Very Long-Lived Mollusks Confirm 17th Century AD Tephra-Based Radiocarbon Reservoir Ages for North Icelandic Shelf Waters
AuthorWanamaker, Alan D., Jr.
Scourse, James D.
Richardson, Christopher A.
Butler, Paul G.
Knudsen, Karen Luise
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CitationWanamaker, A. D., Heinemeier, J., Scourse, J. D., Richardson, C. A., Butler, P. G., Eiríksson, J., & Knudsen, K. L. (2008). Very long-lived mollusks confirm 17th century AD tephra-based radiocarbon reservoir ages for North Icelandic shelf waters. Radiocarbon, 50(3), 399-412.
AbstractMarine sediment records from the north Icelandic shelf, which rely on tephrochronological age models, reveal an average Delta-R (regional deviation from the modeled global surface ocean reservoir age) of approximately 150 yr for the last millennium. These tephra-based age models have not hitherto been independently verified. Here, we provide data that corroborate Delta-R values derived from these sediment archives. We sampled the youngest portion (ontogenetic age) of a bivalve shell, Arctica islandica (L.), for radiocarbon analysis, which was collected alive in 2006 from the north Icelandic shelf in ~80 m water depth. Annual band counting from the sectioned shell revealed that this clam lived for more than 405 yr, making it the longest-lived mollusk and possibly the oldest non-colonial animal yet documented. The 14C age derived from the umbo region of the shell is 951 +/- 27 yr BP. Assuming that the bivalve settled onto the seabed at AD 1600, the corresponding local value of Delta-R is found to be 237 +/- 35 yr by comparison of the 14C age with the Marine04 calibration curve (Hughen et al. 2004) at this time. Furthermore, we cross-matched a 287-yr-old, dead-collected, A. islandica shell from AD 1601 to 1656 from the same site with the live-caught individual. 14C analysis from the ventral margin of this shell revealed a Delta-R of 186 +/- 50 yr at AD 1650. These values compare favorably with each other and with the tephra-based Delta-R values during this period, illustrating that 14C from A. islandica can effectively record 14C reservoir changes in the shelf seas.