Ocean’s largest chlorophyll-rich tongue is extending westward

Abstract

Abstract Upwelling in the Equatorial Pacific nurtures an expansive and westward-stretching chlorophyll-rich tongue (CRT), supporting half of the annual global new production. Surrounding the CRT are the oligotrophic subtropical gyres to the north and south, which are suggested to be expanding under global warming. Yet, how this productive CRT has changed—expanding or contracting—remains unknown. By applying the empirical mode decomposition method to 20-year monthly measurements of chlorophyll concentration from MODIS-Aqua (2002-2022), a significant westward extension of the CRT is found, with its area expanding at a rate of 8.46 × 104 km2/yr. The westward extension of the CRT is attributed to strengthened equatorial upwelling and the Southern Equatorial Current from 2002 to 2022, driven by intensified easterly trade winds as the Pacific Decadal Oscillation predominantly remains in its negative phase during this period. Our results imply a broader cover of productive water along the equator, while its impact on tropical climate, ecosystems and carbon cycle deserves further investigation.