Showing papers by "Hilary Kennedy published in 2002"

Particulate organic matter in Antarctic summer sea ice: concentration and stable isotopic composition

Abstract: The chemical and isotopic data from sea ice collected over a wide area of the Weddell Sea, Antarctica, during the austral summer/early autumn illustrate the range of environmental con- ditions under which ice algae grow. A range of ice types and features were sampled including intact and layered ice floes and surface ponds. Sea ice communities were found in all these environments but the highest biomasses were found either at the base of ice floes, or in the interior of layered floes with quasi-continuous horizontal gaps at or shortly below the water level. In the layered floes, par- ticulate organic carbon (POC) measured in the ice layer immediately overlying the gap water (280 to 6014 µmol dm -3 ) was in excess of what would be predicted if algal growth had occurred in a closed environment. The chemical composition of the gap water was strongly affected by biological activity in the overlying ice, which acts as a physical support for the algae retained within its matrix. The low- est range of POC (27 to 739 µmol dm -3 ) conformed to predictions of algal growth in a closed system and samples were collected from the interior of ice floes where there was essentially no potential for nutrient exchange. The surface ponds displayed nitrate (NO3 - ) exhaustion and total dissolved inor- ganic carbon (∑CO2) reductions consistent with nutrient limited algal growth. The stable carbon iso- topic composition of the particulate organic matter (POM) across all habitat types sampled (δ 13 CPOC -10.0 to -27.3‰) displayed a wide range but was much less variable than the range of POC concen- trations might have implied. The assumption that the highest biomass of algae in sea ice will result in the most positive δ 13 CPOC values cannot be generally applied. The isotopic composition of dissolved inorganic carbon (δ 13 C∑CO2 ) in gap waters and surface ponds varied from 0.15 to 3.0 ‰ and was shown to be commensurate with the changes predicted from NO3 - deficits caused by algal growth.

The influence of shell growth rate on striae deposition in the scallop Pecten maximus

Abstract: The relationship between shell growth rate and striae deposition was investigated in a field study in which groups of juvenile scallops, Pecten maximus, (Pectinidae: Bivalvia) were deployed for monthly periods over a year in the Menai Strait (North Wales). The number of striae deposited per day, inter-striae width (the increment of shell deposited between successive striae) and striae abundance (the number of striae deposited per mm of shell height) all correlated well with measured shell growth rates. During the winter months, when seawater temperatures were minimal (6°C), inter-striae width declined, whilst striae abundance increased, whereas during the summer when seawater temperatures were maximal (18°C), shell growth was rapid with maximum inter-striae width, resulting in a seasonal pattern of narrowly grouped, then widely spaced striae. This seasonal pattern in inter-striae width variation provides an accurate and reliable method for estimating the number of growth cycles and hence the age of P. maximus.

Dissolved organic carbon in sediments from the eastern

Abstract: Profiles of dissolved organic carbon (DOC) were measured in the pore water of sediments from 1000, 2000 and 3500 m water depth in the eastern North Atlantic. A net DOC accumulation in the pore waters was observed, which followed closely the zonation of microbial respiration in these sediments. The concentration of pore water DOC in the zone of oxic respiration was elevated relative to that in the bottom ocean water. The resulting upward gradient across the sediment–water interface indicated a steady state diffusive benthic flux, FDOC, of 0.25–0.44 mmol m � 2 day � 1 from these sediments. Subsequent increase in the concentration of DOC in the pore water occurred only in the sediments from 1000 and 2000 m water depth that supported anoxic respiration, leading to a deep concentration maximum. By contrast, in the sediments from 3500 m water depth, a deep concentration minimum was measured, coincident with minimal postoxic respiration in this near-abyssal setting. The gradientbased FDOC represented approximately 14% of the total remineralized organic carbon (TCR=sum of FDOC and depth-integrated organic carbon oxidation rate) in the sediments from 1000 and 2000 m water depth, while it was 36% of the TCR in the sediments from 3500 m water depth. A covariance of particulate organic carbon (POC) and pore water DOC with depth in the sediments was evident, more consistently at the deepest site. While the covariance can be related to biotic processes in these sediments, an alternative interpretation suggests a possible contribution of sorption to the biotic control on sedimentary organic carbon cycling. The steady state diagenetic conditions in which this may occur can be conceivable for some organic-poor deepsea locations, but direct evidence is clearly required to validate them. D 2002 Elsevier Science B.V. All rights reserved.