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We examine several descriptors of the ocean status to depict the inter-annual variability and to track trends in the large pelagic ecosystem. The most recent El Niño event occurred from January to July 2019. This was a weak event followed by a positive Indian Ocean dipole from July 2019 to January 2020. The ocean response was a 50-80 m deepening of the thermocline in the West Indian Ocean (WIO) and a shoaling of the thermocline of 20 to 60 m above normal in the East Indian Ocean (EIO). From October 2019 to February 2020, the surface chlorophyll concentration decreased from 30 to 60% below normal in the West Indian Ocean and increased from 40 to 200% above normal in the EIO. On the opposite, a La Niña event developed from August 2020 to March 2021, followed by a short negative Indian Ocean dipole in June-July 2021. Over the whole Indian Ocean basin, after 8 years of a low productivity regime (2007-2014), a shift towards positive anomalies of ocean productivity occurred from 2015 on. In 2019-2020, the productivity was back to low levels (-5 to -11%) in the WIO, whilst it remained 5 to 10% above the mean in the rest of the equatorial basin. Trends in dissolved oxygen concentrations (DOC) are also analysed for 1993-2019 in four large regions. The DOC declining trend in the West and East Indian Ocean could have produced a vertical compression in the optimal habitat for skipjack and yellowfin tuna, notably from 2017 to 2019, thus potentially increasing the vulnerability of these species to the surface gears.
