Radiocarbon in organic compound classes of particulate and sedimentary organic matter in the Northeast Pacific Ocean

Radiocarbon (Δ14C) and stable carbon (δ 13C) isotopes are powerful tracers of sources and cycling of organic carbon. I measured Δ14C and δ13C in organic compound classes [lipids, total hydrolyzable amino acids (THAA), total hydrolyzable carbohydrates (TCHO) and the acid-insoluble fraction] of sinking particulate organic carbon (POC, >1 μm) in the deep Northeast Pacific and in sediments (SOC) from the California margin.; The Δ14C values of THAA and TCHO of deep sinking POC are similar to those of plankton in the overlying surface waters, indicating modern source(s) and rapid cycling. In contrast, the Δ14C values of lipids and the acid-insoluble fraction are low, showing that these fractions contain old carbon despite the short turnover time of sinking POC. Likely sources of old organic carbon are incorporation of dissolved organic carbon (DOC) and resuspended SOC laterally-transported from margin sediments. DOC incorporation onto POC was indicated by an incubation experiment performed shipboard in 2000. The Δ14C values of the incubated POC in deep sea water decreased by 90 ± 30‰. Incorporation of resuspended SOC was evidenced by a 6-year time series of Δ14C, δ 13C and C/N (organic carbon to total nitrogen ratio) data of sinking POC in the Northeast Pacific. The intensity of lateral transport of resuspended SOC and riverine POC appeared to be correlated with river runoff from central California with a time lag of three months.; Isotopic results of SOC on a transect across the California margin indicate that lateral transport of resuspended SOC and riverine POC are important for controlling the biochemical composition, and Δ14C and δ 13C signatures of the organic fractions of SOC. Lipids and the acid-insoluble fraction appear to be transported selectively compared to THAA and TCHO. Riverine POC was present on the continental shelf and the relative contribution of riverine POC to each organic fraction was lipids > the acid-insoluble fraction > TCHO > THAA.