Seasonally resolved surface water Δ14C variability in the Lombok Strait: A coralline perspective

We have explored surface water mixing in the Lombok Strait through a bimonthly resolved surface water Delta C-14 time series reconstructed from a coral in the Lombok Strait that spans 1937 through 1990. The prebomb surface water Delta C-14 average is -60.5 parts per thousand and individual samples range from -72 parts per thousand to 134 parts per thousand. The annual average postbomb maximum occurs in 1973 at 122 parts per thousand 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 parts per thousand to 20 parts per thousand. Seasonal high Delta C-14 occur during March-May (warm, low salinity), and low Delta C-14 occur in September (cool, higher salinity). The Delta C-14 seasonality is coherent and in phase with the seasonal Delta C-14 cycle observed in Makassar Strait. We estimate the influence of high Delta C-14 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 parts per thousand and 70 parts per thousand, and between 1955 and 1990, it averages at 40 parts per thousand. The rich Delta C-14 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 Delta C-14 signature in Lombok Strait.