Characterization of Particle Sedimentation in a Subarctic Estuary: a Sediment Trap Study over Two Productivity Seasons

Sinking particulate matter of organic and inorganic origin affects elemental cycles in the water and has the potential to carry marine pollutants (e.g., spilled oil) from the ocean surface to the benthos. The aim of this study was to characterize vertical particle fluxes out of surface waters in a subarctic estuary (Cook Inlet, south-central Alaska), with a history of petroleum-related activities, providing a climatic benchmark of flux conditions that can be referenced in an event of an oil spill. A free-drifting sediment trap was used to measure sedimentation rates of total particulate matter (TPM) at sites in the lower inlet during spring/summer 2018 and 2019. TPM fluxes (TPM_flux) ranged from 9 to 412 g m(-2) d(-1) with 13 to 77% of particulate organic matter in the TPM (POM_flux). Correlation analysis between TPM_flux and POM_flux demonstrated that the inorganic fraction of sinking TPM was the main driver of vertical fluxes at our sites. Flux magnitude did not follow phytoplankton biomass in surface waters as measured by in situ chlorophyll fluorescence at either the coastal or adjacent continental shelf sites. Our results demonstrate that terrestrial runoff in the Cook Inlet region, which can be highly variable at times, drives vertical particle fluxes through the water column with consequences for food supply for benthic communities as well as oil sedimentation in the event of a spill.

Automated summary

This study aimed to characterize the vertical particle fluxes in subarctic estuary surface waters and their potential impact on oil pollution events. The results showed that the sinking rates of particles were mainly driven by the inorganic fraction. The particle fluxes were not related to phytoplankton biomass in surface waters, but were influenced by terrestrial runoff.