Determination of inert and labile copper on GEOTRACES samples using a novel solvent extraction method

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

“…An additional important consideration for these methods is the amount of dissolved Cu that is exchangeable with the added ligand. Findings from Moriyasu and Moffett demonstrate that dissolved Cu in older deep waters is primarily found in an inert form, with implications for speciation calculations 91 . When dealing with samples with a high percentage of inert Cu, an overestimation of a ligand's conditional stability constant will occur unless the inert fraction of dissolved Cu is omitted from the total dissolved Cu used in speciation calculations.…”

“…Both the Cu(II)-IMAC method and the mass spectrometry methods that have been employed thus far to identify and characterize the organic Cu-binding ligand pool in seawater have the potential to rapidly accelerate our understanding of marine Cu complexation, but very few published studies exist [95][96][97][98][99] . Importantly, new work also suggests that a large fraction of dissolved Cu (up to 90%) in deep waters may be inert, which has implications for these analytical methods as well as for dissolved Cu reactivity and bioavailability 91 . Future work that aims to characterize Cu-binding ligands in the marine environment will be particularly insightful to our understanding of the marine Cu cycle.…”

“…3), perhaps approaching levels that are even limiting to growth for some organisms. Recent work that suggests that a large fraction of the dissolved Cu in seawater is likely inert to exchange 91 , and the observation that a large portion of dissolved Cu is associated with very strong ligand complexes 7,16 is important for considering open ocean dissolved Cu reactivity. The impact that organic ligands have on the cycling of dissolved Cu on the basin scale also has important implications for understanding whether dissolved Cu is reversibly scavenged throughout the water column, as has been proposed by a modeling study 182 and some work on Cu isotopes 183,184 .…”

Seasonal dissolved copper speciation in the Strait of Georgia, British Columbia, Canada

“…Nor are we able to decouple the conditionality effect that salinity has on logK cond CuL,Cu 2+ from changes to ligand species between water masses of different salinities. Additionally, CLE-ACSV does not take into consideration inert colloid complexes, which can inadvertently result in elevated logK cond CuL,Cu 2+ values, given these inert species are unexchangeable between the natural Cu pool and SA within the timescales that CLE-ACSV samples are equilibrated (Kogut and Voelker, 2003;Moriyasu and Moffett, 2022). The low correlation between dCu and L concentrations (Figure 5), yet strong correlations individually to the same parameters (i.e., CDOM a 350 , oxygen, PO 3− 4 , and NO − 2 + NO − 3 ), suggests that some ligand pool variability may be due to loss of ligands via photodegradation, while dCu remains.…”

“…To structurally characterize and confirm potential sources of Cu binding organic ligands in the SoG, CLE-ACSV (i.e., under multiple detection windows) should be combined with other techniques, such as HPLC-ESI-MS (McCormack et al, 2003;Ross et al, 2003;Nixon and Ross, 2016), allowing comparisons of speciation data from field samples and those from phytoplankton and bacteria cultures (Whitby et al, 2018). Additionally, ligand parameters should be complemented with concentrations of potential ligands, such as thiols and humic substances (Laglera and Tovar-Sańchez, 2012;Whitby et al, 2018), as well as DOC, CDOM across a wider range of wavelengths, suspended particulate matter, colloidal trace metal fractions (Bertine and VernonClark, 1996;Kogut and Voelker, 2003;Moriyasu and Moffett, 2022) and other proxies, while considering time delays between biological parameters and Cu ligand parameters (Dryden et al, 2007), informed by cell cultures (Leal et al, 1999;Gordon et al, 2000).…”