The effects of growth phase and salinity on the hydrogen isotopic composition of alkenones produced by coastal haptophyte algae

The isotopic fractionation of hydrogen during the biosynthesis of alkenones produced by marine haptophyte algae has been shown to depend on salinity and, as such, the hydrogen isotopic composition of alkenones is emerging as a palaeosalinity proxy. The relationship between fractionation and salinity has previously only been determined during exponential growth, whilst it is not yet known in which growth phases natural haptophyte populations predominantly exist. We have therefore determined the relationship between the fractionation factor, alpha alkenones-water, and salinity for C37 alkenones produced in different growth phases of batch cultures of the major alkenone-producing coastal haptophytes Isochrysis galbana (strain CCMP 1323) and Chrysotila lamellosa (strain CCMP 1307) over a range in salinity from ca. 10 to ca. 35. alpha alkenones-water was similar in both species, ranging over 0.841-0.900 for I. galbana and 0.838-0.865 for C. lamellosa. A strong (0.85 <= R**2 <= 0.97; p < 0.0001) relationship between salinity and fractionation factor was observed in both species at all growth phases investigated. This suggests that alkenone dD has the potential to be used as a salinity proxy in coastal areas where haptophyte communities are dominated by these coastal species. However, there was a marked difference in the sensitivity of alpha alkenones-water to salinity between different growth phases: in the exponential growth phase of I. galbana, alpha alkenones-water increased by 0.0019 per salinity unit (S 1), but was less sensitive at 0.0010 S 1 and 0.0008 S 1 during the stationary and decline phases, respectively. Similarly, in C. lamellosa alpha alkenones-water increased by 0.0010 S 1 in the early stationary phase and by 0.0008 S 1 during the late stationary phase. Assuming the shift in sensitivity of alpha alkenones-water to salinity observed at the end of exponential growth in I. galbana is similar in other alkenone-producing species, the predominant growth phase of natural populations of haptophytes will affect the sensitivity of the alkenone salinity proxy. The proxy is likely to be most sensitive to salinity when alkenones are produced in a state similar to exponential growth.

A design-phase PSA of anuclear-powered hydrogen plant

A probabilistic safety assessment (PSA) is being developed for a steam-methane reforming hydrogenproduction plant linked to a high-temperature gas-cooled nuclear reactor (HTGR). This work is based on the Japan Atomic Energy Research Institute's (JAERI) High Temperature Engineering Test Reactor (HTTR) prototype in Japan. The objective of this paper is to show how the PSA can be used for improving the design of the coupled plants. A simplified HAZOP study was performed to identify initiating events, based on existing studies. The results of the PSA show that the average frequency of an accident at this complex that could affect the population is 7 × 10−8 year−1 which is divided into the various end states. The dominant sequences are those that result in a methane explosion and occur with a frequency of 6.5 × 10−8 year−1, while the other sequences are much less frequent. The health risk presents itself if there are people in the vicinity who could be affected by the explosion. This analysis also demonstrates that an accident in one of the plants has little effect on the other. This is true given the design base distance between the plants, the fact that the reactor is underground, as well as other safety characteristics of the HTGR.