Seasonally resolved surface water Δ 14 C variability in the Lombok Strait: A coralline perspective

We have explored surface water mixing in the Lombok Strait through a bimonthly resolved surface water Δ 14 C time series reconstructed from a coral in the Lombok Strait that spans 1937 through 1990. The prebomb surface water Δ 14 C average is −60.5‰, and individual samples range from −72‰ to 134‰. The annual average postbomb maximum occurs in 1973 at 122‰. The timing of the postbomb maximum is consistent with a primary subtropical source for the surface waters in the Indonesian seas. During the postbomb period, the coral records regular seasonal cycles of 5‰ to 20‰. Seasonal high Δ 14 C occur during March–May (warm, low salinity), and low Δ 14 C occur in September (cool, higher salinity). The Δ 14 C seasonality is coherent and in phase with the seasonal Δ 14 C cycle observed in Makassar Strait. We estimate the influence of high Δ 14 C Makassar Strait (North Pacific) water flowing through the Lombok Strait using a two end‐member mixing model and the seasonal extremes observed at the two sites. The percentage of Makassar Strait water varies between 16% and 70%, and between 1955 and 1990, it averages at 40%. The rich Δ 14 C variability has a biennial component reflecting remote equatorial Indian Ocean forcing and a component in the ENSO band, which is interpreted to reflect Pacific forcing on the Δ 14 C signature in Lombok Strait.