@article{fdi:010089574,
  title = {{I}ron-binding by dissolved organic matter in the {W}estern {T}ropical {S}outh {P}acific {O}cean ({GEOTRACES} {TONGA} cruise {GP}pr14)},
  author = {{M}ahieu, {L}. and {W}hitby, {H}. and {D}ulaquais, {G}. and {T}illiette, {C}. and {G}uigue, {C}atherine and {T}edetti, {M}arc and {L}efevre, {D}. and {F}ourrier, {P}. and {B}ressac, {M}. and {S}arthou, {G}. and {B}onnet, {S}ophie and {G}uieu, {C}. and {S}alaün, {P}.},
  editor = {},
  language = {{ENG}},
  abstract = {{I}ron ({F}e) is an essential micronutrient for phytoplankton growth, but its scarcity in seawater limits primary productivity across much of the ocean. {M}ost dissolved {F}e ({DF}e) in seawater is complexed with {F}e-binding organic ligands, a poorly constrained fraction of dissolved organic matter ({DOM}), which increase {F}e residence time and impact {F}e bioavailability. {H}ere, we present the conditional concentration ({LF}e) and binding-strength (log {K} {F} e ' {L} c o n d ) of {F}e-binding ligands in the {W}estern {T}ropical {S}outh {P}acific ({WTSP}) {O}cean during the {GEOTRACES} {TONGA} cruise ({GP}pr14). {T}he transect crossed the {L}au basin, a region subject to shallow hydrothermal {F}e inputs that fuel intense diazotrophic activity, the oligotrophic {S}outh {P}acific gyre, and the {M}elanesian basin. {O}rganic speciation was analyzed by competitive ligand exchange adsorptive cathodic stripping voltammetry ({CLE}-{A}d{CSV}) using salicylaldoxime at 25 mu {M}. {W}e found a high mean {LF}e of 5.2 +/- 1.2 n{M}eq{F}e (n = 103) across the entire transect, predominantly consisting of intermediate strength {L}2 ligands (84%; mean log {K} {F} e ' {L} c o n d of 11.6 +/- 0.4), consistent with humic-like substances. {DF}e correlated with the humic-like component of the fluorescent {DOM} ({HS}-like {FDOM}), yet the electroactive {F}e-binding humic-like substances ({LF}e{HS}) accounted for only 20 +/- 13% of {LF}e in the mixed layer and 8 +/- 6% in deep waters. {L}igands were in large excess compared to {DF}e (mean excess ligand e{LF}e = 4.6 +/- 1.1 n{M}eq{F}e), suggesting poor stabilization of {DF}e inputs. {H}igh {LF}e (up to 9 n{M}eq{F}e) in samples close to hydrothermal sites could be due to detoxification strategies from plankton communities toward hydrothermally-fueled toxic trace metals other than {F}e, with an apparent dilution of the {DOM} from the {L}au basin into neighboring regions. {W}e also observed a different peak potential of the {F}e salicylaldoxime complex detected by {CLE}-{A}d{CSV} between the {L}au and {M}elanesian basins, and between surface and deep waters. {T}o our knowledge, this change in potential has not previously been reported; whether this represents a novel detection of specificities in {DOM} composition merits further investigation. {C}ompetition between {F}e and competing metals for ligand binding sites could favor {DF}e oxidation and precipitation near hydrothermal vents and explain the absence of strong {F}e stabilization in the {WTSP}.},
  keywords = {iron-binding ligands ; hydrothermal ; diazotroph ; remineralization ; humic substances ; voltammetry ; fluorescence ; {PACIFIQUE} ; {ZONE} {TROPICALE}},
  booktitle = {},
  journal = {{F}rontiers in {M}arine {S}cience},
  volume = {11},
  numero = {},
  pages = {1304118 [19 p.]},
  year = {2024},
  DOI = {10.3389/fmars.2024.1304118},
  URL = {https://www.documentation.ird.fr/hor/fdi:010089574},
}