropy of magnetic susceptibility (AMS) data. The microfabric in Unit I is nondirectional fabric and is characterized by large peds of ~10-100 µm diameter, which are made up of clay platelets (mainly illite) and siliceous biogenic fragments. They are ovoid in shape and are mechanically packed by benthic animals. Porosity decreases from 0 to 60 meters below seafloor (mbsf) in Unit I (from 60% to 50%) in association with macropore size decreases. The microfabric of coarser grain particles other than clay in Unit II is characterized by horizontal preferred orientation because of depositional processes in Subunit IIA and burial compaction in Subunit IIB. On the other hand, small peds, which are probably made of fragments of fecal pellets and are composed of smectite and illite (3-30 µm diameter), are characterized by random orientation of clay platelets. The clay platelets in the small peds in Subunit IIA are in low-angle edge-to-face (EF) or face-to-face (FF) contact. These peds are electrostatically connected by long-chained clay platelets, which are interconnected by high-angle EF contact. Breaking of these long chains by overburden pressure diminishes the macropores, and the clay platelets in the peds become FF in contact, resulting in decreases in the volume of the micropores between clay platelets. Thus, porosity in Subunits IIA and IIB decreases remarkably downward. The AMS indicates random fabric and horizontal preferred orientation fabric in Units I and II, respectively. This result corresponds to that of SEM microfabric observations.In Subunit IIB, pressure solutions around radiolarian tests and clinoptilolite veins with normal displacement sense are seen distinctively below ~170 mbsf, probably in correspondence to the transition zone from opal-A to opal-CT.

Photochemical responses of the diatom Skeletonema costatum grown under elevated CO2 concentrations to short-term changes in pH

Variability in pH is a common occurrence in many aquatic environments, due to physical, chemical and biological processes. In coastal waters, lagoons, estuaries and inland waters, pH can change very rapidly (within seconds or hours) in addition to daily and seasonal changes. At the same time, progressive ocean acidification caused by anthropogenic CO2 emissions is superimposed on these spatial and temporal pH changes. Photosynthetic organisms are therefore unavoidably subject to significant pH variations at the cell surface. Whether this will affect their response to long-term ocean acidification is still unknown, nor is it known whether the short-term sensitivity to pH change is affected by the pCO2 to which the cells are acclimated. We posed the latter open question as our experimental hypothesis: Does acclimation to seawater acidification affect the response of phytoplankton to acute pH variations? The diatom Skeletonema costatum, commonly found in coastal and estuarine waters where short-term acute changes in pH frequently occur, was selected to test the hypothesis. Diatoms were grown at both 390 (pH 8.2, low CO2; LC) and 1000 (pH 7.9, high CO2; HC) µatm CO2 for at least 20 generations, and photosynthetic responses to short-term and acute changes in pH (between 8.2 and 7.6) were investigated. The effective quantum yield of LC-grown cells decreased by ca. 70% only when exposed to pH 7.6; this was not observed when exposed to pH 7.9 or 8.2. HC-grown cells did not show significant responses in any pH treatment. Non-photochemical quenching showed opposite trends. In general, our results indicate that while LC-grown cells are rather sensitive to acidification, HC-grown cells are relatively unresponsive in terms of photochemical performance.