Particulate organic carbon export fluxes across the Seychelles-Chagos thermocline ridge in the western Indian Ocean using ²³⁴Th as a tracer

We investigated the export flux of particulate organic carbon (POC) using Th-234 as a tracer in the western Indian Ocean along 60 degrees E and 67 degrees E transects in 2017 and 2018. The Seychelles-Chagos Thermocline Ridge (SCTR), where production is relatively high due to nutrient replenishment by upwelling of subsurface water, was observed at 3 degrees S - 12 degrees S in 2017 and 4 degrees S - 13 degrees S both 60 degrees E and 67 degrees E in 2018. POC fluxes in 2017 showed no differences between the SCTR and non-SCTR regions. However, in 2018, the POC fluxes in the SCTR regions (8.52 +/- 7.89 mmol C m(-2) d(-1)) were one order of magnitude higher than those observed in the non-SCTR regions (0.63 +/- 0.07 mmol C m(-2) d(-1)), which appeared to be related to the strong upwelling of subsurface water. These POC fluxes were comparable to those observed under bloom conditions, and thus, are important for estimating the efficiency of carbon sequestration in the ocean.