Abyssal seafloor as a key driver of ocean trace-metal biogeochemical cycles
Jianghui Du, Brian A. Haley, James McManus, Patrick Blaser, Jörg Rickli, Derek Vance
Abstract
Abstract Trace elements and isotopes (TEIs) are important to marine life and are essential tools for studying ocean processes 1 . Two different frameworks have arisen regarding marine TEI cycling: reversible scavenging favours water-column control on TEI distributions 2–5 , and seafloor boundary exchange emphasizes sedimentary imprints on water-column biogeochemistry 6,7 . These two views lead to disparate interpretations of TEI behaviours 8–10 . Here we use rare earth elements and neodymium isotopes as exemplar tracers of particle scavenging 11 and boundary exchange 6,7,12 . We integrate these data with models of particle cycling and sediment diagenesis to propose a general framework for marine TEI cycling. We show that, for elements with greater affinity for manganese oxide than biogenic particles, scavenging is a net sink throughout the water column, contrary to a common assumption for reversible scavenging 3,13 . In this case, a benthic flux supports increasing elemental concentrations with water depth. This sedimentary source consists of two components: one recycled from elements scavenged by water-column particles, and another newly introduced to the water column through marine silicate weathering inside sediment 8,14,15 . Abyssal oxic diagenesis drives this benthic source, and exerts a strong influence on water-column biogeochemistry through seafloor geometry and bottom-intensified turbulent mixing 16,17 . Our findings affirm the role of authigenic minerals, often overshadowed by biogenic particles, in water-column cycling 18 , and suggest that the abyssal seafloor, often regarded as inactive, is a focus of biogeochemical transformation 19,20 .