Physical oceanography in the Western Bransfield Strait and Gerlache Strait during Austral summer 1995/96

n the framework of the FRUELA project, two oceanographic surveys were conducted by R/V Hespérides in the eastern Bellingshausen Sea, western basin of the Bransfield Strait and Gerlache Strait area during December 1995 and January 1996. The main hydrographic structures of the study domain were the Southern Boundary of the ACC and the Bransfield Front. The characteristics and zonation of local water masses are discussed in terms of temperature, salinity, dissolved oxygen, nutrient and inorganic carbon concentrations. Concentration intervals for water mass labelling, on the basis of chemical parameters in addition to the common theta/S-based classification, are defined. Silicate seems to be a very good discriminator for local water masses.

Physical properties of firn cores from the 1995/96 and 1996/97 field seasons

The paper focuses on studies of snow-pit samples and shallow firn cores taken during the 1995-96 and 1996-97 field seasons at Amundsenisen, Dronning Maud Land, Antarctica. The dating of the firn is based on the artificial tritium distribution in the snow cover and on several reference horizons identified by electrical measurements. The early 1964 through 1965 horizon is marked by the deposition of sulfate released to the atmosphere during the eruption of the Agung volcano in March 1963; this horizon was detected by dielectric profiling and electrical conductivity measurements; the proof by chemical analysis has still to be seen. At the ten investigated sites on Amundsenisen the 1964-65 horizon was identified 4.1-5.7 m below the surface. The accumulation rates on Amundsenisen are 41-91 kg/m**2/a. The cores are up to 100 years old. A relationship between isotope content and the mean air temperature on a regional scale can be based on measurements of firn temperature at 10 m depth at the drilling sites. Between Neumayer station at the coast and Heimefrontfjella, the temperature gradient of the deuterium content is 9.6 per mil/K. South of Heimefrontfjella, on the Amundsenisen plateau, it is only 5.5 per mil/K. Time series of yearly accumulation rates show no significant trend. For the isotope records a significant trend to higher values with gradients of 0.1-0.2 d2H per mil/a can be seen in five of the ten time series.

Geochemistry of interstitial waters of DSDP Leg 96 sites

Interstitial water studies were done at 9 of the 11 sites visited in the Mississippi Fan and Orca and Pigmy Basins during DSDP Leg 96. High concentrations of sulfate were observed at Mississippi Fan Sites 616, 617, 620, and 623. The maximum sulfate value of 38.8 mM, recorded at Site 617, is the highest ever found in DSDP sediments. Hypersaline interstitial water was observed at Site 618 in Orca Basin. Concentration ratios of salinity to chlorinity and to sodium in interstitial waters are similar to those of Orca Basin bottom water, suggesting that the chemistry of interstitial water is affected by the dissolution of buried salt.