Modern and pleistocene reservoir ages inferred from South Pacific corals

Abstract

This paper presents radiocarbon results from modern South Pacific corals from the Marquesas Islands, Van- uatu, Papua New Guinea (PNG), and Easter Island. All of the measurements are from pre-bomb Porites corals that lived dur- ing the 1940s and 1950s. The data reflect subannual to multiannual surface ocean 14C variability and allow for precise, unambiguous reservoir age determinations. The results are compared with published values from other coral records through- out the South Pacific, with striking consistency. By comparisons with other published values, we identify 3 South Pacific regions with uniform pre-bomb reservoir ages (1945 to 1955). These are 1) the Central Equatorial South Pacific (361.6 ± 8.2 14C yr, 2 σ); 2) the Western Equatorial South Pacific (322.1 ± 8.6 14C yr, 2 σ); and 3) the subtropical Pacific (266.8 ± 13.8 14C yr, 2 σ). The question of how much, and how fast, South Pacific reservoir ages might have varied in the past is addressed by examining a published record from a Pleistocene coral from Vanuatu that lived over a 700-yr period during the Younger Dryas. The average reservoir age at that time was larger than today, by ~150 yr, and exhibited reservoir age variability on a decadal timescale not seen in modern times. Measured paleo-reservoir ages increase sharply in this record by as many as 300 14C yr in 3 decades. These increases are punctuated by smaller reservoir age decreases, on the order of 150 yr. This reservoir age variability provides a rare picture of active ocean ventilation and ocean-atmosphere exchange at the close of the Pleistocene. © 2009 by the Arizona Board of Regents on behalf of the University of Arizona Celebrating 50 Years of Radiocarbon.