Sources, sinks, and cycling of dissolved organic copper binding ligands in the ocean

Abstract

Organic Cu-binding ligands have a fundamental influence on Cu distributions in the global ocean and they complex >99% of the dissolved Cu in seawater. Cu-binding ligands however, represent a large diversity of compounds with distinct sources, sinks and chemical properties. This heterogeneity makes the organic Cu-binding ligand pool difficult to study at the global scale. In this review, we provide an overview of the diversity of compounds that compose the marine Cu-ligand pool, and their dominant sources and sinks. We also summarize the most common analytical methods to measure ligands in marine water column samples. Generally, ligands are classified according to their conditional binding strength to Cu. However, the lack of a common definition for Cu ligand categories has previously complicated data intercomparison. To address this, we provide a general classification for Cu-binding ligands according to their binding strength and discuss emerging patterns in organic Cu-binding ligand distributions in the ocean according to this classification. To date, there is no global biogeochemical model that explicitly represents Cu ligands. We provide estimates of organic Cu-binding ligand fluxes at key interfaces as first order estimates and a first step for future modeling efforts focused on Cu and Cu-binding ligands.

Natural copper-binding ligands in the Arctic Ocean. The influence of the Transpolar Drift (GEOTRACES GN04)

“…At the same time, inputs from bottom sediments were limited. This may explain why deep waters did not present an increase in L Cu and dCu concentrations with depth, as observed in other oceans (Ruacho et al, 2022). Scavenging could remove more dCu than L Cu , as observed in the loss of linearity between the two parameters observed in the deep water (Figure 5B).…”

“…This study found that the TPD was a substantial source of L Cu for the central Arctic surface waters (Tables 1, 2). Overall, the surface L Cu concentrations were higher than the average concentration for open ocean surface waters (~1 nM, Ruacho et al, 2022).…”

“…Copper-binding ligands (L Cu ) are a heterogeneous group of compounds (e.g., thiols, humic substances, exopolysaccharides, and methanobactins), that remain largely unidentified. Ligands are classified according to their conditional stability constant respect to the Cu 2+ ion (log K cond Cu2+L ) into strong (L 1 class) or weak ligands (L 2 class), being 13 the value that differentiates the two groups (Bruland et al, 2000;Buck and Bruland, 2005), that are in a good agreement with Ruacho et al (2022). The biogeochemical cycle of Cu in the Arctic Ocean is still largely unexplored.…”

Ecological Status of Algeciras Bay, in a Highly Anthropised Area in South-West Europe, through Metal Assessment—Part I: Abiotic Samples

“…The contents of the oxidisable fractions of Pb and Cu (3–27% and 5–25%, respectively) may be due to the affinity of these metals for the organic matter that leads to the formation of complexes between them. Cu has tendency to form stable organo-Cu complexes due to its affinity towards humic substances, among other organic ligands [ 83 ]. The release of these elements is caused by the degradation of organic matter or oxidation of sulphides to sulphates under aerobic conditions [ 23 ].…”

Toward a Better Understanding of the Global Ocean Copper Distribution and Speciation Through a Data‐Constrained Model

“…Complexation of Cu by strong organic ligands is also a unique, and potentially important feature of marine Cu biogeochemistry (Ruacho et al., 2022). More than 99% of Cu in the surface ocean is bound by organic ligands (Buckley & van den Berg, 1986; Coale & Bruland, 1988), while free Cu (Cu 2+ ), which is the most bioavailable and toxic species, only accounts for a small portion of the dissolved Cu pool.…”