Bomb C-14 in the Indian-Ocean Measured by Accelerator Mass-Spectrometry - Oceanographic Implications

AMS C-14 measurements on samples collected in the tropical-equatorial Indian Ocean during the INDIGO program (leg II, 1986) are presented and compared with beta-counting results obtained under both INDIGO program and GEOSECS expedition in the Indian Ocean (1978). The most significant observation is a doubling of the bomb-C-14 inventory and mean penetration depth in the equatorial zone. Based on hydrologic considerations, two hypotheses can be proposed: 1) direct influx of Pacific mid-latitude waters through the Indonesian archipelago and 2) advection and/or mixing with Mode Water from the southern gyre of the Indian Ocean. Results obtained with a general circulation model of the ocean suggest that the influx from the Pacific is important in the upper 300m and that below 500m the bomb-C-14 budget is dominated by Mode Water advection.