Temporal and spatial variability in the hydrothermal signature of
sinking particles and sediments in the Western Tropical South Pacific
Ocean
Abstract
Iron (Fe) is an essential micronutrient for phytoplankton, particularly
diazotrophs, which are abundant in the Western Tropical South Pacific
Ocean (WTSP). Their success depends on the numerous trace metals,
particularly iron, released from shallow hydrothermal vents along the
Tonga Arc. This study aimed to explore the impact of hydrothermal fluids
on particulate trace metal concentrations and biological activity. To
identify the composition of sinking particles across a wide area of the
WTSP, we deployed sediment traps at various depths, both close and
further west of the Tonga Arc. Seafloor sediments were cored at these
deployment sites, including at a remote location in the South Pacific
Gyre. The sinking particles were composed of a large amount of
biological material, indicative of the high productivity of the Lau
Basin. A significant portion of this material was lithogenic of
hydrothermal origin, as revealed through Al-Fe-Mn tracing. The sinking
material showed similar patterns between lithogenic and biogenic
fractions, indicating that hydrothermal input within the photic layer
triggered surface production. A hydrothermal fingerprint was suggested
in the sediments due to the high sedimentation rates and the presence of
large, heterogeneous, trace metal-rich particles. The presence of nearby
active deep hydrothermal sources was suspected near the Lau Ridge due to
the large particle size and the significant enrichment of Fe and Mn.
Overall, this study revealed that deep and shallow hydrothermal sources
along with submarine volcanism have a significant influence on the
biogeochemical signature of particles in the Lau Basin at large spatial
and temporal scales.