Decadal Timescale Shift in the ¹⁴C Record of a Central Equatorial Pacific Coral

Abstract

ABSTRACT. Coral skeletal radiocarbon records reflect seawater D 14 C and are useful for reconstructing the history of water mass movement and ventilation in the tropical oceans. Here, we reconstructed the inter-annual variability in central equatorial Pacific surface water D 14 C from 1922-1956 using near-monthly 14 C measurements in a Porites sp. coral skeleton (FI5A) from the windward side of Fanning Island (3°54¢32²N, 159°18¢88²W). The most pronounced feature in this record is a large, positive shift in the D 14 C between 1947 and 1956 that coincides with the switch of the Pacific Decadal Oscillation (PDO) from a positive to a negative phase in the mid-1940s. Although the absolute D 14 C values from 1950-1955 in FI5A differ from the D 14 C values of another coral core collected from the opposite side of the island, both records show a large, positive shift in their D 14 C records at that time. The relative increase in the D 14 C of each record is consistent with the premise that a common mechanism is controlling the D 14 C records within each coral record. Overall, the Fanning D 14 C data support the notion that a significant amount of subtropical seawater is arriving at the Equator, but does not allow us to determine the mechanism for its transport.

Effects of diagenesis on paleoclimate reconstructions from modern and young fossil corals

“…Interestingly, the coral d 18 O and Sr/Ca timeseries track SST well down-core of 1950AD, suggesting that the diagenesis is relatively confined to the middle section of the core. Accompanying coral radiocarbon (D 14 C) measurements from FI5-A (Grottoli et al, 2003) are relatively high in the 1950-1971AD section of the core (Fig. 1C), consistent with the presence of relatively young secondary aragonite cements in this interval.…”

Developments in Radiocarbon Technologies: From the Libby Counter to Compound-Specific AMS Analyses

“…For instance, the ventilation of the Black Sea throughout this time period received special attention (Ballard et al 2000;Ça¢ gatay et al 2003;Giosan et al 2006;EriÅ s et al 2007;Ivanova et al 2007). Work on corals and sclerosponges addressing more recent climate pattern questions is represented for example by (Grottoli et al 2003;Cohen and Hart 2004;Rosenheim and Swart 2007). Figure 11 shows coral 14 C data from the Grottoli paper reflecting the excellent agreement of the AMS measurements performed at CAMS and NOSAMS, pinpointing the +1.7% Δ 14 C shift in 1947 at Fanning Island.…”

Short‐term fluctuations in regional radiocarbon reservoir age recorded in coral skeletons from the Ryukyu Islands in the north‐western Pacific

“…Some studies have reported short‐term fluctuations of Δ R , for example at Fanning Island in the equatorial Pacific (Grottoli et al , ) and off the coast of Peru (Jones et al , , ). Short‐term fluctuations of Δ R have also been reported in the Kuroshio region, including at Ishigaki Island (Hideshima et al , ; Araoka et al , ), although the data used in these studies are not continuous spatially or temporally, which makes it difficult to draw conclusions about the cause of the fluctuations.…”