TY - JOUR
T1 - Detecting time-averaging and spatial mixing using oxygen isotope variation
T2 - A case study
AU - Goodwin, David H.
AU - Flessa, Karl W.
AU - Téllez-Duarte, Miguel A.
AU - Dettman, David L.
AU - Schöne, Bernd R.
AU - Avila-Serrano, Guillermo A.
N1 - Funding Information:
We thank J. Campoy, A. Garry, E. Johnson and C. Rodriguez for help in the field. H. Spero, at the University of California, Davis, performed some of the isotopic analyses. We also thank the skilled boat captains from El Golfo de Santa Clara, Sonora. Thanks also to P. Roopnarine for thoughtful discussions and advice, as well the Octave principal component script. We thank D. Jones, J. Pandolfi and an anonymous reviewer for their helpful comments on an earlier version of this manuscript. Special thanks also to W. Allmon and A. Longinelli whose careful and thoughtful reviews significantly improved this paper. This study was funded by grants from the National Science Foundation, the Eppley Foundation for Research, the Alexander-von-Humboldt Foundation (Lynen Program) and Consejo Nacional de Cienca y TecnologÌa. This is CEAM publication #48.
PY - 2004/3/20
Y1 - 2004/3/20
N2 - In principle, bivalve mollusks living at the same time and in the same place will experience the same temperature and salinity regimes and will have identical annual oxygen isotope (δ18O) profiles. Bivalve mollusks living at different times or in different places are more likely to have different annual δ18O profiles. Thus, differences in annual δ18O profiles can be used to detect temporal or spatial mixing. We devised eight metrics to quantitatively compare sclerochronologically calibrated annual δ18O profiles from different shells: difference in maximum value, difference in minimum value, difference in amplitude, the number of non-contemporaneous isotopic enrichment events (NNEE), the average fortnightly difference (AD), the standard deviation of the average fortnightly differences (SDD), the maximum fortnightly difference (MaxD) and the number of fortnights separating the minimum values. These metrics vary among northern Gulf of California shells from four temporal and spatial categories: (1) same time and same place; (2) same time and different place; (3) different time and same place; and (4) different time and different place. Different time/different place comparisons include comparisons of live-collected shells with shells alive during times of Colorado River flow and shells from a Pleistocene interglacial deposit. The same time/same place comparison has the most similar metric values, whereas comparisons among the different time/different place shells are usually the least similar. Between-shell oxygen isotope differences can reveal temporal or spatial mixing of shells that would be undetectable with radiocarbon or amino-acid racemization dating. Application of the technique to a Holocene deposit with shells in life position reveals that the bivalves were alive at different times, despite indistinguishable radiocarbon ages. Two adjacent but disarticulated Pleistocene shells appear to be both temporally and spatially mixed. The method can detect temporal or spatial mixing in any shell material unaffected by diagenesis, regardless of the age of the specimens.
AB - In principle, bivalve mollusks living at the same time and in the same place will experience the same temperature and salinity regimes and will have identical annual oxygen isotope (δ18O) profiles. Bivalve mollusks living at different times or in different places are more likely to have different annual δ18O profiles. Thus, differences in annual δ18O profiles can be used to detect temporal or spatial mixing. We devised eight metrics to quantitatively compare sclerochronologically calibrated annual δ18O profiles from different shells: difference in maximum value, difference in minimum value, difference in amplitude, the number of non-contemporaneous isotopic enrichment events (NNEE), the average fortnightly difference (AD), the standard deviation of the average fortnightly differences (SDD), the maximum fortnightly difference (MaxD) and the number of fortnights separating the minimum values. These metrics vary among northern Gulf of California shells from four temporal and spatial categories: (1) same time and same place; (2) same time and different place; (3) different time and same place; and (4) different time and different place. Different time/different place comparisons include comparisons of live-collected shells with shells alive during times of Colorado River flow and shells from a Pleistocene interglacial deposit. The same time/same place comparison has the most similar metric values, whereas comparisons among the different time/different place shells are usually the least similar. Between-shell oxygen isotope differences can reveal temporal or spatial mixing of shells that would be undetectable with radiocarbon or amino-acid racemization dating. Application of the technique to a Holocene deposit with shells in life position reveals that the bivalves were alive at different times, despite indistinguishable radiocarbon ages. Two adjacent but disarticulated Pleistocene shells appear to be both temporally and spatially mixed. The method can detect temporal or spatial mixing in any shell material unaffected by diagenesis, regardless of the age of the specimens.
KW - Gulf of California
KW - Mollusks
KW - Oxygen isotopes
KW - Spatial-mixing
KW - Taphonomy
KW - Time-averaging
UR - http://www.scopus.com/inward/record.url?scp=1842433545&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=1842433545&partnerID=8YFLogxK
U2 - 10.1016/j.palaeo.2003.10.020
DO - 10.1016/j.palaeo.2003.10.020
M3 - Article
AN - SCOPUS:1842433545
SN - 0031-0182
VL - 205
SP - 1
EP - 21
JO - Palaeogeography, Palaeoclimatology, Palaeoecology
JF - Palaeogeography, Palaeoclimatology, Palaeoecology
IS - 1-2
ER -