Seamounts modulate upper-ocean ecosystems through a suite of topographically driven dynamical processes, including flow uplift, internal wave breaking, and eddy generation. However, the depth dependence of such seamount-driven ecological regulation remains poorly understood, and the long-term trajectory of surface chlorophyll-a (Chl-a) over seamount provinces in a warming climate has yet to be quantified at the global scale.

Based on a 22-year MODIS Chl-a time-series, this study applies Sen’s slope estimator and Mann-Kendall test to characterize long-term trends in Chl-a concentrations. The results reveal that seamount-induced Chl-a anomalies are persistent over the two-decade period, with significant increases primarily distributed across oceanic fronts and boundary current regions. We further introduce the Gini index to quantify long-term spatial heterogeneity of surface Chl-a across seamount summits. The Gini index displays an increasing trend of 0.57 % yr⁻¹ (R² = 0.788, p < 0.01), indicating widening disparities in surface Chl-a concentrations within seamount domains. Combined with global spatial patterns of Chl-a and seamount geographic locations, we categorized seamounts by bathymetric depth intervals. Bathymetric depth exerts significantly divergent regulatory effects of seamounts on surface Chl-a variability. Spatial analysis through linear fitting of "chlorophyll rings" indicates that the disturbance triggered by seamounts generally extends across an area more than twice the size of the physical topographic footprint. Notably, the impact intensity of certain deep-sea seamounts on surface Chl-a is 23% higher than that of the surrounding background fields.

These findings highlight that the dynamical impacts of deep-sea seamounts on the upper ocean ecosystems are globally non-negligible, with their ecological influence reaching far wider spatial ranges than previously recognized.
 

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