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.

Carbonate properties and oxygen concentrations at time series station DYFAMED

Monthly measurements of pH, alkalinity and oxygen over two years (February 1998-February 2000) at the Dyfamed site in the central zone of the Ligurian-Provençal Basin of the Mediterranean made it possible to assess the vertical distributions (5-2000 m) and the seasonal variations of these properties. Alkalinity varies linearly with salinity between surface water and the Levantine Intermediate Water (marked by a maximum of temperature and salinity). In deep water, total alkalinity is also correlated linearly to salinity, but the slope of the regression line is 15% less. In surface water, the pH at 25°C varies between 7.91 and 8.06 on the total proton scale depending upon the season. The lowest values are observed in winter, the highest in spring and in summer. These variations are primarily due to biological production. The pH goes through a minimum around 150-200 m and a small maximum below the intermediate water. The total dissolved inorganic carbon content (deduced from pH and alkalinity) is variable in surface water (2205-2310 ?mol/kg) and has a maximum in intermediate water, which is related to the salinity maximum. Normalized total inorganic carbon at a constant salinity is strongly negatively correlated with pH at 25°C. The fugacity of CO2, (fCO2) varies between 320 and 430 ?atm in surface water, according to the season. Below the seasonal thermocline, the maximum fCO2 (about 410 ?atm) is located around 150-200 m. The presence of a minimum of oxygen in the intermediate water of this area has been observed for several years, but our measurements made it possible to specify the relationship between oxygen and salinity in deep water. Data from the intense vertical mixing during the winters of 1999 and 2000 were used to calculate the oxygen quantity exchanged with the atmosphere during these periods. The estimated quantity of oxygen entering the Mediterranean Sea exceeds that deduced from exchange coefficients calculated with the formula of Wanninkhof and McGillis. During the vertical mixing in the 1999 winter, fCO2 in surface water was on average below equilibrium with atmospheric fCO2, thus implying that CO2 was entering the sea. However, on this time scale, even with high exchange coefficients, the estimated CO2 uptake had no significant influence on the inorganic carbon content in the water column.

Comparisons of observed ice properties and Envisat Advanced Synthetic Aperture Radar (ASAR) data during Nathanial B. Palmer cruise NBP09-01 and Oden cruise OSO08/09

Envisat Advanced Synthetic Aperture Radar (ASAR) Wide Swath Mode (WSM) images are used to derive C-band HH-polarization normalized radar cross sections (NRCS). These are compared with ice-core analysis and visual ship-based observations of snow and ice properties observed according to the Antarctic Sea Ice Processes and Climate (ASPeCt) protocol during two International Polar Year summer cruises (Oden 2008 and Palmer 2009) in West Antarctica. Thick first-year (TFY) and multi-year (MY) ice were the dominant ice types. The NRCS value ranges between -16.3 ± 1.1 and -7.6 ± 1.0 dB for TFY ice, and is -12.6 ± 1.3 dB for MY ice; for TFY ice, NRCS values increase from ~-15 dB to -9 dB from December/January to mid-February. In situ and ASPeCt observations are not, however, detailed enough to interpret the observed NRCS change over time. Co-located Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) vertically polarized 37 GHz brightness temperatures (TB37V), 7 day and 1 day averages as well as the TB37V difference between ascending and descending AMSR-E overpasses suggest the low NRCS values (-15 dB) are associated with snowmelt being still in progress, while the change towards higher NRCS values (-9dB) is caused by commencement of melt-refreeze cycles after about mid-January.