Investigating iodine-129 in coral cores along East Philippines as a tracer of the North Equatorial Current bifurcation and marker of the Anthropocene

Abstract

Measuring ¹²⁹I in natural archives is an excellent way of reconstructing the historical impacts of human nuclear activities (HNA) and tracing their transport through the environment. Currently, understanding of ¹²⁹I transport from the North to the South Pacific Ocean is limited, given that most HNA were conducted in the northern hemisphere. Here, we show the ¹²⁹I/¹²⁷I time series of two coral cores, namely Calaguas and Cantilan, located along the north (Kuroshio Current) and south (Mindanao Current) bifurcations of the North Equatorial Current (NEC) – a crucial region that acts as a gateway from the North to the South Pacific Ocean. Measurement and mathematical modeling results show that HNA impacts are transported and divided almost equally between the north and south bifurcations of the NEC. Moreover, it takes around three years for the ¹²⁹I signals from the Philippines to reach Australia. In recent times, when ¹²⁹I in the Pacific Ocean has been more saturated, ¹²⁹I transport from the North to the South Pacific Ocean appear to be affected by the variabilities associated with the El Niño Southern Oscillation and the Pacific Decadal Oscillation, as these influence the strengths and positions of the north and south bifurcations of the NEC. Lastly, our results affirm that ¹²⁹I records are excellent candidates for marking the beginning of the Anthropocene.