Bomb radiocarbon
Bomb radiocarbon and climate records in South Pacific Gyre
Published - Radiocarbon
BOMB-PRODUCED RADIOCARBON ACROSS THE SOUTH PACIFIC GYRE—A NEW RECORD FROM AMERICAN SAMOA WITH UTILITY FOR FISHERIES SCIENCE
Allen H Andrews • Nancy G Prouty • Olivia M Cheriton
Coral skeletal structures can provide a robust record of nuclear bomb produced 14C with valuable insight into air-sea exchange processes and water movement with applications to fisheries science. To expand these records in the South Pacific, a coral core from Tutuila Island, American Samoa was dated with density band counting covering a 59-yr period (1953–2012). Seasonal signals in elemental ratios (Sr/Ca and Ba/Ca) and stable carbon (δ13C) values across the coral core corroborated the well-defined annual band structure and highlighted an ocean climate shift from the 1997–1998 El Nin ̃o. The American Samoa coral 14C measurements were consistent with other regional records but included some notable differences across the South Pacific Gyre (SPG) at Fiji, Rarotonga, and Easter Island that can be attributed to decadal ocean climate cycles, surface residence times and proximity to the South Equatorial Current. An analysis of the post-peak 14C decline associated with each coral record indicated 14C levels are beginning to merge for the SPG. This observation, coupled with otolith measurements from American Samoa, reinforces the perspective that bomb 14C dating can be performed on fishes and other marine organisms of the region using the post-peak 14C decline to properly inform fisheries management in the South Pacific.
Published Radiocarbon journal:
Pictured as a CT scan (left) and an X-ray (right) is the slabbed coral core extracted from a reef off Matautuloa Point on the southern side of Tutuila, American Samoa. The continuous CT scan and X-ray show a clear banding pattern across the core with the chronology labeled every 5 yr from the annual band counting (high- and low-density couplet) in the X-ray image. The record begins at the collection date in 2012 and clearly covers regularly spaced bands through to 1953 for a total of 59 yr of growth. The banding structure was consistent through time in each core image with a mean annual growth rate of ∼1.2 cm·yr–1. The serial sampling from the micromill is seen as regularly spaced parallel channels (4–5 mm long) in the X-ray that were cut into the coral. The horizontal marks toward the top of each core segment in the X-ray image are an artifact of the indexing slots used for LA-ICP-MS placement and the white lines on the CT image show the laser scan paths.
This older, generalized map of surface currents of the Pacific Ocean provides an overview of flow patterns and the surface structure of the South Pacific Gyre.
