Interstitial water chemistry of ODP Leg 110 holes

Major-element compositions (Cl-, SO4[2-], Ca2+, Mg2+ , Li+ , K+, Na+ , Sr2+) of interstitial waters obtained from sediment cores along the ODP Leg 110 transect across the Northern Barbados accretionary prism have shown that a complex set of geochemical processes are of importance in this area. In the volcanic ash-rich Pleistocene-Pliocene sediments, alteration reactions involving volcanic ash lead to depletions of Mg2+ and K+. This process is confirmed by the much lower than contemporaneous seawater values of the 87Sr/86Sr ratios of dissolved strontium. In the deeper sediments recovered below the zone of decollement (Sites 671 and 672) large increases in Ca2+ and gradual decreases in Mg2+ , Na+, and d18O (H2O) indicate a potential contribution to the interstitial water chemistry by exchange with underlying basement rocks. This process has been hard to confirm because the drill holes were terminated well short of reaching basement. However, the concentration gradient pattern is consistent with observations in a large number of DSDP drill holes. Finally, but most importantly, low Cl- concentrations in the decollement zone and underlying sand layers, as well as in fault zones at Sites 673 and 674, indicate dilution of interstitial waters. The potential origins of the low Cl- concentrations are discussed, though we are not able to distinguish any mechanism in particular. Our evidence supports the concept of water migration along the decollement and through the underlying sandstones as well as along recent fault zones in the accretionary complex. Interstitial water concentration depth profiles are affected by faulting, thrusting, and overturn processes in the accretionary prism. These processes have caused a diminished diffusive exchange with the overlying ocean, thus explaining increased depletions in Mg2+ and SO4[2-] in sites farther onto the accretionary prism.

Radiocarbon age determination of 16 sites

The thermal diffusion enrichment apparatus in use in Amsterdam before 1967, has been rebuilt in the Groningen Radiocarbon Dating Laboratory. It has been shown to operate reliably and reproducibly. A reasonable agreement exists between the theoretical calculations and the experimental results. The 14C enrichment of a CO sample is deduced from the simultaneous mass 30 enrichment, which is measured with a mass spectrometer. The relation between both enrichments follows from a series of calibration measurements. The over-all accuracy in the enrichment is a few percent, equivalent to a few hundred years in age. The main problem in dating very old samples is their possible contamination with recent carbon. Generally, careful sample selection and rigorous pretreatment reduce sample contamination to an acceptable value. Also, it has been established that laboratory contamination, due to a memory effect in the combustion system and to impurities in the oxygen and nitrogen gas used for combustion, can be eliminated. A detailed analysis shows that the counter background in our set-up is almost exclusively caused by cosmic ray muons. The measurement of 28 early glacial samples, mostly from North-west Europe, has yielded a consistent set of ages. These indicate the existence of three early glacial interstadials; using the Weichselian definitions: Amersfoort starting at 68 200 ± 1100, Brørup at 64 400 ± 800 and Odderade at 60 500 ± 600 years BP. This 14C chronology shows good agreement with the Camp Century chronology and the dated palaeo sea levels. The discrepancy in the age of the early part of the Last Glacial on the 14C time scale and on that adopted for the deep-sea d18 record, must probably be attributed to the use of a generalized d18 curve and a wrong interpretation of this curve in terms of three Barbados terraces.

Hydrogen consumption by gills of Bathymodiolus spp. collected at the Comfortless cove and Lilliput hydrothermal vent fields in May 2006

The discovery of deep-sea hydrothermal vents in 1977 revolutionized our understanding of the energy sources that fuel primary productivity on Earth. Hydrothermal vent ecosystems are dominated by animals that live in symbiosis with chemosynthetic bacteria. So far, only two energy sources have been shown to power chemosynthetic symbioses: reduced sulphur compounds and methane. Using metagenome sequencing, single-gene fluorescence in situ hybridization, immunohistochemistry, shipboard incubations and in situ mass spectrometry, we show here that the symbionts of the hydrothermal vent mussel Bathymodiolus from the Mid-Atlantic Ridge use hydrogen to power primary production. In addition, we show that the symbionts of Bathymodiolus mussels from Pacific vents have hupL, the key gene for hydrogen oxidation. Furthermore, the symbionts of other vent animals such as the tubeworm Riftia pachyptila and the shrimp Rimicaris exoculata also have hupL. We propose that the ability to use hydrogen as an energy source is widespread in hydrothermal vent symbioses, particularly at sites where hydrogen is abundant.