Coupling of near‐bottom pelagic and benthic processes at abyssal depths in the eastern North Pacific Ocean

Abstract

A time‐series site was established in the eastern North Pacific Ocean to study the coupling between near‐bottom pelagic and benthic processes at abyssal depths in an area with well‐documented seasonality in surface water productivity. Particulate total mass (PTM), particulate organic C (POC), particulate total N (PTN), and particulate calcium carbonate [P(CaCO3)] fluxes were measured from sediment trap collections at 600 and 50 m above bottom from February 1990 to October 1991 (606 d). The sea floor at 4,100 m was concurrently monitored with a time‐lapse camera over a 386‐d period from July 1990 to July 1991. During this study, in situ measurements of sediment community oxygen consumption (SCOC) were made and surface sediment samples collected seasonally with a free‐vehicle grab respirometer. PTM, POC, PTN, and P(CaCO3) fluxes exhibited a strong seasonal signal, with episodic peaks from spring through fall and lows in winter. SCOC increased sharply between winter and summer, coinciding with spring peaks in particulate fluxes. Detrital aggregates appeared on the sea floor in pulses over a 6‐month period from July to December 1990, coinciding with periods when particulate fluxes were elevated but delayed ∼1.5 months after the initial peaks in particulate flux. Mobile epibenthic megafauna monitored with time‐lapse photography consisted primarily of holothuroids and echinoids and were twice as active when detrital aggregates were observed on the sea floor as during the rest of the year. Our results show a temporal relationship between the flux of particulate matter entering the benthic boundary layer, the arrival and residence of detritus on the sea floor, and the activity of the sediment community and mobile epibenthic megafauna.