Decoupling of particles and dissolved iron downstream of Greenlandic glacier outflows

Solid-phase Mn speciation in suspended particles along meltwater-influenced fjords of West Greenland

“…The dMn concentration decreased with distance along the fjord, reaching a steady concentration in the range of 16-18 nM in higher salinity surface waters (salinity >23) over 35 km from the inner-fjord. These surface dMn levels are consistent with a recent study of dMn concentrations in the glacially-fed Copper River entering the Gulf of Alaska (Kandel and Aguilar-Islas, 2021) and are generally higher than the corresponding dFe levels (~7 -35 nM in the outer fjord, maximum 230 nM nearest glacier discharge) at the same sample locations (van Genuchten et al, 2021). Particulate Mn was the dominant Mn form in the AM transect, with dMn levels representing 4-30% of total dissolvable Mn (TdMn; maximum TdMn >2000 nM), consistent with the high particle load shown by elevated turbidity.…”

“…Data were collected from transects of up to 100 km in length in fjords with different underlying bedrock geology. The Mn data are also contrasted with Fe data from the same transects, which was first presented in our previous work (van Genuchten et al, 2021), and evaluated in view of other reported Mn datasets in similar geographic environments around Greenland (Aciego et al, 2015;Hawkings et al, 2020;Achterberg et al, 2021;Krisch et al, 2021). These results provide insights into the biogeochemical behaviour of glacially-derived Mn and may help refine predictions concerning future changes to the relative availabilities of Fe and Mn in glaciated coastal regions (Browning et al, 2021;Forsch et al, 2021).…”

“…Element XR) at GEOMAR. To provide a comparison with dMn concentrations, we also report dissolved Fe (dFe) concentrations from the same samples, which were first presented in our previous companion article (van Genuchten et al, 2021). Other trace element concentrations (dissolved Cu, Co and Ni) are reported by Krause et al, (2021) from the same samples and method as per dFe.…”

“…After standing acidified for >6 months, TdMn samples were measured via ICP-MS following 5 to 50 times dilution with 1 M HNO3 to account for the large concentration range (distilled in-house from Romil Superpure grade acid, parts-per-billion level impurities). The accuracy of the dMn measurements was determined from analysis of coastal seawater GSC (GEOTRACES Program) and CASS6 (National Research Council Canada) reference material (measured 2.49 ± 0.84 nM and 37.1 ± 0.83 nM; reference values 2.18 ± 0.075 nM and 40.4 ± 2.18 nM, corresponding to recoveries of 114% and 92%, respectively; dFe values are given in our previous work (van Genuchten et al, 2021)). The limit of detection, defined as 3 standard deviations of blanks, was 64 pM for dMn.…”

“…The decrease in TdMn with distance along the fjord matched the behaviour of turbidity, which was extremely high in the inner-fjord (600 NTU). Turbidity in the inner-fjord was characterized by a thin (< 1 m) near-surface layer of high turbidity that was visibly dissipated in the ship's wake (van Genuchten et al, 2021) and was not likely fully resolved by CTD data at 1 m resolution (i.e., the highest measured turbidity was likely an underestimate).…”