Pre-Bomb Δ14C Variability and the Suess Effect in Cariaco Basin Surface Waters as Recorded in Hermatypic Corals

Abstract

The Delta-14C content of surface waters in and around the Cariaco Basin was reconstructed from radiocarbon measurements on sub-annually sampled coral skeletal material. During the late 1930s to early 1940s, surface waters within and outside of the Cariaco Basin were similar. Within the Cariaco Basin at Islas Tortugas, coral Delta-14C averages -51.9 +/3.3ppm. Corals collected outside of the basin at Boca de Medio and Los Testigos have Delta-14C values of -53.4 +/3.3ppm and -54.3 +/2.6, respectively. Additional 14C analyses on the Isla Tortugas coral document an ~11 decrease between ~1905 (-40.9 +/4.5ppm) and ~1940. The implied Suess effect trend (-3ppm/decade) is nearly as large as that observed in the atmosphere over the same time period. If we assume that there is little to no fossil fuel 14CO2 signature in Cariaco surface waters in ~1905, the waters have an equivalent reservoir age of ~312 yr.