Pre-bomb Δ¹⁴C variability and the Suess effect in Cariaco Basin surface waters as recorded in hermatypic corals

The Δ¹⁴C 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 Δ¹⁴C averages -51.9 ± 3.3‰. Corals collected outside of the basin at Boca de Medio and Los Testigos have Δ¹⁴C values of -53.4 ± 3.3‰ and -54.3 ± 2.6, respectively. Additional ¹⁴C analyses on the Isla Tortugas coral document an ∼11‰ decrease between ∼1905 (-40.9 ± 4.5‰) and ∼1940. The implied Suess effect trend (-3‰/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.