Food energy supply and demand: A discrepancy between particulate organic carbon flux and sediment community oxygen consumption in the deep ocean1

Abstract

Sediment community oxygen consumption (SCOC) and particulate organic carbon (POC) flux to the benthic boundary layer were concurrently measured at five deep‐sea stations on a transect across the eastern and central North Pacific at various times of year. A free vehicle grab respirometer and Alvin‐manipulated grab respirometer were used to measure SCOC. Paired particle interceptor traps (PITs) were used to collect sedimenting small POC at 100 and 600 m above the bottom. SCOC decreased across the transect from the eutrophic coastal areas off southern California to the oligotrophic central Pacific gyre. These rates were generally highest in June and lowest between fall and early spring across the transect with a recurrent pattern in the magnitude of rates measured during the same months but different years. Flux of POC into the benthic boundary layer decreased across the transect from the eutrophic eastern to the oligotrophic central Pacific. No consistent temporal trends were evident in POC flux across the transect, possibly because of small sample sizes, high intra‐station variability, and short‐term deployments (≤7 d). Comparison of concurrently measured supply of POC with organic carbon demand of the sediment community as estimated from SCOC reveals a supply deficit across the transect for all seasons measured. For one nearly synoptic sampling period across the transect in June 1982, the supply‐to‐demand ratio is lowest at the two nearshore stations where current speeds are highest. A predictive equation for SCOC with a least‐squares regression analysis and log‐transformed data revealed that POC flux as the independent variable accounted for only 59% of the variability in SCOC. Direct coupling between SCOC and POC flux is not confirmed by these results, which may be attributed to the limitations of the measurements or other organic carbon sources.