Marine or estuarine radiocarbon reservoir corrections for mollusks? A case study from a medieval site in the south of England

Mollusk shells are frequently radiocarbon dated and provide reliable calibrated age ranges when the regional marine reservoir correction is well-established. For mollusks from an estuarine environment the reservoir correction may be significantly different than the regional marine reservoir correction due to the input of bedrock or soil derived carbonates. Some mollusk species such as oysters are tolerant of a significant range of salinities which makes it difficult to determine which reservoir correction is appropriate. A case study is presented of an anomalous radiocarbon age for an oyster shell paint dish found in the fabric of the ruined nave walls of St Mary's Church, Shoreham-by-Sea, West Sussex, England. Stable isotopes (delta O-18 and delta C-13) were used to establish the type of environment in which the oyster had lived. Paired marine and terrestrial samples from a nearby medieval site were radiocarbon dated to provide an appropriate reservoir correction.

The European oyster (Ostrea edulis) and its epibiotic succession

This study aimed to investigate intra- and inter-site differences in the epibiota on the European oyster Ostrea edulis of different ages and on hard substrata to assess their contribution to biodiversity. This research has shown that shells of O. edulis do show higher species diversity than non-living hard substrata and as oysters grow larger epibiotic diversity will increase. This investigation has revealed that O. edulis possesses biogenic engineering qualities and the value of O. edulis as a vehicle for increasing biodiversity should not be underestimated. Relatively few studies have examined the shell surfaces of Ostrea edulis, which, together with their associated epifauna provide a large portion of the natural hard substrata for sessile filter-feeding organisms, including oysters, in coastal and estuarine ecosystems. It can be considered a keystone species which has an influence on intertidal and subtidal community structures.

Commercial oyster stocks as a potential source of larvae in the regeneration of Ostrea edulis in Strangford Lough, Northern Ireland.

Ostrea edulis was extremely rare in the wild in Strangford Lough from the early 1900s until renewed spatfall was observed at a number of sites in the 1990s. A monitoring programme was undertaken to investigate the presence and distribution of planktonic oyster larvae at nine sites around the lough between June and September in 1997 and 1998 as a precursor to studies of spatfall patterns. Larval densities at sites in the northern basin of the lough were significantly higher than those in the southern basin where larvae were lacking or in low numbers. Densities and sizes of oyster larvae showed significant temporal variation suggesting pulsed larval release. Larval densities also showed significant spatial variation with higher densities at sites closer to commercial stocks pointing to these as the main source of oyster larvae. This hypothesis was supported during a larval flux study over a complete tidal cycle which indicated a 90% net tidal movement of O. edulis larvae from the entrance of the bay where commercial stocks were held to the main body of the lough. Thus the maintenance of dense commercial stocks of flat oysters may provide the key to the redevelopment of native oyster beds in Strangford Lough and elsewhere by providing an initial broodstock nucleus from which larvae can be exported.

Laboratory trials on the effects of different diets on growth and survival of the common whelk, Buccinum undatum L. 1758, as a candidate species for aquaculture.

Newly hatched juvenile Buccinum undatum can be reared under laboratory conditions. Good was growth is achieved when juveniles were fed on combined diets (blue mussel, cod, and fish pellets). Juveniles reached shell heights of 33.0 ± 4.2 mm, 26.9 ± 3.8 ± mm, 23.2 ± 2.2 mm, and 20.1 ± 1.6 mm, after 14 months of fedding on a combined diet, blue mussel, cod, and fish pellets, respectively under ambient sea temperature and salinity. After 14 months juveniles fed blue mussel had the highest survival rates (67%) followed by those fed a combination of all other experimental diets (61%), cod waste (53%) and fish-feed pellets (46%). High mortalities were recorded in most treatments during the summer months between June and September. This species appears to have an aquaculture potential, as juveniles readily feed on artificial diets at an early age, show high survival rates and could potentially reach market size in 2 years or less. The major constraint in realising this potential at present, is the relatively low value of the species; if market values increased as a result of serious depletion of natural populations, hatchery production of juveniles for intensive aquaculture or restocking could become economically viable.

Reuse of construction waste: performance under repeated loading

The use of recycled aggregates has increased greatly over the last decade owing to enhanced environmental sensitivities. The level of performance required by such materials is dependent upon the applications for which they are used. Many recycled construction wastes have adequate shear strength in relation to various geotechnical applications. However, a possible drawback of these materials is the risk of crushing during repeated loading. The work reported in this paper examined two waste materials: crushed concrete and building debris, both regarded as construction wastes. Tests were also performed on traditionally used crushed rock, in this case basalt. The materials were subjected to repeated loading in a large direct shear apparatus. The amount of crushing was quantified by performing particle size analysis of the tested material. The results have shown that both recycled construction wastes were susceptible to particle crushing. The amount of crushing was influenced by both the vertical pressure and the number of loading cycles. This leads to a marked decrease in peak friction angle

Inner-shell photoexcitation of Fe XV and Fe XVI

The configuration-interaction method as implemented in the computer code CIV3 is used to determine energy levels, electric dipole radiative transition wavelengths, oscillator strengths and transition probabilities for inner-shell excitation of transitions in Fe XV and Fe XVI. Specifically, transitions are considered of the type 1s(2) 2s(2) 2p(6) 3s(2) -1s(2) 2s(2) 2p(5) 3l3l' 3l" (l, l' and l" = s,p or d) in FeXV and 1s(2) 2s(2) 2p(6) 3s- 1s(2) 2s(2) 2p(5) 3l3l' (l and l' = s,p or d) in FeXVI, using the relativistic Breit-Pauli approach. An assessment of the accuracy of the derived atomic data is performed.

Radiation damping effects on L-shell photoionization cross- sections of O-like Fe xix and N-like recombination rate coefficients for Fe xx

Photoionization cross-sections out of the fine-structure levels (2S(2)2p(4) P-3(2,0,1)) of the O-like Fe ion Fe XIX have been reinvestigated. Data for photoionization out of each of these finestructure levels have been obtained, where the calculations have been performed with and without the inclusion of radiation damping on the resonance structure in order to assess the importance of this process. Recombination rate coefficients are determined using the Milne relation, for the case of an electron recombining with N-like Fe ions (Fe XX) in the ground state to form O-like Fe (Fe XIX) existing in each of the fine- structure ground-state levels. Recombination rates are presented over a temperature range similar to 4.0 less than or equal to log T-e less than or equal to 7.0, of importance to the modelling of X-ray emission plasmas.

Ionization from the outer shell of Ar by proton impact

Recent results for proton-argon total ionization cross sections [Kirchner Phys. Rev. Lett. 79, 1658 (1997)] show large disagreement between theory and experiment for energies below 80 keV. To address this problem we have employed a recently developed theoretical method with a more pragmatic approach to the charge screening both in the initial and final channels. The target is considered as a one-electron atom and the interactions between this active electron and remaining target electrons are treated by a model potential including both short- and long-range effects. In the final channel the usual product of two continuum distorted wave functions each associated with a distinct electron-nucleus interaction is used. New results in the present calculation show good agreement in total cross sections for the energy range 10-300 keV with the measurement of Rudd [Rev. Mod. Phys. 57, 965 (1985)].