Transport and diagenesis of dissolved and particulate terrigenous organic matter in the North Pacific Ocean

Abstract

Lignin measurements were made on suspended particulate organic matter (POM), total dissolved organic matter (DOM), high-molecular-weight (HMW) DOM, and low-molecular-weight (LMW) DOM in the North Pacific at Station Aloha. Carbon-normalized yields of lignin and δ 13C measurements indicate that while terrigenous organic matter accounts only for ∼1% of DOM in seawater, submicron POM has a substantial terrigenous component. The apparent size distribution and terrigenous nature of the particles is consistent with an aerosol source, but these particles could also be delivered to the ocean via rivers. Ratios of syringyl to vanillyl phenols as well as the fraction of dissolved lignin in HMW DOM provide molecular evidence of photochemical oxidation. Several differences in lignin composition and concentrations were evident between water masses. In particular, concentrations in North Pacific Intermediate Water were a factor of two greater than at all other depths. This is likely a reflection of higher riverine input via the Sea of Okhotsk. These trends suggest that lignin could serve as a general circulation tracer in addition to tracing riverine input and diagenetic processing of terrigenous organic matter in the ocean.