Potential source and diagenetic signatures of oceanic dissolved and particulate organic matter as distinguished by lipid biomarker distributions

Potential biogenic sources of ultrafiltered dissolved and suspended particulate organic matter (UDOM and POM, respectively) from the Sargasso Sea (SS) and North Central Pacific (NCP) Ocean were investigated using lipid biomarker compounds. Organic carbon (OC) concentrations were ~ 20–40 times greater in UDOM than POM and decreased with depth. However, total OC-normalized lipid concentrations were 2–3 orders of magnitude higher in POM than in UDOM. Particulate total lipids decreased 3–10-fold with depth, compared to 10–20% for dissolved total lipids. Total fatty acids (FA), the most abundant lipids, showed similar patterns as total lipids, comprising ~ 62–88% of the total lipids analyzed in UDOM and ~ 57–84% in POM.FA were dominated by straight-chain saturated compounds followed by monounsaturated, polyunsaturated, and branched FA. Polyunsaturated FA were enriched in POM vs. UDOM and in surface vs. deep waters for both UDOM and POM, likely reflecting the algal origins and greater reactivity of surface-derived materials. In both UDOM and POM, sterols of planktonic origin dominated, including cholest-5-en-3β-ol (C₂₇Δ⁵), 24-methylcholesta-5,24(28)E-dien-3β-ol (C₂₈Δ^5,24(28)) and 24-ethylcholest-5-3β-ol (C₂₉Δ⁵), with varying contributions from cholesta-5,22E-3β-ol (C₂₇Δ^5,22), 24-methylcholesta-5,22E-3β-ol (C₂₈Δ^5,22) and 24-ethylcholesta-5,22E-3β-ol (C₂₉Δ^5,22).Factor analysis of lipid biomarkers showed major differences between the UDOM and POM pools and for each pool as a function of depth, but not between the SS and NCP. While UDOM and POM biomarkers were both dominated by autochthonous sources, differences between the two pools suggest potential effects from some combination of source and diagenetic factors. The lipid biomarker data are further evaluated relative to previous studies of radiocarbon (¹⁴C) and elemental (C:N:P) characteristics of UDOM and POM in the SS and NCP.