Temporally-resolved mechanisms of deep-ocean particle flux and impact on the seafloor carbon cycle in the northeast Pacific

Abstract

High-temporal-resolution views of particle flux to the abyssal benthic boundary layer are provided for an eight-month period (October 2014–June 2015) at the long-term monitoring site Station M within the California Current ecosystem. Contributions of fecal pellets and aggregates to particulate organic carbon (POC) flux at 3900 m depth were estimated based on optical sediment trap (Sedimentation Event Sensor) images captured as a time-series of 2 h collections. POC flux estimated from Sedimentation Event Sensor (SES) images explained variation in carbon consumption and the carbon budget balance (supply – demand) with finer resolution than POC flux measurements from bulk collections by a concurrently deployed conventional sediment trap. Indicators of particle transport by benthic boundary layer currents and active transport by zooplankton were evaluated by comparing SES-estimated POC flux to measured current speed and direction, hours since solar noon, and modeled lunar illumination at the surface. Influence of particles (fecal pellets and aggregates) on the carbon budget was evaluated by comparing particle-specific contributions to POC flux with sediment community oxygen consumption (SCOC) measured by the Benthic Rover at 4000 m depth. During the eight-month sampling period, salp fecal pellets delivered an estimated 45% of the total POC flux to the benthic boundary layer and were responsible for an estimated 74% of a temporary carbon surplus in May and June 2015. Salp fecal pellets also appeared to be the primary source of chlorophyll peaks at the site. By contrast, most aggregates appeared to be lower-quality particles possibly sourced from lateral advection and local rebound of recently-settled detritus, which settled according to spring-neap tidal oscillations. Some aggregates may have been fresher, as suggested by non-linear relationships with SCOC and the carbon budget balance. Results suggest sinking particles packaged in surface waters and reaching abyssal depths in fresh condition (e.g. salp fecal pellets) had a greater influence on carbon consumption (e.g. SCOC) and the carbon budget balance than more refractory particles.