High-Abundance Heterotrophic Bacteria Inhabit the 85° E Hydrothermal Plume of the Explosive Volcanic Zone at Gakkel Ridge, Arctic Ocean

While under-ice submarine hydrothermal systems provide critical insights into extremophile adaptations, the ecological impacts of explosive volcanism on these ecosystems remain poorly constrained. We successfully detected evidence of hydrothermal activities and explosive volcanism at 85° E, the eastern volcanic zone, ultra-slow spreading Gakkel Ridge. Hydrothermal plume, surface sediments, and volcanic glass samples were systematically collected to investigate the diversity of microbial communities. Our results revealed two distinct microbial regimes in hydrothermal plume: (1) chemoautotrophic bacteria (<i>Sulfurimonas</i> and <i>SUP05_cluster</i>), prevalent in global basaltic hydrothermal systems, potentially involved in carbon fixation through the CBB and rTCA cycles and (2) <i>Alcanivorax</i> (up to 82.5%), known for degrading hydrocarbons. Sediment profiles showed a depth-dependent decline of <i>Alcanivorax</i>, tightly coupled with TOC (1.05% to 0.45%, r = 0.75, <i>p</i> < 0.05). Additionally, the <i>Alcanivorax</i> MAGs demonstrated their potential in degrading various types of organic carbon, especially in alkane degradation. Strikingly, this pattern contrasts with hydrothermal plumes from effusive volcanic zones (Aurora and Polaris regions), where <i>Alcanivorax</i> was undetectable. We speculate that the surge of <i>Alcanivorax</i> in the 85° E hydrothermal plume was associated with the violent disturbances caused by explosive volcanism. This mechanism accelerates microbial-mediated carbon turnover rates compared to a stable hydrothermal ecosystem.