Solid phase extraction method for the study of black carbon cycling in dissolved organic carbon using radiocarbon

Abstract

a b s t r a c t a r t i c l e i n f oRadiocarbon analysis is a powerful tool for understanding the cycling of individual components within carbon pools, such as black carbon (BC) in dissolved organic carbon (DOC). Radiocarbon (Δ 14 C) measurements of BC in DOC provide insight into one source of aged, recalcitrant DOC. We report a modified solid phase extraction (SPE) method to concentrate 43 ± 6% of DOC (SPE-DOC) from seawater. We used the Benzene Polycarboxylic Acid (BPCA) method to isolate BC from SPE-DOC (SPE-BC) for subsequent 14 C analysis. We report SPE-BC Δ 14 C values, SPE-BC concentrations, and the relative BPCA distributions from Milli-Q water process blanks, two riverine reference standards, as well as a coastal and an open ocean surface water sample. The composition of BC is less aromatic in the ocean samples than those in the river standards. We find higher BC Δ 14 C values in the river standards (+148 to −462‰) than BC in the ocean samples (−592 to −712‰), suggesting that BC ages within oceanic DOC. We report that BC is 4.2 ± 1.0% of SPE-DOC in the open ocean surface sample, or 1.4 ± 0.1 μM C. This work provides the methodological basis by which global BC concentrations, compositions (e.g. relative abundances of BPCA marker compounds) and Δ 14C values can be assessed.

Aging and Molecular Changes of Dissolved Organic Matter Between Two Deep Oceanic End‐Members

“…Furthermore, the surface values reported here are more depleted in 14 C than bulk Δ 14 C‐DOC surface values, which range from −180 to −260‰ in the Atlantic, Pacific, and Indian Ocean basins (Bercovici et al, ; Druffel et al, , ; Druffel & Griffin, ; Follett et al, ; Walker et al, , 2016; Zigah et al, ). However, our results are similar to those Δ 14 C‐SPE‐DOM values reported by Coppola et al () collected in the East Pacific (−318 ± 11‰ and −335 ± 7‰).…”

“…In this study, we extracted 8 L of seawater through 1 g PPL cartridges, whereas previous studies extracted 5 L of seawater (Flerus et al, ; Lechtenfeld et al, ). However, the EE in the previous studies (42 ± 7%) is effectively the same as here and within the same range (~40%) of other published SPE EEs of marine DOM (Coppola et al, ; Dittmar et al, ).…”

“…While our Δ 14 C‐SPE‐DOM data at depth are similar to the whole water in the Pacific, it is known that there is some variability between bulk Δ 14 C‐DOC and Δ 14 C‐SPE‐DOM values. Coppola et al () reported that Δ 14 C‐SPE‐DOM data from marine samples were equal to or lower than that of the Δ 14 C of the total DOC pool. A fraction of the most polar (and presumably labile) portion of the DOM is not recovered with extraction (e.g., molecules such as acetate).…”

Cycling of black carbon in the ocean

“…Seawater samples were measured separately for total DOC (using UV oxidation [ Beaupre et al , ]) and for SPE‐DOC [ Coppola et al , ]. Briefly, SPE‐DOC was extracted from large‐volume filtered water samples (10–15 L for surface and 25 L for deep) that had been acidified to pH 2 (using hydrocholoric acid, analytical grade) and siphoned through a styrene divinyl benzene copolymer resin (Sigma Aldrich Diaion 13605, HP‐20, pore size 200 Å) column at a slow loading rate (two bed volumes per hour, 240 mL h −1 ) [ Coppola et al, ]. In preparation for DOC elution, two bed volumes (30 mL) of Milli‐Q water were passed through the column to remove salts and was discarded.…”

Role of environmental factors and microorganisms in determining the fate of polycyclic aromatic hydrocarbons in the marine environment

“…However, dissolved BC in marine-dissolved organic carbon constitutes an intermediate BC pool prior to sediment deposition (Masiello and Druffel 1998; Ziolkowski and Druffel 2010). BC has been estimated to contribute up to 5% of total dissolved organic carbon (DOC) (Stubbins, Niggemann and Dittmar 2012; Coppola, Walker and Druffel 2015; Coppola and Druffel 2016). The concentration of particulate PAHs in the water column is expected to decrease with depth because PAHs are desorbed and degraded during vertical transport (Lipiatou and Saliot 1991; Dachs et al.…”