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The Belfast Ramped Pyroxidation/Combustion (RPO/RC) facility was established at the 14CHRONO Centre (Queen’s University Belfast). The facility was created to provide targeted analysis of bulk material for refined chronological analysis and carbon source attribution for a range of sample types. Here we report initial RPO results, principally on background material, but also including secondary standards that are routinely analyzed at 14CHRONO. A description of our setup, methodology, and background (blank) correction method for the system are provided. The backgrounds (anthracite, spar calcite, Pargas marble) reported by the system are in excess of 35,000 14C years BP with a mean age of 39,345 14C years BP (1σ = 36,497–43,800 years BP, N=44) with F14C = 0.0075 ± 0.0032. Initial results for standards are also in good agreement with consensus values: TIRI-B pine radiocarbon age = 4482 ± 47 years BP (N=13, consensus = 4508 years BP); IAEA-C6 ANU Sucrose F14C= 1.5036 ± 0.0034 (N=10, consensus F14C = 1.503). These initial tests have allowed problematic issues to be identified and improvements made for future analyses.
This article presents a case study of Lower Lough Erne, a humic, alkaline lake in northwest Ireland, and uses the radiocarbon method to determine the source and age of carbon to establish whether terrestrial carbon is utilized by heterotrophic organisms or buried in sediment. Stepped combustion was used to estimate the degree of the burial of terrestrial carbon in surface sediment. Δ14C, δ13C, and δ15N values were measured for phytoplankton, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and particulate organic carbon (POC). Δ14C values were used to indicate the presence of different sources of carbon, including bedrock-derived inorganic carbon, “modern,” “recent,” “subsurface,” and “subfossil” terrestrial carbon in the lake. The use of 14C in conjunction with novel methods (e.g. stepped combustion) allows the determination of the pathway of terrestrial carbon in the system, which has implications for regional and global carbon cycling.
Carbon (C) and nitrogen (N) stable isotope analysis (SIA) has been used to identify the terrestrial subsidy of freshwater food webs. However, SIA fails to differentiate between the contributions of old and recently fixed terrestrial C and consequently cannot fully determine the source, age, and biochemical quality of terrestrial carbon. Natural abundance radiocarbon (Δ14C) was used to examine the age and origin of carbon in Lower Lough Erne, Northern Ireland. 14C and stable isotope values were obtained from invertebrate, algae, and fish samples, and the results indicate that terrestrial organic C is evident at all trophic levels. High winter δ15N values in calanoid zooplankton (δ15N = 24‰) relative to phytoplankton and particulate organic matter (δ15N = 6‰ and 12‰, respectively) may reflect several microbial trophic levels between terrestrial C and calanoid invertebrates. Winter and summer calanoid Δ14C values show a seasonal switch between autochthonous and terrestrial carbon sources. Fish Δ14C values indicate terrestrial support at the highest trophic levels in littoral and pelagic food webs. 14C therefore is useful in attributing the source of carbon in freshwater in addition to tracing the pathway of terrestrial carbon through the food web.
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