HR: 0800h
AN: PP11A-0238    [Abstracts]
TI: Radiocarbon In Mollusk Shells As Proxy For Peruvian Upwelling: Modern Pre-Bomb Reservoir Effect Correction
AU: * Etayo-Cadavid, M
EM: mfetayocadavid@bama.ua.edu
AF: Department of Geological Sciences, The University of Alabama, Tuscaloosa, AL 35487,
AU: Andrus, C
EM: fandrus@geo.ua.deu
AF: Department of Geological Sciences, The University of Alabama, Tuscaloosa, AL 35487,
AU: Hodging, G
EM: ghodgins@physics.arizona.edu
AF: NSF-Arizona AMS Facility, Physics Department, University of Arizona, Tucson, AZ 85721,
AU: Jones, K
EM: kbjones@arizona.edu
AF: Geosciences Department, University of Arizona, Tucson, AZ 85721,
AU: Landeros, A
EM: alandero@cba.ua.edu
AF: Department of Statistics, The University of Alabama, Tuscaloosa, AL 35487,
AB: Analyses of radiocarbon content in Peruvian pre-bomb mollusk shells revealed short-term changes in vertical mixing and permit calculation of a new regional reservoir effect correction (ΔR) that includes variable confidence intervals to reflect sample time averaging. The rationale of the molluscan proxy is based on the mixing of radiocarbon-depleted deep water with comparatively enriched surface water. As mollusks grow, their radiocarbon content varies with ambient conditions, thus recording upwelling changes through ontogeny. Vertical mixing on the coast of Peru is variable at multiple time scales, often as a result of El Niño/Southern Oscillation (ENSO) activity. Intense upwelling is reflected in low ¹⁴ C concentration in shell carbonate while cessations or reductions in upwelling produce increases in radiocarbon. Four pre-bomb mollusk shells were analyzed for radiocarbon content consecutively from hinge to edge at high spatial resolution. Two shells of {Donax} {marincovichi} (formerly {D.} {obesulus}) collected in Puerto Pariñas (4^o40^'S) and Puerto Salaverry (8^o13^'S) during 1929 and 1926 and two specimens of {Protothaca} {asperrima} collected in Paracas (13^o52^'S) during 1948 were analyzed. The number of subsamples per shell varied between ten and nineteen. Additionally, eight shells of {Argopecten} {purpuratus} from Puerto Salaverry, Callao Bay (12^o 4^' S) and Sechura Bay (5^o 45^'S) collected in 1908 and 1926 were analyzed at lower spatial resolution. Radiocarbon profiles from {Donax} and {Protothaca} show abrupt and significant changes in radiocarbon content, suggesting rapid upwelling variation during the life of the organisms. Lower resolution analysis of {Argopecten} also shows variable radiocarbon content within the shells associated to upwelling changes. Statistical analysis demonstrated no significant difference in the means of multiple ΔRs obtained from the twelve shells. However, ΔR variance was significantly different between shells. These findings suggest that regional average ΔR for Peru (1908 to 1948) remained relatively constant, but significant short-term variability occurred. Based on the statistical analysis of the data we propose a new ΔR correction of 114 years. The confidence interval of this correction is dependant on the degree of time-averaging in the sample(s) analyzed, thus an equation describing the relationship between sampling and ΔR was constructed.
DE: 4964 Upwelling (4279)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting